In view of changes to the world climate system since the 1950s, the United Nations’ Intergovernmental Panel on Climate Change (IPCC) has concluded that continued emission of greenhouse gases (GHG) will cause “further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems” (p8, IPCC Synthesis Report (2014)) [1
]. This conclusion, along with the conclusions of the UN Framework Convention on Climate Change (UNFCCC), has inspired the ongoing efforts of the UN Conference of the Parties (COP) since the 1990s to coordinate international agreements to urgently and substantially reduce greenhouse gas emissions, such as the 1996 Kyoto Protocol [2
] and the 2015 Paris Agreement [3
The efforts that have been invested in achieving agreement on these major international negotiations are a remarkable testament to international concern and support for these goals. However, greenhouse gas emissions have continued to rise [4
]. A key underlying problem is that most of the rise in greenhouse gas emissions (chiefly carbon dioxide, CO2
) since the 19th century is due to the use of fossil fuel-generated energy (coal, oil, natural gas, and peat), which has driven the Industrial Revolution [7
]. This cheap and abundant energy has facilitated unprecedented increases in standards of living, average lifespan, technological advances, agriculture, and world population along with economic growth [7
]. It is clear that, historically, it was a key factor in enabling the development of the current high-income nations [7
]. Gupta (2014) noted that this has been a major source of contention between developing and developed nations in international attempts to reduce global greenhouse gas emissions [10
]. Specifically, if developing nations follow the same well-tested path that nations have historically taken to become developed, this would dramatically increase greenhouse gas emissions, and this raises a debate as to whether international treaties to reduce greenhouse gas emissions are implicitly hindering the development of developing nations [10
On the other hand, several researchers and opinion-makers have argued that a “zero-carbon” alternative post-industrial revolution, involving a transition towards wind- and solar-generated electricity, along with the widespread electrification of transport systems and improvements in energy efficiency (possibly also including bioenergy) is not only feasible, but desirable, e.g., Gore (2006, 2017) [11
], Jacobson et al. (2011, 2015, 2017, 2018) [13
], Klein (2015) [17
], and Goodall (2016) [18
]. Although these claims have been disputed in the scientific literature [19
], they are eagerly promoted by environmental advocacy groups such as Greenpeace [25
] and protest movements such as “Extinction Rebellion” [27
] and “Fridays For Future” [28
], achieving strong currency in both mainstream and social media. This has prompted many political groups and governments to reshape their policy platforms accordingly [29
], e.g., in terms of a “Green New Deal” [31
Given the popularity of this framing, it is unsurprising that many people assume that opposition to these policies arise from ignorance, a lack of concern for the environment, and/or the lobbying of vested interests calling for business as usual [34
]. However, much of the opposition is voiced by environmentalists and researchers who are concerned about environmental and societal problems associated with these policies as well as the lack of critical discussion of the engineering and economic feasibility of these policies [8
Many criticisms of these “zero-carbon” proposals arise from simple engineering and economic practicalities. Some have questioned whether the proposed “green technologies” are able to meet the energy demands of the current population, let alone an increasing population [20
]. For example, from an evaluation of 24 studies of 100% renewable electricity, Heard et al. (2017) found that, “based on our criteria, none of the 100% renewable electricity studies we examined provided a convincing demonstration of feasibility” [21
]. A major engineering problem with wind-, solar-, and also tidal-generated electricity is that these are “intermittent” (also called “non-dispatchable” or “variable”) electricity generation technologies. While it has been argued that this can in principle be overcome through a combination of energy storage [48
] and/or a major continental-scale expansion in the electricity transmission networks [50
], others have noted that the scale of these projects is enormous [19
]. Many have asked why, if reducing greenhouse gas emissions is to be genuinely considered as the top priority, solutions involving increases in nuclear energy and/or transitioning from coal/oil to natural gas are continually dismissed or sidelined [20
Ironically, given that these policies are framed as being environmentally desirable, many of the criticisms are with their environmental impacts. Many researchers are concerned about the negative impacts that “green energies” have on biodiversity [51
]. Some have noted that the transition to these technologies would require a huge increase in the mining of limited resources [45
], with Mills (2020) arguing that, “Compared with hydrocarbons, green machines entail, on average, a 10-fold increase in the quantities of materials extracted and processed to produce the same amount of energy” [45
]. Some note that large-scale wind farms can cause significant local
climate change (as distinct from the global
climate change from greenhouse gas emissions they are purported to be reducing) [59
Pielke Jr. (2005) notes that there are two approaches to reducing the impacts of future climate change: (i) “climate mitigation” and (ii) “climate adaptation” [67
