Thursday, April 20, 2006

Significant Climate Change on the Way

The Post today reports on a new study that confirms the mainstream predictions of global warming:

Climate scientists from around the world have for more than a decade concurred that climate sensitivity's most likely value is in the range of about 2.5 degrees to 8 degrees Fahrenheit. But because many factors can affect global temperatures in poorly understood ways -- including the extent to which the oceans have tempered climate trends -- scientists have not been able to rule out more extreme calculations suggesting a warm-up of 16 degrees Fahrenheit or more.

Moreover, most of the modeling done to date has been based on data gathered over just the past century, a period that has experienced a potentially confounding increase in aerosols that can blunt temperature buildups by reflecting incoming radiation from the sun.

The new work, described in today's issue of the journal Nature, reaches back 700 years. It recalculates the relationship between atmospheric composition and climate, taking into account the climate-affecting impacts of sun-blocking volcanic eruptions; carbon dioxide levels derived from air bubbles trapped in Antarctic ice; and temperature data derived from tree rings.

The result: Climate sensitivity almost certainly falls within the more conventional range of current predictions, with only a 5 percent chance that it will exceed 11 degrees Fahrenheit.

It seems to me that the important thing to take away from the study is that it provides yet more evidence that global warming is real. The lead author is cited as saying that the exclusion of extreme estimates may persuade governments that it is still possible to make a difference by cutting back on carbon emissions. Depending on how the story is presented in the media, I worry that it may have the opposite effect. If the exclusion of higher estimates is overemphasized, it may be cited as an excuse to do nothing. I hope that will not be the case.