- In a business-as-usual carbon emissions scenario — humanity’s current trajectory — two in five land vertebrates could be exposed to temperatures equal to, or exceeding, the hottest temperatures of the past decades across at least half of their range by 2099. If warming could be kept well below 2°C (3.6°F), that number drops to 6%, according to a new study.
- More than one in eight mammal species have already lost part of their former geographical range. In many cases, this means those species no longer have access to some (or sometimes any) of their core habitat, making it much more difficult to survive in a warming world.
- When animal populations continue to decline in an area even after it has been protected, one possible explanation may be that the conserved habitat is marginal compared to that found in the species’ historical range.
- In the light of recent pledges to protect 30% of the planet’s surface, it is important to prioritize the right areas. The focus should be on conserving core habitat — which is often highly productive and already intensively used by humans — while respecting the rights and needs of Indigenous people, many of whom have also been pushed to the margins.
One group of researchers estimated, for example, that at around 3° Celsius (5.4° Fahrenheit) of planetary warming compared to pre-industrial levels, one in two insect species and a quarter of all vertebrates would lose at least half of their geographical range. Such findings are certainly informative (and worrying), but mean temperatures may not be the animals’ biggest problem.
A handful of very hot days may do far more damage to an already struggling species than a degree or two extra; many individuals might perish if their food burns up in a wildfire or vanishes in an intense drought, for example, or they could die due to overheating. And as many researchers have pointed out, the places with the highest increases in mean temperature may not necessarily be the same ones that will experience the highest frequency of extremely hot days — or where the most threatened animals are.
In 2020, a study compiling the fates of more than 500 animal and plant populations from around the world found that most local extinctions (including, for example, the disappearance of a dozen amphibian and reptile species from the lower reaches of Madagascar’s Tsaratanana Massif) had occurred in places where changes in mean temperature had been limited, but where the hottest days had become significantly hotter.
This work inspired a team of four researchers led by ecologist Gopal Murali, then at Ben-Gurion University of the Negev in Israel, now at the University of Arizona, to investigate the extent to which 33,548 terrestrial vertebrate species may be exposed to unusually high temperatures by 2099.
Temperature extremes, plus ecological marginalization, raise species risk: Studies