TCS Daily


Science Steals a Base

By Ronald Bailey - May 1, 2003 12:00 AM

"Experimental models incorporating both anthropogenic and natural factors are consistent with the new analysis showing tropospheric warming," claims the press release heralding a new paper being published today in Science. This paper is supposed to be a knockout blow against the satellite dataset that has consistently and annoyingly (for the global warming alarmists) shown that the earth's atmosphere is NOT warming nearly as much as the computer climate models predict. The new analysis, meant to prove finally that dangerous man-made global warming is real, was done by a team led by long-time global warming proponent Benjamin Santer from the Lawrence Livermore National Laboratory.

So is it true? Have the satellites been wrong about global temperature trends? The paper it turns out is mostly hot air, adding nothing new to the climate change debate. Evidently, the strategy being used by Santer et al. is that if their models don't agree with the data, then change the data.

Since 1979, climatologists John Christy and Roy Spencer at the University of Alabama in Huntsville (UAH) have been using instruments aboard a variety of weather satellites to take the temperature of the earth's atmosphere daily. What they find is that the atmosphere is warming up at a rate of only about 0.05 degrees centigrade (+/- 0.05 C) per decade. This is considerably lower than the rate of warming predicted by the climate computer models. Now it is not unreasonable to think that perhaps the data contain some unaccounted for uncertainties - this is science after all, and you're only as good as your data.

Puzzled by the discrepancy between the satellite data and the models, Frank Wentz, a physicist working at Remote Sensing Systems (RSS) in Santa Rosa California, decided to check into the matter. Since 1979 whenever a new weather satellite was launched to replace old ones, scientists had to cross calibrate instruments taking into account things like orbital differences and slight variations in the instruments. Wentz looked at how the UAH team cross-calibrated the data from each of satellites and found that they had not taken into account variations between satellites due to their orbital decay.

Wentz published a 1998 bombshell paper in Nature claiming to show that once the satellite data were corrected that cooling trend identified by Christy and Spencer would in fact become a warming trend of 0.07 degrees centigrade instead of the 0.05 degree rate of cooling that the UAH team had found between the years 1979 and 1997. This was still considerably below the trend found in most models but it was positive. It is no surprise that global warming proponents hailed the RSS dataset as evidence that they are right.

As conscientious scientists, Christy and Spencer admitted that they had failed to take all of the orbital decay effect into account. They then painstakingly readjusted their data and found that the atmosphere was cooling at a 0.01 degree centigrade per decade rate. It seems that the RSS team had used data that had already been corrected for some of the effects and therefore over-corrected it to create a spurious warming trend.

So what gives now? Santer et al. have done new climate model runs and conclude that because a new RSS dataset conforms more closely to their models, the RSS data must be right, and because the UAH dataset does not conform to their models, it must be wrong. This is a very curious conclusion because models must fit data, not data fit models. A discrepancy between datasets can only be resolved by more empirical research. Data validate models, not vice versa.

Fortunately this can be done. It turns out that there is a completely independent dataset of tropospheric temperatures that can adjudicate between the RSS and UAH data-weather balloon data. The weather balloon data agree well with the UAH dataset and not the RSS dataset. The new Science paper handles this confounding issue by mildly mentioning in passing that there may be a problem with the weather balloon data. However, the paper it cites as evidence for a possible problem actually shows that the UAH data and the weather balloon data are in good agreement .

"The point here is that the models agree with only one tropospheric satellite dataset (Remote Sensing Systems) but they do not agree with any balloon, balloon-based or UAH's satellite datasets," says Christy. "There is no there, there."

So what are the trends in dispute? Christy points out that the latest reanalyzed UAH dataset finds that mid-tropospheric temperatures are rising at about 0.03 degrees centigrade (+/- 0.05 C) per decade. The troposphere is the lowest atmospheric layer, about 18 kilometers (11 miles) thick at the equator to about 6 km (4 miles) at the poles, and contains 80 percent of the total air mass. Meanwhile the RSS dataset finds that mid-tropospheric temperature increases at 0.11 degrees centigrade (+/- 0.02) per decade. What do the weather balloons say? They find that temperatures are essentially flat at a rate of about 0.00 degrees (+/- 0.05) per decade. It's pretty obvious that the weather balloon data undercut the RSS dataset now being relied upon by the global warming proponents.

The new Science paper also suggests that the climate computer models are good at modeling data for the stratosphere (the tenuous air layer above the troposphere) and concludes that therefore they must be good at modeling the troposphere, too. Christy thinks this a classic example of a stolen base. "It's a lot easier to model the stratosphere because you only have to consider radiational effects," says Christy. "The troposphere is much messier. It contains complicated things like clouds, convection, moisture, and dust. Claiming that your models get the stratosphere right tells you almost nothing about how well they model the troposphere."

Nevertheless, Santer's team claims that their models' conformity with the RSS data and their success at modeling the stratosphere "[t]aken together...strengthen the case for pronounced human influence on global climate." However, two independent sets of temperature data say that this conclusion is unwarranted and that this is clearly a case where two wrongs do not make a right. The scientific debate over whether earth is warming dangerously due to man-made influences remains unresolved.

Ronald Bailey, Reason's science correspondent, is the editor of Global Warming and Other Eco Myths (Prima Publishing) and Earth Report 2000: Revisiting the True State of the Planet(McGraw-Hill).
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