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Features May 2004: Volume 1, Number 2
   

It’s the End of the World as We Know It
(continued)

 
     

Our Dirty Air

V, Ramanathan, the Victor C. Alderson professor of Applied Ocean Science

Anyone who has flown into Calcutta or Mexico City or Los Angeles on a sunny winter day will be familiar with the brown haze that hangs over such cities. Scientists and the public alike used to think such problems were severe but localized. However, the work of Veerabhadran Ramanathan and his colleagues has confirmed that particulate pollution, what they call a “brown cloud,” covers huge areas, and doesn’t respect national boundaries. “Air pollution from the United States could be over Germany in two to three days,” Ramanathan says. And air pollution from Asia blows over the United States. “So who is polluting whom?” he asks in a recent biography published by the National Academy of Sciences, in honor of his election to the Academy. “If it’s not overhead, it’s in the backyard of someone else.” Since we are all in someone’s backyard, this is indeed a global issue.

Atmospheric brown clouds contain miniscule particles (also called aerosols) of many different pollutants, but the brown color comes from black carbon. Vehicle exhaust, industrial pollutants and even cooking a hamburger at a fast food restaurant contribute to the problem. “Almost everything we do puts particles in the air,” says Ramanathan.

Although no one wants to breathe that stuff, the effect of brown clouds is much more complex and insidious than the obvious health problems. Air pollution has a huge influence on climate. “So far global warming has focused on temperature change,” Ramanathan says. “Equally or more important is a reduction in rainfall.” The usual prediction given the greenhouse effect is a warmer and wetter climate. “Now we’re thinking it could become warmer and drier.” In Southeast Asia emissions of particulates have skyrocketed in the last 75 years and will continue to do so as the region industrializes.

At the same time, the average summer monsoon rainfall in India has already decreased since the 1950s, more than would be expected given natural variability. When Ramanathan’s models incorporate the effects of particulate pollution, they predict that rainfall will decrease even more in the next few decades. Since droughts have caused widespread famine in the past they could certainly do so again.

Brown clouds affect rain in many ways. One way is by creating inversions. The particles block sunlight and, as any child on the beach knows, anything that blocks sunlight will cool the surface of the earth. But, like all dark objects, black carbon particles also absorb heat and warm the upper parts of the atmosphere. Warm air rises, and across the planet rising warm air causes much of our weather and natural air circulation patterns. But when pollution warms air that is already high in the atmosphere, the cool air is stuck below, and an inversion happens. Inversions inhibit rain because they are so stable. The air doesn’t move around; it can’t rise and cool enough to condense and rain.

And when we do reduce air pollution, as we must for health reasons, we will also reduce its surface cooling effect. What then will be the impact on our climate? “This is what aerosol (particulate) people spend sleepless nights over. While the policy people are arguing over half or one degree of warming, we are thinking it could be much larger,” says Ramanathan. “We don’t know the nature of the greenhouse beast.”

What About Us? A Warmer California

Daniel Cayan, director of the Climate Research Divisions at Scripps

California is expected to have 20 million more people by 2050, the equivalent of adding the population of New York state. This growth will add stresses to our transportation, water supply, air quality, wildfire control and agriculture. “You name it,” says Dan Cayan, who studies the regional effects of climate change in the West, “climate will exacerbate the problem.”

Although on average the entire planet has become warmer over the last century, some places have warmed more than others. “Western North America has participated in that warming big time,” says Cayan, with average temperature increases as much as 3° C. Water is already the Achilles’ heel of our modern way of life in the semi-arid West, and it has and will be affected by warming temperatures.
Mountain streams fed by melting snow in the spring and summer, “are a canary in the coal mine” of global warming, says Cayan. In the last 50 years runoff from these mountain streams has peaked anywhere from five days to three weeks earlier in the spring. The trend is consistent across all of western North America, including the Sierras, the U.S. and Canadian Rockies and Alaska. Under a “business as usual” scenario of future greenhouse gas emissions, Cayan and his colleagues project that peak runoff will advance another 20 to 40 days by the end of the century.

Earlier springs will have unforeseeable consequences on ecosystems. But they will create foreseeable impacts on water supply in California. “We have one of the most volatile year-to-year water supplies in the nation,” Cayan says. Because of that volatility, water storage is vitally important.
If less water is stored in the mountain snowpack, or if it is stored for a shorter time, it means that the state needs more storage somewhere else. That somewhere else is a system of reservoirs such as Lakes Shasta and Oroville. But the state’s reservoir capacity is finite. And reservoirs have competing demands. Not only are they used for water storage, but they are also important for flood control and, increasingly, hydroelectric power. “Only 10 percent or so of California’s electricity is hydropower,” says Cayan. “But that increment is really important when we need it.”

Water managers have the delicate task of deciding when to release water from reservoirs. It’s a gamble, but Cayan hopes that his regional, short-term climate projections will help. “I am trying to provide unbiased and useful information to clarify the decision-making process,” he says.

Do You Feel Lucky?

Global warming is here, and scientists like Cayan are trying to help manage the problem. But how do we really know that climate change is due to human activities rather than natural variation? Computer models provide compelling evidence by using basic laws of physics to simulate the climate, both to understand the past and to predict the future. By trying to recreate the past, modelers can better understand how different factors, everything from ocean currents to volcanic eruptions, affect climate. Barnett, the marine geophysicist at Scripps, and his colleagues are able to accurately simulate the warming that has occurred in the oceans in the last 45 years—but the models only match reality when the effects of human-produced greenhouse gasses are included.

And the predictions these models make for the future,
if we continue to increase emissions, are dire. Although graphs of past climate show plenty of temperature ups and downs, projections for future temperatures are off the page. Ramanathan, the air pollution expert, expresses what must be the feeling of most climate scientists: “The worst is for your predictions to be tested.”

 

Charles Kennel, director of Scripps

About climate change Scripps director Kennel says, “Lead universities, of which we are one, have a profound ethical responsibility to do their share.” Indeed, Scripps and UCSD have one of the most comprehensive groups of scientists working on the problem from all possible angles, and they have been for the last half-century. Somerville describes climate change modeling as “the specialty of the house” in Scripps’ Nierenberg Hall. Can they predict the precise outcomes of global warming? No. But Somerville compares climate change projections to a doctor predicting heart attack risk for an overweight cigarette smoker. Would it be wise for that patient to ignore the doctor’s advice to lose weight and quit smoking, simply because the doctor can’t predict the exact day or time or severity of the heart attack? Is it wise for the United States, currently the largest emitter of greenhouse gasses, to ignore scientists’ warnings?

President Bush has rejected international appeals to curtail emissions, choosing instead voluntary controls that are weighted by economic growth—controls that will allow total emissions to increase substantially. Are these actions wise? Barnett sums it up by quoting Clint Eastwood: “Do you feel lucky?”

Heather Henter is a freelance writer based in San Diego.

RELATED LINKS

Scripps Institution of Oceanography, UCSD
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The Oceans and Global Change
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SIO's Climate Research Division
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Naomi Oreskes, UCSD Historian of Science
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The Indian Ocean Experiment
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SIO's Geosciences Research Division
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SIO's Center for Atmospheric Sciences
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"Virtually all the world's glaciers are melting and those in Glacier National Park will likely be gone in 30 years."