At the request of the authors, this was converted from a poster displayed at the AGU Science Policy Conference, Washington, June 24-26. – Anthony
By Paul C. Knappenberger and Patrick J. Michaels
Center for the Study of Science, Cato Institute, Washington DC
Assessing the consistency between real-world observations and climate model projections
is a challenging problem but one that is essential prior to making policy decisions which
depend largely on such projections. National and international assessments often mischaracterize the level of consistency between observations and projections.
Unfortunately, policymakers are often unaware of this situation, which leaves them
vulnerable to developing policies that are ineffective at best and dangerous at worst.
Here, we find that at the global scale, climate models are on the verge of failing to
adequately capture observed changes in the average temperature over the past 10 to 30
years—the period of the greatest human influence on the atmosphere. At the regional
scale, specifically across the United States, climate models largely fail to replicate known
precipitation changes both in sign as well as magnitude.
On the first count, the near inability of climate model projections to contain the observed
global temperature trends, it is likely that the climate model overestimation of the earth’s
equilibrium climate sensitivity—an overestimation which averages about 40 percent—is
playing a large role in the models’ gross exaggeration of the current rate of temperature
rise (which, for example, has been virtually zero during the past 16 years).
On the second count, the general inability of general circulation models to even get the sign of the observed precipitation changes across the U.S. correct, much less the magnitude, likely stems from the complexities of the climate system on spatial and temporal scales that lie far beneath those of current generation GCMs.
Global Average Surface Temperatures, 2001-2012:
Global Average Surface Temperature Projections, 2001-2020:
U. S. PRECIPITATION
Observed U.S. Precipitation Change:
Projected U.S. Precipitation Change
Number of Years Before Predicted Changes Are Greater Than Natural Variability:
Observations, 1951 – 2005:
Models, 1951 – 2005:
It is impossible to present reliable future projections from a collection of climate
models which generally cannot simulate observed change. As a consequence, we
recommend that unless/until the collection of climate models can be demonstrated to accurately capture observed characteristics of known climate changes, policymakers should avoid basing any decisions upon projections made from them. Further, those policies which have already be established using projections from these climate models should be revisited.
Assessments which suffer from the inclusion of unreliable climate model projections include those produced by the Intergovernmental Panel on Climate Change and the U.S. Global Climate Change Research Program (including the draft of their most recent National Climate Assessment). Policies which are based upon such assessments include those established by the U.S. Environmental Protection Agency pertaining to the regulation of greenhouse gas emissions under the Clean Air Act.
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