Introduction

There is increasing evidence of both direct and indirect adverse effects of climate change on human health worldwide, the latter mediated by disruption in ecological and socioeconomic systems [1]. Many of these effects have been known for some time; yet, despite the accumulating evidence, protecting human health has only recently become a major consideration in global policy discussions on climate change [2]. This increased recognition of health issues, brings new demands for evidence from decision makers and requiring robust scientific data, including on attribution, for knowledge synthesis, and its use to inform policy for health and healthcare for both climate change adaptation and mitigation. The scientific and health communities have important roles, including ensuring that robust evidence is generated, sharing lessons of good practice, and building capacity for action worldwide.

Effective policy responses to the multiple effects of climate change on health require integrating diverse mitigation and adaptation measures. Actions to reduce emissions of greenhouse gases (GHGs) can benefit population health locally and in the near term, such as by reducing exposure to co-emitted air pollutants. These are additional to the environmental and global health benefits that will flow from mitigation as a result of reduced climate hazards and could help, by averting costs of ill health (including impacts on labour productivity) and of health services provision, to offset the costs of tackling climate change. Adaptation actions to support individuals, communities, and governments in coping with unavoidable consequences can reduce the effects of climate change on health. Policies designed to mitigate and adapt to climate change should aim to minimise unintended adverse consequences, assess trade-offs [3], and link to health systems guidance [4]. Developing solutions must be based on the synthesis of available research findings from across multiple disciplines and knowledge systems (including from Indigenous Peoples), while recognising the need to fill critical knowledge gaps with new research and tackle misinformation. There is much more to do in all regions. In the European Union, for example, health co-benefits are now explicitly considered when developing climate change mitigation policies, but their influence on final policy outcomes has been limited [5]. Resilient and innovative responses to climate change require a systems-based approach [1,6] involving coherent and coordinated policy development across all sectors and ensuring “health in all policies.”

One of the problems in using scientific evidence has been the hitherto limited input from low- and middle-income countries (LMICs), resulting in lack of inclusivity in designing research and using research outputs for implementing policy and practice. In this paper, we draw on current work of the InterAcademy Partnership (IAP), the global network of more than 140 academies of science, engineering, and medicine, including evidence from diverse geographical and socioeconomic contexts. We explore issues for the science–policy interfaces in climate change and health, making the case for increasing inclusivity and strengthening capacity in marshalling diverse evidence and perspectives to support climate action. The IAP assessment aims to summarise evidence of the effects of climate change on health and potential solutions within and between regions, taking particular account of the issues for vulnerable groups and the need to respect cultural and other diversity. Furthermore, it aims to stimulate integration of policy and practice at local, regional, and global levels, recognising heterogeneity within and between regions. The conclusions from the project are being discussed with the wider scientific and health communities, with policy makers and other stakeholders.

Health co-benefits of mitigation

Policies proposed to mitigate climate change provide global health benefits through reduced impacts and could also lead to localised improvements in the health of those populations undertaking the mitigation [12]. Parties to the Paris Agreement are required to include a mitigation contribution in their Nationally Determined Contributions (NDCs), and, in this context, it is important to take account of the large opportunities for public health gains [13]. Modelling scenarios analysing the health co-benefits of NDCs for selected countries in Africa, Asia, the Americas, and Europe [14] project a significant reduction of premature deaths related to air pollution, diet, and physical inactivity. Identifying health protection and improvement as priority outcomes in the NDCs requires (i) continuing commitment to measuring and monitoring the health co-benefits; (ii) ensuring policy coherence between climate change and health policy processes; and (iii) that health actions in the NDCs are comprehensive enough to build climate-resilient health systems [13]. Some of these mitigation priorities are summarised in Table 1. Some general principles for selecting climate change mitigation actions can be outlined, including consideration of the potential for cost effective GHG reductions and the resulting health (co-)benefits. Those countries who are the greatest GHG emitters should lead mitigation efforts, but there may be major differences in the sectoral contributions to GHG emissions, and quantification of effects and selection of the location and scale of solutions can still be challenging.

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Table 1. Examples of mitigation actions: linking scientific evidence and policy objectives.

https://doi.org/10.1371/journal.pmed.1003719.t001

Challenges for adapting to health effects of climate change

Some examples of assessment of the scientific evidence are provided in Table 2, drawn from specific regions to illustrate the evidence, but in many cases, the issues are relevant worldwide. Our regional cross-cutting assessments are summarised as follows.

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Table 2. Examples of regional climate change impacts on health with implications for adaptation.

https://doi.org/10.1371/journal.pmed.1003719.t002

Heat.

