One billion people left dangerously exposed to heat stress by gaps in climate monitoring

Melbourne: The year 2023 was the hottest on record. Humidity is rising too. Heat and humidity are a dangerous combination, threatening all aspects of our lives and livelihoods.

Climate change is pushing humid heat dangerously close to the upper limits of what people can survive. Parts of the world are on track for conditions beyond the limits of human tolerance.

Yet our new research shows poor weather station coverage across the tropics leads to underestimates of heat stress in cities. This means global climate change assessments probably overlook the local impacts on people.

Concentrated across tropical Asia and Africa, informal settlements, commonly known as “slums”, are on the front line of climate exposure. The shortfalls in climate monitoring leave these communities dangerously vulnerable to rising humid heat. With few options to adapt, millions could be forced to seek refuge away from the hottest parts of the tropics.

Why is heat such a threat in these places?

Rapid urbanisation that outpaces planned, formal development is driving the growth of informal settlements. Their residents usually lack infrastructure and services, such as electricity and water supply, that many city dwellers take for granted.

More than 1 billion people live in informal settlements. The United Nations expects this number to grow to 3 billion over the next 30 years. In countries such as Kenya or Bangladesh, nearly half the urban populations lives in informal settlements.

Most informal settlements are located in the tropics. Here it is hot and humid year-round, but their residents have few options to adapt to heat stress.

Most households in these settlements are on low incomes. Many residents must work outdoors for their livelihoods, which exposes them to heat and humidity.

On top of this, because informal settlements fall outside official systems and regulations, we often lack data about the threats they face.

What’s missing from climate data?

Most of the world’s population lives more than 25km from a weather station.

This means weather stations rarely capture the full range of temperature and humidity in cities, which are usually hotter than non-urban surrounds the urban heat island effect.

These gaps in monitoring are largest across the tropics where most informal settlements are located.

As individuals we experience heat on a local scale, which isn’t captured by sparse weather station networks or meteorological models.