The number of people living with extreme heat will more than double by 2050 if global heating reaches 2C, according to a new study that shows how the energy demands for air conditioners and heating systems are expected to change across the world.
No region will escape the impact, say the authors. Although the tropics and southern hemisphere will be worst affected by rising heat, the countries in the north will also find it difficult to adapt because their built environments are primarily designed to deal with a cooler climate.
The new paper, published in Nature Sustainability, is the most detailed study yet of how far and how fast different regions will encounter temperature extremes as human-driven global heating rises from 1C above preindustrial levels 10 years ago, towards 1.5C this decade, to 2C, which many scientists predict could occur around mid-century unless governments make rapid cuts to emissions from oil, gas and coal.
This will change the pattern of energy demand for temperature management. Over the coming decades, the northern hemisphere’s heating bill will decrease, while the cooling bill of the southern hemisphere will increase. Separate studies have confirmed that by the end of the century, global energy demand from air conditioning will overtake and then far outstrip that from heating.
For the latest study, extremes were defined by how many days each year temperatures deviate from a temperate baseline of 18C. Using computer models, the authors then mapped where the biggest changes will happen and how many people will be affected.
If the 2C threshold is breached, the new dataset indicates the number of people experiencing extreme heat will increase from 1.54 billion people (which was 23% of the world population in 2010) to 3.79 billion (41% of the projected world population in 2050).
The majority of those affected will be in India, Nigeria, Indonesia, Bangladesh, Pakistan and the Philippines. But the most significant increase in dangerous temperatures will threaten Central African Republic, Nigeria, South Sudan, Laos and Brazil.
In a surprise to the authors, the computer models also found that the greatest shift will occur early in the warming trajectory – near the 1.5C phase, which is where the world is now. This adds urgency to the need to adapt areas such as healthcare, the economy and the energy system.
“This is a really core finding because it tells us that we need to act much earlier in supporting measures for adaptation and mitigation,” said one of the authors, Radhika Khosla, of the Smith School of Enterprise and the Environment at Oxford University. “Overshooting 1.5C of warming will have an unprecedented impact on everything from education and health to migration and farming. Net zero sustainable development remains the only established path to reversing this trend for ever hotter days. It is imperative that politicians regain the initiative towards it.”
She said even relatively wealthy, northern nations will struggle. “No part of the world will be able to shy away from extreme heat. There is a lack of preparedness across nations,” she said.
In the case of the UK, she said buildings and infrastructure are old, inefficient and primarily designed to cope with the cold, so when temperature extremes move in the opposite direction, it poses a challenge to health systems, energy supplies and the economy. In 2023, for example, the UK National Grid asked to fire up two coal-fired power plant units to cope with air conditioner demand from an unusual heatwave.
