[Reader-list] A hot 2010

[Nagraj Adve]

Global warming pushes 2010 temperatures to record highs

Scientists from two leading climate research centres publish 'best
evidence yet' of rising long-term global temperatures

    * Juliette Jowit
    * guardian.co.uk, Wednesday 28 July 2010 18.02 BST


Global temperatures in the first half of the year were the hottest
since records began more than a century ago, according to two of the
world's leading climate research centres.

Scientists have also released what they described as the "best
evidence yet" of rising long-term temperatures. The report is the
first to collate 11 different indicators – from air and sea
temperatures to melting ice – each one based on between three and
seven data sets, dating back to between 1850 and the 1970s.

The newly released data follows months of scrutiny of climate science
after sceptics claimed leaked emails from the University of East
Anglia (UEA) suggested temperature records had been manipulated - a
charge rejected by three inquiries.

Publishing the newly collated data in London, Peter Stott, the head of
climate modelling at the UK Met Office, said despite variations
between individual years, the evidence was unequivocal: "When you
follow those decade-to-decade trends then you see clearly and
unmistakably signs of a warming world".

"That's a very remarkable result, that all those data sets agree," he
added. "It's the clearest evidence in one place from a range of
different indices."

Currently 1998 is the hottest year on record. Two combined land and
sea surface temperature records from Nasa's Goddard Institute for
Space Studies (GISS) and the US National Climatic Data Centre (NCDC)
both calculate that the first six months of 2010 were the hottest on
record. According to GISS, four of the six months also individually
showed record highs.

A third leading monitoring programme, by the Met Office, shows this
period was the second hottest on record, after 1998, with two months
this year – January and March – being hotter than their equivalents 12
years ago.

The Met Office said the variations between the figures published by
the different organisations are because the Met Office uses only
temperature observations, Nasa makes estimates for gaps in recorded
data such as the polar regions, and the NCDC uses a mixture of the two
approaches. The latest figures will give weight to predictions that
this year could become the hottest on record.

Despite annual fluctuations, the figures also highlight the clear
trend for the 2000s to be hotter than the 1990s, which in turn were
clearly warmer than the previous decade, said Stott.

"These numbers are not theory, but fact, indicating that the Earth's
climate is moving into uncharted territory," said Rafe Pomerance, a
senior fellow at Clean Air Cool Planet, a US group dedicated to
helping find solutions to global warming.

The Met Office published its full list of global warming indicators,
compiled by Hadley Centre researcher John Kennedy. It formed part of
the State of the Climate 2009 report published as a special bulletin
of the American Meteorological Society by the US National Oceanic and
Atmospheric Administration, which runs the NCDC temperature series.

Seven of the indicators rose over the last few decades, indicating
"clear warming trends", although these all included annual
fluctuations up and down. One of these was air temperature over land –
including data from the Climatic Research Unit at the UEA, whose
figures were under scrutiny after hacked emails were posted online in
November 2009, but the graphic also included figures from six other
research groups all showing the same overall trends despite annual
differences.

The other six rising indicators were sea surface temperatures,
collected by six groups; ocean heat to 700m depth from seven groups;
air temperatures over oceans (five data sets); the tropospheric
temperature in the atmosphere up to 1km up (seven); humidity caused by
warmer air absorbing more moisture (three); and sea level rise as
hotter oceans expand and ice melts (six).

Another four indicators showed declining figures over time, again
consistent with global warming: northern hemisphere snow cover (two
data sets), Arctic sea ice extent (three); glacier mass loss (four);
and the temperature of the stratosphere. This last cooling effect is
caused by a decline in ozone in the stratosphere which prevents it
absorbing as much ultraviolet radiation from the sun above.

One key data set omitted was sea ice in the Antarctic, because it was
increasing in some areas and decreasing in others, due to reduced
ozone causing changes in wind patterns and sea-surface circulation.
This data set showed no clear trend, said Stott. These figures were
also in the last report from the UN's Intergovernmental Panel on
Climate Change (IPCC) in 2007.

"It's not that the IPCC didn't look at this data, of course they did,
but they didn't put it all together in one place," he added.

The cause of the warming was "dominated" by greenhouse gases emitted
by human activity, said Stott. "It's possible there's some [other]
process which can amplify other effects, such as radiation from the
sun, [but] the evidence is so clear the chance there's something we
haven't thought of seems to be getting smaller and smaller," he said.