]. The first approach, “climate mitigation”, assumes that greenhouse gases are the primary driver of climate change and tries to “reduce future climate change” by reducing greenhouse gas emissions. The second approach, “climate adaptation”, involves developing better systems and infrastructure for dealing with climate change and climate extremes. Pielke Jr. argues that by overemphasizing “climate mitigation”, the UNFCCC and the COP agreements, such as the Kyoto Protocol (and more recently the Paris Agreement), have created a bias against investment in climate adaptation. He also notes that climate mitigation policies explicitly assume that climate change is primarily driven by greenhouse gas emissions, whereas climate adaptation policies often make sense regardless of the causes of climate change. With that in mind, it is worth noting that several recent studies have argued that the IPCC reports have underestimated the role of natural factors in recent climate change (and hence overestimated the role of human-caused factors) [68
Furthermore, in this Special Issue of Energies, Connolly et al. (2020) have noted that, even assuming climate change is primarily due to human-caused greenhouse gas emissions, the amount of global warming expected under business-as-usual policies is heavily determined by a metric called the “climate sensitivity” [6
]. The exact value of this metric is the subject of considerable ongoing scientific debate, but Connolly et al. calculated that, if the value is at the higher end of the IPCC’s range of estimates, then we can expect that the Paris Agreement’s stated goal of keeping human-caused global warming below 2 °C will be broken under business as usual by the mid-21st century, whereas, if the climate sensitivity is at the lower end of the IPCC’s estimates, then the Paris Agreement will not be broken under business-as-usual until at least the 22nd century. In other words, they showed that the scientific community has still not satisfactorily resolved whether reducing greenhouse gas emissions is a problem for this century or the next. This has implications for establishing exactly how urgent the proposed transitions to “low-carbon” policies are. This is important because, notwithstanding concern over the climate change which the associated greenhouse gas emissions might be causing, the existing fossil fuel-driven energy policies have many benefits [8
]. Indeed, it is worth noting that the main greenhouse gas of concern, carbon dioxide (CO2
), is a key component of all carbon-based life, i.e., all known life, and that increasing atmospheric carbon dioxide concentrations have contributed to a partial “greening of the Earth”, i.e., increased plant growth over the last few decades [9
In light of the above criticisms, the reader may wonder whether the current proposed “zero-carbon” energy transition policies based predominantly on wind- and solar-generated electricity are truly the panacea that promoters of these technologies indicate [11
]. This is a key question which we aim to address in this review paper. We hope that, by the end of this review, the reader will appreciate that none of the current energy and electricity sources used by society are a “panacea”. Rather, each technology has its pros and cons, and policy-makers should be aware of the cons as well as the pros when making energy policy decisions. We urge policy-makers to identify which priorities are most important to them, and which priorities they are prepared to compromise on. Sovacool and Saunders (2014) [73
] provide a useful framework for this by comparing and contrasting five different energy security policy packages. They found that all five packages have advantages and disadvantages, and that “energy security is not an absolute state, and that achieving it only ‘works’ by prioritizing some dimensions, or policy goals and packages, more than others” [73
We argue that a key part of this process is recognition of the engineering, environmental, and socioeconomic problems associated with each technology. We stress that the purpose of this review is not to advocate for any particular energy technology, but rather to provide the reader with a greater awareness of the pros and cons of each of the main technologies and energy policies that are currently being promoted. In order to identify these key energy technologies and policies, we have taken advantage of the detailed analysis carried out by the Climate Policy Initiative (https://www.climatepolicyinitiative.org/
) in a series of annual/biennial “Global Landscape of Climate Finance” reports which have estimated the breakdown of the total global climate change expenditure for each year from 2010/2011 [74
] to 2018 [75
We have compiled the data for each year from these reports in Figure 1
and Table 1
. We note that the Climate Policy Initiative also carried out an estimate for 2009/2010 in an early report [76
], but the authors advise that they significantly modified their methodology for subsequent reports, and so we have not included these earlier estimates in our analysis. According to its website, the Climate Policy Initiative is a climate policy think tank that “was founded in 2009 to support nations building low-carbon economies to develop and implement effective climate, energy, and land use policies”. In their reports, they explicitly acknowledge that their calculations likely underestimate the annual global expenditure, “due to methodological issues related to data coverage and data limitations, particularly domestic government expenditures on climate finance and private investments in energy efficiency, transport, land use, and adaptation” (Buchner et al. 2019, p8) [75
]. Nonetheless, they appear to offer the most comprehensive estimates available at the time of writing. Therefore, we believe they offer a useful relative breakdown of global climate change expenditure over the period 2011–2018.
