Climate Change and Non-Communicable Diseases: A Bibliometric, Content, and Topic Modeling Analysis

Abstract

This study examines research on the impact of climate change (CC) on non-communicable diseases (NCDs) using bibliometric analysis, topic modeling, and content analysis. Articles published in the Web of Science database between 2000 and 2024 were analyzed. VOSviewer and Biblioshiny were used for bibliometric analysis and Python for topic modeling. In addition, the 50 most cited articles were content analyzed. The results show that there has been an increasing number of publications over time and that the research originates predominantly from high/very high Human Development Index (HDI) countries, especially China and the United States, rather than from low HDI countries. These countries also have strong international cooperation networks. Topic modeling shows that high/very high HDI countries work on a balanced range of topics, while low HDI countries focus primarily on environmental impacts. Thematic analysis shows that research topics are evolving, diversifying, and deepening. As a result, the literature on CC-NCDs is expanding and deepening, thus providing evidence-based information for global public health interventions. However, in countries with low HDI and the most vulnerability to the impacts of climate change, the volume of publications, thematic diversity, and international cooperation are significantly low. Unfortunately, from a public health policy perspective, global climate change is far from being a problem that any country can solve alone. Global cooperation is, therefore, essential.

1. Introduction

Climate change (CC) is defined by atmospheric scientists as a significant and long-term change in weather patterns [1]. As climatic conditions undergo change, the frequency of weather and climate events, such as storms, extreme heat, floods, droughts, and forest fires, increases [2]. Climate change, with the impact of these weather and climate threats, poses unprecedented challenges to the balance of ecosystems and sustainable life [3]. The Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC) concluded that climate risks are emerging faster and will intensify sooner than previously anticipated; adaptation to increasing global warming will also be more difficult [4]. In addition, climate change creates barriers to sustainable food production (Sustainable Development Goal (SDG) 2: zero hunger), threatens human health (SDG 3: good health and well-being), limits access to safe and accessible drinking water (SDG 6: clean water and sanitation), and negatively impacts aquatic and terrestrial ecosystems (SDG 14: life below water and SDG 15: life on land), making it difficult to achieve the Sustainable Development Goals. Accordingly, SDG 11 (sustainable cities and communities) prioritizes reducing the impact of natural disasters and addressing environmental stress, while SDG 13 (climate action) prioritizes directly addressing climate change and its impacts [5]. The fact that the effects of climate change are being felt more and more every day is increasing the interest and attention of policymakers, decision-makers, and the scientific community. In fact, the term “climate change” has been replaced by the more comprehensive term “climate crisis” to reflect the magnitude and potential consequences of this change, a term that has also been adopted for international use, such as in the COP26 (Conference of the Parties) and World Health Organization (WHO) reports [6,7,8,9].

Climate change has been identified as potentially the greatest health threat of the twenty-first century [10,11]. The health implications of climate change are multifaceted and include, but are not limited to, the following: overexposure to extreme heat and cold; increased frequency of weather disasters; rising air pollution levels; spread of pollen; emergence of food safety risks; inadequate access to food; interruptions in access and functioning of health services and facilities; emerging new infections and their facilitation; increased exposure to ultraviolet radiation; and deterioration of the ecosystem, which is integral to life and health, due to damage to biodiversity in nature. Moreover, climate change exerts a detrimental effect on numerous social determinants of health, including livelihoods, equality, and access to health services and social support structures [3,12,13,14]. In all these aspects, climate change has been predicted to cause deaths, non-communicable diseases, the emergence of new infectious diseases and epidemics/pandemics, and health emergencies by affecting human health both directly and indirectly. Therefore, this has led the scientific world to work intensively on climate change. In their study examining the burden of non-communicable diseases due to high temperatures in the changing climate from 1990 to 2019, Zhang et al. reported that the number of deaths and disability-adjusted life years (DALYs) due to high-temperature-related non -communicable diseases (NCDs) was approximately 150,000 and 3.4 million globally in 2019 [15]. According to the WHO, climate change is expected to cause approximately 250,000 additional deaths per year between 2030 and 2050 due to malnutrition, malaria, diarrhea, and heat stress. However, there is still a significant research gap regarding the health impacts of climate change in the Eastern Mediterranean region (EMR) and Africa, as they are disproportionately affected and particularly vulnerable to climate change [16,17,18].

Despite the efforts of researchers to demonstrate the effects of climate change on human health, epidemiological effects on public health remain difficult to demonstrate due to the need for long-term studies and barriers and research gaps in multidisciplinary research [2,19]. Nevertheless, the growing recognition of the process of climate change has led to increased interest among health researchers in evaluating the potential mechanisms by which climate change may affect health [14].

Given the growing interest in the relevant literature, it may be more beneficial to comprehend and interpret the relationship between climate change and health by addressing the orientation, volume, and growth pattern of studies focusing on climate change and non-communicable diseases over time in a holistic manner. In light of these considerations, bibliometric analysis methods were deemed to be a suitable methodology. However, it was determined that making evaluations with the subject topic modeling (STM) technique, which allows for analyzing how the information obtained in the literature changes according to external common variables, and content analysis, which allows for the conceptual interpretation of the results obtained, will make important contributions in terms of public health and the development of health policies. A thorough analysis of international scientific databases revealed a paucity of research that integrated the examination of climate change and non-communicable diseases with these three approaches.

In this study, the objective was to reveal the development in the literature by examining research articles on the effect of climate change on non-communicable diseases. These articles were published in the Web of Science (WoS) database between 2000 and 2024. A bibliometric analysis, subject modelling analysis, and content analysis were used to achieve this. This study also examined how reputable and qualified journals in the scientific world responded to the effect of climate change on non-communicable diseases.

2. Materials and Methods

2.1. Selecting the Database

The database used in this study, WoS, is a very important academic database that is widely used by researchers. While databases such as Scopus, Dimensions, and Google Scholar offer a large pool of journals, WoS offers a more selective approach due to its indexing policy and a large collection of qualified and respected journals with high impact factors, especially in the scientific world. In this study, publications indexed in the Science Citation Index Expanded (SCIE) and Social Science Citation Index (SSCI) were included in WoS. This platform makes it easier for users to access the highest-quality literature on a particular topic, thanks to its comprehensive filtering options, interdisciplinary access, and powerful bibliometric analysis tools [20]. Furthermore, the platform’s indexing standards and capacity for high-accuracy citation analysis enable users to focus not only on current information but also on the academic impact of relevant research [21]. In addition, the number of predatory journals in WoS is significantly lower than in other databases, which is believed to increase the reliability of the data [22]. The WoS database was used in this study for these reasons.

2.2. Selection of Publications

The publications to be included in the analysis within the scope of this research were obtained from the Web of Science Core Collection (WoSCC) database. A list of publications was created according to the inclusion and exclusion criteria by searching with the specified search terms. A PRISMA flow diagram for the information search in WoS is presented in Figure 1 [23].

2.2.1. Determination of Search Terms

The search was conducted using keywords, with the “Topic” criterion selected among the search criteria in the WoS database. This criterion includes the article title, abstract, and keywords. The objective at this stage was to formulate a search query that would retrieve as many documents as possible while concomitantly minimizing irrelevant results (false positives). The medical keywords used in the publication search were selected from the MeSH (Medical Subject Headings) list, which is accepted as a standard in the medical literature. These keywords were expanded with synonyms (e.g., noncommunicable disease vs. non-communicable disease) to increase the comprehensiveness of the search and minimize the risk of false exclusions: “climate change” OR “changing climate” OR “climate warming” OR “warming climate” OR “global warming” OR “heat wave” and “chronic disease” OR “non communicable disease” OR “noncommunicable disease” OR “non-communicable disease” OR “heart” OR “cardio” OR “hypertension” OR “blood pressure” OR “arterial” OR “vascular” OR “aterosclerosis” OR “hyperlipidemia” OR “dislipidemia” OR “cholesterol” OR “trigliserid” OR “CHD” OR “CVD” OR “pulmonary” OR “lung” OR “respiratory” OR “chronic bronchitis” OR “asthma” OR “COPD” OR “renal” OR “kidney” OR “liver” OR “gastro (gastrointestinal system)” OR “diabetes mellitus” OR “allergy” OR “cutaneous” OR “dermatitis” OR “skin” OR “blood” OR “hematology” OR “immunology” OR “rheumat (rheumatologic diseases)” OR “immun” OR “brain” OR “neurologic” OR “disorder”.

2.2.2. Filtering

In the course of this research, a number of filters were employed in order to identify the publications to be included in the analysis.

Year of publication: 2000 or later.

