Arctic summers to be ice-free earlier?

NOAA scientists in Arctic Canada basin, July 2005
Photo: NOAA, Jeremy Potter

Scientists studying Arctic sea ice say ice-free summers could be on the horizon sooner than many expected. A new analysis by NOAA scientists James Overland (NOAA Pacific marine Environmental Laboratory) and Muyin Wang (NOAA Joint Institute for the Study of Atmosphere and Ocean at the University of Washington) considered three methods of predicting when the Arctic will be nearly ice free in the summer. All three suggest nearly ice-free summers in the Arctic before the middle of this century, says Wang, although the actual dates differ widely. One method suggests the Arctic could be nearly sea ice free in summer as early as 2020.

“Rapid Arctic sea ice loss is probably the most visible indicator of global climate change; it leads to shifts in ecosystems and economic access, and potentially impacts weather throughout the northern hemisphere,” said Overland. “Increased physical understanding of rapid Arctic climate shifts and improved models are needed that give a more detailed picture and timing of what to expect so we can better prepare and adapt to such changes. Early loss of Arctic sea ice gives immediacy to the issue of climate change.”

The paper was published recently online  in Geophysical Research Letters.

Overland said the differences between the models could lead some people to conclude that models are not useful. In fact the opposite is the case, he said. “Models are based on chemical and physical climate processes and we need better models for the Arctic as the importance of that region continues to grow.”

Taken together, the range among the multiple approaches still suggests that it is very likely that the timing for future sea ice loss will be within the first half of the 21st century, with a possibility of major loss within a decade or two, the authors say.

Other recent studies have indicated the key role of shrinking Arctic sea ice in influencing our weather. The shrinking sea ice is shifting polar weather patterns, especially in autumn and winter, according to one new climate modeling study.

Researchers looked at weather patterns in 2007, when sea ice covering the Arctic Ocean hit one of its lowest summer extents since satellite tracking began in the late 1970s.

In autumn and winter, when sea ice would normally insulate the ocean from frigid Arctic air temperatures, the small ice pack meant lots of heat could escape from the ocean into the atmosphere, the study found. The heating changed  atmospheric circulation patterns in the Arctic, said study leader Elizabeth Cassano, a climate scientist at the Cooperative Institute for Research in Environmental Sciences (CIRES) in Boulder, Colorado. The results were published May 21 in the International Journal of Climatology.

Becky Oskin from LiveScience talked to Cassano about the study and quotes:  “What we saw, particularly in the fall and winter, was a decrease in [atmospheric] pressure over the areas of open water.” Areas of high and low pressure drive weather, with low pressure producing stormier weather and high pressure leading to clear, calm days, Cassano said. The group’s computer model generally agreed with weather records from the latter half of 2007, according to the study.

While the summer ice melt had a significant effect into the winter, there was little change in weather patterns in early 2007, before the ice pack shrank, the study found. However, Cassano points out that the climate model doesn’t include a major high-pressure system that was in the Beaufort Sea north of Alaska and played a role in the big ice melt. Its absence could affect the modeling results.

Arctic sea ice, courtesy NOAA

The researchers now plan to examine how the feedback between sea ice and the atmosphere alters weather in the United Statse and other regions, Cassano said. “There’s an open question of how these changes that we see in the Arctic influence the weather that we see here in the mid-latitudes,” she said.

 Given the weird weather we are experiencing in different parts of Europe at the moment, interest in whether climate change could be directly or indirectly responsible is high. Finnish Lapland has been experiencing a heatwave. Colleagues of mine have returned from the south of France complaining it was unexpectedly cold. Here in the normally mild Rhineland, we have also had very low temperatures and heavy rain. Meanwhile southern and eastern parts of Germany are being hit by severe flooding.

Renowned German scientist Stefan Rahmstorf and his colleagues at the Potsdam Institute for Climate Impact Research have apparently been contacted by various media, asking them if the rain and flooding are connected to climate change. He refers readers to a study on extreme weather they published in Nature Climate Change a year ago. Let me close by sharing his quote from that study, which he shares again in the climate blog SciLogs:

“Many climate scientists (including ourselves) routinely answer media calls after extreme events with the phrase that a particular event cannot be directly attributed to global warming. This is often misunderstood by the public to mean that the event is not linked to global warming, even though that may be the case — we just can’t be certain. If a loaded dice rolls a six, we cannot say that this particular outcome was due to the manipulation — the question is ill-posed. What we can say is that the number of sixes rolled is greater with the loaded dice (perhaps even much greater). Likewise, the odds for certain types of weather extremes increase in a warming climate (perhaps very much so). Attribution is not a ‘yes or no’ issue as the media might prefer, it is an issue of probability. It is very likely that several of the unprecedented extremes of the past decade would not have occurred without anthropogenic global warming. Detailed analysis can provide specific numbers for certain types of extreme, as in the examples discussed above.

In 1988, Jim Hansen famously stated in a congressional hearing that “it is time to stop waffling so much and say that the evidence is pretty strong that the greenhouse effect is here”. We conclude that now, more than 20 years later, the evidence is strong that anthropogenic, unprecedented heat and rainfall extremes are here — and are causing intense human suffering.”