Despite this expenditure totaling US$
3660 billion over 8 years, global carbon dioxide (CO2
) emissions have continued rising throughout this period (Figure 2
). This gives occasion to scrutinize expenditures to consider whether the current path holds promise of success. One explanation could be that the total expenditure is still too low, and indeed Buchner et al. (2019) argue that annual global expenditure would need to increase to US$
1.6–3.8 trillion in order to substantially reduce CO2
]. However, Figure 1
and Table 1
show that 55% of the expenditure over this period has been on solar and wind projects, with a further 10% on sustainable transport projects and 7% on energy efficiency. That is, most of the expenditure has gone on the types of policies prioritized by the “zero-carbon” proposals which have been heavily criticized above.
With that in mind, we propose to first describe the world’s current energy usage (Section 2
). Then, we will consider some of the key engineering challenges associated with both the proposed energy transitions and current energy policies (Section 3
). In Section 4
, we will consider some of the key environmental concerns associated with these policies, while in Section 5
we consider some important socioeconomic concerns. In Section 6
, we summarize the pros and cons of all the main energy sources—both those considered in Figure 1
and Table 1
, and those not. In Section 7
, we offer some recommendations for how to interpret these conflicting pros and cons.
5. Socioeconomic Concerns Associated with the Various Energy Technologies
In Section 4.3.3
, we noted that, in the developing world, ~1.3 billion people still do not have access to an electricity supply. Moreover, we noted that ~3 billion people rely on the household burning of solid fuel for most of their energy needs (cooking, heating, and lighting), and that for most of these (~2.4 billion), this fuel usually consists of wood, charcoal, animal dung, or crop wastes [190
]. Technically, these “biomass” fuels are “renewable energies”, but as discussed in Section 3.3.1
, this does not imply that their use is “sustainable”. Technically, biomass is considered “carbon-neutral”, and therefore the promotion of the use of biomass (and the related “biofuels”) is one of the strategies for reducing greenhouse gas emissions (Section 4.1
). Indeed, from Table 1
, we see that at least 3% of the US$
3.66 trillion of global climate change expenditure over the 2011–2018 period has been spent on “biomass and waste” and “biofuels” projects.
Therefore, nominally, it could be argued that, in terms of keeping CO2
emissions low, these developing nations are among the most successful. As discussed in Section 4.1
, many currently consider reducing CO2
emissions to be one of the top priorities for the world, especially in terms of preserving the environment. However, the reality is that this apparent “success” has nothing to do with policies to protect the environment, but is chiefly a result of poverty, especially in rural communities. Indeed, the use of biomass as solid fuel in rural communities has been shown to be a significant driver of tropical deforestation, especially on the African continent [214
More broadly, a substantial body of literature has found empirical evidence that the so-called ”environmental Kuznets curve” (EKC) appears to apply to many environmental indicators, although not all [136
]. The EKC hypothesis developed in the 1990s partly out of earlier debates between the neo-Malthusians and cornucopians in the 1970s (Section 3.3.1
). In 1955, Simon Kuznets proposed an “inverted U curve” relationship between income inequality and economic growth, i.e., that as a country developed economically, income inequality would initially increase, but after some turning point, further economic growth would begin to reduce income inequality again. This became known as the Kuznets curve.
Starting in the 1990s, numerous studies found considerable empirical evidence that for many environmental indicators, particularly those associated with local air pollution (Section 4.3
); there appears to be a similar relationship between economic growth and environmental impacts [136
], i.e., the environmental Kuznets curve (EKC). This implies that, in the short-term, encouraging developing nations to develop may lead to environmental degradation, but that, in the long-term, once they have passed the relevant “turning points”, further development will reduce environmental degradation. However, the same analyses which reveal that the EKC applies to local forms of pollution also show that it does not apply to issues that are more global in nature, e.g., CO2
On the contrary, on average, CO2
emissions appear to increase with economic development. This has led those prioritizing reducing global CO2
emissions to explicitly warn that we should not rely on the EKC to automatically lead to CO2
emissions reductions. Instead, they argue that new paths for development need to be designed which explicitly incorporate CO2
reduction as an additional top priority [10
We want to emphasize some important corollaries of the above:
The goal of reducing global CO2 emissions is directly opposed to the standard pathways of economic development which have been followed historically.
