Impacts of Climate Change on Outdoor Workers and Their Safety: Some Research Priorities

The literature on the potential impacts of climate change on the health of outdoor workers has received limited attention as a whole, and in sub-Saharan African countries in particular. Yet, substantial numbers of workers are experiencing the health effects of elevated temperature, in combination with changes in precipitation patterns, climate extremes and the effects of air pollution, which have a potential impact on their safety and wellbeing. With increased temperatures within urban settlements and frequent heats waves, there has been a sudden rise in the occurrence of heat-related illness leading to higher levels of mortality, as well as other adverse health impacts. This paper discusses the impacts of extreme heat exposure and health concerns among outdoor workers, and the resultant impacts on their productivity and occupational safety in tropical developing countries with a focus on Sub-Saharan Africa, where there is a dearth of such studies. Aside from the direct effects caused by extreme heat exposure, other indirect health hazards associated with increasing heat among this group includes exposures to hazardous chemicals and other vector-borne diseases. In addition, reduced work capacity in heat-exposed jobs will continue to rise and hinder economic and social development in such countries. There is an urgent need for further studies around the health and economic impacts of climate change in the workplace, especially in tropical developing countries, which may guide the implementation of the measures needed to address the problem.


Introduction
Global climate change is among the most visible environmental concerns of the 21st century and these changes have the potential to affect human health, both directly and indirectly. Urban centers in most developing countries are now witnessing rapid population growth. According to the United Nations, the world's urban population is expected to increase to about 57% by 2050. Developing countries will account for more than 90% of future population growth experienced within its cities. With this projection of population growth, the WHO has urged its member states to take decisive action aimed at addressing the health impacts associated with climate change [1]. Despite being one of the most recognized contemporary and future global environmental issues, climate change impacts and it's adverse aspects to human lives, including occupational safety, have received surprisingly little attention [2]. Because of the rapid global urbanization trend, urban heat island (UHI) phenomena are now part of the climatological effects resulting from human activities on the urban environment [3]. Kiefer et al., argued that, despite the existence of considerable research and planning with regard to the public health and environmental aspects of climate change, there is little effort focused on its

Search Strategy and Sources of Information
The study adopted the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to identify relevant materials for inclusion in the study [19]. To identify relevant peer reviewed articles and grey documents we searched the Google Scholar, PubMed, Medline and Web of Science databases from January 2002 to March 2019 for studies that assessed the impact of climate change on workers' health and productivity. In addition, electronic databases searches were supplemented with manual searches for relevant published studies on the subject on international agencies' websites that include the WHO, UNDP, IPPC and ILO. Based on the considered criteria 32 studies were included in the present study from among the initial 745 ones identified earlier (Figure 1). Figure 1. Adopted PRISMA flowchart providing insights as to how the studies were selected [19].
Keywords used during each search included 'climate change impact' and; 'urban heat island', 'extreme heat', 'heat strain and health' heat stress and productivity', 'outdoor workers health', 'occupational health and safety', 'health and safety', 'adaptation'. Only articles that meet the needs of the present paper regarding climate change impacts on workers safety (hazards, risk) and health (disease, chemical exposure, and zoonosis) were considered. No restrictions were applied on articles that reported on workers' health status in relation to the study aim. Because of the target research area, sub-Saharan Africa, articles that considered extreme cold weather conditions were excluded. In addition, studies on the subject but published in any language other than English were excluded. Further exclusion criteria considered are presented in Table 1.

Characteristics of the Considered Studies
The characteristics of the studies here reviewed include ten entries for each: article type, study design, data sources, analysis method, study aim; study population, study theme, intervention, outcome data and outcome measures. Table 2 provides a detailed overview of the 32 studies considered in the review. Geographically the studies varied widely across the countries of the continents of Africa, Asia, Europe, North and Central America and Australia, so as to ensure a wide international basis, hence adding robustness to the findings. The designs varied among the studies and included empirical evidence, systematic reviews; scenario-based assessments, narrative reviews; exploratory studies; survey-based studies; formative research, case studies and ecological study design. Other measures considered in the appraisal of selected studies included reporting style, outcome measures, study design, the fidelity of protocol and possible conflicts of interest.

