explicit
01.07.05, 23:01
Znowu nasza wina ,... Ej wy , echo freaks , idzta siem utopta !!!
uklony
============================================================================
from the June 30, 2005 edition
Does dirty air cool the climate? Study adds a factor to climate-change debate.
==============================================================================
By Peter N. Spotts | Staff writer of The Christian Science Monitor
Over the past several decades, industrial countries have made major strides
in cleaning up pollutants roiling from smokestacks.
But some researchers now say this progress could have a troubling side
effect - accelerating the pace of global warming.
The reason: Tiny pollutant particles, once airborne, can reflect sunlight
back into space, easing temperatures in what is known as aerosol cooling. By
cleaning up industrial pollution, countries are reducing the effect of this
cooling.
Nobody is recommending that nations halt efforts to curb pollution.
Still, when this factor is taken into account, global warming could outpace
the level now forecast by climatologists, a team of European climate
scientists reports in Thursday's edition of the journal Nature. Already,
climate estimates sponsored by the United Nations foresee average
temperatures rising by about 10 degrees Fahrenheit by 2100.
The study doesn't represent a formal forecast, but the team says it
highlights the importance of pinning down the impact of twin changes in the
atmosphere: As aerosol pollutants play an increasingly small role in
affecting temperatures, the effect of changes in greenhouse-gas levels will
play an even more significant role.
"Scientists must pay more attention to this issue as they do more complex
modeling, and the public needs to be aware of the implications," says Meinrat
Andreae, who led the research.
The team made calculations based on a simplified set of equations describing
how the climate system works. Indeed, other researchers liken the effort to a
somewhat sophisticated back-of-the-envelope calculation scientists often
perform to see if a phenomenon is worth a second look.
The results, published a week before the G-8 summit in Scotland, are likely
to add urgency to British Prime Minister Tony Blair's efforts to keep climate
change a headline issue.
But Mr. Blair has been unable to convince President Bush to support mandatory
targets and timetables for emissions reductions. The White House's preferred
approach instead focuses on reducing the US economy's carbon intensity - the
amount of carbon emitted per unit of economic output - by 18 percent over 10
years. It relies heavily on research and market forces to encourage adoption
of technologies to achieve its goals.
The European research team's call for more research also comes as the United
Nations sponsored Intergovernmental Panel on Climate Change (IPCC) is in the
midst of preparing its next set of climate-change reports, set for release in
2007. Researchers had to submit results to journals by mid-May - deadlines
that suggest a flurry of new studies relating to the global climate will come
out over the next year
Researchers are aiming to narrow uncertainties linked to climate sensitivity
and man-made aerosols, because sensitivity determines how much warming could
be expected as concentrations of carbon dioxide and other heat
trapping "greenhouse" gases in the atmosphere grow. Even from the effects of
what humans already have pumped skyward, many researchers believe the
atmosphere's temperature will increase by 2 degrees by 2100. That number
would rise with continued greenhouse emissions.
If the impact of aerosol cooling is small and the climate is less sensitive
to CO2 increases than current estimates hold, warming might fall toward the
low end of projections by the IPCC's science working group. If cooling has
been large and the climate is very sensitive, warming could exceed their
projections.
Uncertainties about aerosol cooling and climate sensitivity to greenhouse
gasses remain large. But as new studies have emerged, the importance of these
two factors has appeared to grow, says Dr. Andreae, who heads the
biogeochemistry department at the Max Planck Institute for Chemistry in
Mainz, Germany. Aerosol cooling may have been greater in the past than we
believed, and the climate may be more sensitive to greenhouse-gas
accumulation.
While the European team's broad description of cooling and sensitivity is the
latest warning, the devil is in the details, other climate scientists say.
For example, the team's calculations appear to be based in part on the
assumption that all of the warming since the 1850s is due to human
activities. The IPCC, in contrast, has been willing to attribute "most" of
the warming over the past 40 years. The difference seems small, only a few
tenths of a degree. But it leads to a lower climate sensitivity than
Andreae's team calculates, notes Theodore Anderson, a climate researcher at
the University of Washington in Seattle.
Moreover, ice core data from the last glacial maximum some 20,000 years ago
place limits on the climate's sensitivity, notes Gavin Schmidt, a climate
researcher at NASA's Goddard Institute for Space Studies in New York. This
leads to a climate system less responsive to changing CO2 levels than the
European team's model implies - and in line with estimates that underlie
current climate-change projections.
In addition, all pollutants are not created equal, both researchers add.
Sulfur-based aerosols from burning fossil fuels tend to reflect sunlight back
into space, acting as an atmospheric coolant. But other aerosols, such as
black-carbon soot, warm the atmosphere. The relative contribution of each is
highly uncertain. But their offsetting effects could lead to weaker aerosol
cooling than Andreae's team suggests. Moreover, aerosols have indirect but
important effects on clouds that the model fails to capture.
If nothing else, the effort highlights the importance of a set of satellite
missions aimed at solving the cloud-aerosol problems. Two satellites are set
for launch later this year that will round out a suite of five satellites
dubbed "the A Train." The satellites orbit Earth in a line so their unique
instruments can cover the same swaths of the atmosphere. The satellites fill
wide gaps in measurements of aerosols, clouds, their movements, and their
interactions with each other and with climate, helping to zero in on the
climate's true sensitivity to a doubling of CO2 concentrations.
