[Vision2020] Met Office: "...increasingly remote possibility" that human activity is not the main cause of climate change...

[Ted Moffett]

http://environmentalresearchweb.org/cws/article/news/41923

Mar 8, 2010
Met Office analysis reveals 'clear fingerprints' of man-made climate change

>From the Guardian<http://www.guardian.co.uk/environment/2010/mar/05/met-office-analysis-climate-change>

It is an "increasingly remote possibility" that human activity is not the
main cause of climate
change<http://www.guardian.co.uk/environment/climate-change>,
according to a major Met Office
<http://www.guardian.co.uk/uk/met-office>review of more than 100
scientific studies that track the observed changes
in the Earth's climate system.

The research will strengthen the case for human-induced climate change
against sceptics who argue that the observed changes in the Earth's climate
can largely be explained by natural variability.

Climate scientists and the UN's climate body, the Intergovernmental Panel on
Climate Change (IPCC) <http://www.ipcc.ch/>, have come under intense
pressure in recent months after the IPCC was forced to admit it had made two
errors<http://www.guardian.co.uk/environment/2010/feb/14/benny-peiser-houghton-ipcc-apology>in
its fourth assessment report published in 2007. Emails
hacked from climate scientists at the University of East
Anglia<http://www.guardian.co.uk/environment/hacked-climate-science-emails>in
November have also sparked a series of inquiries into allegations of a
lack of transparency by researchers and manipulation of the peer review
process.

Asked whether his study was specifically scheduled as a fightback, Peter
Stott, who led the review, said that the paper was originally drafted a year
ago. But he added: "I hope people will look at that evidence and make up
their minds informed by the scientific evidence."

Scientists matched computer models of different possible causes of climate
change – both human and natural – to measured changes in factors such as air
and sea temperature, Arctic sea ice cover and global rainfall patterns. This
technique, called "optimal detection", showed clear fingerprints of
human-induced global warming, according to Stott. "This wealth of evidence
shows that there is an increasingly remote possibility that climate change
is being dominated by natural factors rather than human factors." The paper
reviewed numerous studies that were published since the last IPCC report.

Optimal detection considers to what extent an observation can be explained
by natural variability, such as changing output from the sun, volcanic
eruptions or El
Niño<http://www.guardian.co.uk/world/interactive/2004/aug/15/elnino>,
and how much can be explained by the well-established increases in carbon
dioxide and other greenhouse gases in the atmosphere.

According to Nasa<http://www.nasa.gov/home/hqnews/2010/jan/HQ_10-017_Warmest_temps.html>,
the last decade was the warmest on record and 2009 the second warmest year.
Temperatures have risen by 0.2 °C per decade, over the past 30 years and
average global temperatures have increased by 0.8 °C since 1880.

The evidence that the climate system is changing goes beyond measured air
temperatures, with much of the newest evidence coming from the oceans. "Over
80% of the heat that's trapped in the climate system as a result of the
greenhouse gases is exported into the ocean and we can see that happening,"
said Stott. "Another feature is that salinity is changing – as the
atmosphere is warming up, there is more evaporation from the surface of the
ocean [so making it more salty], which is most noticeable in the
sub-tropical Atlantic."

This also links into changes in the global water cycle and rainfall
patterns. As the atmosphere warms, it has been getting more humid, exactly
as climate modellers had predicted. "This clear fingerprint has been seen in
two independent datasets. One developed in the Met Office Hadley Centre,
corroborated with data from satellites."

Arctic sea ice is also retreating – the summer minimum of sea ice is
declining at a rate of 600,000 km per decade, an area approximately the size
of Madagascar. Again, decreasing sea ice is predicted by climate models.

Rainfall is also on the rise in the higher latitudes of the northern
hemisphere and large swaths of the southern hemisphere, while in the tropics
and sub-tropics, there are decreases. "The already-wet regions are getting
wetter and the dry regions are getting drier," said Stott. "We now have
studies that can identify this fingerprint in the observational data."

The review, published in Wiley Interdisciplinary Reviews: Climate
Change<http://wires.wiley.com/WileyCDA/WiresJournal/wisId-WCC.html>,
found that the natural causes of climate variation, including changing
energy output from the sun and volcanic eruptions, could not explain the
observed changes by themselves. "There hasn't been an increase in solar
output for the last 50 years and solar output would not have caused cooling
of the higher atmosphere and the warming of the lower atmosphere that we
have seen," said Stott.

If the observed climate change was entirely due to solar activity, the
Earth's atmosphere would have warmed more evenly – both the troposphere and
stratosphere would have been affected. Warming due to the Sun would also
have meant temperatures should have increases more quickly early than late
in the 20th century, which is the reverse of what was actually measured.

The review is published as scientists also report a rise in methane
emissions from a section of the Arctic Ocean sea floor. That study,
published today in the journal Science <http://www.sciencemag.org/>, shows
that the permafrost under the East Siberian Arctic shelf, once considered an
safe store of methane, is leaking large amounts of the gas into the
atmosphere. Release of even a fraction of the methane stored in the shelf
could trigger abrupt climate warming as this is a greenhouse gas around 30
times more potent than CO2.

"The amount of methane currently coming out of the East Siberian Arctic
shelf is comparable to the amount coming out of the entire world's oceans.
Sub-sea permafrost is losing its ability to be an impermeable cap," said
Natalia Shakhova, a researcher at the University of Alaska Fairbanks's
International Arctic Research Centre. "The release to the atmosphere of only
one percent of the methane assumed to be stored in shallow hydrate deposits
might alter the current atmospheric burden of methane up to three to four
times. The climatic consequences of this are hard to predict."

   - This article was shared by our content partner the
Guardian<http://environmentguardian.co.uk/>.
   environmentalresearchweb is now a member of the Guardian Environment
   Network<http://www.guardian.co.uk/environment/series/guardian-environment-network>.


 About the author

Alok Jha <http://www.guardian.co.uk/profile/alokjha> is a science and
environment correspondent at the Guardian.
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