Culprits of Climate Change
Scientists suggest that climate change in recent
decades has been mainly caused by air pollution containing non-carbon
dioxide greenhouse gases.
29, 2000 -- Since climate change affects everyone on Earth,
scientists have been trying to pinpoint its causes. For many
years, researchers agreed that climate change was triggered by
what they called "greenhouse gases," with carbon dioxide
from burning of fossil fuels such as coal, oil and gas playing
the biggest role. However, new research suggests fossil fuel
burning may not be as important in the mechanics of climate change
as previously thought.
NASA funded research by Dr. James Hansen of the Goddard Institute for Space Studies, New York, NY, and his colleagues, suggests that climate change in recent decades has been mainly caused by air pollution containing non-carbon dioxide greenhouse gases, particularly tropospheric ozone, methane, chlorofluorocarbons (CFCs) and black carbon (soot) particles.
Above: The annual increase of surface heating attributed
to various greenhouse gases. Since 1950, the rate of greenhouse
heating caused by methane and CFCs has increased faster than
the heating caused by carbon dioxide. [more
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"The good news is that the growth rate of non-carbon dioxide greenhouse gases has declined in the past decade, and if sources of methane and tropospheric ozone were reduced in the future, further changes in climate due to these gases in the next 50 years could be near zero," Hansen explained. "If these reductions were coupled with a reduction in both particles of black carbon and carbon dioxide gas emissions, this could lead to a decline in the rate of climate change."
Black carbon particles are generated by burning coal and diesel fuel and cause a semi-direct reduction of cloud cover. This reduction in cloud cover is an important factor in Earth's radiation balance, because clouds reflect 40 percent to 90 percent of the Sun's radiation depending on their type and thickness. Black carbon emission is not an essential element of energy production and it can be reduced or eliminated with improved technology.
Left: The dense concentration of powerplants, factories, trucks, and automobiles on the U.S. east coast continuously emit soot and other particulate pollutants into the sky that affect the nature of cloud cover. In this false-color satellite image, yellow clouds scattered over the northeast are polluted clouds with small water droplets. Pink clouds over Canada have larger droplets, and are relatively clean. (Image by Daniel Rosenfeld, Hebrew University of Israel) [more information]
Hansen's research looked at trends in various greenhouse gases
and noted that the growth rate of carbon dioxide in the atmosphere
doubled between 1950 and 1970, but leveled off from the late
1970s to the late 1990s.
The other critical piece of information this research is based on, in addition to greenhouse gas levels, is observed heat storage, or warmer ocean temperatures, over the last century. Heat storage in the ocean provides a consistency check on climate change. The ocean is the only place that energy forms an imbalance. In this case a warming can accumulate, and global ocean data reveals that ocean heat content has increased between the mid-1950s and the mid-1990s.
Hansen's paper, "Global Warming in the 21st Century an Alternate Scenario," will appear in the August 29th version of the Proceedings of the National Academy of Sciences.Web Links
Goddard Institute for Space Physics -- home page
Changing Our Weather One Smokestack at a Time -- from earthobservatory.nasa.gov
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