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Sea ice breaking up in spring, near Kulusuk, Greenland.
Sea ice breaking up in spring, near Kulusuk, Greenland. Credit: steve_is_on_holiday/E+/Getty Images.
SEA ICE
13 March 2017 16:04

Humans causing up to two-thirds of Arctic summer sea ice loss, study confirms

Roz Pidcock

Roz Pidcock

03.13.17
Roz Pidcock

Roz Pidcock

13.03.2017 | 4:04pm
Sea iceHumans causing up to two-thirds of Arctic summer sea ice loss, study confirms

Rising greenhouse gas emissions are responsible for at least half, possibly up to two-thirds, of the drop in summer sea ice in the Arctic since the late 1970s, according to new research. The remaining contribution is the result of natural fluctuations, say the authors.

The paper, published today in Nature Climate Change, confirms previous studies which show how random variations in the climate have acted to enhance ice loss caused by rising CO2.

Importantly, the authors state clearly in the paper that their work does not absolve human activity as a driver of Arctic sea ice loss. A News and Views article that accompanies the paper, by Dr Neil Swart from Environment and Climate Change Canada, adds:

“The results of Ding et al. do not call into question whether human-induced warming has led to Arctic sea-ice decline — a wide range of evidence shows that it has.”

Shifting patterns

With temperatures rising at more than twice the speed of the rest of the globe, the Arctic is the fastest warming place on Earth.

Arctic sea ice extent is declining in every season, but particularly quickly in September, when the ice reaches its lowest extent for the year. Since the beginning of the satellite record in 1979, Arctic sea ice cover in September has decreased by around 13% per decade.

Average Arctic sea ice extent for the month of September between 1979 and 2016. Black line shows annual data, and blue line shows the long-term trend. Credit: NSIDC

Average Arctic sea ice extent for the month of September between 1979 and 2016. Black line shows annual data, and blue line shows the long-term trend. Credit: NSIDC

Scientists know the shrinking of Arctic sea ice is, in part, down to greenhouse gases warming the atmosphere and ocean. Today’s study suggests natural factors may have contributed between 30-50% of the decline since 1979, by changing the way air circulates in the Arctic region.

The authors point to stronger summer circulation over Greenland and the Arctic Ocean in areas where sea ice loss in September is highest. The Beaufort, Chukchi and East Siberian Seas have together experienced an average decline of more than 10% per decade, the paper notes.

The changes in atmospheric circulation in the Arctic, thought to originate in the tropical Pacific, increase the amount of water vapour in the lower atmosphere, the paper explains. Together with a shift to fewer clouds, this has increased the amount of solar radiation reaching the ice.

Human contribution

In many ways, the new study is unsurprising since scientists already know that natural variability is driving some of the long-term trend, notes Dr Ed Blockley, polar climate manager at the Met Office Hadley Centre, who wasn’t involved in the study. He says:

“It has long been known that the observed decline in Arctic sea ice, caused by global warming, is also being enhanced by the influence of natural variability in the climate system.”

Neither is the new study surprising in the size of the contribution it attributes to natural variability, says Prof Julienne Stroeve, professor of polar observation and modelling at University College London. She tells Carbon Brief.

“Several papers, including those published by myself, have shown that 50-60% of the ice loss is a result of greenhouse gases, leaving the other 40-50% from natural climate variability.”

The authors themselves say in the paper that their result is “perhaps not surprising” given past estimates that have come up with a similar ball-park figure for the role of natural variability.

The paper is, perhaps, useful in adding more detail to the evolving picture of Arctic sea ice loss, says Dr Twila Moon, a lecturer in cryospheric sciences at the University of Bristol. She says:

“This well-designed study provides the best detail yet to determine how much Arctic sea ice decline is caused by humans and how much is natural environmental change.”

Being able to separate human influence from the effects of natural climate variability helps build a better understanding of what we should expect in the future, says Dr Amber Leeson, a lecturer in glaciology and environmental data science at Lancaster University. The Arctic has been losing summer sea ice much faster than the majority of climate models forecast, she says:

“This research helps explain why predictions of sea ice change made by climate scientists have traditionally underestimated the rate of ice loss over this period.”

This faster-than-expected decline has prompted questions over whether the models used to simulate Arctic sea ice are too conservative, explains Dr Ed Hawkins, a specialist in Arctic sea ice predictability at the University of Reading. He tells Carbon Brief:

“This study suggests that part of this difference may be due to natural atmospheric variations which are causing the sea ice to melt faster than some models have simulated.”

Expectations

Scientists are interested in predicting when the Arctic will become “sea ice-free” in summer – defined as the point at which sea ice extent falls below one million square kilometres. Hawkins tells Carbon Brief:

“Looking ahead, it is still a matter of when, rather than if, the Arctic will become ice-free in summer, but we expect to see periods where the ice melts rapidly and other times where it retreats less fast.”