We stress that this does not in itself preclude the possibility that alternative pathways to economic development which also reduce global CO2
emissions could exist. Indeed, as discussed in Section 4.1
, France and Sweden are two notable examples of developed nations that combined economic growth with relatively low CO2
emissions through investment in nuclear [52
]. Therefore, research into exploring the possibilities of new pathways to economic development is justifiable and laudable [10
]. However, we should acknowledge that new pathways by their very nature will not have been tested to the extent of the standard historic pathways.
Aside from CO2
emissions, and despite the neo-Malthusian predictions discussed in Section 3.3.1
, the EKC studies confirm that the standard pathways to economic development actually lead to reductions in environmental degradation for many aspects of the environment, especially those associated with local pollution.
In other words, the most straightforward routes for helping nations develop and/or reducing world poverty fundamentally conflict with the goal of reducing CO2 emissions. We suggest that even within developed nations, policies to reduce CO2 emissions similarly are often at odds with improving the livelihoods of the less affluent in society.
For example, one policy tool which is often promoted as being potentially useful for reducing CO2
emissions is the implementation of “carbon taxes”. Carbon taxes can take many forms, but typically penalize the use of forms of energy that are associated with relatively high CO2
emissions. Researchers studying the socioeconomic implications of various carbon taxes in multiple countries have found that carbon taxes “tend to be regressive”, i.e., the burden tends to be greatest on the poorest households [235
]. That is, while the absolute tax paid by richer households is often greater, as a percentage of their income it tends to be much lower. Suggestions have been made about how to partially mitigate against this regressive nature by, e.g., explicitly coupling the carbon tax with additional tax breaks for lower income groups for other taxes, or redistributing some of the tax revenue directly to lower-income groups via social welfare supplements [235
]. However, it indicates that carbon taxes have an underlying tendency towards greater income inequality.
Carbon taxes also may be biased against rural dwellers [239
], e.g., if the carbon tax is designed to encourage the use of public transport systems which do not adequately service rural communities. Indeed, the “Mouvement des Gilets Jaunes” (“Yellow Vest Movement”) protest movement in France which began in late 2018 appears to have been motivated by resentment over increasing carbon taxes on motor fuel, which were perceived to be unfairly biased against rural communities that were more reliant on motor transport [241
]. (The name refers to the yellow high-visibility jackets that car-owners are obliged to keep in their car under recent regulations, and hence were worn as a symbol of the movement.) Prud’homme (2019) notes the irony that France happens to already be one of the most decarbonized developed nations, since the French electricity grid is 85% nuclear and hydroelectric [242
Chancel and Piketty (2015) note that there is an additional regressive nature to carbon taxes when considered on an international basis [243
]. That is, the introduction of the same carbon tax to multiple countries will tend to create greater burdens on lower income countries. With that in mind, they have proposed the possibility of creating a global “carbon tax” towards a “climate adaptation fund” where the taxes would be greater for higher-emissions countries, and the funds would be mostly distributed to developing nations [243
There is an additional irony in this conflict between the standard pathways to economic development and reducing CO2
emissions in that developing nations are often the least well-adapted to dealing with climate change and/or weather extremes. For instance, while hurricanes can cause considerable damage when they make landfall in the United States [244
], many neighboring nations in the Caribbean or along the Gulf of Mexico are particularly vulnerable [245
]. Although recent research has confirmed that there has been no long-term trend in the number or intensity of hurricanes making landfall in the area [244
], the destructive nature of these extreme weather events coupled with the infrequency with which they strike any given region can cause devastating effects. Therefore, investment into “climate adaptation” infrastructure, e.g., improved resilience for hurricanes [245
] along with better hurricane response systems can be worthwhile investments in at-risk hurricane zones [67
]. However, these often require substantial economic investment which can be out of reach for lower-income countries. With that in mind, it is surprising that only 5% of the global climate change expenditure over the 2011–2018 period has been spent on “climate adaptation” projects (Figure 1
and Table 1
We agree with Pielke Jr. [67
] and Chancel and Piketty (2015) [243
] that greater investment in “climate adaptation” makes sense if society wants to better respond to climate change and extreme weather. However, we also note from the discussion above that one of the key ways to help developing nations to improve their resilience to weather extremes is to encourage their economic development. In particular, having continuous access to an affordable and reliable electricity and energy infrastructure is essential. With that in mind, Epstein (2014) has made the “moral case for fossil fuels” [8
