Greenhouse Gases Fueled 2006 US Warmth - Report
Date: 29-Aug-07
Country: US
Author: Deborah Zabarenko, Environment Correspondent
The annual average US temperature in 2006 was 2.1 degrees
F (1.16C) above the 20th century average and the ninth
consecutive year of above-normal US temperatures, researchers
at the National Oceanic and Atmospheric Administration wrote.
This is in line with a global warming trend over the past
century that most climate scientists attribute to human-made
greenhouse gas emissions. Greenhouse gases, notably carbon
dioxide from petroleum-fueled vehicles and coal-fired power
plants, build up in the atmosphere and hold in the sun's heat
like the glass walls of a greenhouse.
But other factors also play a role, and when figures for
2006 indicated a near-record-heat year for the contiguous 48
states -- the area for which there are the best statistics --
US climate scientists wondered if this warmth was due to
climate change or to the naturally occurring El Nino.
El Nino seemed a logical culprit, since there were active
El Nino patterns of warm water in the Pacific in 2006 and in
the hottest US year of 1998, said Martin Hoerling of the US
climate administration.
IF NOT EL NINO, THEN WHAT?
Hoerling and his co-authors, writing in the Sept. 5 edition
of Geophysical Research letters, looked back through history
and found that El Nino does not generally cause a rise in US
average annual temperatures. But if not El Nino, what was it?
To find out, they used computer simulations of the impact
of greenhouse gas emissions on temperature that were used by
the UN Intergovernmental Panel on Climate Change. The panel
reported, with 90 percent probability, that human activities
contribute to global warming.
They compared the 18 different simulations for 2006, which
included projections of greenhouse gas emissions, with the
actual average temperature for the United States, and found a
correlation, Hoerling said.
"What we found was a very strong footprint of the observed
warming, consistent with the greenhouse gas effect," Hoerling
said in a telephone interview.
Preliminary data suggested that 2006 was a record warm year
for the contiguous 48 US states but updated numbers showed
last year was 0.08 degrees F (.04C) cooler than 1998.
For most states, 2006 ranked among the 10 hottest years
since 1895. Globally, 2005 was the warmest, edging out 1998,
with 2006 ranked about sixth for the world, Hoerling said.
Hoerling said the difference in US average temperatures
between 2006, 1998 and 1934 was minuscule.
"Those three years are so close to one another ... that's
not really a relevant concern," he said.