As of 12 Mar, sea ice extent remains at a record low, following the lowest February extent in the 38-year satellite record. Source: NSIDC

As of 12 Mar, sea ice extent remains at a record low, following the lowest February extent in the 38-year satellite record. Source: NSIDC

Taking a closer-range view, should we be expecting a record low in summer in 2017?

We don’t really know yet how the summer will shape up, says Stroeve, but the sea ice is particularly vulnerable as we go into this year’s summer melt season, she tells Carbon Brief:

“If we have a favourable weather pattern, such as we saw in 2007, then I wouldn’t be surprised to see this summer reach a new record low…We will have to wait and see.”

Before that, there’s another event that scientists often use to benchmark how one year’s ice cover compares to another. Around March each year, Arctic sea ice reaches its highest extent for the year. With sea ice extent remaining low, following the lowest February extent in the 38-year satellite record, Carbon Brief will be keeping a close eye on how conditions proceed.

Ding, Q. et al., (2017) Influence of high-latitude atmospheric circulation changes on summertime Arctic sea ice DOI: 10.1038/NCLIMATE3241

Sharelines from this story
  • Humans causing up to two-thirds of Arctic summer sea ice loss, study confirms
  • Jai

    Clearly this study reflects the inaccuracy of the CMIP5 ensemble to adequately capture the impact of SE Asian aerosol emissions on the Inter-Tropical Convergence Zone (ITCZ) and the additional tropopause height reductions cased by SO2-driven upper troposphere cooling in the Pacific tropics. If these were adequately modeled, we would see that the long-term negative IPO through the mid 2000s was driven by increased SO2 emissions and that the expansion of tropical water vapor is anthropogenic but suppressed by these emissions (which are rapidly being reduced).

  • “The changes in atmospheric circulation in the Arctic, thought to
    originate in the tropical Pacific, increase the amount of water vapour
    in the lower atmosphere, the paper explains. Together with a shift to
    fewer clouds, this has increased the amount of solar radiation reaching
    the ice.”

    So when can we expect this natural variability to flip back again and see a reduction in the rate of Arctic sea ice loss? Is it controlled by the PDO or ENSO?

    I thought the high pressure was moving over Greenland because that’s the only place cold enough for it to form (Cold Pole)?

    I’m also not sure about the shift to fewer clouds, as there’s an increase in water vapour over the Arctic, coming from lower latitudes and from the Arctic Ocean itself, because of Arctic sea ice loss. In fact, increased cloudiness in autumn and winter (especially these past two winters) are causing record low maximums, this year for both extent and volume.

    All in all, I feel that this is all very theoretical and these scientists aren’t paying enough attention to what is happening on the ground. We may have passed the point where our knowledge on the Old Arctic has become moot.

    • Jai

      “We may have passed the point where our knowledge on the Old Arctic has become moot.”

      This is normal when a rapid transition occurs between bifurcated states

  • john

    Ice is going
    Any dispute with this fact is dismal

  • Bob Wilson

    The paper would be much improved had they modeled more than three months of the Arctic melt and chosen more wisely the anthro climate studies. You can’t melt what wasn’t frozen. Within the narrow time scope, understandable but the Arctic does not start each season with the same inventory of sea ice.

    I am sympathetic to averaging 32 climate models but according to Berkeley Earth some are better at global predictions and others focused on regional effects like SE monsoons. As for asserting the average of 32 models accounts for anthro effects, I prefer a little more details about specifics. For example, dirty snow.

    However kudos for describing the mechanics of summer Arctic ice melt and weather. Eventually weather and climate models will converge and we will be pleased to see this happen.

    My interest in this paper was sparked by outrageous claims by lay press reports that cherry picked for sensational titles. That was not the fault of the authors. It is the times we live in.

    Bob Wilson

  • My own article on this topic looks as much at the reporting of the paper as its substance:

    http://GreatWhiteCon.info/2017/03/is-arctic-ice-loss-driven-by-natural-swings/

    It’s grist to the mill of the “skeptical” porky pie production line. Cue a gazillion retweets of the Daily Fail’s “HALF of Arctic ice loss is driven by natural swings and not global warming, controversial study claims”.

    Meanwhile in the latest news from the beleaguered Arctic, the 2017 sea ice extent maximum is the lowest in the satellite era record:

    http://GreatWhiteCon.info/wp-content/uploads/2017/02/NSIDC-Max-2017.png

    Do you suppose that the “atmospheric general circulation model coupled with a simple ocean–sea-ice model” employed by Ding et al. really captures the dynamics of the “New Arctic”?


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