Solar Activity and the so-called “Little Ice Age”
- 01 Nov 2013, 12:55
- Professor Mike Lockwood
I'm a professor of space environment physics and
a director of research at the University of Reading in the UK. My
particular topic of research is the sun, how it changes over time
and how those changes affect the space environment, the weather and
the climate on Earth.
In the last few years, my work has focused on how
temperatures in the northern hemisphere have responded to periods
in history when the sun has been very quiet. The "activity" of the
sun's magnetic field is related to the number of sunspots that
appear on its surface.
The sun's activity rises and falls on an
approximately 11-year cycle, but also varies on century-long
timescales. It's this research I talked to BBC weatherman Paul
Hudson about in an
interview for the BBC's Inside Out
Unfortunately, I now find myself in the position
cited as predicting that the current rapid decline in solar
activity will plunge the world into a "Little Ice Age".
This is very disappointing as it is not at all
supported by the science.
Weather and climate are inherently complicated -
and uncovering and attributing past changes is very difficult. So
it's worth being clear about the state of the science, as well as
some of the myths, misconceptions and misnomers that abound in this
The "Little Ice Age" wasn't really an ice
Let us start with the term "Little Ice Age". I
personally dislike it and avoid using it, as I don't think it was
an ice age at all.
There is some evidence for a prolonged period of
somewhat lower global mean temperatures beginning in around 1400 to
1500 (estimates vary) and ending sometime between 1700 and
This has been termed the "
Little Ice Age" and is often wrongly linked with the Maunder
minimum in solar activity, a period between about 1650 and 1700
when almost no sunspots were seen.
Annual averages of sunspot numbers since
1650. The Maunder minimum is marked MM. Source: Lockwood et al., (
Indeed, some reports even use the terms "Maunder
minimum" and "Little Ice Age" interchangeably. But the period known
as the "Little Ice Age" began a long time before the start of the
Maunder minimum, and continued long after it ended.
There is very little evidence that the lower
global mean temperatures between 1400 and 1800 were caused by solar
activity - there's more evidence it was associated with volcanic
activity and/or internal
oscillations in the climate system.
During the Maunder minimum there were an
unusually large number of cold winters in Europe. However, there is
no evidence that this was a global phenomenon. Indeed,
our research strongly suggests it was a regional phenomenon and
that the colder winters in Europe would have been accompanied by
warmer ones elsewhere, for example Greenland.
Calling this period of more frequent cold
European winters a "Little Ice Age" or a "mini Ice Age" is hugely
misleading as it implies Europe experienced unremitting cold
throughout the Maunder minimum. This is completely wrong. A good
example of why comes from the Central England Temperature (CET) record,
which extends continuously back to 1659.
If we take the winter averages (December, January
and February) we find the coldest winter on record was 1683/4 -
right in the middle of the solar Maunder minimum. However just two
years later, and still right in the middle of the Maunder minimum,
we have the sixth warmest winter in the whole 353-year CET
What's more, there's no evidence that summers in
the Maunder minimum were any colder than usual. This is not a
"Little Ice Age" - it is not an ice age of any shape or form.
Evidence is growing for a regional effect
of low solar activity
Much of what has been written in the media and on
the internet fails to appreciate the difference between
regional and global climates. My research looks at a potential
link between low solar activity and cold European winters. That's a
regional and seasonal effect and not a global effect.
Statistically, we found a
significant link between the occurrence of cold winters in the long
CET record and solar activity. By "significant" we mean that there
was only a five per cent chance that we were being fooled by a
Using methods like
numerical modelling, we're getting a better understanding of
what could be driving the relationship. The likely mechanism is
that changes in solar ultraviolet output alters the temperature
distribution and winds in the stratosphere in winter and this, in
turn, disrupts the northern-hemisphere jet stream, causing more
frequent "blocking" events.
Analysis of the effect of low solar activity
on winter surface temperatures via blocking events for 1976-2010.
Blue areas are colder than average, orange are warmer. Source:
Lockwood et al., (
This potential mechanism is still a matter of
vibrant debate in the academic community because it is difficult to
understand how the very thin atmosphere in the stratosphere can
influence the much denser troposphere below, where our weather and
Another Maunder minimum would have a very
small effect globally
What is most interesting for me is the current
decline in solar activity. The "exceptional" low minimum in the
11-year solar cycle seen in 2008/9, and the subsequent weakness of
the current solar cycle, are both part of a steady decline that has
been going on since about 1985. This has returned the sun to
conditions last seen around 1910.
this to records of solar activity derived from isotopes stored in
tree trunks and ice sheets we find this decline is faster than any
in the last 9,000 years, increasing the probability that the sun
will return to Maunder minimum conditions within about 50
So what do we think the effect of a return to
Maunder minimum conditions on global mean temperatures would be?
The answer is very little.
In a paper with
scientists from the Met Office's Hadley Centre, we used an energy
balance model to show the slowing in anthropogenic global warming
associated with decline in solar irradiance to Maunder minimum
We found the likely reduction in warming by 2100
would be between 0.06 and 0.1 degrees Celsius, a very small
fraction of the warming we're due to experience as a result of
human activity. Other scientists such as Georg Feulner and Stefan
Rahmstorf from Potsdam, Germany had reached very similar
I've also used observations from the last 50
years to investigate the effect of solar activity on global
temperatures - and like several other authors, I find only a very
You can see this in the graph below from the
recently released IPCC
report. The top panel is global temperature since 1890 and the
other panels show how different factors have contributed to the
changes we've seen. The pink lines are taken from my
Source: Intergovernmental Panel on Climate
Change (IPCC) 5th Assessment Report (
AR5) Chp 10, Figure 10.5 (p10-114).
In the fourth panel, you can see solar activity
has had negligible long-term effect. Compare that to anthropogenic
(human-caused) emissions in the next panel down.
The decline in solar activity right now is
incredibly interesting. It can tell us a great deal about how solar
variability arises and it is giving us new insights as to what the
sun during the Maunder minimum was really like.
Our research tells us very clearly that this
decline has only very small implications for global climate, but it
does also indicate that Europe may have to get used to a higher
frequency of colder winters. These conclusions in no way contradict
each other and I think they are both interesting and