I picked this up with
some interest over the Christmas break as family conversations turned to the
nature of our cold weather, and the recollection of winters past when the
Thames froze – actually something I recall from my childhood although the river
did not freeze as far down as London and the tidal sections of the river. The
debate was around the possibility of a temporary reversal of global warming,
even a mini ice age, perhaps allowing for time for us to find solutions to the
greenhouse gas problem and to adapt to change. The idea seemed interesting and
prima facie credible, but further investigation emphasised the need for more
caution and slightly less optimism. We all agreed this was no reason to reduce
concerns over climate.
……………………………………………..
A model of the Sun's magnetic activity suggests the River Thames may
freeze over within two decades, experts say.
Global Warming Overridden by “mini ice age” that will plunge UK
temperature in 2030, claim mathematicians.
According to research from universities in the UK and Russia, we could
be skating on the Thames in just over a decade.
A flurry of headlines on climate science, including Sky
News , the Mirror,
the Sun,
illustrate the difficulties of reporting serious science and the temptations of
sensational headlines. The fake news sits in the exaggerated headlines, and in
this instance there is an important kernel of real fact which, if the solar
activity projections are correct, may be relevant both to expectations about
climate and potentially to climate policy.
The story is not actually new, but has resurfaced with some particular
publications by scientists working in the field of astrophysics who believe they
have identified some interesting and potentially important features in the
solar cycle. Solar activity, popularly
known as “sunspots”, has often been suggested as a credible explanation of
variations in climate over relatively short periods of a few years, with lower
activity reducing the amount of energy reaching Earth from the sun. The current
story discusses a projected downturn in solar activity over the next 20 – 30
years, starting as early as 2020. One
figure quoted has been the expectation of a 60% downturn in solar activity over
this period, although this translates into a reduction in the energy we receive
from the sun that is an order of magnitude smaller.
Press reports had quickly transformed this story into the
prospect of a mini Ice Age, with the Thames expected to freeze over by 2023,
and the possibility that this would save the world from the devastation of
climate change I was perfectly prepared,
perhaps being of a gullible or over-optimistic disposition, to accept the
reporting at its face value, and to treat the story as mildly encouraging. If it
was correct, then at a minimum it implied more time to put in place measures to
adapt to climate change, and possibly even to develop the technologies that
might allow us to manage or even reverse dangerous concentrations of greenhouse
gases (GHG).
A reality check followed. This is what emerged.
The sunspot story. There is serious research (Professor
Zharkova et al) which forecasts coincidence of cycles in the sun’s activity,
resulting in reduced solar activity. This will result in less energy reaching
Earth, though the reduction is quite small.
Their work presents a model for the sun's magnetic field and sunspots,
which predicting a 60% fall in sunspot numbers when extrapolated to the 2030s.
Crucially, the paper makes no mention of climate. A first failure of science communication was
the Royal Astronomical Society press
release from July 9. This stated that "solar activity will fall by 60
per cent during the 2030s" without clarifying that this "solar
activity" refers to a fall in the number of sunspots, not a dramatic fall
in the life-sustaining light emitted by the sun. A 60% fall in solar energy
would most likely extinguish most life on the planet.
Comparison with earlier “mini ice ages”. This relates to a previous period of "prolonged
sunspot minimum", the so-called Maunder Minimum, between about 1645 and 1715, which coincided with unusually cold
weather believed to have a significant influence on climate. There is
therefore some historical evidence, even after allowing for the more limited
nature of observation and measurement in that period, of low solar activity being
associated with significant cooling.
However even this assertion must be qualified. That mini ice age began before the Maunder minimum
and may have had multiple causes, including the incidence of volcanic eruptions.
Moreover the previous mini-ice age will almost certainly have built gradually,
with ice cover an important part of the mechanism. Whether that mechanism can
be relied on in the immediate future, with shrinking ice caps, is more
debatable.
Will it reverse global warming? The warming effect from more CO2 greatly outstrips the
influence from changes in the Earth's orbit or solar activity, even if solar
levels were to drop to Maunder Minimum levels. There is 40 percent more carbon
dioxide in the air now than during the 17th century. A new Maunder Minimum might
slow climate change, but it is not enough to stop it. Some estimates however suggest
an effect on global temperatures of about a 0.3oC reduction. If
correct, this is a substantial and welcome effect.
Should we relax our efforts to reduce emissions? The answer is clearly not. A Maunder Minimum may conceal
some of the underlying warming trend for a period, but the solar cycle will of
course revert at some point, with an acceleration of warming. Reacting to a
short term movement in what is now a well established trend would be dangerous
or even disastrous on a longer term perspective.
Conclusions. This is an interesting and important element
in the science, although it is still imperfectly understood. We may well see a Maunder
Minimum effect, although it seems unlikely to freeze the Thames in any of its
tidal range. What is important is that we are able to interpret the effect as
accurately as possible as we observe global climate in the years ahead.
