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Spewing from
factory stacks and car tail pipes, carbon dioxide is the poster child of "greenhouse
gases." Most scientists long ago concluded that CO2 is the single
biggest cause of climate change and that cutting its output is the best way
to slow global warming. So why are a tiny but growing
number of atmospheric scientists taking a hard look at parking lots? Because, they say, land-use changes
have at least as much, and perhaps even greater, impact on climate change
than CO2. It's a radical idea that has heated up the scientific community
and is prompting a wider look at the forces behind climate change. The effect
on public policy could be enormous. Do massive asphalt and concrete
"urban heat islands" like Houston or Atlanta really help ratchet up
the global thermostat? What about huge tracts of farmland like those that
span the Midwest? Eugenia Kalnay thinks so. Her
research into the impact of land-use changes on global temperature is getting
attention from other scientists, even if this debate hasn't exactly leaped
into the public arena yet. Earth's surface temperatures
have risen about 1 degree F. in the past century with faster warming in the
past two decades, the National Academy of Sciences reports. The 20th
century's 10 warmest years all occurred in the last 15 years of the century. But according to Dr. Kalnay's
study, published in the journal Nature last spring, urbanization,
agriculture, and other human changes to landscapes in the US - quite aside
from CO2 - account for as much as 40 percent of the temperature rise over the
past 40 years - much larger than previously believed. That could make it a
contender for CO2's crown. Kalnay, a University of
Maryland researcher, was director of environmental modeling at the National
Weather Service from 1987 to 1997. She oversaw development of computer models
for the now ubiquitous three- to five-day forecasts. But it is her recent research
that struck a chord with the scientific community. Kalnay and coauthor Ming
Cai have received a huge amount of both praise and criticism. "We were
both taken aback that instead of the paper going quietly, we got hundreds and
hundreds of comments and questions," she says. Now Kalnay's research, joined
by the work of a growing number of other scientists, has intensified debate
over the relative strength of "climate forcing" factors. Recent studies show that
deforestation in parts of Africa is curbing rainfall in the once-vital
Sahel zone bordering the Sahara desert. Changes in forest cover have also
been shown to affect rainfall and climate far beyond the Amazon Basin. Still
others have shown that planting trees can actually increase the planet's
temperature if done in the wrong climate zones. "Impacts of human-caused
land changes on climate are at least as important, and possibly even more
important, than those of carbon dioxide," says Roger Pielke Sr.,
professor of atmospheric science at Colorado State University and past
president of the American Association of State Climatologists. His group
voted in 2002 to issue a statement almost unanimously concurring that climate
changes are more complex than CO2 changes and include land use. By contrast,
the American Geophysical Union issued a statement last month maintaining CO2
as the key factor. Dr. Pielke and others argue
that land-use changes in a region may have significant effects thousands of
miles away - not unlike the El Niņo effect in which warming zones of the
Pacific Ocean force droughts and weather changes worldwide. That's still theory, of course.
Skeptics point out that only 29 percent of the earth's surface is land - and
only 1 to 2 percent is urbanized. Another 40 percent of land has been
modified by agriculture and deforestation, Pielke says. So can the regional
land-use tail really wag the global dog? Not according to Alan Robock,
an editor of the Journal of Geophysical Research: Atmospheres. He's also seen
no uptick in studies of land-use impact on climate in scientific literature
he's read. "Everybody realizes
modifying land surface is important locally," says Dr. Robock. "If
you're talking globally, though, CO2 is the dominant way humans cause
climate change." Still, the view that human
changes to the landscape are a factor driving climate, too, is gaining some
traction in powerful corners of the scientific community. A report by the
National Academy of Sciences due later this year will examine the warming
effects of non-CO2 agents: aerosols, solar variability, and land-use changes. "The public does not hear
too much about this, because all the climate-change treaties have been
focused on CO2," says Daniel Jacob, a Harvard University professor of
atmospheric chemistry who chairs the panel writing the report. "For a
long time it's been really hard to communicate these other factors to the
policymakers, mainly because it's difficult to find the proper currency for
them." The impact of such change would
begin first with global climate modelers, like Robert Dickinson, president of
the American Geophysical Union. Dr. Dickinson is working to include more
detailed effects from land-surface changes, aerosol, and soot in his climate
model. He says one of his graduate students is pursuing a surface-temperature
study of China. But like many, he still maintains that CO2 is the dominant
force in climate change. Kalnay's research is providing
ammunition for some private groups to argue that global warming is a myth. In
an editorial last June, the Center for the Study of Carbon Dioxide and Global
Change argued that Kalnay's work showed that the impact of CO2 was
overstated. "The warming of the past century or so was nothing more nor
less than the natural recovery of the earth from the global chill of the
Little Ice Age," the Tempe, Ariz., nonprofit reported. Such conclusions irk Peter
Frumhoff, global environment program director for the Union of Concerned
Scientists in Cambridge, Mass. "Just because new research shows there
are other factors to pay attention to [beside CO2, that] doesn't mean there's
any less reason to pay attention to greenhouse gases," he says. Kalnay is undeterred. Having
completed her temperature study of the US, she is working on a global
analysis of 50 years of temperature data. Already, early results from South
America support her conclusions. "Greenhouse gases are undoubtedly very
important," she says. "But the second cause for climate change
is the way we are using the land surface." IMAGINE A PARKING LOT made entirely of grass and trees with little gravel, breathing roads thru it. You’d lose l0% of the cars but gain an ecological feature. Imagine a parking structure with a grassy park on the top floor, with trees. Roof gardens are on all the really posh buildings. City planners of the future. JUST IMAGINE! < BACK TO THE FUTURE
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