Results and Discussion
Based on the period selected (2002-2019) for the included studies, 22 (68.8%) of them were published between 2014 and 2019. Of the 32 papers analyzed, four papers (12.5%) directly considered the impacts of climate change on workers' health in different countries (Ghana, South Africa, Saudi Arabia, Germany, Australia, USA, Italy, India). Four (12.5%) of the papers considered the impacts of climate change, workplace heat exposure and heat stress among female workers. Seven (21.9%) of the papers focused on climate change, workplace heat exposure, heat stress, etc. within the construction industry. Overall, the trends of topics identified from the papers considered include the influence of climate change and heat stress, workplace injury and work productivity.
From the data abstraction undertaken based on keywords adopted; 32 studies selected were grouped into five major themes. This was also done based on their similarities, emerging patterns and differences. The themes that emerged, based on the study categories, include: Among the included studies, the impacts of climate change on workers' health was the major commonality while their major differences were around the interventions considered. Broad findings from the studies revealed that exposure to extreme heat due to climate change is associated with negative health impacts and possible decreases in productivity. In addition, the need for sentinel effects and leading indicators to aid surveillance of climate related occupational effects have also been highlighted in several of the studies. Different study designs were adopted among the studies considered, while a mixed method approach was adopted as the analysis method by 44% of the studies.

Climate Change Impacts on Outdoor Workers' Safety and Health
At the turn of the century, urban areas (especially in underdeveloped and developing countries such as those in sub-Saharan Africa) witnessed a sudden surge of movement from rural settlements into urban areas in search of better living conditions. This trend has resulted in greater pressures to the urban environment, especially considering that around 40% of the population in the African continent are now living in and around urban settlements, as reported by the World Bank. In addition, the migration process has been supported by the diversity of economic and social opportunities available in these urban settlements within the African Continent [48,49]. Temperatures across the African continent are expected to increase faster than the global average, while mean annual precipitation is projected to decrease in and around the Mediterranean and Northern and Southern parts of the continent. However, precipitation in the Western part of the continent will vary. Further to this, the near surface temperatures in most parts of Africa has seen an increased temperature rise of 0.5 • C or more in the last century, with minimum temperatures warming more rapidly than maximum temperatures. These trends may have been influenced by other components of natural variability and human activity [50].
To understand the impacts caused by climate change, there is first the need to understand the phenomenon itself. The availability of manmade heat absorbing features such as concrete buildings, surface modification, pollution generated from automobiles etc. in urban areas has helped increase heat absorption during the day, and its gradual release back into the atmosphere at nighttime. This has had an impact on temperature differences between urban and rural areas, and sped up the urban heat island (UHI) phenomenon in urban areas [48,49]. Another contributory factor to the UHI effect is the absence of moisture in urban areas and increased anthropogenic heating [31]. This increase has been shown to have direct significant effects on outdoor workers' thermal comfort, higher energy usage and air quality, with detrimental health effects and possible mortality increase [49]. The indirect impacts resulting from unsustainable consumption, such as pollution increase and waste generation, are also seen in these areas [44]. In addition, changes in land use and land cover in urban areas has influenced the urban climate and is leading to an increase in temperature [31]. There is now a need for evidence-based studies on climate change adaptation and urban heat island effects in relation to outdoor workers. This can raise awareness of occupational health hazards in order to establish risk awareness and coping strategies among workers, managers, and other stakeholders [25,27,32,38]. While there is anecdotal evidence based on research carried out in other parts of the world regarding excessive heat exposure and its impact on workers' health, safety, productivity and workplace environmental conditions and adaptation strategies, there is a paucity of similar data among outdoor workers in parts of sub-Saharan Africa; especially in a changing climate as perceived today [14,25,29,32,36].

