New Evidence of Global Warming, Maybe Severe

Ice caps in alpine regions throughout the tropics and subtropics are melting at a phenomenal rate while last year, other scientists discovered that the freezing point in the upper atmosphere has been gaining altitude.

Consider the evidence:

"Most of the evidence for warming that we see in these high alpine ice caps is in regions that are already water stressed," Mosley-Thompson said. "These tropical areas are where most of the planet's population lives and where subsistence agriculture is incapable of feeding the population. And in the future, the greatest increase in population will occur here."

They cited the loss of ice volume in the tropical and subtropical ice caps, in the Antarctic Peninsula, and in the Russian Arctic, along with increased snowfall over East Antarctica, as further evidence of change.

Mosley-Thompson said that in spite of this evidence, little will probably be done to address the probable underlying causes of these changes until the people who make environmental policy decisions recognize the immediacy of the problem.

"We're making massive changes to the climate on an unprecedented scale in some parts of the globe," she said. "This kind of discussion has to find its way into the general conversation."

Robert S. Webb, a paleoclimatologist at the Commerce Department's National Oceanic and Atmospheric Administration, described a series of global climate simulations. in a February issue of Nature, the British journal of science.

They found that incorporating near-modern ocean heat transports, reduced glacial atmospheric CO2 levels, and large terrestrial ice sheets, together with feedback mechanisms, are sufficient to lower annual average global surface temperature by about 14 degrees fahrenheit and tropical sea surface temperatures by 10 degrees at the Last Glacial Maximum (LGM).

"While debate continues on the role of the tropics and the ocean in climate change, our results suggest greater climate sensitivity and cooling in the past," Webb concluded.

"Furthermore, the greater global cooling shown in our simulations implies a much greater climate sensitivity than previous estimates. This suggests that the expected warming from carbon dioxide doubling may be closer to [about 8 degrees] warming, rather than more modest estimates of [about half of that]."

Webb's results indicate that the new cooler tropical LGM temperatures inferred from coral material and noble gases in fossil ground waters could have resulted from the combined impacts of greenhouse effects and of ocean heat maintained at near-modern levels during the Last Glacial Maximum.

The coral and ground water evidence and mechanism for tropical cooling described by Webb undercut previously posed arguments that tropical sea surface temperatures have changed little throughout the Cenozoic and that such stability will persist in the future.

At a February meeting of the American Metorological Society, Dr. Roy Spencer of the Marshall Space Sciences Lab, said that the temperature structure of the atmosphere is more complex than we (and our computer models) originally thought.

"The temperatures we measure from space are actually on a very slight downward trend since 1979," said Spencer, also noting that land-based thermometers show a very slight increase, both measurements less than a half of a degree per decade.

"We've concluded there isn't a problem with the measurements," Spencer explained. "...Instead, we believe the problem resides in the computer models and in our past assumptions that the atmosphere is so well behaved. These models just don't handle processes like clouds, water vapor, and precipitation systems well enough to accurately predict how strong global warming will be, or how it will manifest itself at different heights in the atmosphere."

These poorly modeled processes are all related to convection. This is the continual overturning of the atmosphere that occurs as water, evaporated from the Earth's surface, carries excess heat energy into the upper atmosphere where it can be more efficiently radiated to outer space.

This convective redistribution, the scientists theorize, may be part of what causes the interesting height-dependent structure in the temperature variations seen in the data. Spencer says that the models also suffer from "numerical diffusion," wherein water vapor in the lower atmosphere is allowed to unrealistically diffuse into the upper atmosphere, where it acts as a greenhouse blanket.

"All of these effects together make the computer-modeled atmosphere look much more vertically uniform than it probably is," Spencer concluded.