Document type: Article.

WoS Categories: Environmental Sciences, Multidisciplinary Sciences, Neurosciences, Toxicology, Behavioral Sciences, Environmental Studies, Endocrinology Metabolism, Meteorology Atmospheric Sciences, Public Environmental Occupational Health, Genetics Heredity, Clinical Neurology, Immunology, Family Studies, Health Policy Services, Humanities Multidisciplinary, Geriatrics Gerontology, Medical Ethics, Medical Informatics, Medicine Research Experimental, Nanoscience Nanotechnology, Neuroimaging, Pediatrics, Obstetrics Gynecology, Psychology Clinical, Radiology Nuclear Medicine Medical Imaging, Medicine General Internal, Sport Sciences, Reproductive Biology, Rehabilitation

Research Areas: Environmental Sciences Ecology, Meteorology Atmospheric Sciences, Science Technology Other Topics, Public Environmental Occupational Health, Genetics Heredity, Toxicology, Physiology, Development Studies, Psychology, General Internal Medicine, Behavioral Sciences, Health Care Sciences Services, Life Sciences Biomedicine Other Topics, Immunology, Biomedical Social Sciences, Neurosciences Neurology, Endocrinology Metabolism, Pediatrics, Tropical Medicine, Nutrition Dietetics, Research Experimental Medicine, Allergy, Medical Ethics, Psychiatry, Nursing, Pharmacology Pharmacy, Radiology Nuclear Medicine Medical Imaging, Geriatrics Gerontology, Family Studies, Rehabilitation, Medical Informatics, Legal Medicine, Oncology, Respiratory System, Surgery, Cardiovascular System Cardiology, Dermatology, Anesthesiology, Hematology, Emergency Medicine, Medical Laboratory Technology, Pathology.

Web of Science index: SSCI, SCIE.

Language: English.

2.2.3. Inclusion and Exclusion Criteria

The publications were filtered according to keywords, analyzed individually by two researchers, and evaluated according to three criteria. The first criterion was that the research topic was related to climate change; the second criterion was that the parameter analyzed within the scope of the research was non-communicable diseases; and the third criterion was that the publication was a research article and not a news report, letter, or editorial. As a result of this process, a total of 4455 articles that met the determined criteria were identified. Each of these articles was examined in detail by two experts one by one, and 721 articles were determined to be suitable for the scope of this study and included in this study. The data collection process was completed on 27 November 2024.

2.3. Export of Data

All publications found as a result of scanning within the scope of the determined keywords were selected and transferred to the “Marked List” in the WoS database. The data transferred to the “Marked List” in the WoS database was downloaded in the form of “Full Record and Cited References” and in “Plain Text” format from the record content options on the interface that appears with the “Export to Other File Formats” option. The exported data included information such as titles, authors, countries, institutions, journals, and citations.

2.4. Data Analysis and Reporting

2.4.1. Bibliometric Analysis

During the stage of bibliometric analysis of the data, descriptive statistics of the evaluation results were given as numbers and percentages for categorical variables. The IBM SPSS 23.0 (Statistical Package for the Social Sciences) program and Excel were utilized for these analyses. VOSviewer version 1.6.20 and the open-source bibliometric software Biblioshiny from RStudio version 4.4.1 were utilized to perform bibliometric analysis [24].

Various analysis tools, such as VOSviewer, citespace, bibliometrix, Biblioshiny, sciMAT, Pajek, etc., have been developed for use in bibliometric analysis and offer different analysis and visualization capabilities. In this study, VOSviewer and Biblioshiny software, which are among the most frequently used software in bibliometric analysis by other researchers in the literature, were preferred to be used because they offer comprehensive bibliometric analysis options, facilitate data visualization, provide professional quality visualizations, are free of charge, and provide the opportunity to perform the analyses intended in this research [25].

The countries that contributed to the literature on the impact of CC on NCDs were analyzed with Biblioshiny, and the data were mapped through the Flourish platform (see Figure 4).

In the network visualization of author keywords and country collaborations, prepared with VOSviewer version 1.6.20, items are represented by tags and a circle (see Figures 5 and 6). The magnitude of an item’s representation, indicated by its label size and the size of its circle, is directly proportional to its associated weight. The color of each element is determined by the cluster it belongs to, and the lines between the elements represent the connections.

The thematic map, prepared with Biblioshiny, provides a visualization of the most salient themes within a given research field (see Figure 7). This analysis generates clusters of keywords and identifies themes in the literature. The 2 × 2 matrix in the thematic map gives four quadrants, where the size of the bubble expresses the occurrence of keywords. The upper right quadrant is characterized by the presence of “motor themes”, which represent the most extensively discussed topics within the field. In the upper left quadrant are the “niche themes”, which indicate well-developed but isolated themes. In the lower right quadrant are the “basic themes”, which, despite their limited development, show a high level of centrality and relevance to the literature. Finally, in the lower left quadrant are the “emerging or declining themes”, which either emerge or decline in importance. Thematic evolution, prepared with Biblioshiny, provides an interesting and broad picture of the development of the field and provides information on changing research focal areas in the literature over defined periods (see Figure 8). Such longitudinal analyses facilitate the identification of how topics converge or divide into multiple themes. The Sankey diagram, a graphical representation employed to visualize the outcomes of the thematic evolution analysis facilitated by Biblioshiny, was developed within the Flourish platform.

2.4.2. Topic Modeling

The Python 3.12 programming environment and associated topic modeling libraries were used for topic modeling analysis. An advanced topic modeling technique was applied, which extends the capabilities of Latent Dirichlet Allocation (LDA) by incorporating document-level metadata (e.g., year of publication, geographical region, or journal source) into the modeling process [26,27]. This approach enables STM to not only identify latent topics but also to analyze how these topics vary with respect to external covariates. Each topic is identified by the most representative keywords, which are terms that occur together frequently in the dataset and are statistically associated with the topic and their prevalence (%) in the dataset. For example, a topic labeled “extreme heat waves” might contain keywords such as “heat”, “wave”, “extreme”, “risk”, and “health” (see Table 3) [28,29]. The utilization of these keywords offers a concise representation of the thematic content of the topic, providing a brief overview of the key elements and concepts that define the topic, thus facilitating a concise understanding of its thematic content. The search for thematic categories from the researched topics was carried out by rigorously categorizing the topics at the intersection of climate change and health, with the focus being on identifying the main thematic areas. The prevalence of the categories is expressed in percentages [30,31,32]. The topic trends table shows the distribution of the topics between 2015 and 2024 (%) and their acceleration (ACC) from 2015 to 2024 (see Table 4).

2.4.3. Content Analysis

In the course of the present study, a selection was made of 50 articles with the highest number of citations from among the publications that were the subject of evaluation. The content analysis that was conducted focused on the limitations and results of the studies. Initially, three research questions (RQs) were identified for the purpose of content analysis:

RQ1: 

What have we learnt from research on the impact of climate change on non-communicable diseases?

RQ2: 

What recommendations have been developed in research on the impact of climate change on non-communicable diseases?

RQ3: 

What are the limitations of research on the impact of climate change on NCDs?

The most appropriate sections to reflect the answers to these questions were considered to be the limitations and conclusion sections. These sections of the articles were first read carefully by considering the research questions and then coded. The subsequent step involved categorizing the codes based on their relationship with each other.

2.5. Ethical Approval

This study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Karadeniz Technical University Medical Faculty (protocol code: 2024/261 and date of approval: 25 December 2024).

3. Results

3.1. Bibliometric Analysis

3.1.1. Trends in Article Publication by Year

When the number of research articles published on the effects of climate change on non-communicable diseases by year was examined, it was found that the number of research articles in this field increased year by year, and 13.0% (94) of the research articles were published in 2023, 11.9% (87) in 2024, and 10.7% (77) in 2022. No data were available for 2000 as there were no articles published in that year. The number and distribution of research articles published on the effects of climate change on non-communicable diseases by year are presented in Figure 2.

3.1.2. Metrics of the Top 20 Journals

The analysis of the top 20 journals in the field of climate change and non-communicable diseases shows that Science of The Total Environment leads with the highest number of publications (70 articles), followed by Environmental Research (53 articles) and the International Journal of Environmental Research and Public Health (48 articles). These journals are all indexed in SCIE, and several are also indexed in SSCI. The journal Environmental International stands out with the highest Journal Impact Factor (JIF) of 10.3, closely followed by Environmental Health Perspectives, with a JIF of 10.1. Journals such as Environmental Pollution and Plos Medicine also show significant impact, with JIFs of 7.6 and 10.5, respectively (

Table 1. Number of publications, Citation Indexes, and Journal Impact Factors for the top 20 journals with the highest number of publications on the impact of CC on NCDs.

