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A new cutting:edge experiment aims to discover how
exactly cosmic rays and the Sun may influence the formation of
low:level clouds, and possibly climate change.
More than two centuries ago, the British
Astronomer Royal William Herschel noted a correlation between
sunspots ? an indicator of solar activity : and the price of
wheat in England. He suggested that when there were few
sunspots, prices rose.
However, up until recently, there was little to
back up this hypothesis. Today, inside an unassuming ? some
would say decrepit:looking ? building at Cern, the Cloud
(Cosmics Leaving OUtdoor Droplets) experiment might help
explain how the Sun affects the climate.
It was a decade ago that Danish researchers first
suggested that cosmic rays generated by exploding stars known
as supernovas help generate low:altitude clouds.
The theory is that when this radiation penetrates
the Earth's atmosphere, it accelerates the formation of
aerosols, or clusters of molecules, which may then grow to
become the basis of cloud droplets.
A cloud with a larger number of droplets reflects
the incoming sunlight more efficiently and lives longer, which
produces a cooling effect. Experts say that variations of just
a few per cent could have a significant influence on the
Earth's climate.
"We want to reproduce what happens in the
atmosphere," said Jasper Kirkby, leader of the Cern Cloud
team. "We want to understand how you could get from a cosmic
ray to a cloud droplet, and in which parts of the atmosphere
this could be occurring."
Since solar activity determines how much cosmic
radiation reaches lower altitudes, any effect on clouds may
explain how the Sun's variability affects the climate.
Earth's atmosphere
At Cern, a high:energy beam of particles mimicking
cosmic rays is aimed at a so:called prototype reaction
chamber, used to recreate the Earth's atmosphere. The full
detector, which will involve a more advanced reaction chamber
and a cloud chamber, will not be ready until 2010.
By adjusting the chamber's temperature and
pressure, researchers can reproduce conditions found at
different altitudes and latitudes, and hopefully determine
which ones lead to aerosol formation.
The project was slow in getting off the ground.
It's taken almost a decade to overcome some preconceived
ideas, as Kirkby explained.
"With an interdisciplinary experiment like Cloud,
and a research topic a little ahead of its time," he told
swissinfo, "it was difficult to get the funding because it
does not fit into a normal framework."
Another problem is the ambient scepticism in the
scientific community about a relationship between cosmic rays
and climate.
"This link is not properly established for the
moment," said Urs Neu of the Swiss Forum for Climate and
Global Change. "There is too much uncertainty about whether
this radiation has an effect or not."
Global warming
Another explanation may be a little more prosaic.
Current models suggest greenhouse gas emissions are the prime
culprits behind recent climate change, in this case global
warming. Suggestions that currently unknown factors might play
a role are not necessarily welcome.
"The cosmic ray theory has been used by people who
want to deny human influence on global warming," added
Neu.
Nobody on the Cloud team is claiming that cosmic
rays alone determine the environment. "If there really is an
effect then it would simply be part of the climate change
cocktail," says Kirkby.
"What we want to understand is if, and by how
much, this natural phenomenon contributes to the climate mix.
We need to understand how clouds are affected to reduce the
uncertainties from climate predictions."
The first results of the Cloud prototype
experiment are expected next summer, while data from the
complete project should be available in 2010. In the meantime,
the project team knows it can get on with its work.
"With so many people sceptical about this theory,
we know we won't be disturbed," said Kirkby, who is, no doubt
about it, perpetuating a long tradition of blue:sky research
at Cern.
swissinfo, Scott Capper in Geneva
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