Scientists have recently discovered that the shift in global temperatures of 5 degrees to 10 degrees Celsius at the beginning of the Eocene Epoch (roughly 55.8 million years ago) caused "large and rapid" shifts in the range as well as the morphology of a variety of plants.

• Wing, Scott L. et al. "Transient Floral Change and Rapid Global Warming at the Paleocene-Eocene Boundary." Science 310(5750): 993-996. 11 November 2005 at www.sciencemag.org

The authors state that these ancient climate shifts mirror those projected over the next century as greenhouse gas emissions lead to rapid global warming. They conclude that a similar level of change in the range of plant species can be expected as human-induced climate change proceeds.

Implications: Geologically, periods of rapid temperature change have been associated with mass extinctions, including of marine and terrestrial organisms. While temperature changes of 5 degrees to 10 degrees Celsius are at the upper end of the range of the global average increase projected over the next century, they are consistent with expected temperature changes in higher latitudes. The observation that ancient flora shifts were quite rapid, and that species migrated both across continents, and within continents suggests a similar pattern may be observed today, although human activities -- including urban features and agriculture -- may block continent-scale migrations. It thus seems likely that ecosystems will be disrupted as species both seek to move and decline in the face of climatic change.