The BBC discusses changes in the sun - and why they don’t mean an ice age is on the way
- 09 Aug 2013, 12:15
- Roz Pidcock
Could changes deep within in the sun soon see us skating on a
frozen-over Thames? The question of the sun's role in climate
change - and the prospect of an icy future - pops up in the media
from time to time.
This morning, it was the BBC's turn on the Today Programme. The
slot did a pretty good job of explaining that although changes in
the sun have affected climate in the past, greenhouse gases are now
the dominant factor driving temperatures up.
topic was the imminent
flip in the sun's magnetic field, the force responsible for
driving sunspot activity. Steve Tobias, professor of maths at Leeds
University, explained how this switch happens about every 11 years,
when the sun's output is at the highest point in a natural
Asked whether the sun's waxing and waning contributes to climate
change. Professor Tobias explained:
"It does feed in but it's a very small
effect. The sun's total irradiance actually varies by a fraction of
a percent, so the direct forcing is very small … it may have
indirect effects for the climate but I think I should stress
current global warming trends are not really due to changes in the
Presenter Justin Webb pressed a bit more, saying "but years ago
the sun created an ice age, didn't it?"
The simple answer is yes. But as Tobias explained, human
activity is now the main driver climate change, not the sun - a
mistake that has led some parts of the media to suggest we're
headed for a '
mini ice age'. Here's a closer look at what the sun has to do
with our climate.
Scientists know changes in the sun's activity have
consequences for earth's climate. Chris Rapley, professor of
climate science at University College London, told Carbon Brief
"Climate science shows that the sun does
have an influence on climate; this is not controversial. The planet
responds to changes in the flux of energy that it intercepts from
Just this week, a paper in the journal
Nature described how variations in the
amount of solar energy reaching earth over the last million years
have been a major contributor to the ebb
and flow of earth's vast ice
On shorter timescales, the sun's energy also rises and falls on
an 11-year cycle. The graph below shows how solar activity has
changed in the last four centuries.
"Mini ice age"
As Tobias explains, the sun went through a period of prolonged
solar activity beginning in the late 17th Century - known as
the Maunder Minimum. This lasted for around 70 years and coincided
with the beginning of what's known as the Little Ice
During the LIA, parts of the northern hemisphere cooled by as
much as two
degrees Celsius - causing the River Thames to freeze over
Could it happen again? The sun's activity has been in
slow decline for the last few decades. Scientists
have speculated that the trough as part of the next 11-year
cycle (called 'cycle 25') could be a
particularly low one - perhaps even
another Maunder-style minimum.
This has led some commenters and
parts of the media of the media to conclude that we are on the
verge of another LIA. There are two reasons why this is wrong.
The sun is not the only factor
Recent research suggests the Maunder Minimum was only
one factor in bringing about the LIA. In fact, it may be more
closely linked to unusually intense volcanic activity and
interactions between sea ice and ocean currents during the
At a recent
conference, scientists explained how a major atmospheric
circulation known as the North Atlantic Oscillation (NAO)
was in a negative phase at the onset of the LIA, which amplified
the cooling effect of a reduction
in solar output and volcanic activity.
This, in turn, affected the distribution of sea ice in the
Arctic and disrupted a major ocean circulation that distributes
heat across the globe, known as the Atlantic Meridional Overturning
In other words, a fall in temperature to rival the LIA would
need more than a drop in solar activity.
Bigger human influence
Even if we did see a return to a Maunder-style low in solar
activity, earth's climate is very different now to how it was in
the 17th century.
Scientists have modelled the expected temperature
drop over the 21st century due to waning solar activity - and
they found that the change is likely to be dwarfed by the much
bigger warming effect of greenhouse gases in the
This echoes the IPCC's
last report on the science underpinning climate change. It
"In today's atmosphere, the radiative
forcing from human activities is much more important for current
and future climate change than the estimated radiative forcing from
changes in natural processes."
In other words, changes in the sun's activity might have a small
but noticeable effect on earth's temperature, if man-made
greenhouse gases weren't having a much bigger one.