For the first time ever, scientists behind one of the world's
most comprehensive weather assessments say they can perceive the likely
impact of human-influenced climate change on specific extreme weather
events.
Drought map from June 2011, showing the intensifying drought in Texas and northern Mexico. Credit: NOAA. What
the study found was increasing evidence that specific events, and
patterns of events, can now safely be attributed to man-made global
warming and its growing impact on intense storms, extreme floods,
unusual cold spells, prolonged heat waves and drought.
The '
State of the Climate'
report, issued jointly each year by the National Oceanic and
Atmospheric Administration (NOAA) and the American Meteorological
Society (AMS), looks at global weather events, climate patterns, and the
implications of flunctuating air temperatures and ocean currents.
This year, the group also released a supplemental paper, titled
Explaining Extreme Events of 2011 from a Climate Perspective (pdf), which looks specifically at extreme weather events through the lense of global climate change.
“Every weather event that happens now takes place in the context of a changing global environment."
- NOAA's Kathryn D. Sullivan
“2011 will be remembered as a year of extreme events, both in the United States and around the world,”
said Deputy
NOAA Administrator Kathryn D. Sullivan, Ph.D. “Every weather event that
happens now takes place in the context of a changing global
environment. This annual report provides scientists and citizens alike
with an analysis of what has happened so we can all prepare for what is
to come.”
Peter Stott, from Britain's National Weather Service which also contributed to the report,
said:
"We are much more confident about attributing [weather effects] to
climate change. This is all adding up to a stronger and stronger picture
of human influence on the climate."
"While we didn't find evidence that climate change has affected the
odds of all the extreme weather events we looked at, we did see that
some events were significantly more likely. Overall we're seeing that
human influence is having a marked impact on some types of extreme
weather."
The Guardian's Fiona Harvey
reports:
Attributing individual weather events, such as floods, droughts and
heatwaves, to human-induced climate change – rather than natural
variation in the planet's complex weather systems – has long been a goal
of climate change scientists. But the difficulty of separating the
causation of events from the background "noise" of the variability in
the earth's climate systems has until now made such attribution an
elusive goal.
To attribute recent extreme weather events – rather than events 10
years ago or more – to human-caused climate change is a big advance, and
will help researchers to provide better warnings of the likely effects
of climate change in the near future. This is likely to have major
repercussions on climate change policy and the ongoing efforts to adapt
to the probable effects of global warming.
Researchers found the 2011 crop-destroying drought and heat wave in
Texas was "roughly 20 times more likely" the result of man-made climate
change -- warming due to greenhouse gasses -- than of natural climate
variation,
CBS News reported.
Other key findings
:
NOAA's
State of the Climate in 2011 report was published today by the Bulletin
of the American Meteorological Society. (Credit: NOAA).
-
Warm temperature trends continue:
Four independent data sets show 2011 among the 15 warmest since records
began in the late 19th century, with annually-averaged temperatures
above the 1981–2010 average, but coolest on record since 2008. The
Arctic continued to warm at about twice the rate compared with lower
latitudes. On the opposite pole, the South Pole station recorded its
all-time highest temperature of 9.9°F on December 25, breaking the
previous record by more than 2 degrees.
- Greenhouse gases climb: Major greenhouse gas
concentrations, including carbon dioxide, methane, and nitrous oxide,
continued to rise. Carbon dioxide steadily increased in 2011 and the
yearly global average exceeded 390 parts per million (ppm) for the first
time since instrumental records began. This represents an increase of
2.10 ppm compared with the previous year. There is no evidence that
natural emissions of methane in the Arctic have increased significantly
during the last decade.
- Arctic sea ice extent decreases: Arctic sea ice
extent was below average for all of 2011 and has been since June 2001, a
span of 127 consecutive months through December 2011. Both the maximum
ice extent (5.65 million square miles, March 7) and minimum extent (1.67
million square miles, September 9) were the second smallest of the
satellite era.
- Ozone levels in Arctic drop: In the upper
atmosphere, temperatures in the tropical stratosphere were higher than
average while temperatures in the polar stratosphere were lower than
average during the early 2011 winter months. This led to the lowest
ozone concentrations in the lower Arctic stratosphere since records
began in 1979 with more than 80 percent of the ozone between 11 and 12
miles altitude destroyed by late March, increasing UV radiation levels
at the surface.
- Sea surface temperature & ocean heat content rise:
Even with La Niña conditions occurring during most of the year, the
2011 global sea surface temperature was among the 12 highest years on
record. Ocean heat content, measured from the surface to 2,300 feet
deep, continued to rise since records began in 1993 and was record high.
- Ocean salinity trends continue: Continuing a trend
that began in 2004 and similar to 2010, oceans were saltier than average
in areas of high evaporation, including the western and central
tropical Pacific, and fresher than average in areas of high
precipitation, including the eastern tropical South Pacific, suggesting
that precipitation is increasing in already rainy areas and evaporation
is intensifying in drier locations.
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