The science take: Solar activity and ice ages
- 10 Oct 2011, 14:50
- Verity Payne
new paper, published online today, has been interpreted by
some journalists as heralding a "mini 'ice age'". This echoes
similar claims made earlier this year after the press became
aware that the sun's activity has been unusually low over the last
But as numerous commentators have pointed out,
the claim that we face a new ice age simply does not fit with what
the science shows. So does this latest research proclaim a mini ice
age? We take a look at what the paper actually says.
It has long been known that the sun's activity fluctuates on a
roughly 11-year cycle, and periods of low solar activity have been
associated with changes in winter weather patterns. Originally
solar activity level was determined by counting sunspots, with less
sunspots meaning less solar activity. However, recent advances in
satellite technology have enabled researchers to monitor solar
activity more accurately, and have
found that the change in UV radiation from the sun over the
solar activity cycle is between 4 and 6 times larger than
British scientists have used the new satellite data to estimate
the difference between UV radiation when solar activity is at its
peak, and when it is at a minimum. The researchers then ran a
climate model which simulates the ocean and atmosphere under both
scenarios, and compared the two sets of results.
The researchers found that the solar minimum scenario prompts a
specific climate pattern during the winter months. UV is absorbed
in the stratosphere, around 50 km up in the atmosphere, so during
solar minimum when there is less incoming UV radiation, a layer of
relatively cold air forms in the stratosphere. This changes how
large masses of air flow, as Sarah Ineson, UK Met Office, explains:
"What we're seeing is UV levels
affecting the distribution of air masses around the Atlantic basin.
This causes a redistribution of heat - so while Europe and the US
may be cooler, Canada and the Mediterranean will be warmer, and
there is little direct impact on global temperatures."
Under a solar maximum scenario, the researchers found the
The findings might go some way to explaining the severe winters
experienced in Northern Europe and the US since 2008. It's possible
it could also help scientists to more accurately predict the
severity of coming winters, as Adam Scaife from the UK Met Office
"Assuming these new satellite data are
correct... then as the 11-year solar cycle is predictable, it's
going to contribute some predictability for European and indeed UK
weather. You'll never be able to predict the precise temperature of
the third week in January or whatever, but you might be able to say
'this winter is more likely to be warm' or 'more likely to be cold'
with more accuracy."
In summary, if the satellite observations are correct, then
solar minima can cause more severe winters in the US and northern
So just how do some journalists jump from that to predicting a
"mini 'ice age'"?
During the late 17th and early 18th centuries there was a period
of low sunspot activity which lasted for around 70 years and
coincided with part of the what was (unhelpfully) labelled the 'Little Ice
Age' - a period of cooling affecting parts of the globe that
lasted around 300 years.
Now there seems to be a common mistaken belief that low solar
activity leads inevitably to the world entering a new ice age,
which confuses an actual ice age with the 'Little Ice Age'. This
conclusion disregards the wealth of scientific research in this
Whilst the sun's effect on climate is important, providing as it
does nearly all of the energy to power Earth's climate system, its
temperature effect is actually superimposed on the
more dominant climate forcing provided by increasing greenhouse
research disputes any notion that solar activity was the
dominant driver of the Little Ice Age. Furthermore, climate model
that a Maunder Minimum-type solar minimum would impose a
cooling of around 0.3 ˚C, which, although noteworthy, is marginal
compared to the projected warming of
2 - 4.5 ˚C likely to result from man-made greenhouse gas
emissions over the coming century.