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Planetary health is defined as “the health of human civilisation and the state of the natural systems on which it depends,”5 emphasising the importance of protecting, restoring, and regenerating ecosystems to support the flourishing of all forms of life.6 Planetary health recognises the connectivity of earth systems, meaning that breaching one boundary will affect others. When developing interventions in one domain it is therefore essential to consider how other domains will be affected. For example, although the primary objective of promoting plant predominant diets may be to improve health and/or reduce GHG emissions, it could deliver other environmental benefits by mitigating freshwater depletion, land system degradation, and biodiversity loss. Human and environmental goals can be described as direct or (co-)benefits, depending on the objectives and design of the intervention (box 2). Health “co-benefits” of climate action are framed as the ancillary benefits of mitigating climate change—for example, the health effects of reduced air pollution from phasing out fossil fuels. Prioritising interventions with multiple benefits can garner traction and funding towards accelerated climate action that improves near term health and environmental outcomes, while reducing longer term effects, such as the global burden of undernutrition from climate change.2 However, robust evidence from real world implementation is needed to support allocation of local resources to the design, delivery, and uptake of such actions.

that improves near term health and environmental outcomes, while reducing longer term effects, such as the global burden of undernutrition from climate change.2 However, robust evidence from real world implementation is needed to support allocation of local resources to the design, delivery, and uptake of such actions. Reductions in misdiagnosis of asthma and improved care pathways for chronic obstructive pulmonary disease (COPD) can drive reductions in greenhouse gas emissions attributed to use of inhalers that emit high levels of greenhouse gases. For example, optimal symptom control and the introduction of comparable treatments with a lower GHG footprint such as dry powder inhalers, can reduce emissions from traditional inhalers and their misuse or overuse.7 These interventions could also benefit vulnerable populations exposed to air pollutants from wildfires, agriculture, and fossil fuel combustion that are likely to exacerbate respiratory conditions. Optimal symptom control for COPD can also reduce pharmaceutical waste and plastic pollution, contributing to the transgression of the planetary boundary on novel entities.

populations exposed to air pollutants from wildfires, agriculture, and fossil fuel combustion that are likely to exacerbate respiratory conditions. Optimal symptom control for COPD can also reduce pharmaceutical waste and plastic pollution, contributing to the transgression of the planetary boundary on novel entities. Policies to reduce energy dependency on fossil fuels through renewable energy technologies aim to reduce GHG emissions contributing to climate change. They can also reduce pressures on planetary boundaries for atmospheric aerosol loading and ocean acidification, with cascading benefits for biodiversity loss. The transition to renewable energy sources such as wind or solar power can result in health co-benefits from reduced exposure to air pollution. The extent of these co-benefits will depend on the scale of such policies and on context.2 Trade-offs for planetary health will also need to be considered in this transition. For example, a switch to biofuel production can place additional pressure on biodiversity, land use, and freshwater systems. A transition to bioenergy generation could also threaten food security and livelihoods for indigenous populations or low income communities, if land use systems are forcibly altered.2

transition. For example, a switch to biofuel production can place additional pressure on biodiversity, land use, and freshwater systems. A transition to bioenergy generation could also threaten food security and livelihoods for indigenous populations or low income communities, if land use systems are forcibly altered.2 Cash transfers for women and small scale entrepreneurs in low income countries are poverty reduction initiatives that can foster economic empowerment and gender equality among vulnerable or marginalised populations.8 Economic resilience can create health benefits through improved access to healthcare or other indirect behaviour changes, such as access to electricity for cooking and lighting. Emerging evidence suggests that cash transfers could therefore be an effective adaptation measure. Environmental benefits may accrue when cash transfers are used to incentivise transitions towards sustainable agricultural practices, or away from livelihood practices that create environmental harms, such as logging and deforestation.7 However, these initiatives need to be well designed to avoid harming marginalised communities or inadvertently encouraging other environmentally harmful practices. The effectiveness of interventions relies on coherence within the wider system, so a planetary health perspective encourages holistic identification and minimisation of trade-offs—for example, the effect of biofuels on health and biodiversity (box 2).