Journal	Articles	SCIE	SSCI	JIF *
Science of The Total Environment	70	+		8.2
Environmental Research	53	+		7.7
International Journal of Environmental Research and Public Health	48	+		2.2
International Journal of Biometeorology	42	+		3
Environment International	36	+		10.3
Environmental Science and Pollution Research	23	+		3.5
Environmental Health Perspectives	22	+		10.1
Environmental Health	20	+		5.4
Plos One	19	+		2.9
Scientific Reports	19	+		3.8
Bmc Public Health	14	+		3.5
Environmental Pollution	12	+		7.6
Urban Climate	12	+		6
International Journal of Environmental Health Research	11	+		2.2
Air Quality Atmosphere and Health	9	+		2.9
Frontiers in Public Health	9	+	+	3
Epidemiology	7	+	+	4.7
Plos Medicine	7	+		10.5
Bmj Open	6	+		2.4
Climatic Change	6	+		4.8

A plus sign (+) indicates that the journal is indexed in the respective database (SCIE or SSCI). JIF: Journal Impact Factor, SCIE: Science Citation Index Expanded, SSCI: Social Sciences Citation Index. * Journal Impact Factor (JIF) values for the year 2023 according to Web of Science.

).

3.1.3. Distribution of Articles by Country

The distribution of articles by country was analyzed. Figure 3 shows the top 20 countries with the highest number of publications according to the country of the corresponding author. Figure 4 visualizes the distribution of publications by the country of the co-authors (Figure 4a) and corresponding authors (Figure 4b) on the map using the number of publications. The number of countries contributing to the literature on the impact of CC on NCDs is 51, counting the countries of the corresponding authors, and 68, counting the countries of the co-authors. In Figure 3, the sum of the blue and orange lines refers to the number of publications associated with the country of the corresponding author. The blue line, representing SCPs (single-country publications), indicates the proportion of publications where all authors belong to the same country as the corresponding author. Conversely, the orange line, representing MCPs (multi-country publications), signifies the proportion of articles with at least one author from a country other than the country of the corresponding author. The analysis encompasses a total of 51 countries with research article publications in the analyzed literature. The five countries with the highest number of publications are China (n = 221), the United States of America (USA) (n = 142), Australia (n = 53), Spain (n = 36), and Korea (n = 34).

Figure 4 maps the geographical distribution of countries that have or have not contributed to the literature on the impact of climate change on NCDs and presents the global impact of climate change map, highlighting multiple severe impacts, courtesy of the Met Office [33]. The first map (Figure 4a) visualizes the distribution of article counts based on the countries of all co-authors, with countries shaded according to the number of articles that they contributed. The second map (Figure 4b) shows the distribution of articles based on the country of the corresponding author. Similarly, both maps show that China and the USA have the largest number of publications and that a large part of the African region does not contribute to the literature. In both maps, countries with no published articles are shown in gray, while the color gradient from light green to dark green indicates an increasing number of publications. In this combined figure, the countries most vulnerable to the multidimensional impacts of climate change overlap with most of the countries with low publication production.

In addition, this study grouped the author countries based on the United Nations Development Program Human Development Index (UNDP-HDI) and the WHO regional classification and analyzed the frequency distribution of the publications [34,35]. According to the HDI, very high HDI countries contributed 59.6% of the publications, followed by high HDI countries with 37.2%, medium HDI countries with 2.8%, and low HDI countries with 0.6%. By region, the Western Pacific region contributed 45.2%, followed by the European region with 25.7%, the Americas region with 23.9%, the Eastern Mediterranean region with 2.2%, the Southeast Asia region with 1.7%, and the African region with 1.4%.

3.1.4. Network Visualization of International Collaborations and Author Keywords

In this study, co-authorship analysis was performed for a total of 36 different countries with a minimum number of five documents (Figure 5). It can be seen that the top three countries with the highest number of articles, i.e., the USA, China, and Australia, have strong academic collaborations and high productivity levels. In particular, the collaboration between the USA and China shows high citation and link strength. Australia and the United Kingdom are other countries that also show high link strength and strong collaborations. Geographically, European and North American countries have the most intense collaborations, while Asian and African countries have more limited collaborations. India, Iran, Vietnam, and Bangladesh have lower levels of collaboration but show increasing academic engagement.

In the context of the analysis conducted on author keywords, a total of 1115 author keywords were analyzed, with a minimum of five occurrences, and eight clusters consisting of 96 keywords with strong links were produced. The subsequent Figure 6) illustrates the clustering of author keywords according to color and the number of items.

Looking at the clusters derived from the analysis, it is clear that, with the exception of cluster 7, each group highlights the health outcomes associated with climate change parameters, providing valuable insights into the health effects examined alongside environmental factors. Cluster 1 (26 items, red) mainly highlights the strong associations between climate change, air pollution and respiratory diseases, allergic diseases, and children’s health. Cluster 2 (22 items, green) highlights the link between commonly used climate change terms, such as ambient temperature and diurnal temperature range, and cardiovascular disease, respiratory mortality, and vulnerable populations. Cluster 3 (17 items, dark blue) shows a strong relationship between temperature and heat waves and mortality and morbidity. Cluster 4 (13 items, yellow) represents the effects of respiratory diseases, air temperatures, and pollution. Cluster 5 (seven items, purple) illustrates the links between meteorological events (humidity, extreme weather, urban heat island, meteorological factor) and chronic obstructive pulmonary disease and dehydration. Cluster 6 (six items, light blue) shows the relationship between heat, cold, and health problems, such as hypertension and stroke. Cluster 7 (five items, orange) forms a more focused group, focusing on specific health issues such as hospital admissions, cardiovascular disease, and respiratory problems. The list of keywords in each cluster is presented in

Table 2. Clusters of author keywords from the impact of CC on NCDs literature (source: VOSviewer).

Clusters		Keywords
Cluster 1	26 items, red	climate change, air pollution, asthma, climate, ozone, allergic diseases, environmental health, epidemiology, global warming, health effect, particular matter, human health, pm2.5, allergic rhinitis, child, generalized additive mixed model, pollen, atopic dermatitis, child health, hot temperature, aeroallergen, air quality, cardio-respiratory diseases, interaction, non-communicable disease, pollution
Cluster 2	22 items, green	cardiovascular disease, distributed lag analysis, diurnal temperature range, ambient temperature, extreme temperature, China, case-crossover, cold spell, emergency admissions, temperature variability, vulnerable groups, cardiovascular mortality, elderly, respiratory mortality, year of life lost, attributable fraction, cause-specific mortality, high temperature, relative humidity, projection, disease burden, lag effect
Cluster 3	17 items, dark blue	temperature, mortality, heat wave, morbidity, hospitalization, extreme heat, health, public health, vulnerabilities, adaptation, drought, Vietnam, socioeconomic, heat-related illness, excess heat factor, flood, Spain
Cluster 4	13 items, yellow	respiratory disease, effect modification, emergency, air temperature, attributable risk, chronic kidney disease, fine particulate matter, time series, ageing, childhood asthma, circulatory disease, cold wave, urbanization
Cluster 5	seven items, purple	chronic obstructive pulmonary disease, heat stress, meteorological factor, humidity, dehydration, extreme weather, urban heat island
Cluster 6	six items, light blue	heat, weather, cold, hypertension, stroke, cause of death
Cluster 7	five items, orange	hospital admissions, respiratory, cardiovascular, apparent temperature, South Africa

Author keywords in each cluster are ranked according to their frequency of occurrence.

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3.1.5. Thematic Analysis

The thematic analysis of research articles in the field of the impact of climate change on non-communicable diseases is presented with a thematic map focusing on the conceptual structure of the literature in this field and a thematic development analysis focusing on the evolution of research themes.

The thematic map, based on author keywords, is presented in Figure 7. Upon examination of the predominant themes within the research, it is evident that “Bayesian analysis, diabetes mellitus, green space, heat exposure, and productivity” emerge as the themes that exhibit the highest density and centrality values. A plethora of niche themes were identified in the extant literature on the impact of climate change on non-communicable diseases, suggesting that the concept may develop especially in relation to themes of “dehydration, occupational heat stress, and workload”. Among the major themes identified in the research, “climate change, air pollution, asthma, temperature, mortality, and heat wave” have both a large size and high centrality. In contrast, there is a paucity of themes in the lower left quadrant, which include “drowning, storm asthma, ischemic stroke, and causes of death”. In light of the emergent field of research concerning the nexus between climate change and non-communicable diseases, these subjects warrant further exploration and expansion.

