Understanding heat as a design as well as environmental issue, Luisa Amann considers how Foster + Partners promote urban cooling in their projects, with reference to work that is currently on view at the Venice Biennale.

In 2024, for the first time on record, average global temperatures clearly exceeded 1.5˚C above pre-industrial levels. This overshoots a key threshold established by the Paris Agreement, a treaty in which 195 nations pledged to tackle climate change, that called for the immediate and rapid reduction of emissions by forty-three percent. Climate change acts as a threat multiplier, exacerbating existing inequalities across regions, communities, and demographics. One of the most significant challenges that climate change poses is that of extreme heat, which will become more frequent and intense as these thresholds are exceeded.

For practitioners of the built environment, extreme heat presents a rapidly growing problem. Sixty percent of the global population is projected to live in cities by 2050, reflected in the ongoing expansion and sprawl of urban development worldwide. These developments introduce buildings, road, pavements, and infrastructure that absorb heat to a greater degree than natural surfaces (such as vegetation and water). As a result, cities feel and measure as hotter than nearby rural regions – a phenomenon known as the ‘urban heat island’ (UHI). Without thoughtful intervention, the frequency and intensity of UHIs will multiply and compound in cities, placing a disproportionate heat burden on their populations, and potentially making them uninhabitable.

Heat burden – or heat stress – is the physiological and psychological effect that heat has on the body. This is a burden that will be exacerbated as extreme heat events intensify; it is also a burden that is not experienced equally among populations. Physical differences between people can lead to different experiences of the ‘same’ heat. Varying experiences of heat are also the result of where people are in a city, how they move around it and when, as well as their access to cool spaces. Considered together, research has shown that extreme heat tends to trigger more adverse effects on vulnerable and marginalised populations – an insight that is termed ‘thermal inequality.’ This makes extreme heat a sociopolitical, architectural and urban planning problem as well as an environmental one.

The relationship between UHIs, climate change, urban planning, and social inequality forms the basis of inquiry in the German Pavilion at the 2025 Venice Biennale. The following article presents some of the research that is displayed at the pavilion, including a Space Syntax study of the effects of UHIs on pedestrian mobility in London, alongside additional research and projects by Foster + Partners that consider the problem of UHIs at a landscape and design level. Through understanding the challenges posed by urban heat, its emergence as a socio-spatial phenomenon linked with the development of the modern city, and how extreme heat disproportionately affects vulnerable populations, more equitable ways forward can be proposed.

Full article: Urban Heat Islands and Climate Vulnerability