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Climate Effects "largely Irreversible For 1,000 Years"

Sigh. Today brings yet more cheerless news on the climate-science front. At this point I might start reading James Inhofe's press releases just to preserve my sanity. Or else post cute puppy pics. Here's the Los Angeles Times write-up:

Even if by some miracle the nations of the world could bring carbon dioxide levels back to those of the pre-industrial era, it would still take 1,000 years or longer for the climate changes already triggered to be reversed, scientists said Monday.

The gas already here and the heat that has been absorbed by the ocean will exert their effects for centuries, according to an analysis published in the Proceedings of the National Academy of Sciences.

Over the long haul, the warming will melt the polar icecaps more than had previously been estimated, raising ocean levels substantially, the report said. And changes in rainfall patterns will bring droughts to the American Southwest, southern Europe, northern Africa and western Australia comparable to those that caused the 1930s Dust Bowl in the U.S. ...

"The policy relevance is clear: We need to act sooner, even if there is some doubt about exactly what will happen, because by the time the public and policymakers really realize the changes are here, it is far too late to do anything about it," [UC Colorado climatologist Kevin] Trenberth said.

Here's the study. That first sentence in the Times write-up isn't quite accurate: The study doesn't mention anything about returning to pre-industrial levels, which would entail somehow sucking carbon out of the air. What the report says is that even if we phased out all fossil-fuel emissions today, some negative effects—rising sea levels, drought—would still occur, since the changes already wrought by carbon in the air and ocean willl linger on for a thousand years. (If we did find a way to take carbon out of the air, some of the atmospheric effects might get reversed, though the changes to ocean temperature and chemistry might still prove irreversible.)

More to the point, as the study notes, pushing atmospheric carbon concentrations up even further, from their current level of 385 parts per million (ppm) to something like 450 to 600 ppm, will exacerbate the situation considerably—further altering rainfall patterns and boosting the likelihood of large Dust Bowl-like conditions in places like the U.S. Southwest and southern Europe, lasting for millennia rather than a decade or two. (By the way, the world's on track to hit about 1,000 ppm by century's end.)

As Joe Romm points out, the paper's authors make an astute criticism of some of the economic models used to figure out the costs and benefits of acting on climate change: "Discount rates... assume that more efficient climate mitigation can occur in a future richer world, but neglect the irreversibility shown here." Right. Sometimes you hear it argued that we should postpone action on greenhouse gases until we have snazzier technologies to help us out. But as we pump carbon into the air, we're "locking in" future impacts on the climate system—effects that later cuts won't be able to reverse.

But wait, one could fairly ask, won't curtailing emissions be even more crushing? Won't it just be easier and cheaper for us to adapt, somehow, to large irreversible dust bowls? Not likely. Tom Laskawy reminds us of one way to consider all this, citing a McKinsey Global Institute study on the costs of gliding below 450 ppm: "The macroeconomic costs of this carbon revolution are likely to be manageable, being in the order of 0.6–1.4 percent of global GDP by 2030. To put this figure in perspective, if one were to view this spending as a form of insurance against potential damage due to climate change, it might be relevant to compare it to global spending on insurance, which was 3.3 percent of GDP in 2005." Thinking of mitigation as a form of insurance strikes me as a useful way to frame the issue, and at that, it starts to look like quite the bargain.

--Bradford Plumer