Last Updated: Saturday, 12 November 2005, 09:16 GMT
Water builds the heat in Europe
By Richard Black
Environment Correspondent, BBC News website
Clouds over Moscow. Image: AP
There will be some parts of the world affected by strong feedback and
others not
Rolf Philipona
Water vapour rather than carbon dioxide in the atmosphere is the main
reason why Europe's climate is warming, according to a new study.
The scientists say that rising temperatures caused by greenhouse gases
are increasing humidity, which in turn amplifies the temperature rise.
This is potentially a positive feedback mechanism which could increase
the impact of greenhouse gases such as CO2.
The research is published in the journal Geophysical Research Letters.
The scientists involved have used research networks and weather stations
across Europe to measure temperature, humidity and longwave radiation,
which plays a key role in the greenhouse effect.
Not from the Sun
"We observed that between 1995 and 2002, the amount of longwave
radiation coming downwards to the Earth in Europe increased
significantly, whereas solar radiation did not," said study leader Rolf
Philipona, from the World Radiation Center in Davos, Switzerland.
The greenhouse effect: An animated guide
Longwave radiation comes from molecules of gases such as carbon dioxide,
methane, and water vapour which have absorbed solar radiation after it
has hit the Earth's surface and been reflected back up through the
atmosphere.
"We wondered if this effect was simply because of a temperature increase
at the surface - you would just get more radiation going up, and so more
coming back down," Dr Philipona told the BBC News website.
"But we allowed for this, and for the impact of extra clouds, but still
we found an increase."
The researchers calculated that this increase is partly down to higher
concentrations of the gases such as carbon dioxide which are often
described as causing the "man-made greenhouse effect"; but increased
water vapour appears to have a larger effect, accounting for about 70%
of the observed temperature rise.
Not all regions of Europe are affected equally.
Between 1995 and 2002, Eastern states appear to have warmed by a rate
equivalent to about 2C per decade - considerably faster than their
western counterparts.
According to the new study, that may well be down to humidity
differences; broadly speaking, humidity has risen fast in the east but
not in the west, where evaporation may be limited by the dryness of the
Iberian peninsula.
Undervalued water
Instruments in Alpine station. Image: Rolf Philipona
The ASRB unit at Gornergrat in the Alps measures longwave radiation
Although rising concentrations of carbon dioxide, methane, nitrous
oxides and other gases are almost certainly driving the global rise in
temperature observed in recent decades, the natural greenhouse effect -
without which the world would be considerably colder - is largely down
to atmospheric water vapour.
Because human activities change its concentrations very little, it is
generally not mentioned in discussions of modern-day greenhouse warming.
But climate scientists have been aware for decades that mechanisms
involving water vapour could amplify temperature increases, and have
attempted to model these effects in computer simulations.
Researchers sceptical about projections of human-induced climate change
base their criticism partly on what they see as flawed simulations of
water vapour and clouds.
So will this discovery force a re-evaluation of climate models? William
Ingram, from the UK's Meteorological Office and Oxford University,
believes not.
"This careful study confirms that this aspect of the climate system is
behaving broadly as expected," he told the BBC News website.
"It is therefore consistent with projections by the scientific consensus."
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Barnes Glacier, Ross Island. Image: Glaciers Online/Micheal Hambrey
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But Rolf Philipona believes there might be regional implications which
had not been appreciated before.
"There will be some parts of the world affected by strong feedback and
others not - perhaps even a drying in some places," he said.
"We would see that water vapour would go up where there is enough water
on the ground."
An increased concentration of water vapour is just one of the feedback
mechanisms which could change or amplify the progress of human-induced
global warming.
Others include:
* melting of ice, leading to a greater absorption of sunlight
* the conversion of forests from net absorbers of carbon dioxide to
net producers
* the release of trapped methane from permafrost.
Recent studies indicate that the first two of these mechanisms may
already be in train.
[permaculture] BBC NEWS | Science/Nature | Water builds the heat in Europe,
Lawrence F. London, Jr., 11/12/2005