The ABCs of Global Warming
Orthodox News
CO2Science.org, October 31, 2007
http://www.co2science.org/scripts/CO2ScienceB2C/articles/V10/N44/C1.jsp
Reference
Ramanathan, V., Ramana, M.V., Roberts, G., Kim, D., Corrigan, C., Chung, C.
and Winker, D. 2007. Warming trends in Asia amplified by brown cloud solar
absorption. Nature 448: 575-578.
Background
The authors of this important new study write that light-absorbing and
light-scattering aerosols "contribute to atmospheric solar heating and
surface cooling," and that "the sum of the two climate forcing terms - the
net aerosol forcing effect - is thought to be negative and may have masked
as much as half of the global warming attributed to the recent rapid rise in
greenhouse gases," but they caution that there is "at least a fourfold
uncertainty in the aerosol forcing effect."
What was done
In an observational program that studied this phenomenon as it has never
been studied before, Ramanathan et al. employed "three lightweight unmanned
aerial vehicles that were vertically stacked between 0.5 and 3 km over the
polluted Indian Ocean," which "deployed miniaturized instruments measuring
aerosol concentrations, soot amount and solar fluxes" within the infamous
atmospheric brown clouds (ABCs) that have been demonstrated to envelop "most
of Asia and the adjacent oceans" during "the six-month-long tropical dry
season," when "convective coupling between the surface and the troposphere
is weak [and] aerosol solar heating can amplify the effect of greenhouse
gases in warming the atmosphere while simultaneously cooling the surface."
What was learned
The seven scientists found that "atmospheric brown clouds enhanced lower
atmospheric solar heating by about 50 per cent" during the period of their
study; and they say that general circulation model simulations suggest that,
over the Indian Ocean and Asia during the long tropical dry season,
"atmospheric brown clouds contribute as much as the recent increase in
anthropogenic greenhouse gases to regional lower atmospheric warming
trends."
What it means
For a huge and important part of the world - where the situation could well
get worse before it gets better - only half of the observed lower
atmospheric warming trend of the past few decades has been either natural or
greenhouse-gas-induced (take your pick), while the other half appears to
have come courtesy of the region's infamous ABCs. One can only wonder,
therefore, what the case may be over other polluted parts of the planet.
Perhaps aerosols there may also be adding to global warming instead of
subtracting from it, which would appear to be a real possibility considering
the enormous fourfold uncertainty Ramanathan et al. associate with the net
aerosol forcing effect.