NCAR Report Based on Flawed Science

Published July 1, 2003

A news release from the National Center for Atmospheric Research (NCAR) claims a “New Look at Satellite Data Supports Global Warming Trend.” But the NCAR result is based on the wishful thinking of well-known global warming promoters, rather than on solid science.

The NCAR findings were published by the journal Science on May 1 at The lead author is Benjamin Santer of Lawrence Livermore National Laboratory. Santer became notorious for surreptitiously altering the text of a crucial chapter in the 1995 United Nations Intergovernmental Panel on Climate Change (IPCC) Report on Climate Change in order to make it conform to the politically inspired IPCC Summary for Policymakers.

Competing Trends

The NCAR study is based on an analysis of weather satellite data by Frank Wentz and his colleagues at Remote Sensing Systems (RSS). They proclaim a warming trend of about 0.1º C per decade between 1979 and 1999. Those results are at odds with previous analyses of the same satellite data by John Christy and Roy Spencer of the University of Alabama at Huntsville (UAH), who found virtually no warming over the 20-year period.

Over the past 25 years, a series of instruments aboard 12 U.S. satellites has provided a unique temperature record extending as high as the lower stratosphere. Each sensor intercepts microwaves emitted by various parts of the atmosphere, with the emissions increasing as temperatures rise. These data are used to infer the temperature at key atmospheric layers.

Since the 1990s, the absence of an observed warming signal in satellite-derived atmospheric temperatures has stood in contrast to a distinct warming trend in temperature readings at the Earth’s surface. A 2000 report from the National Research Council concluded both trends might be correct–the global atmosphere might be warming more quickly near the ground than higher up. All theoretical climate models, however, predict a higher rate of warming for the atmosphere than for the surface.

The RSS group found a warming trend of 0.16º F per decade in the layer between about 1.5 and 7.5 miles high, compared to a trend of 0.02º F in the previously published UAH analysis. Both estimates have a margin of error of nearly 0.2º F (plus or minus). The RSS results would be a closer match with surface warming, as well as with computer-model simulations, and are therefore preferred by the NCAR group.

New Study Flaws

But the RSS results are most likely not correct.

Wentz presented the RSS analysis of the satellite data on December 4 in Washington, DC at a panel organized by the federal Climate Change Science Program. Christy, Santer, and I were members of the panel and heard his presentation, but there was no time for discussion of his startling results.

Wentz was kind enough to give me a copy of his full paper so I could study it. It is a careful piece of work that must be taken seriously, but that does not make it correct. I mailed him a number of comments, to which his coauthor, Carl Mears, responded. I then suggested they perform some crucial tests on the internal consistency of their results. There has been no reply so far. I also received comments from Christy discussing the weak points in the RSS work.

Independent atmosphere temperature data from radiosonde instruments carried aloft in weather balloons do not support RSS but agree with the UAH result of a negligible warming trend (which will become even smaller as the 1998 El Niño warming is gradually washed out). Of course, the balloon data have problems of their own that require correction.

But the surface data at weather stations are subject to large corrections as well. A most important one–and difficult to remove completely–is the well-known “urban heat island” effect. (See “Study Documents False Warming Trend,” Environment & Climate News, June 2003.) The urban heat island effect is the local heating produced over time by the expansion of housing, traffic, and energy consumption in the vicinity of city-based weather stations.

Finally, we have a large amount of non-instrument data from “proxies” for thermometers. Such proxies include measurements of the widths of tree rings, isotope data from ocean and lake sediments, ice cores and corals, etc. All of these can be calibrated in terms of temperature. I have personally examined many of these published results and have yet to find any that show a recent warming. It is another strong piece of evidence in support of the conclusion that the surface data from city-based weather stations are contaminated by local heating effects and cannot be relied on to support global warming.

If, as suspected, the RSS analysis is not correct, then the NCAR study is mostly hot air. As science journalist Ron Bailey points out: “Evidently, the strategy being used by Santer et al. is that if their models don’t agree with the data, then change the data.”

S. Fred Singer is professor emeritus of environmental sciences at the University of Virginia and president of the non-profit Science & Environmental Policy Project in Arlington Virginia.