Last Thursday, David Deming wrote an opinion piece in The Norman Transcript that questioned global warming. Deming, a geophysicist at the University of Oklahoma, is welcome to his opinion on global warming, but it is not shared by the vast majority of climate scientists. Many of the things Deming wrote are correct but some very important ones are not. His article was constructed to misinform the public about current scientific understanding of global climate change. We provide more accurate information based on recent scientific assessments of climate change for policymakers by the National Research Council (NRC) of the National Academy of Sciences.

Deming's article states that "late-twentieth-century temperatures are not anomalous or unusually warm." He describes the Medieval Warm Period as a time of unusually warm weather that began around 1000 AD and implies that it was warmer than the present. The 2001 NRC report "Climate Change Science: An Analysis of Some Key Questions" concluded "Weather station records and ship-based observations indicate that global mean surface air temperature warmed between about 0.4 and 0.8?C (0.7 and 1.5?F) during the 20th century." The 2006 NRC report "Surface Temperature Reconstructions for the Last 2,000 Years" concluded "It can be said with a high level of confidence that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries." and "... temperatures at many, but not all, individual locations were higher during the past 25 years than during any period of comparable length since A.D. 900." Based on these NRC conclusions, Deming is wrong.

Deming says that meteorologists cannot reliably forecast what the temperature will be in 50 years because they can't predict what the temperature will be in 30 days. He confuses weather forecasting with climate change projections. Reliable weather forecasts for temperature at a location can be made only for about the next seven days because of the chaotic nature of weather systems. Climate is the average weather over years and climate projections provide estimates of the average changes in temperature on decadal time scales. Climate models used to make these projections reliably simulate the observed global-scale warming over the 20th Century when the observed increases in greenhouse gases and aerosols are included. The 2001 NRC report "Climate Change Science: An Analysis of Some Key Questions" states "Climate change simulations for the period of 1990 to 2100 yield a globally-averaged surface temperature increase by the end of the century of 1.4 to 5.8?C (2.5 to 10.4?F) relative to 1990."

The American Geophysical Union, the professional society for geophysicists like Deming, says in its position statement in 2003 on "Human Impacts on Climate" that "Atmospheric carbon dioxide concentrations have increased since the mid-1700s through fossil fuel burning and changes in land use. ... It is virtually certain that increasing atmospheric concentrations of carbon dioxide and other greenhouse gases will cause global surface climate to be warmer."

Deming describes the uncertain nature of scientific knowledge and supports truth, objectivity, and sound science. There are uncertainties in climate change science but there are also many things that climate scientists know with high confidence. As the NRC report to President Bush summarized in 2001 "Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. Temperatures are, in fact, rising. The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability. Human-induced warming and associated sea level rises are expected to continue through the 21st century." Assessment of scientific studies since 2001 strengthens these conclusions.

Submitted by David Karoly Williams, professor of Meteorology University of Oklahoma; Fred Carr, Mark and Kandi McCasland professor of Meteorology director, School of Meteorology University of Oklahoma; Ken Crawford, regents' professor of Meteorology Oklahoma State Climatologist University of Oklahoma; Peter Lamb, George Lynn, Cross Research professor of Meteorology director Cooperative Institute for Mesoscale Meteorological Studies University of Oklahoma; John Snow, professor of Meteorology University of Oklahoma.

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