Emerging evidence suggests that cash transfers could therefore be an effective adaptation measure. Environmental benefits may accrue when cash transfers are used to incentivise transitions towards sustainable agricultural practices, or away from livelihood practices that create environmental harms, such as logging and deforestation.7 However, these initiatives need to be well designed to avoid harming marginalised communities or inadvertently encouraging other environmentally harmful practices. The effectiveness of interventions relies on coherence within the wider system, so a planetary health perspective encourages holistic identification and minimisation of trade-offs—for example, the effect of biofuels on health and biodiversity (box 2). Coherence of interventions may be assessed across different planes: vertical (eg, levels of governance), horizontal (eg, across municipal departments or sectors), and temporal (eg, planning for future generations).9 To effectively measure the planetary health costs and benefits of interventions delivered across spatial and temporal planes, contextually appropriate and credible evaluative tools will be needed. Some tools already exist in public health and can be adapted to consider the complexity of the natural and built environment, notably the Medical Research Council (MRC) guidance on the development and evaluation of complex interventions.10

l planes, contextually appropriate and credible evaluative tools will be needed. Some tools already exist in public health and can be adapted to consider the complexity of the natural and built environment, notably the Medical Research Council (MRC) guidance on the development and evaluation of complex interventions.10 Robust empirical research relies on the transdisciplinary application of credible methods to evaluate climate and health interventions. Randomised controlled trial are rarely feasible in climate change adaptation and mitigation research, but there are exceptions. For example, a randomised trial of the effectiveness of home upgrade interventions in low income households in Australia found reductions in greenhouse gas emissions, reported breathlessness, mental ill health, and healthcare costs.11 A range of research designs need to be used, including natural experiments, with the confidence in findings graded to inform decision making. However, this, depends on reporting standards across health and environmental domains.12

nhouse gas emissions, reported breathlessness, mental ill health, and healthcare costs.11 A range of research designs need to be used, including natural experiments, with the confidence in findings graded to inform decision making. However, this, depends on reporting standards across health and environmental domains.12 Evidence synthesis can elucidate key insights for decision makers but has limited value if environmental or health outcomes are not transparently reported in primary studies.2 12 Standardised reporting of emissions of different GHGs—for example, by converting the global warming potential of GHGs into carbon dioxide equivalent emissions (CO2e)—can support efforts to translate and synthesise evidence.2 Similarly, standardised metrics for human health outcomes (eg, reduced years of life lost or disability adjusted life years) would allow a harmonised understanding of intervention effects. Defined indicators to measure changes across other natural systems are also under development (table 1).1 Checklist to inform a planetary health perspective on the design and evaluation of complex interventions for climate and health Key populations for climate resilient development include low income, coastal, or disaster prone settings; older people; pregnant women and children; indigenous peoples; displaced people; and people with disabilities. Checklist derived from MRC guidance on complex interventions for public health,8 an umbrella review by the Pathfinder Initiative,2 and authors’ experience.

Reductions in misdiagnosis of asthma and improved care pathways for chronic obstructive pulmonary disease (COPD) can drive reductions in greenhouse gas emissions attributed to use of inhalers that emit high levels of greenhouse gases. For example, optimal symptom control and the introduction of comparable treatments with a lower GHG footprint such as dry powder inhalers, can reduce emissions from traditional inhalers and their misuse or overuse.7 These interventions could also benefit vulnerable populations exposed to air pollutants from wildfires, agriculture, and fossil fuel combustion that are likely to exacerbate respiratory conditions. Optimal symptom control for COPD can also reduce pharmaceutical waste and plastic pollution, contributing to the transgression of the planetary boundary on novel entities.

Policies to reduce energy dependency on fossil fuels through renewable energy technologies aim to reduce GHG emissions contributing to climate change. They can also reduce pressures on planetary boundaries for atmospheric aerosol loading and ocean acidification, with cascading benefits for biodiversity loss. The transition to renewable energy sources such as wind or solar power can result in health co-benefits from reduced exposure to air pollution. The extent of these co-benefits will depend on the scale of such policies and on context.2 Trade-offs for planetary health will also need to be considered in this transition. For example, a switch to biofuel production can place additional pressure on biodiversity, land use, and freshwater systems. A transition to bioenergy generation could also threaten food security and livelihoods for indigenous populations or low income communities, if land use systems are forcibly altered.2