Figure 8 presents an analysis of the thematic evolution of the research literature based on author keywords, which is indicative of the evolving research focus over specific periods. The thematic evolution of the literature during the period 2000–2024 was analyzed by dividing it into five distinct time periods (2001–2005, 2006–2010, 2011–2015, 2016–2020, 2021–2024). In the initial period (2001–2005), “climate change and mortality” emerged as the predominant themes. In the subsequent period (2006–2010), there was an increase in the volume of research on “mortality, hospital admissions, global warming, and air pollution”, which also became areas of focus. In the third phase (2011–2015), while the “climate change” theme continued, we saw the emergence of new parameters related to climate change, such as “ozone, meteorological factors, ambient temperature, and heat stress”, and health-related themes, such as “allergic diseases and cardiovascular diseases”. In the fourth period (2016–2020), new themes such as “environmental health, child health, allergic diseases, dehydration, hypertension, COPD (chronic obstructive pulmonary disease), and acute kidney injury” were added to the health-related themes. Recently (2021–2024), themes such as “climate change, drought, air pollution, and particulate matter”, as well as “hypertension, allergic diseases, asthma, and cardio-respiratory diseases”, have emerged.

3.2. Topic Modeling Analysis

3.2.1. Structural Topic Modeling

In this study, STM was applied to analyze the thematic structure of the literature focusing on the impact of climate change on NCDs. As a result of this analysis, 24 topics were identified, and the topics are presented in

Table 3. Discovered topics and keywords for the impact of CC on NCDs literature.

Topic Name	Topic Keywords	Rate
Temperature Effects	temperature, effect, lag, risk, model, extreme, high, China, distribute, cold, rr (relative risk), relative, day, low, daily	11.77%
Future Climate Scenarios	future, scenario, increase, population, model, project, estimate, emission, projection, disease, health, burden, global, impact, death	6.37%
Extreme Heat Waves	heat, wave, extreme, event, day, effect, impact, increase, risk, period, duration, health, percentile, higher, daily	5.54%
Temperature Thresholds	temperature, degree, increase, daily, day, threshold, cold, ambient, effect, mean, maximum, summer, hot, weather, model	5.26%
Hospital Admission	admission, hospital, disease, increase, kidney, heat wave, morbidity, health, renal, day, temperature, respiratory, emergency, association, injury	5.12%
Air Pollution Effects	air, pollution, ozone, effect, increase, health, respiratory, pollutant, exposure, interaction, concentration, particulate, level, matter, quality	4.99%
Public Health Impact	health, impact, public, environmental, local, outcome, risk, policy, care, disease, adverse, community, report, human, find	4.71%
Weather Risks for Stroke	hospitalization, stroke, risk, increase, association, ischemic, exposure, patient, dust, acute, day, associated, case-crossover, weather, cardiovascular	4.57%
Occupational Heat Exposure	heat, worker, exposure, stress, work, rate, blood, strain, cardiovascular, kidney, function, thermal, outdoor, physiological, compare	4.43%
Disease Burden Estimates	burden, disease, temperature, attributable, COPD (chronic obstructive pulmonary disease), death, high, yll (years of life lost), life, global, fraction, ecu (emergency care utilization), region, rate, estimate	4.29%
Pollen Allergies	pollen, allergic, symptom, season, patient, ad (allergic disease), allergy, concentration, rhinitis, sensitization, tree, skin, grass, count, prevalence	4.16%
Temperature Variability	tv (temperature variability), variability, temperature, exposure, association, disease, increase, flood, cardiovascular, adult, humidity, annual, estimate, long term, emergency	4.02%
Meteorological Impact	drought, meteorological, daily, variable, period, humidity, factor, impact, rainfall, pressure, incidence, region, respiratory, relative, condition	3.88%
Pediatric Emergencies	visit, asthma, emergency, ed (emergency department), department, child, outpatient, childhood, association, patient, hospital, exacerbation, increase, age, relationship	3.74%
Mortality Causes	mortality, death, cause, respiratory, cardiovascular, increase, city, excess, age, all-cause, disease, total, non-accidental, cause-specific, heat	3.60%
Thermal Stress	index, weather, stress, temperature, condition, human, thermal, winter, disease, utcı (universal thermal climate index), health, cardiovascular, type, hot, air	3.32%
Gestational Heat Exposure	exposure, pregnancy, birth, temperature, heat, maternal, association, ambient, associate, outcome, week, risk, increase, woman, gestational	3.19%
Patient Management	patient, factor, risk, disease, consultation, income, illness, incidence, rate, chronic, level, model, control, participant, individual	3.05%
Residential Heat Effects	urban, heat, green, space, vulnerability, rural, increase, island, city, environment, country, population, effect, high, rate	2.91%
Water Quality Effects	water, salinity, effect, child, health, lake, coastal, participant, respiratory, hypertension, increase, bp (blood pressure), pressure, blood, food	2.77%
Risk Factors in Elderly	age, population, disease, risk, older, elderly, individual, group, sex, higher, factor, people, heat, vulnerability, status	2.35%
Weather Risks for CVD	cold, cvd (cardiovascular disease), spell, cardiovascular, disease, rural, effect, association, energy, group, weather, impact, heat, efficiency, apparent	2.22%
Diurnal Temperature Effect	dtr (diurnal temperature range), season, range, age, admission, diurnal, cvd (cardiovascular disease), disease, effect, cardiovascular, hospital, rd (respiratory disease), extremely, tcn (temperature change between neighboring days), er (emergency room)	2.08%
Respiratory Risk Modeling	effect, respiratory, city, health, risk, estimate, different, model, characteristic, level, country, region, compare, modification, potential	1.66%

in descending order of percentage. In addition, the top 15 keywords associated with each topic provide further insights into the focus areas of this study.

The topics demonstrate that the intersection of climate change and NCDs covers a broad spectrum of areas, ranging from “temperature effects” to “Air Pollution Effects”, “hospital admission” to “extreme heat waves”, and “Residential Heat Effects” to “Weather Risks for Stroke” (Table 2). The top five most discussed topics were “temperature effects” (11.77%), “Future Climate Scenarios” (6.37%), “extreme heat waves” (5.54%), “temperature thresholds” (5.26%), and “hospital admission” (5.12%). In contrast, the least addressed topics included and “Weather Risks for CVD (cardiovascular disease)” (2.22%), “Diurnal Temperature Effect” (2.08%), and “Respiratory Risk Modeling” (1.66%).

3.2.2. Exploring Thematic Categories from Discovered Topics

The analysis focused on identifying key thematic areas and categorized, in detail, the intersections of climate change with NCDs. Thus, by examining the prevalence and distribution of issues, it provided insights into how climate affects NCDs and informs future research directions. As shown in Figure 9, the analysis reveals four major thematic categories—“climate factors” (38.92%), “environmental impact” (22.58%), “public health projections” (18.01%), and “Risks for NCDs” (20.50%)—each capturing a significant portion of the research landscape at the intersection of climate change and health. These categories collectively emphasize the diverse ways in which climate change influences NCDs and broader public health concerns.

The alterations and acceleration of the subjects identified over the past decade are outlined in

Table 4. Trends of each discovered topic.

