The Christian Science Monitor
If you're concerned about forecasts of long-term global warming, you might be worried about the wrong thing.
The United States National Academy of Sciences warns that sudden, unexpected climate changeon a scale that could cause widespread drought or plunge Earth into a deep freezeposes a more immediate danger.
The evidence? Embedded in ancient tree rings and ice cores are signs that quick, drastic change is a fundamental characteristic of Earth's climate. These data show that the climate can switch abruptly from one modesuch as an ice ageto another, such as a milder interglacial period, climatologists say.
Humans have no remembered experience of such sudden, far-reaching shifts. If one were to occur in the near future, human civilization could be vastly ill-equipped to adjust.
The Academy's National Research Council (NRC) organized a study to assess this knowledge, which has come to a head over the past five years. The NRC report was distributed at a meeting of the American Geophysical Union held in early December in San Francisco.
Flipping the Climate Switch
In a sense, the report notes, humanity has been living in the meteorological equivalent of a fool's paradise. Agriculture and other aspects of civilization have developed during a period of relatively benign climate.
The workings of this climate system can be likened to a light fixture that is controlled by both a dimmer and an on-off switch, says Richard Alley of Pennsylvania State University in University Park, chair of the NRC study. You can continuously change the light level by turning the dimmer dial. But nothing may happen until you push hard enough to throw the switch. Then the lights abruptly go out.
"It's clear that climate has both dimmer dials and switches," says Alley.
In the case of global warming, for example, is the heat-trapping effect of greenhouse gases such as carbon dioxide twiddling a dimmer dialand is it also pushing on a switch that might suddenly flip the climate?
The NRC committee emphasizes that it isn't trying to alarm people. But it does want to inject a sense of urgency into discussions of climate change to encourage research. Currently, scientists do not understand what drives drastic changes, which in turn means they cannot simulate or forecast them.
Path of No Regrets