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Science Forum Index » Philosophy Forum » Next decade 'may see no warming'...
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| turtoni... |
 Posted: Wed Jun 18, 2008 6:31 pm |
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http://news.bbc.co.uk/2/hi/science/nature/7376301.stm
"The Earth's temperature may stay roughly the same for a decade, as
natural climate cycles enter a cooling phase, scientists have
predicted.
A new computer model developed by German researchers, reported in the
journal Nature, suggests the cooling will counter greenhouse warming.
However, temperatures will again be rising quickly by about 2020, they
say. Other climate scientists have welcomed the research, saying it
may help societies plan better for the future.
See how modelled temperatures may develop
The key to the new prediction is the natural cycle of ocean
temperatures called the Atlantic Multidecadal Oscillation (AMO), which
is closely related to the warm currents that bring heat from the
tropics to the shores of Europe.
The cause of the oscillation is not well understood, but the cycle
appears to come round about every 60 to 70 years.
Imagine the payoff of knowing with some certainty what the next 10
years hold in terms of temperature and precipitation
Professor Michael Schlesinger
It may partly explain why temperatures rose in the early years of the
last century before beginning to cool in the 1940s.
"One message from our study is that in the short term, you can see
changes in the global mean temperature that you might not expect given
the reports of the Intergovernmental Panel on Climate Change (IPCC),"
said Noel Keenlyside from the Leibniz Institute of Marine Sciences at
Kiel University.
His group's projection diverges from other computer models only for
about 15-20 years; after that, the curves come back together and
temperatures rise.
"In the long term, radiative forcing (the Earth's energy balance)
dominates. But it's important for policymakers to realise the
pattern," he told BBC News.
Deep patterns
Modelling of climatic events in the oceans is difficult, simply
because there is relatively little data on some of the key processes,
such as the meridional overturning circulation (MOC) - sometimes
erroneously known as the Gulf Stream - which carries heat northwards
in the Atlantic.
Only within the last few years have researchers begun systematically
deploying mobile floats and tethered buoys that will, in time, tell us
how this circulation is changing.
Atlantic circulation
Enlarge Image
As a substitute for direct measurements of the MOC, the Kiel team used
data going back 50 years from the Labrador Sea, where warm water gives
up its heat to the atmosphere and sinks, before returning southward
lower in the ocean.
Combining this ocean data with established models of global warming,
they were able to generate a stream of model results that mimicked
well temperatures observed in the recent past over the north Atlantic,
western Europe and North America.
Looking forward, the model projects a weakening of the MOC and a
resulting cooling of north Atlantic waters, which will act to keep
temperatures in check around the world, much as the warming and
cooling associated with El Nino and La Nina in the Pacific bring
global consequences.
"We have to take into account that there are uncertainties in our
model; but it does suggest a plateauing of temperatures, and then a
continued rise," said Dr Keenlyside.
'No distraction'
The projection does not come as a surprise to climate scientists,
though it may to a public that has perhaps become used to the idea
that the rapid temperature rises seen through the 1990s are a
permanent phenomenon.
"We've always known that the climate varies naturally from year to
year and decade to decade," said Richard Wood from the UK's Hadley
Centre, who reviewed the new research for Nature.
"We expect man-made global warming to be superimposed on those natural
variations; and this kind of research is important to make sure we
don't get distracted from the longer term changes that will happen in
the climate (as a result of greenhouse gas emissions)."
Ocean buoys should produce more data about the Atlantic oscillation
Dr Wood cautions that this kind of modelling is in its infancy; and
once data can be brought directly from the Atlantic depths, that may
change the view of how the AMO works and what it means for the global
climate.
As with the unusually cold weather seen recently in much of the
northern hemisphere - linked to La Nina conditions - he emphasises
that even if the Kiel model proves correct, it is not an indication
that the longer-term climate projections of the IPCC and many other
institutions are wrong.
Michael Schlesinger, the US scientist who characterised the AMO in
1994, described the new model as "very exciting".
"No doubt we need to have more data from the deep ocean, and we don't
have that at present," the University of Illinois at Urbana-Champaign
researcher told BBC News.
"But imagine the payoff of knowing with some certainty what the next
10 years hold in terms of temperature and precipitation - the economic
impacts of that would be significant." |
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