Our Dirty Air
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| 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
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| 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.”
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| 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. |