Under high-emissions scenarios, large increases in heat-related deaths (and in net deaths including the possible effects of reduced cold exposure) are projected by late this century in warmer regions, such as the central and southern parts of America or Europe, and, particularly, Southeast Asia. There is a lack of data on which to base projections for Africa [26]. However, a recent systematic review of the United Kingdom literature [27] found that extreme heat exposure is often an invisible risk, whose impacts on health are not always recognised, and that there is insufficient policy action to prepare for direct or indirect effects of heat on health. Local actions, such as reducing heat island effects by better urban planning, including increasing green spaces, can reduce heat-related deaths. High temperatures also have other deleterious consequences, for wildfires, food systems, labour productivity, and pathogen distribution and replication that are discussed later.

Flooding.

Flood risk is increasing around the world because of climate change and the interaction with socioeconomic development, including increased urbanisation and inadequate planning [28]. The various climate-induced causes include sea level rise, extreme weather events, excess precipitation, thawing permafrost, and melting glaciers, all of which are exacerbated by land-use changes, particularly urbanisation. There are multiple short-term health consequences such as accidental injuries or death, as well as waterborne and vector-borne diseases in some regions, linked to impaired quality of water for drinking and sanitation. There are also longer-term consequences resulting from ecosystem degradation, including chemical contaminants, as well as increasing mental health challenges and cardiovascular disorders, although more evidence is needed.

Wildfires.

While fires can play a natural role in different ecosystems, they can also have a devastating long-term effect on ecosystems. Increasing temperatures and decreasing precipitation should be significant factors in the origin or increased frequency of wildfires worldwide, and a recent review has summarised the growing evidence linking climate change with increasing wildfire risk [29]. The ability to quantify and attribute the health consequences of pollutants from fires is challenging, but exposure to wildfire smoke is associated with increased all-cause mortality, and the particulate matter from wildfires may be more lethal than that from urban settings [30].

Food and nutrition security.

Climate change is already adversely affecting the yield and quality of crops in many regions, and these impacts are compounded by other environmental changes, for example, soil and water degradation in consequence of added chemicals (fertilisers, pesticides, and herbicides), largely the result of industrial agriculture. The consequences for undernutrition, especially for vulnerable groups, will be compounded increasingly as heat- and humidity-induced declines in labour productivity affect growing numbers of subsistence farmers [31]. Furthermore, climate-related disruptions to local food systems have important implications for cultural continuity and livelihoods that underpin health and well-being, especially for Indigenous Peoples, farmers, and fishers who have close relationships with the environment [32].

Infectious diseases.

A link between climate change and diverse infectious disease threats has been observed worldwide [2], in association with other aspects of globalisation that drive changes in both ecosystems and human behaviour. As a consequence of more favourable environments for mosquitos, WHO estimates that there will be significant increases in malaria and in other vector-borne viruses such as dengue, chikungunya, and Zika in some regions. Shifting distribution patterns of infectious diseases as a result of climate change are a global concern, both from increasing levels in locations where the diseases already exist and from their expansion into new areas.

The examples presented in Table 2 do not themselves determine how action should be focused or integrated across sectors and levels of governance. These issues are addressed further subsequently, but we emphasise here that integrated action, whether horizontal (across sectors) or vertical (between levels of governance), must not lead to any deflection of responsibilities.

Conclusions

Many policy solutions are advanced at a national level, including adaptation in health and social systems: Now, it is increasingly important to take account of the health implications for climate change policy integration in all sectors and to bring the interventions to scale [1]. We emphasise that there must be more commitment from policy makers to integrate health into National Adaptation Plans and NDCs of GHG emission reductions under the Paris Agreement. In addition to required national actions, health policy objectives must have regional considerations when there are cross-border threats emerging such as air pollution or infectious diseases. Pollution from industrial, urban, or agricultural origin near to national borders can have major consequences for neighbouring countries (for example, in the Indian subcontinent [45]). Interregional implications (spillover effects) may also be relevant, if national or regional policy action in one area, inadvertently or not, leads to adverse consequences elsewhere. For example, many nations are currently exporting their lack of environmental sustainability by importing food/biomass generated unsustainably elsewhere. Competition between food, feed, and fuel for the effective use of natural resources requires consideration of multiple factors in understanding trade-offs and setting priorities [46]. Protection of natural resources is also highly relevant in the search for natural climate solutions. Specific examples (in flood protection and for forest conservation as a carbon sink) have already been mentioned, and there is now a significant evidence base [47] from solution-oriented research on natural options in both mitigation and adaptation with benefits for health. In considering coordinated responses to environmental risks, it is essential to tackle the challenges for climate change and biodiversity together [48].

