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Climate: Hockey sticks and hobby horses

By DAN WHIPPLE   |   April 6, 2005 at 6:30 PM   |   Comments

BOULDER, Colo., April 4 (UPI) -- UPI's Climate was reminded the other day there is a broad spectrum of interpretations of the science behind global climate change.

Roger Pielke Jr., a professor of environmental studies at the University of Colorado in Boulder and the author of an excellent science Web log called Prometheus, took to task a recent column on adapting to warming, saying, "You equate 'climate skeptics' with those who support adaptation. Most climate skeptics do not support adaptation because it would mean admitting that there is a problem needing to be adapted to in the first place."

Pielke added many who support adaptation are not skeptical of climate science at all.

"Perhaps (they should be) more accurately described as 'climate realists," he said.

We don't want to put words in Pielke's mouth, but we may hazard to guess he considers himself a realist.

Among hard-core climate skeptics, there are also gradations of opinion, ranging from "nothing unusual is happening" to "something might be happening, but it is no big deal," to "human activity is not the cause," "humans will easily adjust without much conscious effort," and so on.

One reason it is so difficult to characterize opposition to climate science is the skeptics' objections tend to run in fads. They will glom onto one piece of evidence like pit bulls, shake it until it bleeds, and then move on to something else.

In fairness, the climate science community majority changes its emphasis, too, as it tries to generate public interest in the subject. They have trotted out sea-level rise, disease increase, biodiversity loss and other issues, generally to a collective yawn from the commonweal.

The favorite hobby horse of the contrarians used to be the discrepancy between tropospheric temperature records and surface records. Climate models suggest these two data sets should show roughly equal warming, but according to the authoritative data collected from satellite observations kept by the University of Alabama at Huntsville, this is not the case.

The hardest-core skeptics sometimes claim the satellite record shows no warming, but this also is not correct. The UAH team has measured an increase of 0.14 degrees Fahrenheit (0.08 degrees Celsius) per decade, while NASA surface measurements have shown a 0.22 degrees F (0.12 degrees C) increase per decade. The difference is significant, but the tropospheric record does show warming.

In fact, according to Chick Keller, visiting scientist at the Institute of Geophysics and Planetary Physics at the Los Alamos National Laboratory in New Mexico, the UAH record and the surface data sets agree well in the northern latitudes.

"It is in the equatorial ocean area that there is disagreement," Keller told Climate.

A recent piece in the magazine New Scientist that reviewed the skeptical arguments said, however, because of new interpretations of that data set by other scientists, skeptics no longer rely too heavily on this "no warming" argument.

Keller said the UAH scientists John Christy and Roy Spencer -- the chief guardians of the satellite data -- make an important point.

"Spencer and Christy keep singing the same song: 'We agree with the balloon data,'" Keller said, referring to temperature data collected from the lower troposphere via ground-launched balloons. "It's like a great big rock in the middle of the road."

He added that the new constructions of the satellite data present some compelling arguments.

Having trotted past the satellite data, the latest hobby horse the skeptics are riding involves alleged flaws found in the "hockey stick," a graph of temperatures over the last thousand years produced by University of Virginia paleoclimatologist Michael Mann and colleagues. The Mann reconstruction shows a sharply rising average temperature at the end of the 20th century, with narrower ranges than similar reconstructions and a Medieval Warm Period that is cooler than the present.

There are numerous other paleoclimate reconstructions that show more or less the same thing as the Mann graph, so it is something of a mystery why the skeptics have fastened on to Mann's. It could be because it is crisp, clear and was featured in the Intergovernmental Panel on Climate Change report in 1998. Its fame was assisted when Princeton University's Jerry Mahlman picturesquely called it the "hockey stick."

It is quite possible there are errors in the Mann reconstruction, but at least seven other independent reconstructions have generated approximately the same results.

"They attack the Mann thing and it stands for everything else," Keller said. "You'd think that Mann was the only guy who did this."

Respected paleo reconstructions also have been compiled by Duke University's Thomas Crowley, the University of Arizona's Jonathan Overpeck, and P.D. Jones of the Climatic Research Unit of the University of East Anglia.

The Web site RealClimate.org, in which Michael Mann participates, said earlier this year: "So let's assume for argument's sake that Mann, Bradley and Hughes made some terrible mistake in their statistical analysis, so we need to discard their results altogether. This wouldn't change our picture of the last millennium (or anything else) very much: Independent groups, with different analysis methods, have arrived at similar results for the last millennium."

RealClimate continues: "The details differ (mostly within the uncertainty bounds given by Mann et al., so the difference is not significant), but all published reconstructions share the same basic features: they show relatively warm Medieval times, a cooling by a few tenths of a degree Celsius after that, and a rapid warming since the 19th century. Even without Mann et al., we'd still be stuck with a 'hockey stick' type of curve -- quite boring."

There are other types of evidence that could overthrow some of the conventional wisdom on climate. Proxy records from boreholes seem to show it got colder than proxies at the surface. The reason for the discrepancies are not understood, but they could be result of local land use or climate variations, or they might represent something more important.

Also, if the climate models are not properly accounting for solar output variations, that could throw a spanner in the works -- though most recent developments in this research have indicated solar variability is less important in overall climate, not more.

There definitely is some room to doubt the consensus about climate change, because nothing in science is ever 100 percent certain, but most lines of evidence indicate dramatic, human-caused warming lies in the future.

--

Climate is a weekly series examining the science behind and potential impact of global climate change, by veteran environmental reporter Dan Whipple. E-mail: sciencemail@upi.com

© 2005 United Press International, Inc. All Rights Reserved. Any reproduction, republication, redistribution and/or modification of any UPI content is expressly prohibited without UPI's prior written consent.
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