Urban Heat Island (UHI) and Occupational Health Impacts on Outdoor Workers
An urban heat island (UHI) is an urban area that exhibits higher temperatures compared to the rural or suburban surroundings. The UHI effect is due to various factors, such as air pollution, anthropogenic heat, urban architecture and variations in precipitation patterns [31,48]. The UHI impacts on human health through the exposure to increased temperatures and can be problematic specifically during heat waves [48]. While the UHI effect affects the public in general, there is also the need for attention to the effects it poses on the health of workers specifically. Heat exposure has been previously linked to various adverse health effects, from the aggravation of minor conditions such as general discomfort, heat cramps, respiratory difficulties, heat stroke to increased chances of hospitalization and even death [4][5][6]25,49].
Health impacts from UHI are more severe during the summertime, the season of immensely high temperature or heat waves. Thus, heat-related mortality is likely to increase in future due to climate change [31,51]. Heat mortality may occur due to the overloading of the cardiovascular and respiratory systems, as physiological reactions to heat exposure. The physiological reactions that take place are increased heart rate, increased body temperature, increased sweating, fluctuation of blood flow towards the skin from the central organs, and dehydration [52]. The Urban Heat Island is also a nocturnal phenomenon, resulting in increased temperature at night due to the release of heat. This increased temperature causes a lack of relief at night and prevents the body from recovering from the heat exposure experienced during the day [53].
The UHI phenomenon can lead to an increase in energy consumption due to the demand for more use of cooling devices, thus increasing the overall electricity use. The companies which supply the electricity rely on power plants which typically use fossil fuels to meet the required demand, which results in the release of air pollutants and emission of greenhouse gases. These gases include Sulphur dioxide, nitrogen oxides, carbon monoxide, among others, all of which negatively impact air quality and contribute to ground-level ozone formation, particulate matter generation and acid rain. The elderly population, minors and those with existing heart conditions are most likely to be affected by these effects [51,54]. Increases in wind speed may help to reduce the severity of [24], but only to a limited extent.
Along with climate change, the impact of heat in the urban area will increase in the future. People working in hot weather involving heavy physical activity without appropriate protection are at increased risk of suffering from heat-related health effects [1,55]. In the urban inner cities, the major effect of UHI is human discomfort which is well documented in previous urban heat stress studies [56]. The UHI effect increases the temperature in cities exposing the urban population to more heat stress compared to rural areas [43]. In August 2003, during two weeks of extreme heat more than 1000 deaths and several associated illnesses of people aged 20-70 occurred in France [55] which greatly impacted the nations working group.
The 'heat island effect' is partly responsible for the current changes in temperature in many cities. People working outdoors (such as traffic wardens, fire fighters, road sweepers, landscapers' petty traders, construction workers etc.), during the hottest periods face an additional 3-5 • C increase in temperature which will make heavy work very challenging [40]. When working in a hot environment, workers (including healthy ones) are under tremendous strain. Their sweating (body's cooling mechanism) efficacy is reduced due to limited air movement towards the skin. In addition, the protective clothing used by workers which protects them from exposure to chemicals, trauma, and other pollutants, may hinder evaporative heat loss, further reducing the sweating efficacy. Another factor that may increase UHI is the inadequate intake of water which results in dehydration, and therefore reduces sweating and resultant heat loss. Dehydration also contributes to impairment of mental and physical performance [25,27,42].
There is a strong relationship between the UHI effect and urban planning. This is due to the fact that the absence of trees and vegetation in urban areas affects the transpiration process. The implementation of proper vegetation in urban areas helps cool the surroundings, resulting in increased evapotranspiration and reducing the UHI effect. Other measures include the use of water bodies to reduce thermal load and decreasing the anthropogenic heat [44]. Table 3 lists some examples of health impacts of UHI on outdoor workers.