Topic Name	2015	2016	2017	2018	2019	2020	2021	2022	2023	2024	ACC 2015–2024
	%	%	%	%	%	%	%	%	%	%
Temperature Variability	0.00	2.94	4.76	6.67	12.20	1.72	6.00	2.60	5.32	5.81	⇑ 0.58
Pollen Allergies	0.00	2.94	4.76	2.22	4.88	1.72	6.00	1.30	4.26	4.65	⇑ 0.47
Residential Heat Effects	0.00	2.94	4.76	0.00	2.44	3.45	4.00	5.19	4.26	4.65	⇑ 0.47
Disease Burden Estimates	3.45	2.94	4.76	4.44	4.88	5.17	6.00	6.49	4.26	6.98	⇑ 0.35
Air Pollution Effects	3.45	2.94	7.14	2.22	4.88	3.45	4.00	5.19	3.19	6.98	⇑ 0.35
Weather Risks for CVD	0.00	2.94	0.00	0.00	2.44	1.72	0.00	1.30	6.38	3.49	⇑ 0.35
Thermal Stress	0.00	0.00	0.00	4.44	0.00	6.90	8.00	3.90	5.32	3.49	⇑ 0.35
Water Quality Effects	0.00	2.94	2.38	2.22	2.44	5.17	6.00	2.60	2.13	3.49	⇑ 0.35
Diurnal Temperature Effect	0.00	2.94	0.00	0.00	2.44	0.00	4.00	3.90	3.19	3.49	⇑ 0.35
Future Climate Scenarios	6.90	8.82	4.76	6.67	7.32	10.34	4.00	3.90	5.32	9.30	⇑ 0.24
Hospital Admission	3.45	8.82	7.14	6.67	4.88	5.17	8.00	1.30	5.32	5.81	⇑ 0.24
Patient Management	3.45	2.94	4.76	2.22	0.00	3.45	8.00	3.90	2.13	5.81	⇑ 0.24
Weather Risks for Stroke	3.45	2.94	2.38	4.44	2.44	10.34	0.00	5.19	4.26	5.81	⇑ 0.24
Gestational Heat Exposure	0.00	0.00	4.76	2.22	4.88	0.00	2.00	5.19	8.51	2.33	⇑ 0.23
Risk Factors in Elderly	3.45	2.94	2.38	2.22	2.44	1.72	0.00	2.60	1.06	4.65	⇑ 0.12
Pediatric Emergencies	0.00	17.65	2.38	2.22	0.00	0.00	8.00	5.19	3.19	1.16	⇑ 0.12
Occupational Heat Exposure	6.90	0.00	0.00	0.00	4.88	10.34	2.00	5.19	5.32	3.49	⇓ −0.34
Extreme Heat Waves	6.90	2.94	9.52	6.67	7.32	3.45	0.00	1.30	5.32	2.33	⇓ −0.46
Public Health Impact	6.90	5.88	2.38	6.67	4.88	6.90	2.00	6.49	4.26	2.33	⇓ −0.46
Respiratory Risk Modeling	6.90	8.82	2.38	2.22	0.00	0.00	0.00	2.60	0.00	2.33	⇓ −0.46
Mortality Causes	6.90	0.00	0.00	2.22	0.00	0.00	4.00	3.90	1.06	2.33	⇓ −0.46
Temperature Effects	13.79	5.88	9.52	24.44	19.51	5.17	10.00	19.48	13.83	8.14	⇓ −0.57
Meteorological Impact	10.34	5.88	7.14	2.22	4.88	10.34	6.00	0.00	2.13	0.00	⇓ −1.03
Temperature Thresholds	13.79	2.94	11.90	6.67	0.00	3.45	2.00	1.30	0.00	1.16	⇓ −1.26

ACC: acceleration. The symbol ⇑ indicates positive acceleration, while the symbol ⇓ represents negative acceleration.

.

The distribution of the four themes—climate factors, environmental impact, Risks for NCDs, and public health projections—across the WHO regions reveals distinct regional patterns.

At the HDI level, low HDI countries are overwhelmingly focused on environmental impact (83.3%), with minimal attention to other themes. As the HDI increases, the distribution becomes more balanced, with high HDI countries focusing more on Risks for NCDs (29.1%) and climate factors (25.4%), while very high HDI countries show a more even spread across all themes, particularly environmental impact (32.2%) and Risks for NCDs (22.0%) (Figure 10a).

In the Africa region, environmental impact is the most prevalent theme, accounting for 62.5%. In the Eastern Mediterranean region, environmental impact (43.8%) and public health projections (41.7%) are the dominant themes. In the European region, the distribution of themes is more balanced, with environmental impact being the most emphasized (32.6%), followed by climate factors (26.2%), Risks for NCDs (22.6%), and public health projections (18.7%). In the Americas region, environmental impact is the leading theme at 43.2%, followed by climate factors (20.4%), public health projections (18.4%), and Risks for NCDs (18.1%). In Southeast Asia, environmental impact (33.3%) and Risks for NCDs (30.0%) are the most prominent themes. In the Western Pacific region, the themes are relatively evenly distributed, with climate factors (31.4%) leading, followed by Risks for NCDs (27.3%), environmental impact (22.7%), and public health projections (18.6%) (Figure 10b).

3.3. Content Analysis

Evidence of the growing interest in the topic is evident in the increasing number of academic publications. However, it is also valuable to present the parameters examined in the context of the impact of climate change on non-communicable diseases. The results of the qualitative content analysis in this section are centered on the research questions derived from the limitations and conclusions sections of the studies. The 50 most cited research articles were included in the content analysis. The numerical distribution and total citations (TCs) of the 50 most cited articles by year, country, affiliation, and journal are shown in

Table 5. The numerical distribution and total citations (TCs) of the 50 most cited articles by year, country, affiliation, and journal.

		n	%	TCs
Year	2001	1	2	466
	2002	2	4	355
	2003	2	4	286
	2004	2	4	447
	2006	3	6	1242
	2007	3	6	688
	2008	5	10	1514
	2009	5	10	1087
	2010	4	8	947
	2011	3	6	1168
	2012	4	8	600
	2013	4	8	508
	2014	6	12	1084
	2015	3	6	1867
	2016	2	4	503
	2017	1	2	198
Affiliation *	University of London	2	4	1878
	Harvard University	5	10	1295
	Yale University	1	2	760
	Universite Paris Cite	1	2	688
	Athens Medical School	2	4	623
	Columbia University	1	2	529
	National and Kapodistrian University of Athens	1	2	475
	Maastricht University	1	2	466
	Australian National University	1	2	443
	Seoul National University (SNU)	3	6	414
	Chinese Center for Disease Control and Prevention	2	4	406
	Complutense University of Madrid	2	4	355
	University of Michigan System	2	4	312
	Fudan University	2	4	307
Country *	USA	16	32	4015
	UK	5	10	2518
	China	7	14	1140
	Greece	3	6	1098
	Spain	5	10	893
	France	2	4	810
	Australia	2	4	628
	Netherlands	2	4	612
	South Korea	3	6	414
Journal *	Environ Health Persp	9	18	2943
	Lancet	2	4	1828
	Int Arch Occ Env Hea	3	6	1014
	Epidemiology	5	10	883
	Int J Epidemiol	3	6	773
	Occup Environ Med	2	4	716
	P Natl Acad Sci Usa	3	6	646
	Am J Epidemiol	2	4	644
	Sci Total Environ	4	8	563
	Environ Health-Glob	1	2	491
	Environ Res	2	4	307
	Int J Biometeorol	2	4	291

The data are sorted by total citations (TCs), except for years. * Affiliations, countries, and journals with n = 1 and TCs < 300 among the top 50 most cited articles are not presented in the table and are as follows. Affiliations: Russian Academy of Sciences, University of Texas System, University of Oxford, Pompeu Fabra University, University of York—UK, National Oceanic Atmospheric Admin (NOAA)—USA, Imperial College London, University of Adelaide, Centre for Research in Environmental Epidemiology, Peking University, Autonomous University of Madrid, Czech Academy of Sciences, Netherlands National Institute for Public Health and the Environment, Universidade de Sao Paulo, Exponent, University System of Georgia, Southern Medical University—China, Kalyani University, Nanjing University, Emory University, University of Genoa, University of California System, Universite Paris Saclay, and Princeton University. Countries: Russia, Czech Republic, Brazil, India, and Italy. Journals: Sci Rep-Uk, Jama-J Am Med Assoc, Environ Int, Bmc Public Health, Eur J Public Health, Part Fibre Toxicol, Environ Sci Technol, Environ Pollut, Ind Health, Ann Allerg Asthma Im, J Allergy Clin Immun, and Atmos Chem Phys.

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The following questions were addressed in the content analysis, and the codes and categories specified under each question were derived accordingly:

RQ1: 

What have we learnt from research on the impact of climate change on non-communicable diseases?

Vulnerable Population: The most emphasized vulnerable group in the studies was the elderly. Other vulnerable groups included populations in different regions, people with chronic diseases, women, children, middle-aged men, and people living alone.

Morbidity: The most frequently analyzed variable was high temperature, followed by heat waves. Other climate change variables, such as the diurnal temperature range, ozone, particulate matter, and cold weather/spells, were reported less frequently with regard to their effect on morbidity.

Mortality: The most frequently examined variable related to mortality was heat waves, followed by cold weather/spells and then high temperatures. Other climate change variables, such as the diurnal temperature range, temperature variability, ozone, particulate matter, and the interaction between climate change and air pollution, were also examined, albeit to a lesser extent.

Hospital admission: The parameter that was the most emphasized as a driver of hospital admissions was heat waves. Other significant variables included high temperatures and the diurnal temperature range.

Healing effect: In a particular study, the healing effect of green areas on the health outcomes of climate variables was reported.

RQ2: 

What recommendations have been developed in the research on the impact of climate change on non-communicable diseases?

