The images are ominous. Rising water rapidly covers large areas of New York and other major cities in Al Gore'ês movie. Similar graphics show large portions of Seattle and Olympia underwater by 2100. A sports magazine cover shows a player knee deep in a flooded baseball stadium.
The threat of sea level rise is the most commonly cited threat of climate change. It is often used to justify the at-all-costs approach to address greenhouse gas emissions. Frequently these images are combined with the claim that 'êscientists'ê are warning of catastrophic ocean flooding.
Such claims are not only misleading. They also undermine the principle that our approach to reducing carbon emissions should be based on 'êscientific consensus.'ê
The "consensus" most often cited as the basis for sea-level rise projections is the 2007 United Nations'ê Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. It is called the largest and most comprehensive scientific document ever created. And it is often used as a bludgeon against anyone who questions the science of climate change.
Less often, however, is it actually read. As a result, many of the common claims about the impacts from climate change diverge widely from the actual science of climate change. The misleading and exaggerated claims about sea level are a prime example of this divergence.
Rather typically, Dan Siemann of the Seattle office of the National Wildlife Federation wrote recently that, 'êIn the lifetime of a child born today, sea levels could rise 3 to 6 feet.'ê Earlier this year, the Obama Administration released a graphic showing a 'êmedium'ê estimate of two feet of sea level rise in Puget Sound. Gov. Gregoire justified her climate change executive order this year by citing threats from rising sea level as one of the two 'êmost significant impacts of climate change.'ê
But what does the science actually say?
In 2001, the IPCC'ês report estimated 'êwe project a sea level rise of 0.09 to 0.88 m for 1990 to 2100, with a central value of 0.48 m,'ê or a median rise of 19 inches over 100 years. As time has passed, the estimated rise has declined significantly. The latest report, released in 2007, says (p. 409) sea level rise under a business'êas-usual scenario would be 8 to 19 inches. It should be noted that under the most aggressive scenario (p. 820) to reduce CO2 emissions, sea levels would still rise between 7 and 15 inches. That means the gap between the most aggressive and costly policy and the business-as-usual approach is only two to three inches.
Using this data, University of Washington scientists applied the numbers locally. They found (p. 10) that the most likely amount of sea level rise in the Puget Sound is 13 inches over 100 years. On the Olympic Peninsula, the increase is only two inches of rise due to vertical geological uplift. The highest possible rise, according to U.W. scientists, is 50 inches, an amount they call 'êvery unlikely.'ê
These low numbers are one reason U.W. Atmospheric Sciences Professor David Battisti told The Seattle Times earlier this year: "I'm not worried about Greenland sliding into the sea. I'm not worried about sea levels going up.'ê
Those who continue to believe climate-induced sea level rise is a catastrophic threat have a few responses to these critiques. First, some advocates cite the possibility that these projections are low and that some scientists believe that climate change will cause significant melting of ice in Greenland or Antarctica. The IPCC, however, has considered this and has rejected such scenarios 'êbecause a basis in published literature is lacking.'ê If alarmists are going to cite the 'êscientific consensus,'ê they cannot simply ignore that consensus whenever it'ês convenient, otherwise it simply becomes a game of picking the science you like to fit your preferred policy.
Second, environmental activists argue that we must prepare for expensive but unlikely scenarios to prevent serious costs. Such an approach would be comparable to saying we should be willing to spend virtually anything to prevent a serious meteor strike on the earth, because the impacts could be so catastrophic. Even if we destroyed the economy, the risk is worth it. But policymakers who took such an approach would destroy the economy chasing after scary, but highly unlikely, threats. Ignoring the costs and focusing only on the potential impacts leads to an approach that President Obama'ês regulation czar Cass Sunstein has called 'êliterally incoherent, simply because regulation itself can create risks.'ê
Finally, activists argue that while sea level may not be as big an issue as once believed, there are other issues that justify an at-all-costs approach to climate change. One of the new issues increasingly mentioned is acidification of the oceans. This sort of shifting from one claim to the next has the feel of staying one step ahead of the science. Indeed, advocates often make claims in areas where the science is immature, like acidification, and has not been reviewed by the IPCC, precisely because such ambiguity is useful in stressing worst-case scenarios and because emotion can most easily guide policy where facts are sparse.
It may come as a surprise, after reading this, that I support efforts to reduce greenhouse gas emissions. It seems clear that carbon emissions create some risk of climate change and that we ought to take steps to mitigate and adapt to those risks. However, if we are frivolous about the nature of that risk, exaggerating it to justify policies like cap-and-trade which are costly and ineffective, then we will almost certainly cause more damage than we prevent, and erode any political consensus to take sensible steps, based on good science.