Over 40% of land vertebrates will be affected by extreme heat by the end of the century if we continue emitting greenhouse gases with a ‘business as usual’ scenario. According to a new study, the worst affected regions, such as the Mojave Desert in the US, will have 100% of species living there exposed to extreme heat.

Across the world, from Pakistan to Spain, extreme heat threatened millions and took thousands of lives last year — but that’s just human lives. Although we pay less attention to it, animals are suffering a far greater scourge; after all, they don’t have air conditioning and running water, and their adaptation options are limited. Even in terms of research, there’s been relatively few attention given to how animals will face against extreme heat.

When researchers do look at this, they tend to be optimistic. But what if our optimistic climate scenarios don’t happen? A new study looked at that, analyzing what climate woes animals will have to face under various climate scenarios. In particular, the researchers from the University of Arizona mapped the effects of extreme heat on over 33,000 land vertebrates by looking at maximum temperature data between 1950 and 2099, looking at five predictions of climate models based on different levels of emissions.

Extreme heat and land animals

Under a high global warming scenario (4.4C), roughly 41% of land vertebrates will be exposed to extreme heat that breaks the historical record, and if won’t just be during the summer. The study found 3,000 land animals (11% of all species) will experience extreme heat for over six months of the year, especially amphibians and reptiles.

When faced with a lower temperature of 3.6C, about 28% of land animals will face extreme heat. Under a more modest intermediate warming scenario of 2.7C, only 15% of the animals will experience adverse heat. Finally, in a low warming scenario of 1.8C, in line with the Paris Agreement, only 6% of animals will endure extreme heat events.

The Gran Chaco in South America, the Sahel and Sahara in Africa, the Mojave Desert in the US would be the region most affected by the extreme heat, the researchers said, with all species there under severe risk. While it’s not possible to say if the areas would be uninhabitable, it’s more likely that more species would become extinct.

This is super scary. Already, animals are having trouble adapting to the warming we’ve seen so far — and things will get worse. But how much worse is an important question, and this is what this study has focused on: showing that every fraction of a degree matters greatly, and can be the difference between survival and extinction for many species.

The science has never been clearer: we’re causing the level of greenhouse gases in the atmosphere to surge, and these gases are heating the planet. Unless we’ll manage to impose drastic greenhouse cuts soon, we’ll be headed for irreversible climate damage.

Extreme temperatures kill over five million people a year globally, with heat-related deaths continuing to rise, according to previous studies. While humans can shelter, and many drink as much water as they want, that’s not the case for animals. Heat stress can cause die-offs and wipe out ecosystems, as happened in 2021 in Canada.

Global average temperature has increased by 1.1C compared to the pre-industrial period, with visible effects on biodiversity overall. Avoiding a much larger temperature increase would be very good news not just for humans but also for animals, as seen by the study. But doing so will require much more ambitious climate action this decade.

The study was published in the journal Nature.