Public health interventions: The most frequently proposed course of action in the extant research is the development of public health interventions for the health impacts of climate change. As public health interventions, it is recommended to increase adaptive capacity by expanding the range of climate change impact prediction and prioritizing vulnerable groups in the interventions to be made. In addition, based on the research findings, it is recommended that prevention interventions should be developed (prevention practice), health promotion programs should be implemented (health promotion), community-specific action plans should be implemented (action plan), and cold waves should not be neglected in public health interventions.

New research: A recurrent recommendation in research proposals is the initiation of novel research endeavors. In this instance, the emphasis is placed on documenting evidence of the impact of climate change on health, with a particular focus on other regions and societies. Other common recommendations include diversification of the effect of more mixers and an increase in the number of different weather variables (e.g., wind speed, humidity, etc.), evaluation of the adaptive capacity of communities, provision of new recommendations to policymakers, increase in research duration, and diversification of the definitions of heat/cold waves used in research.

Public policy: In the context of public policy, the most salient recommendation pertained to the formulation of health service plans that proactively address anticipated health requirements. In addition, governments must consider the interaction with climate change, improve air quality, fight climate change, implement workplace policies to combat heat stress in workplaces, eliminate health inequalities, implement public policies by taking into account the different sensitivities of regions (regional regulations), and publish public messages (public notice).

Warning system: The research suggested the creation of warning systems for heat waves and cold waves.

RQ3: 

What are the limitations of the research on the impact of climate change on NCDs?

Climate data source/classification: The two most frequently cited limitations of the studies were that the meteorological data utilized in the analyses of the effects of climate change parameters on human health were obtained from monitoring stations (air temperature monitoring station) and that the definitions (temperature definitions/limits) employed for the parameters evaluated were insufficient to demonstrate the real effect. In another study, the limitations were the use of the parameter ambient temperature, which may be a modifier of many factors, and the fact that air pollution and pollen data were obtained from a single monitoring station (air pollution monitoring station, pollen monitoring station).

Lack of confounding factor data: It was asserted that a number of confounding factors, including, but not limited to, air pollution, influenza pandemic data, other meteorological variables, the effect of air conditioning, ozone levels, personal risk factors, ambient conditions, and vacation days, were not evaluated in the studies.

Population size/variety: Another limitation that was emphasized was the lack of city diversity, race/ethnicity, sample size, and different climatic zones in terms of population characteristics.

Health data source/identification: Limitations were reported that included limited access to data and possible errors in the registration of diagnoses/ICD selection. These limitations may have an effect on the results of the research.

Time length: Finally, in fewer studies, the short duration of the study and the inability to demonstrate the prolonged impact of climate change on health were reported.

4. Discussion

A review of the literature was conducted using prominent databases and search engines, including Scopus, Web of Science, and Google Scholar. The results indicated a predominance of bibliometric research focusing on the nexus between climate change and human health, with a particular emphasis on food security, infectious diseases, and public health [17,36,37]. This subject was only briefly addressed in the keyword analysis of a select number of bibliometric analysis studies on climate change and human health [38,39].

4.1. Trends in Article Publication by Year

A close analysis of the distribution of research articles by year reveals a marked increase in the number of publications, particularly since 2010. It is noteworthy that over half of the research articles were published in the last five years, with 2023 marking the highest publication rate. However, it is important to note that this study covers the period until December 2024, and, therefore, the number of publications in 2024 may be higher. In Sweileh’s bibliometric analysis article, which covers the years 1980–2019 and examines the relationship between general health and infectious diseases and climate change, it is observed that the annual growth of publications was higher than 2007; in Raval’s bibliometric analysis of research articles on the impact of climate change on public health dynamics between 2000 and 2023, it is observed that publications in this field show exponential growth after 2018, but the highest rate was reached in 2009 [17,40]. Kolsky’s bibliometric analysis of climate change publications in Pubmed, a health database, between 2009 and 2022, also supports this. It states that the publications increased significantly after 2010, with half of them being published between 2019 and 2022 [39].

As demonstrated by the bibliometric analysis of studies evaluating the literature on the impact of climate change on human health in different aspects, the number of publications in this field has increased over the last 15 years, a finding that is in line with the results of our own research. Moreover, this increase has become more pronounced in the last 5 years. As emphasized in the literature, the increasing scope and severity of the adverse impacts of climate change are likely to have increased academic interest in the topic among scientists [41]. In addition, the increase in the number of climate and health datasets, which provide the opportunity to examine the interactions between climate change and non-communicable diseases in a more systematic and in-depth manner, and the widespread use and easy accessibility of these data, are also likely to have supported the increase in the related research.

4.2. Metrics of the Top 20 Journals

The main common characteristics of the top 20 journals in Table 1 are that they are important resources that seek solutions to global problems by producing scientific knowledge in areas such as environmental science, public health, and climate change and that the publications in these journals are highly cited. These journals stand out as peer-reviewed, multidisciplinary scientific platforms that involve international collaborations and publish research that guides policymakers. Research published in these journals can influence not only the academic world but also environmental policies, public health strategies, and climate change mitigation plans. Since environment and public health are interdisciplinary topics, researchers from different fields, such as environmental engineering, medicine, biology, meteorology, epidemiology, and sociology, collaborate in these journals. However, positive changes in the number of scientific publications, citation rates, and international collaborations related to global climate change can have a significant impact on policy-making processes, particularly in the health sector. Today, advances in communication, information, and informatics can guide policymakers and decision-makers who rely or wish to rely on scientific information and can help encourage or even compel other policymakers and decision-makers to engage in social accountability, transparency, and evidence-based practices.

4.3. Distribution of Articles by Country and International Collaboration

The distribution of articles by country, based on the Human Development Index (HDI) levels of the countries and regional classifications, revealed significant disparities in research production. Countries with very high or high HDI levels, such as China, the United States, Australia, Spain, South Korea, and some Western European countries, stand out as major contributors to the literature. Furthermore, these countries also have the highest levels of academic collaboration. In Fu and Waltman’s bibliometric analysis of global climate change research published between 2001 and 2018, the countries that published the most articles were reported as the USA, China, the UK, Australia, and Germany, and it was revealed that China’s number of publications increased rapidly since 2010 [42]. The results were thought to be due to the fact that these countries have strong scientific infrastructure, good access to research funding, robust academic collaboration networks, and high academic interest in the research area under study.

A total of 50% of the research was reported from China (30.7%) and the USA (19.7%). Moreover, China and the USA are the two largest emitters of greenhouse gases, which has a very significant impact on climate change. In the wake of international agreements, both the US and China have initiated a series of cooperative endeavors to decelerate and adapt to climate change. However, despite China’s leadership in global CO₂ emissions and its ratification of the Paris Agreement, its actions are not aligned with its stated goals, primarily due to its continued reliance on fossil fuels [43,44]. In contrast, the United States, the second largest producer of greenhouse gas emissions, appears to have abdicated its responsibility due to policy ups and downs and its withdrawal from the Paris Agreement [45,46]. In this context, policymakers should not ignore the efforts of scientists in this area of research and the extensive scientific data available.

On the other hand, a third of the world’s countries do not contribute to the research papers published in this field. According to the Notre Dame Global Adaptation Initiative rankings, which assess a country’s capacity to provide resources and financing to adapt to climate change, the top twenty most vulnerable countries, particularly those in Africa, largely overlap with countries that have not contributed to the literature on the impact of climate change on non-communicable diseases [47]. According to the Met Office’s projections of the global impact of climate change, countries in Africa and South America that are expected to be the most affected by climate change stand out for their research gaps [33].

Given the uneven distribution of the literature and international collaboration across countries and the high vulnerability of these countries to climate change, this situation represents a significant barrier to both the development of effective adaptation strategies and the representation of regional and global health outcomes in the literature. These findings should encourage researchers to focus on underrepresented regions, strengthen scientific collaboration, and motivate low-income, research-disadvantaged regions to conduct studies on climate change and health impacts. Policymakers should also take steps to strengthen scientific research infrastructure, increase research incentives, and support regional collaboration in low- and middle-HDI countries. In this way, global health policy can become more inclusive and provide a more equitable and effective approach to tackling climate change.

4.4. Network Visualization of Author Keywords

The VOSviewer analysis of author keyword networks reveals the multidimensional nature of the research on the impact of climate change on non-communicable diseases (NCDs). Each cluster links specific climate parameters to different health outcomes. For example, cluster 1 links air pollution, ozone, and pollen to allergic diseases, while cluster 2 links temperature variability and extreme temperatures to cardiovascular and respiratory diseases.

