Nearly half of vertebrates will face extreme heat by the end of the century

By the end of this century, nearly half of the planet’s terrestrial vertebrates could face extreme heat waves far beyond what they are adapted to withstand. The situation would be even worse for reptiles and amphibians and for species that live on islands, because of the restricted territories they occupy.

These worrying conclusions have just been published in an article in the scientific journal Nature, one of the most important in the world, by an international team of researchers. The scariest numbers refer to a scenario in which the production of gases that warm the planet remains high in the coming decades. This would lead to a temperature increase of 4.4°C (relative to the pre-Industrial Revolution average) by 2099.

If that happens, the team calculates that 41% of terrestrial vertebrates would be exposed to extreme heat waves unparalleled to what we see today. In the case of amphibians and reptiles, the percentage rises to 55% and 51%, respectively.

In a more optimistic scenario, which considers that all countries will meet their current targets to combat the climate crisis, the global temperature rises by 2.7ºC and the proportion of species at risk of mega-heatwaves drops to 15% — still far from ideal .

The work, coordinated by Gopal Murali, a postdoctoral researcher at the University of Arizona (USA), also includes the participation of scientists from institutions in Israel and Switzerland. According to the team, although most research on the subject takes into account the increase in average temperature on a global and regional scale, it is also important to map the risk of extreme weather events —in this case, large temperature spikes— because they are the ones that can end up having the most severe effects on animal populations.

To make the estimates, they took into account, on the one hand, computer simulations that seek to estimate how the climate will be by the end of the century, in different scenarios (which depend on the possible amount of gases that cause global warming produced by human action ). In addition, they mapped the maximum temperatures that vertebrate species faced between 1950 and 2005.

Based on these data, they defined that an “extreme thermal event” of the future would be a period of at least five consecutive days in which the temperature would be greater than 99% of the maximum heat recorded in the interval 1950-2005. The analysis also took into account factors such as frequency (how many times a year), duration (how many consecutive days) and intensity (maximum temperature) of these extreme thermal events.

In the worst-case scenario, Gopal Murali and his colleagues calculate that, on average, terrestrial vertebrate species will be exposed to 70 days of extreme thermal events in 2099—that is, 15 times more than the historical average. In many temperate regions, arid and semi-arid environments and most of South America, including the Amazon, this number could be even higher, exceeding 100 days per year.

In addition to the greater vulnerability of reptiles and amphibians and species that live in drier environments (which, therefore, are already at the limit of acceptable temperatures), the team identified that both the Amazon and many regions with islands rich in biodiversity (Caribbean, Pacific islands, Madagascar, Indonesia, Australia) are especially at risk under these conditions. “The restricted distribution of island species could be one of the reasons for this,” Murali explained to Sheet.

In the case of islands, this means that such species would basically have nowhere to run, as their habitats are naturally more limited than those located on continents. But the case of reptiles and amphibians is similar even on continents, because they seem to depend on very particular local conditions. Thus, there would be no point in trying to migrate to cooler places, for example, because they would “bump” with other species already present there.

As the body temperature of amphibians and reptiles is also often dependent on the temperature of the environment, extreme heat events increase the risk of profound derangements in their metabolism. This was not included in the analysis, but it is another source of concern.

“When we look at the relationship between the physiological thermal limit [do organismo dessas espécies] and the baseline temperature that we used to define the extreme events, we found that this temperature was higher than the physiological limits,” says Murali. “So we are being conservative and underestimating the impact on these species. However, our model did not include adaptive physiological mechanisms, such as behavioral regulation of body temperature, that could mitigate the effects of extreme heat.”