Are the climate models that form the foundation of greenhouse warming predictions fundamentally flawed? That has been the argument of some scientists and "greenhouse skeptics" over the past few decades. The main issue has been the inability of the climate models to reproduce the relatively low amount of warming observed by satellites and weather balloon instruments in the troposphere (the lower portion of the atmosphere that extends up to elevations of about 40,000 feet.) This discrepancy was a prime argument Senator James Inhofe (R-Oklahoma) used in his famed 2003 speech when he referred to the threat of catastrophic global warming as the "greatest hoax ever perpetrated on the American people." Greenhouse skeptic S. Fred Singer, who has probably more Congressional testimony about global warming under his belt than any other scientist, headlines his website with the quote, "Computer models forecast rapidly rising global temperatures, but data from weather satellites and balloon instruments show no warming whatsoever. Nevertheless, these same unreliable computer models underpin the Global Climate Treaty." Michael Crichton also used the tropospheric warming discrepancy to give climate models a bad rap in his State of Fear novel. (Remarkably, Crichton--a science fiction writer--was summoned by Sen. Inhofe in September of 2005 to testify before Congress on the issue of climate change.) However, the arguments of these global warming skeptics were dealt a major blow with the issuance this week of a press release by NOAA's Climate Change Science Program refuting their main argument.
The Climate Change Science Program study, which was commissioned by the Bush Administration in 2002 to help answer unresolved questions on climate, found that it was the measurements, not the models, that were in error. Their report, issued on Wednesday, stated, "there is no longer a discrepancy in the rate of global average temperature increase for the surface compared with higher levels in the atmosphere." They cautioned, however, that discrepancies still existed in some regions, particularly the tropics. Greenhouse skeptics will undoubtedly point to this smaller remaining discrepancy as evidence that climate models cannot be trusted, but the authors of the report thought it more likely that the measurements were flawed. Chief Editor Dr. Thomas Karl, director of NOAA's National Climatic Data Center, concluded in the report: "Discrepancies between the data sets and the models have been reduced and our understanding of observed climate changes and their causes have increased. The evidence continues to support a substantial human impact on global temperature increases."
The satellite measurements that were found to be in error were taken beginning in 1978 by Microwave Sounding Units (MSU) operating on NOAA polar-orbiting satellites. According to a description of the MSU data available on the web site where the data is archived:
"The instruments in the MSU series were intended for day to day operational use in weather forecasting and thus are not calibrated to the precision needed for climate studies. A climate quality dataset can be extracted from their measurements only by careful intercalibration of the nine distinct MSU instruments."
Dr. John Christy of the University of Alabama, Huntsville, made a series of efforts to perform the careful intercalibration needed beginning in the 1990s, and for over a decade successfully defended his conclusion that the MSU instruments were showing a much lower level of tropospheric warming than what climate models predicted. Christy was probably the most quoted scientist by the "greenhouse skeptics" during that period, and testified numerous times before Congress about his findings. However, a series of papers published in 2004 and 2005 showed that the satellite intercalibration methods used by Christy were incorrect, and Christy publicly credited the authors of the new studies with finding a real source of error. Christy is also one of the co-authors on the Climate Change Science Program study.
So can we trust the climate models now? That will remain a matter of debate, but now we know that these models have successfully performed at least one major prediction that their detractors thought was wrong. With the climate models validated by the collapse of the greenhouse skeptics' main argument against them, it is apparent that their predictions of possible catastrophic climate change need to be taken seriously.
For further reading: The Economist printed a easy to understand article in August 2005 summarizing the new research exposing the satellite and weather balloon measurement errors, and realclimate.org has a more technical discussion.