Heat Stress and the Performance of Outdoor Workers
While individuals are in general capable of acclimatizing to different levels of heat, it is worth noting that every worker also has an upper limit to heat exposure, stress beyond which will become unbearable and may cause health related ailments and-in extreme cases-can lead to mortality. Understandably, there is limited, or no adaptation measures considered for outdoor workers involved with constant physical labor and working in humid conditions. There is an increased likelihood of these workers experiencing heat stress, which could lead to reduced work performance and capacity, with potentially significant economic consequences [39]. Wherever the ambient temperature exceeds 35 • C, there is a greater chance of it causing fatigue and physical exhaustion among workers in general. There is also an increased risk of errors, which could be catastrophic, especially where concentration is required for the safe handling and operation of machinery. Outdoor women worker's health is another problem that has drawn attention recently; in particular, during pregnancy as it creates additional heat stress problems. Respiratory and cardiovascular disease, secondary to exposure to poor air quality, has been found to have a larger impact on women because of their greater propensity for higher deposition of particulate matter in lung tissue [17,33,59]. In general, outdoor workers are faced with elevated risks of heat-related illnesses (HRI). However, pregnant women exposed to extreme heat are faced with additional health risks, including poor pregnancy health and birth outcomes, as highlighted in earlier reports [17,26,33,34,59]. This calls for empowering women through provision of education and awareness as a means of improving mitigation and mitigation policy intervention.
As earlier mentioned by Kjellstrom et al., there are two pathways that extreme heat exposure impacts could manifest in workers [36]. Both physiological and psychological tasks and heat balance within the human body are determined by six fundamental factors that include; air temperature; radiant temperature; humidity; air movement (wind speed); clothing; and the metabolic heat generated by human physical activity. As such, perceptual awareness alongside the control over work conditions, work rates, and work limits are immediate adaptation mechanisms against heat exposure among individual workers. To address the physiological impact caused by heat exposure, several heat stress indices have been developed. These have been developed in order to help in the prediction of physiological strain experienced among workers due to exposure to stressful environmental conditions [15,28,29,35,36]. The use of indexes provides information between climate parameters (air temperature, air humidity, air movement over the skin (wind speed) and heat radiation (i.e., from the sun)) which can then be linked to a corresponding physiological strain. The results of these indices can be used in the design or establishment of safe work practices, work limits and work conditions. Wet Bulb Globe Temperature (WBGT) was developed by the US Army in the 1950s to help reduce exposure to excess heat. WBGT is now the most widely used tool for occupational heat stress assessment. It takes into consideration four environmental factors; air temperature, relative humidity, wind speed, and radiation [30,60]. However, clothing type, activity and acclimatization can significantly impact on the adaptation strategy adopted by the individual, despite the use of WBGT to quantify heat stress tolerance [29,61]. As such, the interpretation of the WBGT value requires these factors to be taken into account.
Guidelines for the application of WBGT on occupational heat exposure recommend maximum heat exposures for jobs with various work intensities. They also need to account for the number of work hours after which a worker will be required to take a break to avoid the core body temperature exceeding 37 • C [40]. Reference to WBGT 'reference values', (the point at which some preventive action should be taken) as developed by the international standard [62], provide further guidance on the different levels of work where workers will need hourly rests, or rests of 25, 50 and 75% (rest/work ratios).

