John R. Christy, a professor of atmospheric science at the University of Alabama, Huntsville, and Alabama's state climatologist, is an expert on Earth's recent temperature history, as derived from microwave sensors on polar-orbiting satellites. Though he has contributed since the early 1990s to reports of the Intergovernmental Panel on Climate Change—the large collaboration of scientists that regularly assesses global warming for the United Nations—Christy considers the expert consensus overstated and unduly alarmist.
IEEE Spectrum: Tell us please about your work on the world's temperature and its significance.
John Christy: Since 1978, we've been able to monitor the bulk atmospheric temperature, which tells you whether heat has been accumulating or not. What we've found is an upward trend over 31 years of about 13/100 of a degree Celsius per decade. But you also see typical ups and downs: During the first two decades, temperatures were fairly flat, and increases were below the three-decade average. But with the big 1997 El Niño, there was a shift upward, and after that, temperatures were flat again but above average.
Spectrum: How does this record from microwave satellite observations differ from the temperature record compiled from other sources?
JC: Readings taken at the surface show 0.16 or 0.17 degrees of warming per decade—a bit more than the microwave readings. That may not seem such a great difference, but climate models indicate that if greenhouse gases are causing this warming, the upper atmosphere ought to be warming by about 1.2 times that of the surface, not less.
Spectrum: Is this discrepancy at the heart of your issues with what's often described as the "consensus temperature record"? Professors at the University of East Anglia, in the UK, have played a big role in establishing that record, and I see that in their hacked e-mail, you are one of the individuals who was mentioned most frequently in a negative way.
JC: They rely on readings from surface thermometers, but those have often been affected by developments like urbanization and deforestation, so they are not a precise proxy for what's going on in the atmosphere, where greenhouse gases are supposed to have their largest effect.
Spectrum: What has been the relationship between the East Anglia researchers and Britain's Hadley Centre for Climate Prediction and Research? (Former Prime Minister Margaret Thatcher set up Hadley two decades ago, locating it with Britain's prestigious Meteorological Office, to be a world authority on all matters having to do with climate change.)
JC: I was a visiting scientist at Hadley for two summers and got to see firsthand how they work together with East Anglia. At the end of the month, East Anglia's Phil Jones would send the land data to Hadley, which would take a critical look and combine that with their sea-surface data, and then the two teams would release what would be known as the HadCRU (for East Anglia's Climatic Research Unit) temperature data set.
Spectrum: So what's described as the "consensus temperature history" is, in effect, the Hadley-East Anglia history?