In its most recent Countdown report on health and climate change (2024) The Lancet stated that rapid changes in climate and decades of insufficient action to address the climate emergency, mean that people all around the world now face “record-breaking threats to their well-being, health and survival”.³

The Pan American Health Organization (PAHO) classifies the impacts of climate change on human health through three pathways:⁴

1. Direct impacts – morbidity and mortality caused by heat stress and extreme weather events such as storms, floods etc.⁵
2. Indirect impacts through natural systems including allergic disorders due to elevated air pollution and increased incidence of vector-borne diseases caused by rising temperatures.
3. Indirect impacts through socioeconomic systems for example food insecurity leading to malnutrition.

While there has been considerable progress recognizing the physical impacts of climate change, less attention has been paid to mental health impacts – this has been called the “invisible injustice”.⁶ Fig. 1 highlights the impact of climate change on health as well as drawing out the broader implications for mental health.

Climate change is a global phenomenon, but not a uniform one. Geographical, environmental, cultural, socioeconomic and population trends all play an important role in shaping the health impacts of climate change. The impact of climate change on health can vary significantly both between countries and even within countries5 – making context a critical consideration in research and programmatic responses.

The available evidence on climate change suggests that already vulnerable groups are disproportionately affected by its negative impacts. Implementation researchers should be alert to the risks of climate change exacerbating existing health inequities or reversing previous gains. As outlined in the section on Addressing health inequities and vulnerabilities in CCH.

Fig. 2 gives an overview of vulnerability factors and climate-related hazards, and their impact on health outcomes and health systems. Climate change impacts health both directly and indirectly, and is strongly mediated by environmental, social and public health determinants.

At the 78^th World Health Assembly, held in Geneva in 2025, global leaders set a target to “ensure health systems and health care facilities are climate-resilient, low-carbon and environmentally sustainable”.¹⁰

While the impact of climate change on health is well established, the impacts on health systems have only come to the fore more recently.² As the effects of climate change are non-linear, unpredictable and in flux, future-proofed health systems must be both adaptive and constantly evolving in order to respond to predicted and unforeseen challenges.² Health systems should prepare for increased demand as climate change negatively impacts health and well-being, as well as disruption caused by climate change, for example weather events that cut off supply chains.¹¹

With the health sector contributing 5% of global greenhouse gas emissions, decarbonizing health systems and facilities can also significantly improve health outcomes and sustainability.¹² WHO’s Implementing the global framework on well-being at country level: policy pathways (2025) highlights the importance of developing low-carbon health systems, with the ultimate aim of achieving net zero emissions.¹²

“Implementation science for climate change and health adaptation should take place within [the] context of iterative risk management and systems-based approaches; otherwise, it may miss opportunities to increase resilience as vulnerabilities shift, better practices develop, and the climate continues to change.” Boyer et al (2020)¹³

The intersection of climate change and health has become a key topic in global health and is one of the four health challenges targeted in the TDR Strategy 2024–2029,¹⁴ however research on climate and health “remains patchy”¹⁵ and there are substantial gaps in evidence.¹⁶ Recent reviews of trends in CCH research have found that most studies focused on health vulnerabilities to climate change¹⁵ or the causal relationship between climate change and health,¹⁷ rather than focusing on more actionable topics such as the effectiveness of mitigation and adaptation strategies. There are even fewer examples of IR studies in the context of CCH.^13,17,18

As countries scale up their CCH efforts, there is a critical need for national-level evidence to inform government decision-making.⁵ The WHO Draft global action plan on climate change and health (2025) highlights the need for IR in the context of CCH – to develop a robust evidence base as well as to identify global and regional knowledge gaps, with a focus on intervention effectiveness and the impact of climate change on the health of vulnerable populations.¹⁰

The role of IR in bridging the “know–do” gap between research and action^16,18 and rapidly translating research into “widespread, real-world use”² is particularly valuable in the context of climate change, which is developing at an alarming pace.

IR plays a critical role in tackling the complex, evolving challenges at the intersection of climate change and health. Its strengths include the ability to support “de-implementation” by identifying and discontinuing interventions that are ineffective or harmful in certain settings; a flexible, systems-based approach that can adapt to dynamic real-world conditions; and its inherently multidisciplinary nature, which enables investigation of the health, social and economic impacts of climate-related interventions.^2,15 These qualities make IR particularly well suited to guiding practical, context-specific responses to the changing conditions of the climate crisis.

Fig. 3 synthesizes key recommendations for IR approaches to advance CCH adaptation research, highlighting strategies to enhance intervention effectiveness, address context-specific challenges and promote health system resilience.