New research to examine role of aerosols in climate change
Washington, September 6 : A group of scientists affiliated with the International
Geosphere-Biosphere Programme (IGBP) have proposed a new framework to account more
accurately for the effects of aerosols on precipitation in climate models.
The increase in atmospheric concentrations of man-made aerosols-tiny particles
suspended in the air-from such sources as transportation, industry, agriculture, and urban
land use not only poses serious problems to human health, but also has an effect on
weather and climate.
Recent studies suggest that increased aerosol loading may have changed the energy
balance in the atmosphere and at the Earth's surface, and altered the global water cycle
in ways that make the climate system more prone to precipitation extremes.
It appears that aerosol effects on clouds can induce large changes in precipitation
patterns, which in turn may change not only regional water resources, but also may change
the regional and global circulation systems that constitute the Earth's climate.
The proposed framework improves scientists' ability to simulate present and future
climates by integrating, for the first time, the radiative and microphysical effects of
aerosols on clouds.
The radiative effects of aerosols on clouds mostly act to suppress precipitation,
because they decrease the amount of solar radiation that reaches the land surface, and
therefore cause less heat to be available for evaporating water and energizing convective
rain clouds.
Microphysical effects of aerosols can slow down the conversion of cloud drops into
raindrops, which shuts off precipitation from very shallow and short-lived clouds.
Model simulations suggest that this delay of early rain causes greater amounts of cloud
water and rain intensities later in the life cycle of the cloud.
This suggests that rain patterns are shifting, leading to possible drought in one area
and flooding downwind in another area. In addition, greater cooling below and heating
above leads to enhanced upward heat transport.
Model simulations have shown that greater heating in the troposphere enhances the
atmospheric circulation system, shifting weather patterns due to changes convective
activity.
Investigations of aerosol/precipitation effects are especially relevant to policy
issues, as effects on the hydrological cycle may affect water availability, a great
concern in many regions of the world.
The IPCC, in its latest climate change assessment report, declared aerosols to be "the
dominant uncertainty in radiative forcing".
Therefore, aerosols, clouds and their interaction with climate are still the most
uncertain areas of climate change and require multidisciplinary coordinated research
efforts.
To that end, the team of scientists is participating in a new, international research
project designed to study the connections between aerosols, clouds, precipitation and
climate (ACPC project).
--ANI
