Are Skies Dimming Over Earth?
Data Suggest Human Pollution Can Lead to Darker Days
By AMANDA ONION
Scientists have long argued that human activity may be warming the Earth through a process known as the greenhouse effect. Now studies show we may also be having a different kind of impact: global dimming.
Researchers with the Pacific
Northwest National Laboratory in
"The main suspect is
increasing air pollution, which produces haze and cuts down on the solar
radiation reaching the surface," said L. Ruby Leung of the U.S. Energy
Department. Leung points out there has been a ninefold increase in fossil-fuel emissions from
Is pollution truly turning down the
dimmer switch over the Earth? Other work over the last few years has found a
similar decline in the amount of solar radiation hitting the entire planet
since the 1950s, while noting a slight increase since the 1990s. These most recent findings,
published in the journal Geophysical Research Letters, support that past work
and were based on the readings of nearly 500 ground-based instruments
But some scientists argue we can't yet be sure what's going on.
Potential Clues Lost as 'Goresat' Satellite Scrapped
"The observations we have at
this point just aren't good enough," said Robert Charlson
of the Department of Atmospheric Sciences and Department of Chemistry at the
In fact, last month NASA scrapped a
program that might have offered key evidence one way or the other. Initially
dubbed "Goresat" by Republicans in Congress
because it was first promoted by Vice President Al Gore in the late 1990s, the
Deep Space Climate Observatory was designed to hover and observe an entire
sunlit side of the Earth for long periods. The satellite, Charlson
argues, might finally have offered solid data about so-called global dimming --
as well as warming. The device was built and scheduled to launch in 2001. The
2001 terror attacks and then the loss of
As a result, researchers looking into the possibility of global dimming are limited to basing their work on scant satellite data and ground-based instrument readings.
Judging What's Real
Rachel Pinker of the
Others are more confident that the
dimming is happening and that pollution is the main cause. Martin Wild, an
atmospheric scientist at the Swiss Federal Institute of Technology in
If these preliminary numbers are right and the brightness of the skies is being altered by pollution levels, the effects could be widespread, Leung points out. From slower plant growth to less frequent precipitation, further dimming could eventually lead to food and water shortages in some regions. The fact that the phenomenon might also be skewing the intensity of global warming also holds consequences, argues Charlson, since it's important to carefully measure effects in order to curb them.
"It makes sense -- there are good reasons why we expect man-made particles to affect the Earth globally," Charlson said. "We just need the observations, and we need to do them much better if we want to come up with some solutions."