Climate change could be 'irreversible' for 1,000 years? Gulp!
Rather than a call to throw up one's hands in discouragement, the results show the importance of acting quickly to reduce emissions and so limit the very long-lived effects
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Solomon's group looked at three climate features: warming itself; changes in rain and snowfall patterns; and sea-level rise, absent any contribution from Greenland or Antarctic ice caps. (For a tidy summary, colleague Eoin O'Carroll has a tight post here.)Skip to next paragraph
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These three, the team says, involve aspects of climate where scientists have already identified some level of contribution from the effects of rising greenhouse-gas levels, where an understanding of the physical mechanisms driving the changes are well in hand, and where model projections are consistent despite other differences in the models.
They based their work on a range of possible targets for stabilizing carbon-dioxide concentrations in the atmosphere, but focused on a particular range: 450 molecules for every million in the atmosphere parts per million by volume (ppm) to 600 ppm. Concentrations as of 2007 stand at about 383 ppm, according to the Global Carbon Project, compared with 280 ppm at the start of the Industrial Revolution.
The 450-600 range is of special interest, since 450 by the year 2100 represents a target widely cited in negotiations for a new global climate treaty, which its architects hope will be ready to take over when the 1997 Kyoto Protocol's first five-year "commitment period" expires in 2012. The 600 is a business-as-usual emissions path.
In short, if CO2 concentrations peak at 450-600 ppm, declines in rainfall during the dry season in regions such as the US Southwest or the Mediterranean are comparable to the Dust Bowl drought in the US during the 1930s and those seasonal declines persist for millenniums. Sea level from heat expansion alone rises by an average of up to three feet through the year 3000.
For simplicity's sake, they didn't take a large number of secondary effects into account. And projections of melting of Greenland's and Antarctica's ice caps are still too uncertain to include. The levels Solomon's team projected are a minimum, based on better-understood physical processes. The results appear in the issue of the Proceedings of the National Academy of Sciences for the week of Jan. 26, 2009.
Records of past climate regimes over tens of millions of years or more and the geophysical processes involved, such as those Dr. Archer explores in his book, certainly add weight to the way Solomon and her colleagues have framing the global warming issue in terms of irreversibility.
Long-term change v. public perceptions
But as calls to action, some analysts wonder if that's enough to galvanize the public.
When pollsters ask about global warming as a stand-alone issue, in some surveys people tend to say it's serious and requires action. Some have even responded that they'd even pay higher energy costs if that helped underwrite the move to more climate-friendly ways to meet energy needs.