Occupational Health Hazards and Effects Related to Climate Change
There are links between prevailing climatic factors and occupational health hazards that can be associated to climate change. Likely hazards due to climate change and their effects on vulnerable outdoor groups, as well as aliments associated with occupational exposure to excessive heat have been identified. These include; heat-associated self-reported nausea or vomiting, painful muscular spasms, confusion, dizziness, or fainting, hot dry skin and self-reported heat strain according to previous studies [6,25,36].
Outdoor workers in certain occupational sectors such as agriculture, construction, transportation, utility maintenance, oil production, firefighting and other emergency services are usually among the first to experience the effects of climate change. These are exacerbated in most instances by the need to wear protective clothing, which can lead to heat stress. In addition, such effects could have a far-reaching impact on their health and the nation's economy. Excessive environmental heat is seen as the most frequent climate change impact and as such, with prolonged hot weather, outdoor workers health in sub-Saharan African countries, are at risk from heat-related outcomes (Table 1).
Where these workers are exposed to a higher temperature than 37 • C, for their body to stay at a healthy temperature they will have to lose this excessive heat through sweat evaporation. However, as earlier reported [59] high external air humidity and clothing type were identified as limitations sweat evaporation and regulation of body temperature. Therefore, to avoid heat stroke workers will need to reduce their work rate, take more rest, and rehydrate. However, Moda and Alshahrani [25] reported that outdoor workers on construction sites in Saudi Arabia described the lack of palatable water as a key set back to their water intake and rehydration. This is often caused by the portable water provision on site becoming warm during the day due to lack of a cooler, thus leaving the workers dehydrated, exhausted and at some point, experiencing severe fatigue among other symptoms reported. In addition, heat stress and fatigue suffered by these workers negatively impacted their levels of alertness and work capacity. This led to the frequent occurrence of safety lapses leading to a high risk of injury at work. Most workplaces in developing countries do not have a heat stress index on site, therefore workers rely on environmental temperature references from the weather station for the city, as reported by Moda and Alshahrani [25]. Unfortunately, the immediate local ambient temperature could vary from that reported by the weather station and the workers might be exposed to a more extreme temperature than reported.
Apart from the effects of extreme heat, a higher temperature can lead to increased ground-level ozone and fine particulate matter air pollution, thereby increasing the risk of cardiopulmonary dysfunction, reduced lung function and other respiratory illnesses (Table 3). These other effects also increase the level of carbon dioxide in the air and promote plant growth and the release of airborne allergens, which could increase allergic reaction and asthma episodes among vulnerable groups [63][64][65]. To help visualize climate change impacts and related occupational safety and health issues, Schulte and Chun [5] developed a conceptual framework. This framework highlights the impact climate change is likely to have on the workplace among different workers, including occupational morbidity, mortality, and injury as influenced by several driving and contextual factors. The likely hazards that will occur in different settings may include increased ambient temperature; air pollution; ultraviolet (UV) radiation; extreme weather; expanded vector habitats; industrial transitions and emerging industries; and changes in the built environment.
Release and exposure to environmental chemicals due to increased heat is expected to increase through various routes. These include increased pesticide use, changes in transport pathways such as dust proliferation, increased chemical dispersal from storm runoff, and increases in chemical spills from floods and fires [20]. Several workers in trades or industries using or producing petroleum products (such as coal etc.), and those working in close proximity where the combustion of these products occur (such as traffic wardens, taxi/bus drivers, road maintenance etc.) are vulnerable to polycyclic aromatic hydrocarbon (PAH) exposure. However, their impact due to climate change are said to vary. In addition to this, the presence and exposure of legacy pollutants (persistent substances like DDT, dioxins, PCBs, mercury, etc.) that have accumulated in environmental reservoirs (such as surface soils, sediments, and forests), especially among workers in certain occupations (Table 4), could be influenced by climate change [20,21]. These pollutants impact health, including, but not limited to, cancer, adverse reproductive outcomes, impaired neurodevelopment, and disruption of the endocrine and immune systems [21].
In addition, workers in areas with poor water drainage management and areas that encourage vector breeding are affected by extreme climate events. This is especially concerning considering that some of these vector borne diseases i.e., yellow fever, malaria, dengue and chikungunya are sensitive to climatic changes and likely to expand in geographic zones and affect a diverse range of worker populations [10,11,66]. The burdens associated with vector borne diseases tend to be much higher in developing countries. For instance, the per capita mortality rate from vector-borne diseases is projected to be 300 times greater in developing nations than in developed regions. This is due in part to their prevalence in the tropical regions and low socioeconomic development, which has a negative impact on the quality of health care services delivered [10].