Clusters 3 and 7 highlight the burden on health systems, with keywords such as “hospitalization” and “hospital admission”, while geographical keywords, such as “Spain”, “Vietnam”, and “South Africa”, highlight regional differences in research focus and the need for localized adaptation strategies.

The analysis highlights the health impacts of climate change on vulnerable demographic groups, such as “children” in cluster 1, “vulnerable groups” and “elderly” in cluster 2, and “frailty” in cluster 3. Keywords such as “socioeconomic” and “adaptation” in cluster 3 emphasize the role of socioeconomic factors in adapting to these impacts. Each cluster represents a unique research focus that collectively reflects the diverse approaches in the field. Future work should capitalize on these findings to develop targeted strategies to reduce climate-related health risks.

4.5. Thematic Map

The thematic map displays the distribution of themes that show how parameters related to climate change and non-communicable diseases are shaped and how future research opportunities can be identified. Density indicates the frequency with which a theme is internally linked, while centrality is a measure of the frequency with which it is linked to other themes. High density means further and in-depth development of a theme, while high centrality means more connections with other themes or placement in a central location in a particular area of research [48]. In this section, the prominent themes of the engine, basic, niche, and emerging or declining themes on the thematic map, with their density and/or centrality values, will be discussed.

As demonstrated in Figure 5, within the domain of motor themes, which are meticulously delineated and frequently identified within the research landscape, particularly the themes “Bayesian analysis, diabetes mellitus, and green space” emerge as prominent entities due to their elevated centrality and density metrics. Bayesian analysis is a pragmatic and theoretically congruent instrument for deriving inferences concerning climate change and formulating decisions predicated on those inferences [49]. The research findings indicate that it is an analysis method that has developed in the research field, is frequently used with other study topics, and can be used in future research. In the Zilbermint review on diabetes mellitus, which is another theme, it is stated that there may be a direct and indirect relationship between diabetes mellitus and the health effects of climate change, and that health problems exacerbated by climatic events, especially cardiovascular disease, are effective on health outcomes, such as mortality, morbidity, and hospital admissions [50]. As reported in the relevant studies, diabetes mellitus is a theme that is both highly associated with other themes and actively studied because of its sensitivity in terms of health problems triggered by climate change (cardiovascular disease, kidney injury, respiratory disease, etc.) and health outcomes, such as mortality, morbidity, and hospitalization, and because it is a directly affected health outcome [51,52,53,54]. Green space is recognized in the literature as an effective parameter in reversing the negative health consequences of climate change. It is considered to be a theme with high centrality due to its association with other themes in the literature and high density due to its frequency of study in relation to its increasing importance in terms of the health outcomes it mediates; it is also an effective method to mitigate the effects of climate change [55,56]. In this respect, the trends in the research in the literature on green spaces also provide a basis for SDG 11 (sustainable cities and communities) in terms of the positive effects of green spaces on health and their use as an adaptation strategy to climate change [5].

The high centrality of the themes “temperature, mortality, heat wave, climate change, air pollution, and asthma” among the basic themes obtained as a result of the research demonstrates that these themes have a significant impact on the literature, are frequently studied themes in the field, and have strong connections with other themes. Nevertheless, these themes are not thoroughly explored due to their low density values. This finding indicates that the extant body of knowledge in the relevant literature is predominantly shaped around these themes.

Among the niche themes defined as well-developed themes, the prominent themes “dehydration, occupational heat stress, and workload” have higher centrality and density than the other niche themes. This finding indicates that the research is making more and more connections in these areas and has a strong body of knowledge in itself. As stated in the literature, high temperatures cause dehydration in outdoor workers, parameters such as increasing temperature and humidity increase occupational heat stress among workers, and there is a facilitating effect of an increased workload in terms of negative health outcomes; therefore, the relationship between these themes and occupational health is revealed [57,58]. The repercussions of climate change have been demonstrated to be associated with renal, cardiovascular, mental, and respiratory health outcomes among workers, which may elucidate their centrality [59,60,61]. Consequently, given the established relationship between these themes and occupational health, it is recommended that they be a focal point of research with the potential to contribute interdisciplinary significance. As a result, given the relationship between these topics and occupational health, they are recommended as a focus for research importance and should be considered in terms of ensuring safe working environments, especially when trying to achieve SDG 8 (decent work and economic growth) [5].

The fact that niche themes, such as “biomarkers, kidney injury, comorbidity, older people, risk factors, and chronic disease”, come to the fore with low centrality and high density values shows that the literature has started to develop in the field of chronic diseases and vulnerable groups, even if it has not yet established much connection with other themes. Conversely, emerging or declining themes exhibit lower centrality and density. For example, the theme “cause of death” exhibits the lowest centrality and density, indicating that this theme has minimal interaction and connectivity within the domain. A similar observation can be made for themes such as “ischemic stroke, storm asthma”, and “flooding”, which also exhibit lower centrality and intensity values, indicating that these themes are not yet the focus of significant research or are less prevalent.

4.6. Thematic Evolution

The thematic evolution analysis demonstrates the magnitude, diversification, and interconnectedness of themes in the domain of the impact of climate change on NCDs across periods. The thematic evolution analysis demonstrates an augmentation in the diversity of research subjects pertaining to both climate change and NCDs, accompanied by a shift in the relative weighting of these themes over time. With the growing interest in climate change, the diversity and definitions of the parameters utilized to accurately ascertain its impact have expanded, novel analysis methods have been developed, and the necessity to investigate the relationship with additional health outcomes and risk factors has emerged [62,63,64]. In the first period, 2001–2005, the theme “climate change” was dominant in terms of climate change. As the periods progressed, the theme “climate change” continued to be the main theme and its weight increased, but it showed a great diversification with parameters related to climate change, such as “global warming, ambient temperature, heat waves, temperature variability, and ozone”, and new themes related to environmental events, such as “air pollution, flood, and drought”. Health-related topics revealed that while “mortality” dominated the discourse in the initial period, it subsequently lost its sway in the following periods. This was accompanied by the emergence of themes such as “hospital admission, heat stress, allergic disease, heat-related illness, dehydration, hypertension, acute kidney injury”, and “chronic obstructive pulmonary disease”. The findings of this analysis demonstrate that the research subjects in this domain continue to be predominantly influenced by the overarching theme of climate change. It is hypothesized that the salience of the climate change theme has increased over time, as evidenced by its correlation with health concerns. The mounting significance of environmental issues, such as flooding and drought, in the context of global climate change is evident. Moreover, the findings of the analysis indicate a proliferation of studies addressing increasingly specific health-related concerns. However, given the health burden of non-communicable diseases and the escalating effects of climate change on environmental risks, it is anticipated that there are numerous additional areas to be explored concerning the impact of non-communicable diseases. Expanding the scope of research on the health impacts of climate change, as demonstrated in this study, provides policymakers with valuable insights for advancing SDG 3 (good health and well-being). In addition, the increasing depth of research on the health consequences of the environmental impacts of climate change provides a strong scientific basis for supporting SDG 6 (clean water and sanitation). Furthermore, by elucidating the environmental and health impacts of climate change, this research can contribute to the formulation of effective climate change adaptation policies under SDG 13 (climate action) [5].

Another feature of thematic evolution analysis is that it reveals the relationship between themes across periods. While the “climate change” theme was mostly related to “mortality” between 2001–2005 and 2006–2010, the “climate change” theme has shown a great expansion and diversification in the years 2011–2015 and later, showing connections with diseases such as “cardiovascular disease, cardio-respiratory diseases, and chronic obstructive pulmonary disease (COPD)” and environmental variables such as “air pollution, heat waves, and temperature variability”. This shows that the studies on both climate change and health dimensions have deepened in the literature examining the effects of climate change on non-communicable diseases.

4.7. Topic Modeling Analysis

Topic modeling is a sub-field of text mining that aims to reveal both explicit and implicit topics in documents. It has been an area of increasing importance in recent years [26]. Structural Topic Modeling (STM) analysis methodically delineates the identified topics, documents their trends over the past decade, and categorizes them. The diversity of topics explored reveals the multifaceted interaction between climate and health, and the categories derived from the topics reveal the various ways in which climate change affects non-communicable diseases, the most studied topics in the field, and the changing interests of the scientific community in these topics.

The “climate factors” category, the largest category, highlights the central role of climatic variables in shaping health outcomes, while the “environmental impact” category draws attention to specific environmental risks exacerbated by climatic conditions and their impacts on health, including topics such as air pollution and pollen allergies. The “Risks for NCDs” category focuses on the direct links between climate factors and non-communicable diseases, and the “public health projections” category draws attention to issues, such as the effects of climate change on public health, mortality and disease burden, vulnerable groups, and patient management, and emphasizes the importance of targeted interventions.

