May 4, 2006

Reconciliation…

By and large, the much-touted new report by U. S. Climate Change Science Program (USCCSP) titled Temperature trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences, amounts to little more than throwing water on a fire that has, for the most part, already gone out.

For many years, it seemed as if there was a significant discrepancy between the trends in temperature measured at the earth’s surface (currently increasing at a rate of about 0.17ºC/decade) and those in the lower atmosphere measured independently by weather balloons and satellites (which were significantly less). That this difference existed was an indication that climate models run with increasing levels of greenhouse gases were getting things wrong, because they indicate that the lower atmosphere should actually warm at a slightly faster rate than the surface. Thus, this discrepancy formed one of the cornerstones of the argument that climate models were not accurately capturing the behavior of the observed earth/atmosphere systems and thus they should not be used as reliable predictors of future conditions.

However, through prolonged and careful scrutiny, it was discovered that both the weather balloon observations and those made from orbiting satellites contained varying amounts of “artificial” cooling, that when corrected for, brought their measurements more or less in line with surface measurements (the degree of more or less depends on exactly how these corrects are applied). These findings have been published in the peer-reviewed scientific literature over the past several years, and are summarized in the USCCSP report. Additionally, the USCCSP report finds that newer climate models do not universally project that, as a global average, temperature trends in the lower atmosphere should exceed those of the surface. With this finding, the USCCSP concludes, that within the current bounds of error (which, in some cases are still large) that these three records—surface temperature trends, lower atmospheric temperature trends, and projected temperature trends from climate models—are in agreement.

While this conclusion, is perhaps appropriate for the global average temperatures, it is not so for some, arguably more important, regional temperatures. For instance, in the tropical regions, the USCCSP report finds that climate models predict more warming aloft than at the surface, while even the corrected observations generally indicate that there has been a greater amount of warming at the surface than in the lower atmosphere. This distinction is an important one, for it lies at the heart of the issue as to whether or not the current enhanced level of Atlantic hurricane activity is properly related to anthropogenic global warming. More warming at the surface than aloft is a factor leading to more intense hurricanes (as has been observed), while more warming aloft than at the surface (as predicted by climate models) tends to act to keep hurricanes in check. The fact that the observations don’t match climate model forecasts suggests that our current active hurricane period is likely part of a longer-term natural oscillation rather than primarily an effect of an enhanced greenhouse effect.

Further, Dr. Roger Pielke, Sr., a pioneer in the study of how local/regional changes in the landscape can impact the climate, resigned as the lead author of one of the chapters of the USCCSP report, because he felt that the editors of the report were downplaying the impacts of other local/regional impacts that may be effecting the observed temperature trends and thus their efforts at reconciling the surface and the lower atmospheric observations were compromised by failure to take into account other possible influences. Pielke Sr.’s resignations stemmed from the inadequacies in how he felt his concerns were being handled which he felt led to a biased report. For more on Dr. Pielke’s perspective, please visit his blog (http://climatesci.atmos.colostate.edu/2006/05/02/ccsp-report-published/).

All in all, the USCCSP report provides further evidence that the established rate of temperature rise is modest and at the low end of the predictions made by the Intergovernmental Panel on Climate Change (IPCC) in their Third Assessment Report (TAR). A low-end, modest warming is associated with low-end, modest impacts—some of which may be negative, some of which may be positive, but most of which can be dealt with and adapted to.




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