], arguing that the standard pathways to economic development making extensive use of coal, oil, and/or gas have been well tested and should be encouraged. Others caution that this would lead to substantial increases in CO2
emissions, and favor the development of nuclear instead [20
]. Helm (2018) argues that a temporary transition from coal and oil to gas for a few decades could offer a compromise between the two approaches that would allow time for a slower long-term energy transition [41
Finally, we note that there are often societal conflicts associated with energy policies when they impact on indigenous peoples without adequate consultation. Klein (2015) describes the struggles of indigenous peoples in Canada and Australia to restrain the fossil fuel industry from degrading their lands and waters [17
], but the materials needed for other energy sources also pose a threat of severe adverse impacts on indigenous peoples, such as
silver mining on the Xinca indigenous peoples of Guatemala [117
lithium mining on Atacama communities in Argentina [249
cobalt mining on indigenous peoples in Katanga, Democratic Republic of Congo [250
uranium mining on the Mirarr people of Australia’s Northern Territory [251
Hydroelectric dams can likewise have severe impacts on the Munduruku [252
] and other indigenous peoples throughout the Amazon Basin [156
Additionally, Gilio-Whitaker (2019) [253
] and Estes (2019) [254
] have detailed the impacts on Native American land rights of a range of energy industries. Gilio-Whitaker frames the contamination of Indian lands and waters for uranium mining and fossil fuel extraction, along with the flooding of ancestral lands to construct hydropower dams, as processes in the displacement and colonization of Native Americans. Estes [254
] similarly documents the history of construction of hydroelectric dams as a driver of dispossession of Lakota people and of coerced population shifts from their traditional lands to urban centers. Both authors have detailed the series of events by which the Dakota Access Pipeline was laid through Native American lands in North Dakota, without the consent of the Standing Rock Sioux Tribe, whose lands and waters are placed at risk of contamination by pipeline leaks. From the perspective of these indigenous scholars, it seems that the settler state consistently engages in coercive practices to impinge on indigenous lands, regardless of which energy technology is under development. Kelly (2016) notes failure to consult as one of the causes of failure of ambitious projects, and this seems relevant in the context: regardless of which energy technologies we choose, consultation with indigenous peoples is required to safeguard land rights, social equity, and wellbeing [20
In the introduction, we argued that none of the main energy sources currently available or currently used (Section 2
) should be considered as a “panacea”. Instead, each energy source has its pros and cons and we recommend that energy policy-makers consider both. In Table 2
, we summarize the key engineering and environmental concerns which we considered in Section 3
and Section 4
, respectively, for each of the main energy sources. For brevity, we have not included the socioeconomic concerns which were discussed in Section 5
, but we recommend these also be explicitly considered.
In Section 3.1
, we noted that the three “intermittent” (or “non-dispatchable”) energy sources, i.e., wind, solar, and tidal, are very unsuitable for societies that require a continuous, on-demand, electricity supply. This is indeed what has been the norm since the age of electrification began in the early 20th century. We urge policy-makers to recognize that policies which rely on any of these three sources as part of their grid will face increasing problems of grid instability with increasing penetration of the network. Although advocates of these three sources imply that these problems can be partially overcome through the use of energy storage technologies and/or major continental-scale transmission networks, this appears to be based more on wishful thinking than pragmatism.
We note that wind farms also cause considerable local climate change (Section 4.2
) and can cause problems for biodiversity (Section 4.4
). Although wind farms are associated with relatively low direct CO2
emissions (Section 4.1
), we suggest that the local night-time soil heating effect of wind farms may be leading to an increase in biological CO2
emissions, which may cancel some (or perhaps all) of the savings relative to other energy sources (Section 4.2.4
In terms of power density, the three main fossil fuels (coal, oil and gas) and nuclear are orders of magnitude better than any of the renewables (Section 3.2
). Currently, those four technologies account for 89% of the world’s energy usage (Section 2
), so policies which significantly reduce that percentage may potentially lead to engineering problems due to the reduction in power density. We note that the power density of biomass and biofuels is by far the lowest. As a result, policies which significantly increase the use of biomass and/or biofuels will require particularly large land areas. In Section 4.4
, we note that this can lead to increased deforestation and major biodiversity impacts.
