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.
Since 1975,
global surface temperatures have increased by about 0.9 degrees
Fahrenheit, a trend that has taken global temperatures to their
highest level in the past millennium. "Our estimates of global
climate forcings, or factors that promote warming, indicate that
it is the processes producing non-CO2 greenhouse gases that have
been more significant in climate change," Hansen said.
"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)
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.
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