In addition to national and regional policy action, there is considerable scope for integration at the global level. Some of the current policy opportunities for embedding adaption and mitigation solutions worldwide, to underpin the objectives for health, social justice, sustainability, and survivability, include collective action on the Sustainable Development Goals (SDGs), the current discussions of the UN Framework Convention on Climate Change (UNFCC) and UN Convention on Biological Diversity (CBD), and regional initiatives by the offices of other UN bodies, in particular WHO, Food and Agriculture Organization (FAO), and UNEC (United Nations Economic Commission). Action is also possible as part of G7 and G20 Presidency’s initiatives and when linked to other strategic initiatives in pursuit of the circular economy and bioeconomy. In all cases, there are crucial roles for the scientific community in advising on the opportunities for science and technology, connecting to innovation, policy, and practice. Coherent policy development requires both vertical integration (local–regional–global) and horizontal integration between sectors, and both can be consolidated through the SDG framework. However, this requires careful planning. For example, although decarbonisation measures can benefit multiple SDGs, poorly designed ones may incur harm if generating resource conflicts or excluding communities [49]. There is concern that, as decarbonisation goals are increased to meet the Paris Agreement targets, so does the potential for adverse social outcomes, particularly increased inequity. To avoid these negative consequences, it is vital to clarify and agree objectives for triple wins on environment, health, and equity.

In the past decade, there has been a surge of international agendas to address global challenges: A focus on human health helps to catalyse the strengthening and linkage of these agendas [42] in driving national and regional policy decisions. The global context is important to strengthen and safeguard those goods and services that are provided on a scale beyond countries and can only be achieved collectively, for example, GHG emissions reductions, rule-based trade, food and nutrition security, pandemic prevention and management, and shared science. Mitigation measures may be initiated at local or regional level but require globally shared commitment to decarbonisation, with the imperative for the high emitters to act decisively. Shared objectives require collective action to tackle environmental and institutional risks and their transmission in an uncertain and rapidly connected world. Hitherto, policy making has often focused on reactive strategies but must now be more anticipatory, based on robust evidence, and with commitment to monitoring and auditing impacts to document the accumulating experience to improve future policy. While there are evidence gaps to be filled by new research, these should not be used as an excuse to delay action in developing policy on the basis of the best available science.

There is great heterogeneity within and between regions, but the findings of IAP’s regional-to-global projects confirm the potential value in sharing knowledge that will inform policy and practice worldwide. Utilising diverse evidence streams from the regional assessments necessitates embracing and supporting both more quantitative and qualitative research, the latter to understand the lived experiences of climate change impacts on health outcomes, as well as the contexts within which adaptation and mitigations efforts unfold. For example, other recent work on climate change and health issues for Arctic populations and their neighbours by IAP together with EASAC and the US National Academies of Science Engineering and Medicine [50] included discussion of impacts on Indigenous People, their contribution to transdisciplinary research efforts, and the value of traditional knowledge.

One research priority is to better understand the barriers limiting the implementation of action on climate change. Dismantling these barriers partly depends on effective public engagement by the scientific and health communities to articulate both the health threats associated with climate change and the solutions to the threats. Improving awareness about the health implications and countering misinformation can be a potent way to encourage public willingness to mitigate climate change through changing behaviour [7]. Another barrier to implementation rests on assumptions about the high economic costs of change. To what extent does perception of immediate economic costs inhibit the influence of health co-benefits on the development of mitigation policies [5]? There is evidence to suggest that including health in the cost-benefit analysis of mitigation measures strengthens the case for setting and meeting ambitious policy targets [7]. Further studies on cost-effectiveness of health effects are warranted to challenge the perception that change necessarily entails high costs and to contribute to the broader, transdisciplinary, multi-sectoral evidence base on the costs of action and inaction [51,52].

The political momentum for tackling climate change must accelerate, and there are significant upcoming opportunities to inform and influence public policy. For example, health issues are highly relevant to the 2021 UK Presidency themes for the Conference of the Parties (COP26) of the UNFCCC (adaptation and resilience; energy transitions and natural habitats; clean transport; cities and the built environment; and financial systems; see https://ukcop26.org). As noted in the Introduction, the scientific and health communities have important roles to play in these discussions, leading by example with actions in the health sector itself [53], and, more broadly, to share lessons of good practice, build capacity for action worldwide, and ensure that robust evidence is generated. But this is not enough, there is also a collective responsibility to use the principles of co-design with stakeholders to help build user receptivity at the science–policy interface as part of integrated goals to inform policy development, public engagement, and transformation of systems.

Supporting information