Scientists have
produced further compelling evidence showing that modern-day climate
change is not caused by changes in the Sun's activity.
The research contradicts a favoured theory of climate "sceptics", that
changes in cosmic rays coming to Earth determine cloudiness and
temperature.
The idea is that variations in solar activity affect cosmic ray
intensity.
But UK scientists found there has been no significant link between
cosmic rays and cloudiness in the last 20 years.
Presenting their findings in the Institute of Physics journal,
Environmental Research Letters, the University of Lancaster team
explain that they used three different ways to search for a
correlation, and found virtually none.
This is the latest piece of evidence which at the very least puts the
cosmic ray theory, developed by Danish scientist Henrik Svensmark at
the Danish National Space Center (DNSC), under very heavy pressure.
Dr Svensmark's idea formed a centrepiece of the controversial
documentary The Great Global Warming Swindle.
Wrong path
"We started on this game because of Svensmark's work," said Terry Sloan
from Lancaster University.
"If he is right, then we are going down the wrong path of taking all
these expensive measures to cut carbon emissions; if he is right, we
could carry on with carbon emissions as normal."
Cosmic rays are deflected away from Earth by our planet's magnetic
field, and by the solar wind - streams of electrically charged
particles coming from the Sun.
The Svensmark hypothesis is that when the solar wind is weak, more
cosmic rays penetrate to Earth.
That creates more charged particles in the atmosphere, which in turn
induces more clouds to form, cooling the climate.
The planet warms up when the Sun's output is strong.
Professor Sloan's team investigated the link by looking for periods in
time and for places on the Earth which had documented weak or strong
cosmic ray arrivals, and seeing if that affected the cloudiness
observed in those locations or at those times.
"For example; sometimes the Sun 'burps' - it throws out a huge burst of
charged particles," he explained to BBC News.
"So we looked to see whether cloud cover increased after one of these
bursts of rays from the Sun; we saw nothing."
Over the course of one of the Sun's natural 11-year cycles, there was a
weak correlation between cosmic ray intensity and cloud cover - but
cosmic ray variability could at the very most explain only a quarter of
the changes in cloudiness.
And for the following cycle, no correlation was found.
Limited effect
Dr Svensmark himself was unimpressed by the findings.
"Terry Sloan has simply failed to understand how cosmic rays work on
clouds," he told BBC News.
"He predicts much bigger effects than we would do, as between the
equator and the poles, and after solar eruptions; then, because he
doesn't see those big effects, he says our story is wrong, when in fact
we have plenty of evidence to support it."
But another researcher who has worked on the issue, Giles Harrison from
Reading University, said the work was important "as it provides an
upper limit on the cosmic ray-cloud effect in global satellite cloud
data".
Dr Harrison's own research, looking at the UK only, has also suggested
that cosmic rays make only a very weak contribution to cloud formation.
The Svensmark hypothesis has also been attacked in recent months by
Mike Lockwood from the UK's Rutherford-Appleton Laboratory.
He showed that over the last 20 years, solar activity has been slowly
declining, which should have led to a drop in global temperatures if
the theory was correct.
The Intergovernmental Panel on Climate Change (IPCC), in its vast
assessment of climate science last year, concluded that since
temperatures began rising rapidly in the 1970s, the contribution of
humankind's greenhouse gas emissions has outweighed that of solar
variability by a factor of about 13 to one.
According to Terry Sloan, the message coming from his research is
simple.
"We tried to corroborate Svensmark's hypothesis, but we could not; as
far as we can see, he has no reason to challenge the IPCC - the IPCC
has got it right.
"So we had better carry on trying to cut carbon emissions."
http://news.bbc.co.uk/1/hi/sci/tech/7327393.stm
