Impacts of climate warming on terrestrial ectotherms across latitude

*Program on Climate Change and Department of Oceanography and
^§Department of Biology, University of Washington, Seattle, WA 98195; and
^¶Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523

Edited by David B. Wake, University of California, Berkeley, CA, and approved March 3, 2008 (received for review October 4, 2007)

Abstract

The impact of anthropogenic climate change on terrestrial organisms is often predicted to increase with latitude, in parallel with the rate of warming. Yet the biological impact of rising temperatures also depends on the physiological sensitivity of organisms to temperature change. We integrate empirical fitness curves describing the thermal tolerance of terrestrial insects from around the world with the projected geographic distribution of climate change for the next century to estimate the direct impact of warming on insect fitness across latitude. The results show that warming in the tropics, although relatively small in magnitude, is likely to have the most deleterious consequences because tropical insects are relatively sensitive to temperature change and are currently living very close to their optimal temperature. In contrast, species at higher latitudes have broader thermal tolerance and are living in climates that are currently cooler than their physiological optima, so that warming may even enhance their fitness. Available thermal tolerance data for several vertebrate taxa exhibit similar patterns, suggesting that these results are general for terrestrial ectotherms. Our analyses imply that, in the absence of ameliorating factors such as migration and adaptation, the greatest extinction risks from global warming may be in the tropics, where biological diversity is also greatest.

Footnotes

^†To whom correspondence may be addressed. E-mail: cdeutsch{at}atmos.ucla.edu or tewksjj{at}u.washington.edu
Author contributions: C.A.D. and J.J.T. contributed equally to this work; C.A.D. and J.J.T. designed research; C.A.D. and J.J.T. performed research; C.A.D., J.J.T., R.B.H., K.S.S., C.K.G., D.C.H., and P.R.M. analyzed data; and C.A.D., J.J.T., and R.B.H. wrote the paper.
↵ ^‡Present address: Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095.
↵ ^‖Present address: Department of Biology, Queen's University, Kingston, ON, Canada K7L 3N6.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0709472105/DCSupplemental.
Freely available online through the PNAS open access option.