New research projects widespread permafrost thaw with 1.5 degrees of warming
- 21 Feb 2013, 20:00
- Roz Pidcock
A global temperature slightly warmer than today's could be
enough to cause widespread thawing of Arctic permafrost,
potentially releasing billions of tonnes of carbon dioxide into the
atmosphere, says a new study. We investigate what this really means
for the climate.
new research suggests that based on what's happened in the
Earth's past, global temperatures 1.5 degrees Celsius above
pre-industrial levels could cause vast areas of carbon-rich
permafrost to thaw. Global temperature has already risen
0.75 degrees since the turn of the 20th
What is permafrost?
Permafrost is permanently-frozen ground land in high latitudes.
concerned that as atmospheric temperatures
rise, heat penetrates further into the ground, causing
permafrost to thaw.
As the permafrost thaws, microbes degrade the carbon within it -
a process that releases carbon dioxide and methane into the
atmosphere. Methane is a powerful greenhouse gas - around 25 times
more effective at trapping heat than carbon dioxide
over a 100-year cycle.
So scientists are concerned that greenhouse gases released from
thawing permafrost could amplify global
warming. Further warming means more permafrost thawing and
so on, in a self-reinforcing cycle.
Understanding how permafrost has changed throughout earth's
history can offer clues about how sensitive it is to global
temperature. In the new study, scientists reconstructed how the
amount of permafrost in high northern latitudes has changed over
the past 500,000 years.
In that time, the earth has gone through several natural
temperature cycles with cold periods, known as glacials,
interspersed with warmer periods, known as
The team of UK, Russian, Swiss and Mongolian scientists
analysed samples of stalagmites and stalagtites from caves in
Northern Asia and Siberia, using radioactive dating
techniques to precisely determine their ages.
Stalagmites and stalagtites only grow when the temperature
is above zero degrees. So being able to date periods of growth
provides a record of when permafrost existed and when it
When the scientists compared their permafrost record against
global temperature changes over the last 500,000 years, they found
the two varied closely with one another. Perhaps unsurprisingly,
the most extensive permafrost thaw occurred in the warmest
interglacial, about 400 thousand years ago. At that time, global
temperatures were 1.5 degrees above pre-industrial
Today, permafrost exists north of about 60 degrees latitude
in the northern hemisphere - extending halfway down Russia and
Canada and spanning the whole of Greenland. During the warmest
interglacial, the permafrost boundary was pushed much further
north, the scientists say - meaning less permafrost
The researchers concluded that a similar level of warming in
the future - this time due to human rather than natural causes -
could have the same shrinking effect. And if permafrost does thaw
to this extent, it could lead to the "substantial release" of
carbon into the atmosphere.
While studies like this help pin down how sensitive
permafrost could be to temperature rise, they don't answer the
question of how much carbon is held in permafrost. As Professor
Julian Murton from the University of Sussex told Carbon
"[T]he area of permafrost in the
northern hemisphere is larger than the whole of Canada's land mass
(about 10 million square kilometres) and the number of [carbon
measurements] is very limited."
The new study is valuable, Murton added, but
more studies are needed to determine how the exchange of carbon
between the land and the atmosphere would be affected by a
similarly large shrinking event today.
Murton also warned that while the past can offer clues as to
how permafrost may develop in the future, there could be important
differences in vegetation and snow cover, which could affect how
quickly permafrost thaws.
Cause for concern?
Scientists have already found evidence that permafrost is
undersea in the Arctic and, more recently, in
Antarctic. This has led some media outlets
to talk about permafrost as
"the methane time bomb". We have discussed
the appropriateness - or otherwise - of this phrase before
We asked Professor Murton how worried we should we be about
thawing permafrost. He told us:
"With substantial global warming
projected during the 21st century, which almost certainly will be
amplified in Arctic regions (due to feedback effects in the global
climate system), we should be concerned about greenhouse gas
release from thawing permafrost."
But, he added that until scientists have more information
about where exactly the carbon is stored and how much there is,
it's difficult to predict exactly how much carbon dioxide or
methane could be released.
A question of timing
There is also an issue of
how long it takes for carbon to be released from
permafrost. As Professor David Archer, expert on the climate impact
of frozen carbon on land and under the ocean at the University of
Chicago, told us recently:
"[T]he release rate of carbon from both
of these sources [is] fairly slow, both in comparison with
present-day methane emissions from tropical wetlands, and relative
to fossil fuel carbon release as CO2."
So carbon released from permafrost is likely to have a
much smaller impact on climate in the near future than carbon
dioxide released from burning fossil fuels. Or as Archer put
"Don't worry about the methane, worry
about the carbon dioxide. If carbon dioxide emissions aren't
stopped, methane will just be a thin bit of frosting on the cake,
and if carbon dioxide is fixed, methane won't be a problem."
So carbon dioxide emissions from burning fossil fuels may
still the biggest source of global warming in the short term. But
with temperatures expected to rise to levels where widespread
permafrost thaw has occurred in the past, the release of carbon
from permafrost may well be important in climate projections for
the coming centuries.
Vaks. A et al., (2013) Speleotherms reveal 500,000-year history
of Siberian permafrost. Science DOI: 10.1126/science.1228729