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NEW
VIEWS ON THE CULPRITS OF CLIMATE CHANGE
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.
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