Cash transfers for women and small scale entrepreneurs in low income countries are poverty reduction initiatives that can foster economic empowerment and gender equality among vulnerable or marginalised populations.8 Economic resilience can create health benefits through improved access to healthcare or other indirect behaviour changes, such as access to electricity for cooking and lighting. Emerging evidence suggests that cash transfers could therefore be an effective adaptation measure. Environmental benefits may accrue when cash transfers are used to incentivise transitions towards sustainable agricultural practices, or away from livelihood practices that create environmental harms, such as logging and deforestation.7 However, these initiatives need to be well designed to avoid harming marginalised communities or inadvertently encouraging other environmentally harmful practices.

The 2021 MRC guidance for complex interventions highlighted a range of transferable study designs, methods, and tools across four stages of intervention feasibility, design and identification, implementation, and evaluation for public health.10 Its pragmatic and pluralistic approach encourages public health researchers to change their research perspective, “shifting the focus from the ‘binary question of effectiveness’ to whether and how the intervention will be acceptable, implementable, cost effective, scalable, and transferable across contexts.”10 Complex interventions for planetary health may have a wider intended scale and impact than many health interventions. They may challenge existing systems and models that are driving unsustainable trends. Current MRC guidance recognises four perspectives: efficacy, effectiveness, theory based, and systems.10 Yet, stronger guidance is needed to leverage these perspectives in ways that consider connections between natural and human systems and the transdisciplinary approaches required to evaluate co-benefits and trade-offs of interventions designed with both health and environmental goals. For example, while the 2021 MRC guidance encourages evaluation considerate of the whole system, it offers little practical guidance on integrating systems tools such as systems dynamic modelling and life cycle assessments, often used in climate mitigation studies, into intervention design and evaluation.

nmental goals. For example, while the 2021 MRC guidance encourages evaluation considerate of the whole system, it offers little practical guidance on integrating systems tools such as systems dynamic modelling and life cycle assessments, often used in climate mitigation studies, into intervention design and evaluation. Other frameworks exist to support complex intervention research, such as the RE-AIM framework, which defines five real world contextual features for evaluation as: reach, effectiveness, adoption, implementation, and maintenance.14 RE-AIM informs the necessary conditions for the transferability and scaling of interventions by encouraging researchers, practitioners, and policy makers to consider these elements early in design. Both RE-AIM and the MRC guidance could be adapted to integrate natural systems, with deeper recognition of the built and natural environment and consideration of larger scales of implementation, understanding that planetary health impacts will also likely occur in non-intervention settings and arise for generations to come.

RE-AIM and the MRC guidance could be adapted to integrate natural systems, with deeper recognition of the built and natural environment and consideration of larger scales of implementation, understanding that planetary health impacts will also likely occur in non-intervention settings and arise for generations to come. High level frameworks exist to encourage sustainable practice and evaluation but there are no widely applied guidelines for the empirical evaluation of complex interventions for planetary health. Guidelines were recently developed for the modelling and reporting of health and GHG outcomes of climate mitigation studies.15 These guidelines encourage standardised measures and quality reporting of modelled outcomes from exposures, such as air pollution. This guidance aims to tackle incomparable estimates emerging from studies applying different assumptions or mathematical functions. However, these guidelines do not inform the design or conduct of real world complex interventions.

easures and quality reporting of modelled outcomes from exposures, such as air pollution. This guidance aims to tackle incomparable estimates emerging from studies applying different assumptions or mathematical functions. However, these guidelines do not inform the design or conduct of real world complex interventions. Tools are currently being adapted or developed to inform transparent design and prioritisation of interventions for planetary health.6 Health impact assessments and environment impact assessments also offer prospective and comprehensive insights but can take time; more work is needed to understand their applicability to empirical research.16 Trade-offs may be identified early by using policy aids such as multicriteria decision tools. These decisions can, however, require a difficult balance of often incommensurate values such as financial revenue, ecosystem recovery, or sociocultural benefits. This makes the transparent and quality reporting of intervention prioritisation and planetary health assessment even more important.11

