A chat with environmentalist John Christy...

He's one of the authors of the IPCC report, and is director of the Earth System Science Center at University of Alabama-Huntsville...

In laymen's terms, what's wrong with the surface temperature readings that are widely used to make the case for global warming?

First is the placement of the temperature stations. They're placed in convenient locations that might be in a parking lot or near a house and thus get extra heating from these human structures. Over time, there's been the development of areas into farms or buildings or parking lots. Also, a number of these weather stations have become electronic, and many of them were moved to a place where there is electricity, which is usually right outside a building. As a result, there's a natural warming tendency, especially in the nighttime temperatures, that has been misinterpreted as greenhouse warming.

Are there any negative consequences to this localized warming?

It's a small impact, but there is an indication that major thunderstorms are more likely to form downwind of major cities like St. Louis and Atlanta. The extra heating of the city causes the air to rise with a little more punch.

Have you been able to confirm your satellite temperature readings by other means?

Weather balloons. We take satellite shots at the same place where the balloon is released so we're looking at the same column of air. Our satellite data compares exceptionally well to the balloon data.

During your House Ways and Means testimony, you showed a chart juxtaposing predictions made by NASA's Jim Hansen in 1988 for future temperature increases against the actual recorded temperature increases over the past 20 years. Not only were the actual increases much lower, but they were lower than what Hansen expected if there were drastic cuts in CO2 emissions - which of course there haven't been. [Hansen is a noted scientist who was featured prominently in Al Gore's global warming documentary, "An Inconvenient Truth."] Hansen was at that hearing. Did he say anything to you afterwards?

We really don't communicate. We serve on a committee for NASA together, but it only deals with specific satellite issues. At the Ways and Means hearing, he was sitting two people down from me, but he did not want to engage any of the evidence I presented. And that seems to be the preferred tactic of many in the alarmist camp. Rather than bring up these issues, they simply ignore them.

(Contacted by Fortune, Hansen acknowledges that his 1988 projections were based on a model that "slightly" overstated the warming created by a doubling in CO2 levels. His new model posits a rise of 3 degrees Celsius in global temperatures by 2100, vs. 4.2 degrees in the old one. Says Hansen, "The projections that the public has been hearing about are based on a climate sensitivity that is consistent with the global warming rate of the past few decades." Christy's response: "Hansen at least admits his 1988 forecasts were wrong, but doesn't say they were way wrong, not 'slightly,' as he states." Christy also claims that even Hansen's revised models grossly overestimated the amount of warming that has actually occurred.)

I know you think there's been something of a hysteria in the media about melting glaciers. Could you explain?

Ice melts. Glaciers are always calving. This is what ice does. If ice did not melt, we'd have an ice-covered planet. The fact is that the ice cover is growing in the southern hemisphere even as the ice cover is more or less shrinking in the northern hemisphere. As you and I are talking today, global sea ice coverage is about 400,000 square kilometers above the long-term average - which means that the surplus in the Antarctic is greater than the deficit in the Arctic.

What about the better-safe-than-sorry argument? Even if there's a chance Gore and Hansen are wrong, shouldn't we still take action in order to protect ourselves from catastrophe, just in case they're right?

The problem is that the solutions being offered don't provide any detectable relief from this so-called catastrophe. Congress is now discussing an 80% reduction in U.S. greenhouse emissions by 2050. That's basically the equivalent of building 1,000 new nuclear power plants all operating by 2020. Now I'm all in favor of nuclear energy, but that would affect the global temperature by only seven-hundredths of a degree by 2050 and fifteen hundredths by 2100. We wouldn't even notice it.