CLIMATE CHANGE

May 2004
		A team of international ecologists using a computer model to predict the effects of climate change say as many as 1 million species could be on the way to extinction by the year 2050. One of the study's authors, Lee Hannah, and environmental experts Daniel Botkin and Patrick Michaels answer your questions.

Forum Introduction Will climate change act as a catalyst for new species? Is climate change the result of human activity or a natural phenomena beyond our control? Do we know anything about species extinction rates from the relatively recent "little ice age"? Can climate change be reversed, as opposed to deterred? Does the impact being made by humans in this (brief) period really explain world-wide shifts in climate? For every study that claims to observe climate change, there are others that seem to refute it. Wouldn't we all be better served by a global campaign to address air quality? What, if any, are the potential upsides of global warming?	Stefan Daystrom of Los Angeles asks: Climate change has occurred before in relatively recent history: the "little ice age" less than a millennium ago (though I'm not clear on whether we have data to show it was global or only data showing it definitely took place in Europe). Do we know anything about species extinction rates related to that? Daniel Botkin responds: The little ice age is the name for a very cold period between about 1550 and 1850 (including the time of settlement of America by Europeans -- the winters really were cold then). There is little evidence about specific species extinctions, in part because there was little concern and less study of rare and endangered species during that time. However, modern scientific research suggests that the little ice age did not have much effect on the distribution and abundance of trees and forests, at least in North America. Although a powerful effect on people, it was too short and too small a change to effect forests. It seems unlikely that the little ice age was a major cause of extinctions. Because of the lack of studies during that time, we have to be cautious in extrapolating from what seems not to have happened then to what might happen now. For one thing, our alterations of landscapes have made it more difficult for species to migrate in response to climate change. Lee Hannah responds: The little ice age reversed too quickly and our scientific knowledge of species distributions at that time was too scanty to expect detectable extinctions. Patrick Michaels responds: A very good question! I have some reservations about the notion that the Little Ice Age (LIA) was very localized, because it is obvious in Southern Hemisphere mid-latitude glaciers. The work that says it was local is by my colleague at University of Virginia, Michael Mann, and, in my opinion, represents an outlier in a much larger field of paleoclimate studies that indicates a global event. Time will tell on this. But be advised that the political process very much likes Mann's work because it makes current climate seem more unusual, so it was very heavily featured in the latest climate compendium by the United Nations. Frankly, it was overemphasized and the U.N. has been severely criticized as a result. That's doesn't make Mann's work wrong, mind you, but be advised that the wheels of science can turn very slowly and the jury is still far from a decision on this! You have also brought up the major flaw in the Thomas et al extinction paper that appeared in Nature in January. They calculated a roughly 15 percent extinction rate for climate changes as small as 0.8 degrees Celsius. Which means, obviously, that there should have been massive extinctions associated with the LIA and especially with the so-called "Climatic Optimum," a period when global temps were 1-2 degrees Celsius higher than today, ending about 4,000 years ago. The extinctions were not observed in the LIA. There is a large extinction associated with the beginning of the warm period, particularly in North America, mainly of many large mammals --which points to the invasion of North America by Homo sapiens as the cause. Ditto for Australia, earlier, when the aboriginals got to the giant wombat and other large marsupials.