New guidance will strengthen evidence on health effects of climate mitigation

Climate mitigation actions, measures that aim to reduce greenhouse gas (GHG) emissions, can bring major health co-benefits in the near term. Previous evidence from the Pathfinder Initiative highlights that climate mitigation can improve health through three main pathways: reducing air pollution by phasing out fossil fuels and transitioning to clean, renewable energy; shifting to healthy, sustainable diets; and increasing physical activity through active travel (walking and cycling). Studies modelling the health effects of climate mitigation quantify the scale of these potential health benefits, and can increase support for more ambitious action to accelerate progress towards net-zero targets. 

While evidence on the health benefits of climate action is growing, modelling studies often use different approaches and ways of measuring outcomes, which can make it harder to compare results and use the evidence to guide policy and real-world action. 

To address this challenge, experts from the Pathfinder Initiative research team at the London School of Hygiene & Tropical Medicine (LSHTM) have produced a new resource, the Guidance for Health Effects of Mitigation Modelling Studies (GHEMMS) checklist, to guide best practice for the design, conduct and reporting of Health Effects of Mitigation (HEM) modelling studies. The GHEMMS checklist, published in the Lancet Planetary Health, will help to strengthen and harmonise the evidence base for action, enabling evidence from different studies to be compared and used more effectively in decision making. Increasing comparability of studies and efficiency in evidence synthesis will in turn support the facilitation of evidence-based implementation of effective, healthy, and equitable climate mitigation actions. 

The GHEMMS checklist is the first structured checklist produced to support these modelling studies and is most relevant for primary researchers from a range of disciplines who are modelling the GHG and health impacts of climate mitigation actions and want to maximise the impact of their research. 

The development of the checklist was informed by findings from an umbrella review (review of reviews) of evidence on the health benefits of climate mitigation carried out by the Pathfinder Initiative research team, published in the Lancet Pathfinder Commission report. The review brought together and quantified studies that modelled GHG emissions reductions and health effects from climate mitigation actions, and showed significant diversity in GHG measurements, timescales, spatial scales, and health exposure and outcome measures, impeding the harmonisation of evidence. An absence of transparency, clarity, and completeness in how research is conducted and reported also created challenges in bringing together the evidence; interventions and context were often only briefly described, and baseline emissions levels (the amount of GHG emissions that would occur if no additional mitigation actions are carried out beyond existing policies and practices) were frequently omitted. The Pathfinder Initiative umbrella review also found that the equity implications of actions were rarely considered in studies, making the inclusion of equity a priority in developing the GHEMMS checklist.

The authors followed a three-step process to develop and refine the checklist: reviewing available tools and existing literature; engaging with researchers, policymakers and other interest-holders to incorporate diverse and expert perspectives; and piloting and finalising the checklist. 

While the checklist is not yet mandated by funders, therefore limiting resources and incentives for its use, researchers should, at a minimum, prioritise the key points in their research: 

• Better defining the study context and wider system;
• Clearly defining the mitigation action(s) and business as usual, considering the policy levers or societal shifts necessary to reach such a change;
• Engaging with interest-holders as much as resources and networks allow;
• Considering the target audience of their research, using this to report outcome measures which will have the greatest impact; 
• Transparency of methods, making use of supplementary material to maximise knowledge sharing and trust in evidence.

The researchers note that although GHEMMS aims to be global in scope, the development of the current checklist was informed by findings from published studies, the majority of which present evidence from high-income countries (HICs). The limited number of studies from low- and middle-income countries (LMICs) reflects the lack of funding for research in LMICs, and a focus on adaptation in these countries rather than mitigation due to their small contribution to global GHG emissions relative to HICs. However, the authors emphasise that climate mitigation will be increasingly important in LMICs due to rising emissions, as well as the potential health and economic benefits of adopting low-GHG development pathways. The authors note that future work should focus on adapting the checklist to inform research relating to LMICs, with an emphasis on the need to integrate climate mitigation and adaptation actions. 

Tamzin Reynolds, Research Fellow at LSHTM and lead author of the publication, said: “We know climate mitigation can bring major health benefits, but to translate evidence into action and maximise impact, studies need to be consistent and comparable. The GHEMMS checklist gives researchers practical guidance for the design and reporting of modelling studies, helping to strengthen the evidence base for climate and health decision-making. Going forward, it will be important to adapt the checklist for different regional and income contexts, particularly where evidence is currently limited.”