Adaptation of Workers to Occupational Heat Stress: Some Research Priorities
There is the need for occupational climate change policies be considered at a micro level, especially since adaptive capacity may vary between groups, communities, and individuals and will rely on the vulnerability level, resilience, and resource availability as the global temperature continues to rise. Heat stress exposure and associated health effects cannot be ignored in the workplace, especially in sub-Saharan Africa where climate change is more pronounced. On this note, it is imperative that climate change adaptation be considered at various workplace levels and is not a collectivist approach, which does not take into account the diverse needs of the varying workers.
The intergovernmental Panel on Climate Change (IPPC) affirmed that if the present climate change trend persists, by the middle of the century, high temperatures and humidity would probably compromise outdoor working. Thus, leading to lost work capacity and reduced labor productivity among vulnerable populations, such as that in sub-Saharan Africa, and will eventually cause economic loss. To avoid productivity and economic loss and social ramifications resulting from extreme heat exposure among outdoor workers, there is a need for employers to consider measures capable of protecting workers and their businesses through investment into appropriate climate change adaptation measures [12,59]. Historically, individuals working under extreme climate have tried different measures aimed at adapting to their work conditions. They include, working with light cloth, dousing themselves with water to regulate their internal body temperature, consumption of water, taking intermittent breaks etc., however, these techniques require further scientific measures aimed at complementing these tools, especially where it is insufficient for coping with extreme hot weather conditions. Key research priorities need to meet this challenge. It is firstly important to investigate effective adaptation measures to ensure workers involved in heavy labour are not faced with an increased risk of heat stress, which could affect their health, work performance and work capacity [39]. Further to this, there is also a need to consider the right adaptation strategy among workers when developing occupational guidelines. These guides should take into account several factors likely to play a role in climate change and heat exposure, which could affect the individual's sensitivity to heat tolerance [5]. In addition, there is also a need to consider intervention strategies around workers coping mechanisms, including adaptation and social protection measures when designing engineering solutions. Furthermore, research on the role of administrative controls along with studies on how to enhance education and awareness on the management of climate change and heat exposure among workers in general is considered timely, especially in Africa. There is also the need to ensure the establishment of a platform capable of overcoming barriers to climate change adaptation and heat stress risk which takes into consideration resource availability and technological advancements in tropical regions [38].

Conclusions
From the studies considered, it is evident that the frequency and intensity of extreme hot weather conditions due to climate change, extreme workplace heat exposure and the abatement of workplace ill health and injury will continue to present challenges, in the developing countries located in the tropics, and the globe at large, especially in fast-paced work environments. To date, most studies on climate change impacts and health have focused on the general public's health. Limited documented evidence exists on climate change impact on occupational health and safety among outdoor workers, especially in developing countries in sub-Saharan Africa where its impact is mostly felt. While approaches are considered for the protection of workers from extreme heat exposure due to climate change, there is also the need for the development of appropriate surveillance programmes, thus enabling the proper assessment of occupational heat exposure and related injury and illness because of climate change extremes within different occupational sectors.
As a result of paucity of up to date data on outdoor workplace heat exposure, workplace climate change adaptation strategies and other relevant related health and safety issues, the assessment of impacts of climate change and how it affects workers in the tropical countries such as Africa is considered timely. This includes the need for current information on the effective management of climate change impacts. In addition, gender response to climate change impacts on the continent workforce will require the development of more evidence, where a high proportion of women now work in fast-paced outdoor industries that include agriculture, mining and construction. To strengthen the knowledge of climate change, workplace heat exposure and related workplace injury and to guide safety adaptation measures, there is a need for multidisciplinary research to help in the quantification and forecast of workers hazards exposure by occupation and location in these countries where the impact of climate change is more pronounced. Research areas proposed in the assessment of climate change impacts on outdoor workers productivity and occupational safety include: • Assessment of climate change impacts among vulnerable outdoor workers; such as pregnant women, children elderly in the continent • Occupational heat stress and adaptation of sustainable measures • Association between heat stress exposure and response under varied working conditions • Assessment of combined effects associated with heat stress and other related environmental and physical stressors • Development of micro adaptation alternatives to tackle workplace climate change challenges To measure the occupational illness and injury burden among outdoor workers, research that considers the relationship between socioeconomic status and other relevant indicators that affect climate change, and occupational safety and health of these workers is further advocated for. Another area of study that needs looking at is the interplay between climate change, occupational hazards, and workers vulnerability. This is needed in order to help with the development of suitable climate change adaptation and risk management initiatives.
To conclude, climate change policy needs to take into consideration that at each micro level adaptive capacity may vary between groups, communities, and individuals and will rely on the vulnerability level, resilience, and resource availability. As such, there is a need to avoid a collectivist approach, as this approach does not acknowledge these differences.