Arctic summers could be nearly ice free by 2050
- 07 Mar 2013, 16:35
- Freya Roberts
In the not-too-distant future, Arctic summers could be largely
ice-free. But pinpointing exactly when is not easy. A new analysis
of the most commonly-used methods suggests Arctic sea ice extent
could drop below one million square kilometres before 2050. And
when that happens, there will be consequences for climate and
Sea ice in the Arctic has
declined rapidly in the last few decades, in large
part due to greenhouse gas emissions. In September 2012, Arctic
sea ice reached its lowest
extent since satellite records began in 1979. A new study in
Geophysical Research Letters suggests that before 2050, Arctic
summers could be almost entirely ice-free.
The Arctic doesn't need to be completely ice-free to feel the most
significant impacts on climate and transport. As the ice melts,
sunlight that previously would have been reflected by ice is
instead absorbed by the ocean leading to
further warming. And as
new research out this week highlights, the shrinking and
thinning of sea ice means ships will be able to traverse old fabled
routes and cut new ones, straight across the centre of the
Forecasting sea ice
Climate model predictions made just
a few years ago suggested the Arctic was unlikely to become
largely ice-free until the end of the century. But climate models
can be too
how sensitive the Arctic is to rising temperatures. Given the speed
of sea ice decline in recent years, their estimates seem
So instead, many recent studies have used other forecasting
new research looks at the pros and cons of the three main tools
scientists have available - looking back at past patterns,
estimating how likely big melt events like the 2012 one are, and
using only climate models which predict the fastest rates of ice
Trends say 2020
One way to predict how sea ice might change in the future is to
look back at past trends and assume they will continue in the
future. Scientists have been using ice-ocean models, like the
Pan-Arctic Ice Ocean Modeling and Assimilation System
(PIOMAS), to simulate past changes in ice volume. But the
models can only look backwards, as scientists have to use wind and
temperatures from records to simulate changes in the ice.
To look forward, scientists would have to assume temperature and
wind patterns, which drive changes in sea ice, will be the same in
the future as they are now. But that won't necessarily be true,
since atmospheric conditions fluctuate naturally. These variations
can disguise a long term warming trend. That's especially important
since scientists can't rule out that these natural fluctuations
have altered Arctic
weather patterns in recent years.
not a perfect system. But if you assume current trends
continue, the authors say the Arctic could be ice-free by 2020.
Indeed, prominent scientists like Peter Wadhams have
used this approach to suggest we're looking at an ice-free
Arctic as soon as 2016.
Big melts say 2030
A second approach to predicting Arctic ice loss is to look at the
frequency of big melt events like the summers of 2007 and 2012.
Summers with unusually rapid sea ice loss accelerate the decline in
sea ice cover; melting some of the thicker and older ice which
normally survives from one year to the next. By looking at how
frequently these big melts occur, scientists can estimate how many
more it will take to reach a nearly ice-free Arctic.
It's quite an inexact approach, because scientist have to make
assumptions about how regularly big melts will occur in the future.
If it's once every five years, as recently experienced, the authors
say nearly ice-free conditions could be reached by 2028. But again,
if natural variability has sped things up recently, it could take a
Other studies using this approach suggest the Arctic could be
ice-free in summer in the 2030s. One suggests that date could be
and another puts it in the
"next few decades" - so perhaps between 2030 and 2040.
Rapid loss models say 2040
The third technique is to look only at specific climate models
which predict rapid ice loss. Climate models give a range of
predictions about when the Arctic might be ice free, as seen in the
graph below. Normally we look at their average (shown in
September sea ice extent projections under the RCP8.5 (high)
emissions scenario. Source:
Overland & Wang, 2013
But if we only look at models that match up with the rate of ice
loss in recent years (shown in black), the Arctic could be nearly
ice-free around the 2040s.
Using climate models has its advantages. Their predictions are
based on physical processes to a stronger degree than the big melts
approach, and simulate the ocean, ice and atmosphere altogether,
which the trend approach can't.
But there are drawbacks, too. Picking a subset from the wide range
of models that exists, simply because it fits current conditions,
is no guarantee that it accurately represents reality. In fact,
some of the subsets that seem to be a good fit at the moment don't
do a very good job of matching past changes.
Is one approach right?
Each of these methods to predict when the Arctic will be nearly
ice-free has its own merits. All three techniques rely on both
scientific grounding and expert opinion, but to different degrees.
The authors conclude that, for now, it's not possible to say one is
more likely to be right than the other.
It might seem that the methods are at odds - based on the current
trend method, the Arctic could be ice-free by around 2020. Judging
by the frequency of big melt events, it could be more like 2030.
And using worst-case scenarios from climate models, it could be
more like 2040.
Taken together, however, all three methods broadly suggest the
same thing - that Arctic summers could be nearly ice-free before
the second half of the century begins.