iteria decision tools. These decisions can, however, require a difficult balance of often incommensurate values such as financial revenue, ecosystem recovery, or sociocultural benefits. This makes the transparent and quality reporting of intervention prioritisation and planetary health assessment even more important.11 Indigenous knowledge systems embody holistic perspectives, including responsibility and respect for the wellbeing of the planet, offering a vital understanding of land stewardship.17 Yet these knowledge systems remain fundamentally underrepresented in global climate governance and intervention guidance. Inclusion and equity are the main determinants of health and of population resilience, so the prioritisation and inclusion of diverse voices through co-design and participatory approaches is critical, as is recognising and addressing power dynamics in intervention conduct and evaluation.1 2 Researcher perspectives and theoretical positioning of guidance need to be explicitly considered and transparent to improve the quality and relevance of available evidence to meet the needs of vulnerable populations.18 An operational planetary health perspective for designing, implementing, and evaluating complex health interventions, would: Support the systematic application of transdisciplinary tools and actor engagement Prioritise interventions with co-benefits for natural and human systems Enable timely evaluation of mitigation and adaptation measures, to reduce risks and enhance value for money Facilitate evidence synthesis by promoting harmonised approaches to design and evaluation

Adapted guidance should be reflexive to the study context, actors, and researcher perspectives involved. It should enable the prospective identification of intervention risks on planetary health in a holistic manner, considering potential trade-offs and related mitigation measures, and co-benefits. However, some immediate and pragmatic steps that researchers and practitioners can take are to better define the intervention context and the wider system, considering health, social, and environmental factors and their connections; define intervention and objectives for health and natural systems, considering intended and unintended outcomes; identify near to long term monitoring and impact indicators; select credible and appropriate methods for monitoring and evaluation; and report transparently on implementation and scalability.

ir connections; define intervention and objectives for health and natural systems, considering intended and unintended outcomes; identify near to long term monitoring and impact indicators; select credible and appropriate methods for monitoring and evaluation; and report transparently on implementation and scalability. Table 1 presents a practical checklist to help ensure a planetary health perspective in the delivery and evaluation of complex interventions. Not every item will be relevant to every study, but the aim is to prompt researchers to consider them systematically. The checklist emphasises the value of credible and appropriate tools, with clear and transparent reporting, rather than hierarchical study designs. Diverse approaches and methods can work coherently across the stages of intervention feasibility, design and identification, implementation, and evaluation. Existing tools can be readily adapted to consider key factors, such as political support, the built and natural environment, and their connections to health. It encourages a shift in researcher perspective to the application of existing approaches such as systems mapping, programme theory, or logic models, to prioritise interventions that tackle immediate and future needs for planetary health.

ical support, the built and natural environment, and their connections to health. It encourages a shift in researcher perspective to the application of existing approaches such as systems mapping, programme theory, or logic models, to prioritise interventions that tackle immediate and future needs for planetary health. When resources are limited, researchers can still aim to identify intervention objectives that recognise connections between health and natural systems, develop useful evaluation questions for policy and practice, and embed evaluative tools early or from design stages of complex interventions. More funding may be needed to support transdisciplinary engagement. Lack of quality data or resources will often prevent documentation of the effects of a specific intervention—for example, dietary data at the appropriate spatial scale to infer health effects. This is more likely when it is a new intervention or there is no available comparator, as is often true of national policies. Theory based, dialogical approaches, and planetary health rapid impact assessment tools can then take a life cycle perspective across natural systems to inform relevant evaluation questions.6 8 19 It will take concerted efforts from funders, researchers, potential users, and affected populations to work towards a collective reform of existing practices. We live and work in unprecedented times, and an unprecedented response from researchers, policy makers, and practitioners is needed to address these contemporary challenges.

concerted efforts from funders, researchers, potential users, and affected populations to work towards a collective reform of existing practices. We live and work in unprecedented times, and an unprecedented response from researchers, policy makers, and practitioners is needed to address these contemporary challenges. Implementation of climate change mitigation and adaptation policies is needed to protect and improve health Updated guidance is needed to assess the effects of climate related interventions on human health, equity, and prosperity in the near and long term A planetary health lens, integrating human health and earth systems, can inform the evaluation of complex interventions by assessing (co-)benefits, trade-offs, and risks to vulnerable and affected populations