The results of the topic model analysis indicate that while “temperature effects”, “extreme heat waves”, and “temperature thresholds”, which are evaluated under the category of “climate factors” in the 2001–2024 time period, were the most studied topics in all years, there has been a decline in interest in these topics in recent years. It was determined that the theme “temperature variability” in this category increased with the highest acceleration, and the topics “diurnal temperature effect” and “Future Climate Scenarios” also accelerated positively. This shows that there is an increase in interest from commonly used terms in research to new terms in climate factors, similar to previous findings.

A decline in the utilization of public health impact and mortality causes—related topics within the public health projections category—was observed. Conversely, an increase in the employment of disease burden estimates, patient management, and risk factors in elderly subject-related topics was evident. The decline in the focus on mortality and the rise in topics concerning the elderly and vulnerable groups are in alignment with the findings of our thematic analysis. A general increase in the utilization of all subjects in the Risk for NCDs and environmental impact categories was observed, with fluctuations in the weighting between years.

The results of both the thematic analysis and the topic modeling analysis show the current trends in scientific publications, where NCDs and the health effects of environmental factors caused by climate change are actively explored and developed as research topics. The fact that the scientific community has been interested in and investigated topics that change over time is important in terms of generating evidence on different topics. This scientific evidence should be monitored and taken into account not only by scientists but also by policymakers or decision-makers in the design of public policies. For example, should the goal of policymakers or public administrators in controlling heat waves be to take reactive measures only when temperatures rise? Or should it be to tighten air quality standards and to effectively and continuously implement evidence-based practices and mechanisms to ensure social adaptation and resilience to prevent their release into the environment? Or should it be to develop prevention and early warning programs integrated into national health systems, perhaps developed in international cooperation, to reduce the burden of disease from climate change? In developing these strategies, could an examination of the current knowledge and interest of the scientific community provide important solutions and strategies for both environmental sustainability and public health? These and similar questions indicate that changes in the scientific community on these issues should be taken into account in the formulation of public policy. Normally, the world of science studies many topics, and, over time, there are natural differentiations and changes in the topics studied. However, in the context of global climate change and, in particular, its effects on health, it would not be wrong to say that it has become imperative for public policymakers or decision makers to closely follow the work of the scientific world with a view to the future.

The distribution of the four themes (public health projections, NCD risks, environmental impacts, climate factors) based on the UNDP HDI and WHO regional classification shows that research themes differ according to the level of development and geographical location of countries. Low- and medium-HDI countries tend to focus primarily on environmental impacts, while high- and very-high-HDI countries have a more balanced distribution across the four themes. Similar differences can be observed across regions. Environmental impacts dominate the research themes in Africa and the Eastern Mediterranean regions, while the distribution of themes in other regions is more balanced. Several factors may underlie the regional and developmental differences in research themes. The presence of sufficient financial and scientific infrastructure (e.g., number of researchers, equipment, reliable and long-term data collection) and the adoption of advanced health systems and public health approaches are likely to positively influence the diversity and volume of research [65,66]. In contrast, in countries with limited resources, researchers and policymakers may be more likely to focus on urgent and life-threatening issues [67]. Therefore, the finding that certain issues are under-researched in a region or at a certain level of development should not be interpreted as an indication that these issues are not a problem for that region. On the contrary, the under-research of these issues may lead to serious health problems and hinder global efforts to address the health impacts of climate change. As emphasized in previous sections of the Discussion, it is critical to understand the research gaps in each region and the reasons for these gaps.

4.8. Content Analysis

By systematically analyzing textual data, content analysis helps to illuminate complexities in the literature on the topic of interest, reveals research trends as well as their effects, and provides valuable information for evidence-based practice [68]. In the present study, a content analysis of the results from the top 50 most cited articles was conducted to address the research questions concerning the outcomes, recommendations, and limitations of high-impact articles in the field of research. Accordingly, it is important to recognize that the results of the content analysis primarily reflect the findings and limitations of these top 50 articles, which are recognized for their substantial impact due to their high citation rates, rather than providing insights into contemporary research trends. The analysis yielded critical inferences with regard to public health. The findings of the research indicate that particularly vulnerable individuals, such as the elderly and those afflicted with chronic diseases, constitute the demographic groups with the highest risk in this process. This makes it imperative that public health interventions targeting the general population also focus on the specific needs of vulnerable groups. The results of the analysis, in which climate change parameters, such as heat waves and air pollution, and environmental factors are associated with health outcomes, emphasize the need to increase adaptation strategies for these parameters. Studies examining the relationship between climate change and non-communicable diseases have focused more on health outcomes, and studies showing the effect of interventions to mitigate climate change individually or socially are limited. One of the studies evaluated drew attention to the healing effect of green spaces on the consequences of climate change.

However, the content analysis reveals that the existing studies have limitations, including meteorological data limitations, inadequate assessment of confounding factors, and short follow-up periods. These shortcomings indicate the necessity for the adoption of more long-term, holistic, and multidisciplinary approaches in public health research.

4.9. Limitations and Strengths

The most significant strengths of our research are as follows. The present study is the first to address the relationship between climate change and non-communicable diseases by employing a combination of bibliometric analysis, which examines the external characteristics, trends, and growth patterns in the literature in international scientific databases; topic modeling, which assesses how information is shaped in the context of common variables; and content analysis, which provides a conceptual interpretation of the results. It is anticipated that this study will make significant contributions to the scientific community and its readers. These contributions include an examination of the evolution of the scientific world’s interest in the subject over time, the identification of emerging topics, and the identification of potential new topics. This study also provides a comprehensive analysis of the lessons and suggestions derived from the articles, underpinned by robust evidence. A further strength of our study is that Web of Science databases, which contain a range of reputable and qualified journals, were used to examine journals with high impact factors.

The present study is subject to several limitations. Firstly, the extant literature on climate change and non-communicable diseases was still growing when this study was completed; publications that entered the literature after the data list was extracted were excluded. Secondly, the use of the Web of Science (WoS) database in this study may have introduced certain limitations. One such limitation is WoS’s emphasis on highly cited journals with high impact factors, which may result in the under-representation of less frequently cited but still important studies. In addition, because WoS primarily indexes articles published in academic journals, it may have inadvertently excluded gray literature—such as reports, conference proceedings, policy documents, and dissertations. Furthermore, due to the over-representation of certain disciplines in the WoS database, studies that are not indexed in WoS but contain valuable findings may have been omitted from the analysis, potentially leading to a biased representation of the existing literature. Furthermore, the analysis was conducted exclusively in the English language, which may have resulted in the exclusion of articles written in other languages. Thirdly, while the search query focused on a broad range of keywords describing climate change and non-communicable diseases, there may be keywords that were not covered.

5. Conclusions

This study reveals the impact of climate change on non-communicable diseases (NCDs) using bibliometric, topic modeling, and content analysis results from a large number of articles published in the Web of Science database, a major indexing system in the scientific community. The results indicate that the link between climate change and NCDs has received increasing attention in academic research over time and that the dynamic change and diversity of research topics in the relevant literature has expanded scientific knowledge in this area. The growing scientific interest and knowledge on the impact of climate change on NCDs are expected to shape health policies and adaptation strategies.

However, when assessed by the level of human development and regional factors, there are significant disparities in the distribution of research numbers and the diversity of research topics. In particular, the number of published articles is significantly lower in countries with low and middle levels of development, according to the Human Development Index, and in the African, Southeast Asian, and Eastern Mediterranean regions. Policymakers should take steps to strengthen the scientific research infrastructure in these regions, increase incentives for research, and promote global health collaborations. In addition, we suggest that future interdisciplinary research in this area specifically address the identified gaps in underrepresented regions. These targeted studies can help fill the existing knowledge gaps and provide more comprehensive insights into regional differences in the public health impacts of climate change.

Chronic diseases are generally multifactorial and long-term in nature. To prevent these diseases, national programs are generally developed and implemented, either broadly for chronic diseases or specifically for conditions such as diabetes, hypertension, and COPD. Evaluating the overall results of this study, it is clear that these programs can also set targets for addressing environmental factors in prevention strategies for these diseases. From a public health perspective, global climate change is, unfortunately, no longer an issue that any one country can solve on its own. Global cooperation is, therefore, essential. Given that chronic diseases often have irreversible long-term effects once diagnosed, it is not unreasonable to predict that the relationship between global climate change and chronic diseases will continue to be studied in various dimensions and aspects.