The Department of the Interior is expected to announce soon that polar bears have been designated a threatened species under the Endangered Species Act. The justification for such a move will not be that polar bears are actually declining. Rather, the justification will be based on speculation that they may decline in the future as a result of global warming. Global warming, so the argument goes, is causing Arctic sea ice to melt, and, unless that process is arrested, polar bears will be unable to survive because they need Arctic sea ice to reach their primary source of food: seals.

As might be expected with a speculative scenario, there is uncertainty about whether it is actually true. However, there is certainty that if Interior goes through with the designation, it will give the department enormous power to regulate economic activity under a polar bear mitigation plan. Hopefully, before the government puts shackles on the economy, it weighs very carefully the significant uncertainties about whether the polar bear is actually threatened.

Ken Green of the American Enterprise Institute has a new paper detailing the many problems with the supposed global warming/sea ice/polar bear link. Green notes in particular that while there has been some evidence of sea ice loss in the Arctic, there is not enough evidence to conclude global warming is the culprit.

• An October 2007 NASA study concluded that changing wind patterns are responsible for sea ice loss. New wind patterns have compressed sea ice and moved it into the Transpolar Drift Stream which has taken the ice to lower latitudes where it has melted.
• A study reported in Nature in January 2008 reported that Artic heating has been happening higher in the atmosphere than predicted by global warming models. Meanwhile, the predicted warming at the earth’s surface has not been detected. Green comments: “What the data seem to indicate is that heat from the tropics is being transported to the Arctic by wind patterns that are not well understood.”

If global warming isn’t the cause of recent sea ice loss, then there is no reason to assume that the loss of sea ice is a long-term trend.

There are also significant uncertainties about how the loss of sea ice will impact polar bear populations. Analysts use a tool called population viability analysis (PVA), which is fraught with problems. Green writes:  Read rest...

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