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In global warming, all research is local

Regional or local conditions can change, even reverse, expectations based solely on world studies.

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Ozone is a tricky gas. In the stratosphere, it shields us from the sun's ultraviolet radiation. But it's an obnoxious pollutant at ground level. Now research tells us that it also impairs the ability of plants to absorb the global-warming gas carbon dioxide (CO2). That dampens the hopeful assumption that plants will take enough CO2 out of the air to partly offset the emission of that gas from burning fossil fuels.

It also highlights a significant weakness in scientists' ability to assess global-warming climate change. Various types of air pollution can change the way planetwide average warming affects local or regional climates.

Thus local circumstances can reduce, or even reverse, expectations based solely on global studies. The new ozone study, led by Stephen Sitch with England's Hadley Center for Climate Change, illustrates this.

Ozone pollution reduces plant CO2 uptake by as much as one-third, depending on local ozone concentrations. These vary widely around the world.

To take proper account of the ozone effect in climate simulations, scientists need more detailed knowledge of local ozone concentrations throughout the globe and how these change over time. The Hadley study, published online by Nature last month, is a first step in gaining such knowledge.

New research on sooty, so-called "brown cloud" pollution makes a similar point.

Veerabhadran Ramanathan at Scripps Institution of Oceanography in La Jolla, Calif., leads an ongoing study of these clouds over southern Asia and the Indian Ocean. His progress report in Nature earlier this month showed that the clouds trapped enough heat to double global warming over the Himalayan glacier region. This is speeding up the melting of those glaciers – Earth's third-largest frozen fresh water reservoir.

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