In Section 4.4
, we also note that hydroelectricity can lead to threats to biodiversity as well as contribute to deforestation. There can also be socioeconomic concerns associated with hydroelectricity, due to the displacement of people in the area. In Section 5
, we noted that this is a particular concern for indigenous peoples in certain regions, such as the Amazon River Basin.
One of the main limitations of hydroelectricity and of geothermal is that both technologies are heavily dependent on local geography requirements (Section 4.1
). Geothermal can be very effective in regions with thermal springs (e.g., Iceland), and hydroelectricity can be very effective in certain mountainous regions with large local rivers (e.g., Norway). However, suitable sites are quite limited geographically.
The three main fossil fuels (coal, oil, and gas) have collectively powered most of the Industrial Revolution since the 19th century, and, as of 2018, they still provide 85% of the world’s energy. Because these are finite resources, there is concern about how long society can continue to rely on them. However, as discussed in Section 3.3.2
, the estimated known reserves of coal, oil, and gas should provide enough energy at current rates for several more decades at least, and historically the known reserves have continued to expand over time to surprise commentators that have predicted “peak oil”, “peak gas”, or “peak coal”. Therefore, while we should recognize them as finite resources, they are still in plentiful supply—for now, at least.
On the other hand, in Section 4.1
, we saw that these fossil fuels are the highest net emitters of CO2
per kWh of electricity, and in Section 4.3
, we noted that their use is associated with air pollution, although various approaches have been proposed to reduce the amount of air pollution.
As an aside, we do not include peat among the three fossil fuels mentioned above, as peat resources are relatively limited and only comprise a significant fraction of energy usage in a few places, e.g., Ireland [130
], although De Decker (2011) has noted that peat was an important fuel in the pre-industrial Middle Ages for The Netherlands [255
Finally, nuclear energy has created a lot of public concern, chiefly about potential accidents and/or the safe disposal and management of waste. That said, in Section 4.1
, we noted that, while nuclear accidents have on average been the most expensive, they were responsible for only 2.3% of the deaths in energy-related accidents. Moreover, supporters of nuclear argue that the disposal and management of waste can be, and is, satisfactorily resolved.
Given that all of the energy sources have their advantages and disadvantages, the reader may be wondering which ones to use. We suggest that policy-makers who are trying to decide between various energy policies should consider what their main priorities are, and which priorities they are prepared to compromise on. This may be different for different countries, and may change over time.
For example, suppose a government considers reducing CO2
emissions one of its top priorities. In Section 4.1
, we suggested seven different approaches for this, but noted that each conflicts with other priorities (also summarized in Section 6
). If protecting biodiversity is also a top priority, then the use of biomass should be avoided, and that of hydroelectricity or wind energy should be treated warily. Meanwhile, if having a stable and reliable electricity supply is also a top priority, then the use of any of the intermittent sources (wind, solar, or tidal) should be minimized, and governments may want to prioritize the use of nuclear, or transition from coal or oil to gas, or invest in carbon capture and storage (CCS) technology.
On the other hand, suppose a government is trying to increase economic growth and/or to improve social equity. In that case, cheap, affordable, and reliable electricity is probably a top priority. Therefore, some combination of coal, oil, gas, and nuclear would probably make sense. If geothermal or hydroelectricity are suitable for the area, they may also be worth considering. If reducing CO2 emissions is also a top priority, then they may want to reduce the amount of fossil fuels they use and develop more nuclear (as France and Sweden have done, for instance), whereas if avoiding the use of nuclear is a higher priority, then they might want to consider using more fossil fuels instead.
Looking at the breakdown in the US$
3.66 trillion which has been spent on global climate change expenditure over the period 2011–2018, as described in Figure 1
and Table 1
, we saw that 55% was allocated to solar and wind energy projects. This is a very large allocation for two energy sources which have many disadvantages, as summarized in Section 6
. Meanwhile, only 5% has been spent on climate adaptation, even though investing in climate adaptation can dramatically improve the ability of societies to deal with climate change and weather extremes. This suggests that global climate change expenditure is not being allocated using a critical assessment of the pros and cons of the key policies. We hope that the analysis in this review can remedy this in time.