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 (CO2) 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-CO2 greenhouse gases, particularly tropospheric
ozone, methane, chlorofluorocarbons (CFCs),
and black carbon (soot) particles.
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-CO2
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 CO2 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.
Hansen's
research looked at trends in various greenhouse
gases and noted that the growth rate of
CO2 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.
More
information on the paper can be found at:
http://www.pnas.org/papbyrecent.shtml.
NASA's
Office of Earth Sciences, Headquarters,
Washington, DC, sponsor research that studies
how human-induced and natural changes affect
our global environment. For more information
about the Earth Sciences Enterprise, please
see: http://www.earth.nasa.gov.
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