A study conducted by a team of Stanford researchers has drawn out a grim scenario of what is likely to befall land-bird species worldwide as average temperatures continue to rise, narrowing the range limits of their increasingly vulnerable habitats. Cagan Sekercioglu, the study's lead scientist, estimates that up to 30% of the world's land birds could go extinct by 2100 if present trends continue.Although a great majority of land-bird species - 79%, according to Sekercioglu - is not yet even considered to be endangered, that could all change very dramatically if immediate action is not taken to combat global warming. Using data from the latest IPCC summary report and a wide range of likely scenarios, Sekercioglu and his colleagues modeled changes to the elevational limits of the ranges of over 8,400 species; the worst-case scenario of a 6.4°C temperature uptick produced the 30% extinction projection.
The authors attribute most of the challenges facing the land birds to vegetational shift - a process by which plants, under conditions of thermal and hydrologic stress, are forced to move to higher elevations. Topography and the ever narrowing elevational ranges of their habitats are cited as the most problematic consequences - though they also touch upon the effects of rising temperatures and changing environmental factors.
"It's like an escalator to extinction. As a species is forced upwards and its elevational range narrows, the species moves closer to extinction," explains Sekercioglu. "To effectively monitor the rate of change as warming progresses, especially in the species-rich tropics, we need a lot more data on birds' distributions and on the speed and extent of birds' elevational shifts in response to climate change."
Of greatest concern is the authors' finding that each extra degree of warming will have increasingly disproportionate consequences: For example, if current temperatures were to rise by 1°C, we would likely see 100 extinctions; assuming temperatures were to rise by 5°C, however, an additional 1°C then would trigger a much larger number of extinctions, 300-500.