Is climate change all just a recovery from the Little Ice Age?
- 16 May 2012, 14:36
- Verity Payne
The Little Ice Age, a cooler period of the Earth's recent
history, may have been a global event rather than confined to the
northern hemisphere, according to a paper
published last week.
Some climate skeptic blogs are
excited about this finding, and have taken it as a starting
point to argue that the rise in global surface temperature over the
last few decades is just a natural recovery from the Little Ice
Age, implying that it has nothing to do with, for example, man-made
emissions of carbon dioxide. We asked one of the co-authors of
the paper whether this is a valid interpretation.
The Little Ice Age (
LIA) was a period of colder than average temperatures and
glacier advance between 16th and mid-19th centuries. This new
paper adds to evidence suggesting that the LIA was a global event,
rather than a regional event - something that is still under
debate by scientists.
It documents temperature on the West Antarctic Ice
Sheet dipped to around half a degree Celsius cooler than
average between the years 1400 and 1800, according to a borehole
record. This roughly coincides with a more pronounced cooling
observed in records from Greenland, suggesting that the cooling was
probably global in scale.
Because it suggests a global effect, this paper lends weight to
theories that waning solar activity (the LIA coincides with a 70
year period of low solar activity called the 'Maunder Minimum')
and/or climate-cooling volcanic emissions caused the LIA, rather
than changes to oceanic currents.
Although the paper hasn't received any media coverage that we
can see, climate skeptic bloggers highlighted the research, saying
that its findings "imply that the 0.7C global warming since 1850
simply represents a recovery from the Little Ice Age."
We spoke to Jeffrey Severinghaus, Professor of Geosciences at
the University of California's Scripps Institution of Oceanography,
to find out whether he agrees with this interpretation of his work.
He calls such interpretations a "red herring", saying that whilst
the warming since 1850 is "in part due to the recovery from the
Little Ice Age", that doesn't hold true for warming of the last 50
years, which is a "very different animal" from the warming of the
last 160 years.
Severinghaus explained to us that the LIA is thought to have
"The Sun underwent an increase in its
energy output, especially in the ultraviolet part of the spectrum,
at the end of the Little Ice Age, and there was a lull in major
So the warming between 1850 to 1950 was:
"consistent with warming caused by
increases in solar output and decreases in climate-cooling
increase in solar output has occurred in the past 50 years,
and volcanism has not changed
significantly. These facts are undisputed. So
natural factors cannot explain the warming of the past 50
So in recent decades, the planet has warmed in a different
"The warming of the past 50 years has
been mostly at night, and it has been accompanied by profound
stratospheric cooling, both "fingerprints" of an unnatural
As we have pointed out in previous blogs, only considering the
surface temperature record does not tell the whole story about how
much the Earth's climate system has warmed. And, as Severinghaus
explained to us, assuming scientists base global warming theory
solely on the surface temperature record is not sound. He told
"The real basis for prediction of future
warming is that basic physics tells us that carbon dioxide absorbs
heat, and human emissions of this gas will cause (and are causing)
a rise in its atmospheric concentration. These facts are also
Severinghaus also cautioned against another common misconception
by climate skeptic commentators:
"We have long known that climate can
change for natural reasons. But to assert that this implies that
humans cannot also change the climate, is like saying that forest
fires cannot be set by careless campers because lightning also
causes forest fires. It is simply illogical. Climate change has