Thresholds and limits

Climate resilience is often framed in terms of emergency response or infrastructure such as energy systems and transport networks. Alongside these, the resilience of the people themselves who rely on those services or operate the infrastructure is essential.

That is physiological resilience: the capacity of people to maintain health, function and make decisions under environmental stress – as well as recover afterwards. Rising heat, deteriorating air quality and disruption to food systems place strain on physiological resilience, often before failures in the wider system are visible.

Physiological thresholds provide warning signals of where resilience is under stress i.e. where action is required to prevent conditions overwhelming the body. Physiological limits mark conditions where resilience fails.

Key points for policymakers

Climate change is causing rising temperatures, increased air pollution and disruption to food systems. This impacts the physiology of people around the world, making it more difficult for their body to stay healthy and function normally. Physiological harm can begin well before official warning levels are reached, especially for vulnerable groups. Policies based on how the human body responds to heat, pollution and food insecurity can protect people earlier and more effectively, and show why climate action to reduce emissions is essential.

In this sense, physiological resilience is a core component of climate resilience: it determines whether people can live, work and function as environmental conditions change.

What needs to happen:

• Trigger protection earlier: Set warning systems and safety standards so action starts before people become unwell, not only once extreme conditions are reached.
• Design for vulnerable groups: Use population-level physiological thresholds, derived from evidence across groups and exposure contexts, as triggers for system-level protection. These thresholds must be differentiated to protect vulnerable groups such as older adults, pregnant people, young children, babies and those with long-term illness (mental and/or physical).
• Account for combined risks: Plan for heat, air pollution and poor nutrition together, since they often occur at the same time and make each other more dangerous.
• Shift responsibility to systems: Build protection into workplaces, housing, public services and emergency planning, rather than expecting individuals to judge when conditions are unsafe.
• Test whether adaptation is enough: Check whether proposed adaptation measures can realistically protect people as risks increase, rather than assuming people can always adjust.
• Cut emissions to tackle climate change: Treat cutting emissions and air pollution as essential for keeping conditions within what people can safely tolerate.