The extent of Arctic sea ice on Aug. 26, 2012, the day the sea ice dipped to its smallest extent ever recorded in more than three decades of satellite measurements. The line on the image shows the average minimum extent from the period covering 1979-2010. Click on the image for a larger version. Credit: NASA/JPL.
The National Snow and Ice Data Center announced Monday that Arctic sea ice is at its lowest extent since satellite observations began in the 1970s. The previous record, set in 2007, saw the Arctic Ocean covered with 1.61 million square miles of ice, but on Sunday, the coverage was just 1.58 million square miles. What makes this milestone especially significant is that there are still two or three weeks left to go in the melt season.
“We still have a little time left,” said NSIDC’s Julienne Stroeve in an interview, “but the rate of melting in August has been really fast, the fastest we’ve ever seen.” It’s starting to slow down, she said, “but I doubt we’ve seen the true minimum.”
It’s not just a new Guinness record that’s at stake here. The rapid decline in Arctic sea ice during the past several decades is one of the most visible signs of manmade global warming.
Arctic ice, whether on land or on the sea, is a powerful reflector that bounces a lot of sunlight back into space rather than letting it warm the Earth. When that ice melts, it exposes the darker ground or water underneath, turning the region into an energy absorber rather than a reflector. Sea ice is especially vulnerable to melting, and over the past 30 years or so there’s been a downward trend in sea ice coverage in summer. The result is a feedback loop that accelerates global warming, with melting ice leading to more warming of the water below leading to more melting
The Arctic is warming at nearly twice the rate of the rest of the globe, largely due to those feedback loops. In addition, recent research shows that the loss of sea ice cover may be contributing to extreme weather events throughout the Northern Hemisphere, and may be partly responsible for major cold air outbreaks and paralyzing snowstorms in the northeastern U.S. and western Europe during the past few years.
This trend isn’t perfectly steady, since year-to-year weather conditions can affect the melt for a particular season. In 2007, for example, Stroeve said, wind patterns brought warm air into the region and pushed significant amounts of ice out of the Arctic ocean. “This year,” she said, “conditions were kind of chaotic. We did have a big storm in August that broke the ice into smaller pieces, but the breakup was easier because the ice was already thin."
The ice was thin in large part because of the meltbacks in previous summers. In places where the ice doesn’t melt, any additional freezing that happens during the winter can make the so-called multi-year ice even thicker. In places where it does melt, by contrast, the winter refreezing creates thinner first-year ice, which can melt with relative ease the following summer. Since 1980, the average thickness of Arctic sea ice has been cut nearly in half.
That trend is virtually certain to continue, until at some point the Arctic Ocean will be completely ice free for at least part of the summer, turning the planet’s greatest heat shield into a global-warming accelerator. Exactly when that will take place isn’t clear. “Current models show this happening before 2050,” Stroeve said. “But the trends we observe make me think it could happen earlier than that.”
The record loss of Arctic sea ice this summer will echo throughout the weather patterns affecting the U.S. and Europe this winter, climate scientists said on Wednesday, since added heat in the Arctic influences the jet stream and may make extreme weather and climate events more likely.
The “astounding” loss of sea ice this year is adding a huge amount of heat to the Arctic Ocean and the atmosphere, said Jennifer Francis, an atmospheric scientist at Rutgers University in New Jersey. “It’s like having a new energy source for the atmosphere.” Francis was one of three scientists on a conference call Wednesday to discuss the ramifications of sea ice loss for areas outside the Arctic. The call was hosted by Climate Nexus.
On August 26, Arctic sea ice extent broke the record low set in 2007, and it has continued to decline since, dropping below 1.5 million square miles. That represents a 45 percent reduction in the area covered by sea ice compared to the 1980s and 1990s, according to the National Snow and Ice Data Center (NSIDC), and may be unprecedented in human history. The extent of sea ice that melted so far this year is equivalent to the size of Canada and Alaska combined.
The loss of sea ice initiates a feedback loop known as Arctic amplification. As sea ice melts, it exposes darker ocean waters to incoming solar radiation. The ocean then absorbs far more energy than had been the case when the brightly colored sea ice was present, and this increases water and air temperatures, thereby melting even more sea ice.
Peter Wadhams, the head of the polar ocean physics group at the University of Cambridge in the U.K., told BBC News on September 6 that the added heat from sea ice loss is equivalent to the warming from 20 years of carbon dioxide emissions. Carbon dioxide is the main greenhouse gas that is causing manmade global warming.
During the fall, when the sun sets once again and the Arctic Ocean begins to refreeze, the heat in the ocean gets released back into the atmosphere. Since the jet stream, which is a corridor of strong winds at upper levels of the atmosphere that generally blows from west to east across the northern mid-latitudes, is powered by the temperature difference between the Arctic and areas farther south, any alteration of that temperature difference is bound to alter the jet stream — with potentially profound implications. It just so happens that the jet stream steers day-to-day weather systems.
Francis published a study last year in which she showed that Arctic warming might already be causing the jet stream to become more amplified in a north-south direction. In other words, the fall and winter jet stream may be getting wavier. A more topsy-turvy jet stream can yield more extreme weather events, Francis said, because weather and climate extremes are often associated with large undulations in the jet stream that can take a long time to dissipate.
“We know that certain types of extreme weather events are related to weather that takes a long time to change,” Francis said.
While there are indications that the jet stream is slowing and may be more prone to making huge dips, or “troughs,” scientists have a limited ability to pinpoint how this will play out in the coming winter season.
“The locations of those waves really depends on other factors,” Francis said, such as El Niño and a natural climate pattern known as the Arctic Oscillation. “I can only say that it’s probably going to be a very interesting winter,” she said.
Francis’ work has linked Arctic warming to the unusually cold and snowy winters of 2009-10 and 2010-11, during which the U.S. East Coast and parts of Europe were pummeled by fierce winter storms and experienced cooler-than-average conditions. The winter of 2011-12 was much milder, by comparison, but Francis said it, too, was consistent with her research. Not all meteorologists agree on the Arctic connection theory, but that may change with time.
Jim Overland, an oceanographer at NOAA's Pacific Marine Environmental Laboratory, said the inconsistency of the past three winters doesn’t mean the Arctic connection hypothesis is invalid.
“People like direct causality, [the notion that] if you lose the ice every year it will cause the same effect,” Overland said. But the chaotic nature of the atmosphere means that all that scientists can say with a high degree of confidence is that “the number of [extreme] events somewhere are destined to increase” as a result of rapid Arctic climate change, Overland said.
Jennifer Francis is a research professor at the Institute of Marine and Coastal Sciences at Rutgers University (Ph.D Atmospheric Sciences from University of Washington).