2 pressures that compound instead of add
A land vertebrate is any amphibian, bird, mammal or reptile that lives on land, as opposed to a fish or a marine mammal. Extreme heat means periods of temperature far beyond what a species evolved to survive. Land use change means converting wild land into farms, cities or roads. A study published in the journal Global Change Biology, led by researcher Reut Vardi and 4 coauthors, modeled these 2 pressures together instead of separately, and found they compound each other rather than simply adding up.
Our research highlights the importance of considering the potential effects of multiple threats together to get a better estimation of their potential impact.
Dr Reut Vardi, lead author of the study, a postdoctoral researcher at the University of Oxford. Source 2.
A single named example shows what that compounding looks like. The African bush viper, a snake, is projected to lose 81% of its suitable habitat to land use change and 76% to extreme heat by 2100, under 1 mid range scenario the study modeled, an overlap the study calls a more than additive effect, meaning the 2 pressures together destroy more habitat than simply adding their separate effects would predict.
How many species are at risk of extinction from climate change
An emissions scenario is a modeled future path for the pollution that traps heat in the atmosphere worldwide. A higher emissions scenario means more of that pollution and more warming. The study ran 4 such scenarios against its 29,657 assessed species. Under its lowest emissions scenario, 3,333 species would face unsuitable conditions across their entire range by 2100. That figure rises to 4,242 under a moderate scenario, 6,607 under a 3rd scenario the study calls high conflict, and 7,895 under its highest emissions scenario, close to 1 in 4 of every species the study assessed. About 2.4 times as many species face this risk under the highest emissions scenario as under the lowest, a MAOWCE calculation from those 2 counts the paper itself states.
These 4 values are the study own 4 socioeconomic and emissions scenario pairings for the same end of century point in time, 2100, not 4 separate years on a timeline.
Show the numbers
| Lowest emissions | 3333 |
| Middle scenario | 4242 |
| High conflict | 6607 |
| Highest emissions | 7895 |
The study names the Sahel, naming Sudan, Chad and Mali, the Middle East, naming Afghanistan, Iraq and Saudi Arabia, and Brazil as the places where this combined effect is most pronounced.
Which animal groups carry the most risk
Under the lowest emissions scenario, amphibians already lose over 23% of their 2015 range to unsuitable conditions on average, and reptiles lose over 13%. Mammals lose under 4% and birds lose under 2% under that same scenario. Amphibians and reptiles carry more of this risk than birds and mammals in every one of the 4 scenarios the study ran.
The study states amphibians and reptiles face over these shares, and mammals and birds face under these shares, so these are threshold values, not exact measurements.
Show the numbers
| Amphibians | 23 |
| Reptiles | 13 |
| Mammals | 4 |
| Birds | 2 |
A 2nd study finds the same pattern
A separate peer reviewed study, published 6 months earlier by a different research team in the same journal, looked at 1,634 land vertebrates the International Union for Conservation of Nature, the global body that assesses extinction risk, already lists as threatened by climate extremes. That study tracked 33 hotspots holding 85% of the world bird, mammal and amphibian diversity, and found 29 of those 33 hotspots are set to see extreme heat events rise in frequency faster than the global average, independent confirmation that the risk the lead study in this article describes is accelerating rather than easing.