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Scientists question global warming theory

Climatologists say broad theory is too simplistic to explain temperature drops in industrialized areas and other complex climate changes

YOU don't have to be a weather scientist to see what's wrong with the global-warming theory. You only have to look around on a hazy day.

Man-made aerosol particles - so tiny a million of them could crowd on to a pin head - are forcing scientists to adopt a new view of what changes Earth's climate.

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Carbon dioxide (CO2), released by burning fossil fuels, and other so-called ``greenhouse'' gases create the effect of trapping heat in the atmosphere. But cooling by the aerosols offsets this warming influence in industrialized regions.

Ironically, these particles also are produced by burning fossil fuels.

``The term `global warming'... couldn't be farther from the truth,'' says atmospheric chemist Robert Charlson at the University of Washington in Seattle. He explains that the term is misleading because it is based on averages such as the average annual temperature of Earth.

Yet, Professor Charlson observes: ``We're not concerned with the average temperature of the planet. We're concerned with rainfall in Kansas.'' Climate change, he adds, is non-uniform with significant regional differences.

Climate analyst Jeffrey Kiehl with the National Center for Atmospheric Research in Boulder, Colo., has charted those differences.

His map (reproduced here) shows regional cooling - not warming -

for large parts of the industrialized Northern Hemisphere. Scientists, Dr. Kiehl says, now recognize that man-made climate change is not ``just a greenhouse effect.'' They see that ``it's a regional effect... strongly tied to local [aerosol] sources.''

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Charlson sees ``a revolution in the way certain segments of the [research] community think about climate change,'' calling it a ``paradigm shift.'' Global warming is too simplistic a concept to do the job.

Charlson explains that the ``paradigm shift'' lies in realizing that the influences forcing climate change are physically and geographically complex. Moreover, he adds, ``The whole story isn't in yet.''

Here's what's going on. Basically, greenhouse warming is a good thing. Without naturally occurring greenhouse gases - mainly water vapor and CO2 - Earth would be too cold to support life. However, human activity - mainly burning coal, oil, and natural gas - has loaded the air with additional greenhouse gases. Atmospheric CO2 concentration has risen from a preindustrial 280 parts per million (ppm) to the 1990 value of 353 ppm.

If that CO2 increase is projected into the future, using today's relatively crude computer-based climate models, the average planetary temperature rises several degrees. That's global warming.

Enter the aerosols. They arise from the same sulfur air pollution that produces acid rain. Industrial sources spew out sulfur dioxide gas at a rate of five metric tons a second.

The Northern Hemisphere accounts for about 90 percent of this outpouring. The chemistry that goes on in clouds and fog incorporates the sulfur into sulfate compounds. These end up mainly as droplets of sulfuric acid and ammonium sulfate. They form an aerosol whose particles are on the order of 0.001 millimeters in diameter. That's what you see on a hazy day.

These aerosol particles scatter incoming sunshine, sending some of it right back into space. That's a direct cooling effect. The particles also have an indirect influence through their effect on clouds. Cloud drops form on them. This tends to produce clouds with many more small droplets than they would have naturally. This adds to the clouds' reflectivity, again sending sunshine back into space. Also, it tends to suppress drizzle so the clouds persist.

There's more to the effect on clouds than this. Scientists don't fully understand it. Charlson calls it ``a devilish kind of problem'' because it is so complicated and subtle. He notes, for example, that suppressing precipitation could change the atmosphere's water-vapor balance with unknown climatic consequences.

All of this adds up to what Charlson calls ``a more sober'' view of what is involved in climate change. It also leaves policymakers with new uncertainties. Measures to curb CO2 pollution may still be justified in terms of energy conservation. But there is little scientific basis for believing that they will prevent undesirable climate change even if they do restrict future greenhouse warming.

For example, cutting back on power-plant emissions to control acid rain and CO2 pollution may have an unintended counter-productive effect. Sulfate aerosols don't last long in the atmosphere. Cut back their production and their cooling influence would quickly diminish. If they have been masking greenhouse warming in some areas, ``there's a possibility of getting a warming spurt,'' Dr. Kiehl says.

In fact, there is little basis now for knowing what kind of climate change may be going on today, climatologists now realize. Looking for trends in temperature data has been a false guide. Commenting on this earlier this summer in the journal Nature, climatologist Tom Wigley with the University Corporation for Atmospheric Research in Boulder observed: ``If searching for the fingerprint of anthropogenic climate change is like searching for a needle in a haystack, then we've been looking in the wrong haystack.''

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