Colorado State University Atmospheric Scientist Says Land-Use Change, Other Factors Make Future Climate Unpredictable

A Colorado State University atmospheric scientist is among those who are looking askance at the global-warming-doom-in-2100 scenario when it doesn’t take into account factors such as changes in ground cover.

Roger Pielke Sr., professor of atmospheric science and Colorado’s state climatologist, is one of a growing body of researchers who think that the way regional and national assessments are conducted are incomplete. He’s referring to the Intergovernmental Panel on the Climate Convention and the United States National Assessment. Both predict dire hikes in temperature by 2100, based on predicted release of greenhouse gases; however, neither study includes the effect of changes of ground cover in making those estimates.

In a press briefing Feb. 18 at the American Association for the Advancement of Science meeting in San Francisco, Pielke will join a number of other earth scientists in assessing components of the complex, interrelated planetary environment.

"You have to look at the climate system as a series of integrated questions," Pielke said. He agrees that global and regional temperatures are affected by human activity; he doesn’t agree that the changes are due solely to the anthropogenic release of greenhouse gases. Yet, that’s the principal factor in most climate change models.

As state climatologist in rapidly growing Colorado, Pielke has been interested in land-use changes-not just the paving of prairie, but the conversion of short-grass prairie to irrigated agricultural fields. He spent a recent sabbatical year working with Colorado State and government plant ecologists to learn more about the effects of vegetation as part of the climate system.

Pielke offers two examples to illustrate that knowledge of the amount of human input of greenhouse gases won’t tell us what the climate will be like in 2100.

First, he points out, land-use change already has had an effect on regional and global climate at least as large as changes attributable to the radiative effect of doubling anthropogenic greenhouse gases. In other words, for all the heat trapped by man-made greenhouse gases, the effects of paving fields, turning them to irrigated agriculture and letting them reforest, for example, produce equal countereffects. Second, should carbon dioxide emissions double, as some scenarios suggest, the effect on vegetation growth would have a more immediate effect on regional (and perhaps global) climate than would the radiative effect of doubled carbon dioxide. Plants can absorb more carbon dioxide, which affects their growth and, therefore, their coverage area and amount of water vapor they transpire into the air. The area they cover affects their role within the earth’s climate system.

Pielke concludes that temperature averages a century hence are completely unpredictable.

"We don’t know if it’s going to be warmer, colder or the same as now," he said. "We don’t know how global climate will integrate across oceans, land masses, continental ice and the atmosphere."

Pielke emphasizes that climate "beyond a season or two" is not predictable. Instead of determining the possible temperature and figuring out what that would do to the environment, Pielke proposes exploring "vulnerabilities." "We should try to estimate the envelope of all plausible future regional and local climates and resulting environmental stresses," he said. "We need to decide what’s immediate, what’s mitigatable and what we’re going to be forced to adapt to.

"History has seen and recorded worse droughts than any of these models predict, for example," he said. "We need to first see if we can protect ourselves against what happened in the past. We need to then generate perturbations of past climates-the driest 10 years in a row, for example-and see how we can protect ourselves in an environmentally sensitive way."Pielke said that dealing with systemic issues about the earth that involve feedback and direct effects have to be dealt with in a multidisciplinary way. "We need to work from the bottom up, asking what are the possible local and regional threats, rather than focusing on the global scale and working from the top down," he said.