Warming's biggest wallop aimed at wildlife, not people

Global warming will affect societies around the world through more prolonged droughts, more intense rains and flooding, changes in the timing of seasonal rainfall and snowmelt, and a projected increase in the spread of animal- and insect-borne diseases, scientists say.

But it will affect plant and animal species even more dramatically. A shift in climate zones could lead to extinction of some species and the spread of others, according to a report set to be released Friday by the Intergovernmental Panel on Climate Change.

In turn, many of these ecological shifts will affect humans, writes Chris Field, founding director of the Carnegie Institution's department of global ecology at Stanford University, in an e-mail from the IPCC talks in Brussels. "A large fraction of the impacts of climate change on people are transmitted through ecosystems."

If the average temperature rises by 1.8 degrees C (3.2 degrees F.) by the end of this century – the low end of the IPCC's projected range – it would still be possible to set up preserves and maintain almost all of the planet's major ecosystems and the species they contain, says Camille Parmesan, a biologist at the University of Texas in Austin. But if temperatures rise much higher than that, "We're going into a realm Earth hasn't seen for a very long time. Most of the species we have on Earth did not evolve under that warmer climate."

Already, the global climate has warmed an average of 0.7 degrees C during the 20th century, she notes. So far, the ecological changes have been relatively benign.

What's worrisome is if heat-trapping greenhouse-gas emissions continue to accumulate under the IPCC's "business as usual" scenario, says John Williams, who studies plant dynamics at the University of Wisconsin at Madison. If that happens, up to 48 percent of Earth's land surface will lose existing climate zones, he and two colleagues recently calculated.

That loss is at the cold ends of the spectrum – largely toward the poles and at high altitudes in the tropics. At the same time, some 12 to 39 percent of the planet will see hotter – or what the team calls "novel" – climate zones.

How novel? The prolonged drought the US Southwest has experienced is probably not temporary, says an international team of scientists. Instead, it's likely to be a manifestation of the northward expansion of a belt of subtropical, dry climate conditions. If the team's projections are correct, the Southwest's average climate conditions will be just as dry as the drought or the Dust Bowl. The team's results appear in Friday's issue of the journal Science's online service.

Not all effects will be harmful, many experts agree. High latitudes would experience a longer growing season. And increased carbon-dioxide concentrations in the atmosphere have stimulated plant growth worldwide – at least for now.

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