Global Warming Creates a Stairway to Heaven
Climate change is leading to increased temperatures, especially noticeable in mountains and other cooler climes. Many animals and plants, especially in the tropics where temperatures are more uniform, prefer certain temperatures and may even die when it gets too hot.
Currently, 21% of world’s bird species face a risk of extinction, defined as being threatened or near threatened with extinction according to the World Conservation Union (IUCN). In our recent paper in the scientific journal Conservation Biology, titled “Climate change, elevational ranges, and bird extinctions” (Sekercioglu, Schneider, Fay & Loarie, in press), we show that bird species’ elevational ranges have a positive correlation with improved conservation status. Therefore, reductions in birds’ elevational ranges caused by climate change are likely to increase the extinction likelihood of a bird species. The increased risk of extinction can be calculated by using the relationship we describe in our paper and extinctions can be estimated by modeling elevational shifts that will be caused by climate change. These relationships are likely to apply to other terrestrial organisms (amphibians, mammals, etc), but more research is needed on this.
Habitat change makes the situation worse because there may be no habitat to move into in many places, even if the mountain is tall enough. We combined habitat loss and global warming scenarios for 2100 to estimate the numbers of land bird species that will be threatened and/or driven to extinction by climate change by 2100. Our best guess is that climate change effects, exacerbated by habitat loss, will result in about 400–550 land bird extinctions by 2100, based on a best-guess of 2.8 °C warming. This is 5-7% of all land bird species. With 1 °C surface warming or less, bird extinctions are likely to remain below 100 species. In the worst case, however, with 6.4 °C warming and extensive habitat loss, as many as 2500 land bird species may be committed to extinction, 30% of all land birds. Aquatic birds, such as penguins, are also threatened by climate change, but we did not estimate their extinction likelihood, due to the different dynamics involved.
Each additional degree of warming will have increasingly devastating effects. Bird extinctions increase faster than climate change, so even slowing down climate change by a few degrees will save hundreds of bird species. We have little data on many bird species and we urgently need much better data on where the birds are and how they are responding to climate change, especially on tropical mountains.
The take home message is that, climate change, exacerbated by habitat loss, will reduce the ranges of hundreds of bird species, sometimes to the point of extinction. With increasing warming, the extinctions will increase in an accelerating fashion, not linearly, and will be especially severe for tropical mountain species, most of which are endemic and have small ranges. Our best guess is that climate change effects, exacerbated by habitat loss, will result in about 400–550 land bird extinctions by 2100, based on a 2.8 °C warming. The worst case scenario predicts about 2500 bird extinctions, 30% of all land bird species or 26% of all bird species.
Until now, habitat loss, exploitation (e.g. hunting, pet trade), and introduced species (e.g. cats, rats, dogs, pigs) have been the main drivers of species extinctions. These factors have mostly affected islands and lowlands, and mountain species have been relatively safe. However, climate change will affect intact montane (and polar) habitats most and its victims will mainly be those species not presently threatened by habitat loss or hunting. Large numbers of species, thus-far largely unaffected by human actions, are in danger of extinction from climate change.
If we do not slow down climate change, we can expect hundreds of bird extinctions. At the very least, that means the disappearance of many fascinating life forms and the world will be the poorer for it. Birds are one of the best conserved groups and most other groups (e.g. plants, amphibians, fish, mammals, mollusks) are more threatened with extinction than birds. The same extinction dynamics apply to many of them and many of these species will also disappear due to the combined effects of habitat loss and climate change. Disappearances of so many species will also have long-term ecological effects that are very hard to predict, but are unlikely to be favorable to humanity.