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Arctic summers could be nearly ice free by 2050

  • 07 Mar 2013, 16:35
  • Freya Roberts

Source: Tom Thiel

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 people.

Open water

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 the journal 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 ocean.

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 conservative, underestimating how sensitive the Arctic is to rising temperatures. Given the speed of sea ice decline in recent years, their estimates seem increasingly optimistic.

So instead, many recent studies have used other forecasting approaches. The 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 loss.

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.

So it's 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 little longer.

Other studies using this approach suggest the Arctic could be ice-free in summer in the 2030s. One suggests that date could be around 2035, 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 yellow).

Models

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.

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