Up to half of the Arctic's melt might be totally natural



Scientists have known for a while that the Arctic is melting. The signs are everywhere—from the famed Alaskan Iditarod course being moved multiple times due to lack of snow, to the emergence of starving polar bears with nowhere to hunt.

But while scientists are certain that the Arctic is melting at an alarming rate, they aren't really sure why.

Although anthropogenic climate change accounts for some of the melting, Arctic ice is disappearing much faster than climate change models predict it should. A new study in Nature Climate Change sheds new light on the mystery.

"There is a mismatch between the model's output and the observation," said lead author Qinghua Ding, a professor in the Geography Department at the University of California Santa Barbara. "Observation shows very fast, very abrupt sea ice melting, whereas the climate model cannot capture the fast melting."

arctic sea ice trends

Neil Swart / Nature Climate Change

September Arctic sea-ice extent. The red line shows satellite observations, and the grey lines show 50 possible alternative realizations of internal variability, derived from the (mean adjusted) Canadian Earth System Model version.

To understand why, Ding and his team focused on the connection between September sea-ice extent (or how much of the Arctic sea had at least 15 percent sea ice) and the preceding summer's (June-August) atmospheric circulation. Ding knew from earlier work that tropical circulation can affect seasonal variability of sea ice in the Arctic.

Under normal conditions—in other words, when climate change isn't a factor—the North Atlantic Oscillation (a weather phenomenon due to a mass of air over Greenland that controls wind patterns and storm tracks) causes year-to-year weather variability in the Arctic. When the North Atlantic is in its positive oscillation (circulating from left to right), it keeps the jet stream high and keeps cooler air in the Arctic. When it's in its negative oscillation, it allows the cooler air to escape the Arctic, resulting in warmer Arctic temperatures. These are broad trends, and some areas can warm up during a negative oscillation and vice-versa—but the Arctic overall will behave accordingly. What Ding's previous work showed was that tropical air patterns from the Pacific can affect the North Atlantic Oscillation. The new study uses this knowledge to model how these natural patterns change the Arctic.

"In the model we turned off all CO2 forcing," said Ding, or all climate changes that were "forced" by the addition of carbon dioxide into the atmosphere. "And we still got some sea ice melting, that was very similar to the observation."

To understand how adding more air to the North Atlantic Oscillation could warm the Arctic, Ding says it helps to think of a flat bicycle tire.

"If you keep pumping air into a flat tire, if you touch your frame of your tire it gets warmer and warmer," said Ding. "You're doing some work to push air into your tire, and the tire has just a certain volume, so as you push air into a certain volume it becomes very condensed and becomes warmer."

But even if the added air is warming the Arctic, who's to say that the shifting circulation isn't itself due to climate change?

13 PHOTOS
Global warming, climate change impacting Patagonia's massive glaciers
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Global warming, climate change impacting Patagonia's massive glaciers
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 29: Ice calves from the Northern wall of the Perito Moreno glacier in Los Glaciares National Park, part of the Southern Patagonian Ice Field, on November 29, 2015 in Santa Cruz Province, Argentina. Certain areas of glacial ice take on a bluish hue due to light refraction. The Southern Patagonian Ice Field is the third largest ice field in the world. The majority of the almost 50 large glaciers in Los Glaciares National Park have been retreating during the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey (USGS) reports that over 68 percent of the world's freshwater supplies are locked in ice caps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 28: Runoff cascades from the edge of Heim glacier in Los Glaciares National Park, part of the Southern Patagonian Ice Field, the third largest ice field in the world, on November 28, 2015 in Santa Cruz Province, Argentina. The majority of the almost fifty large glaciers in the park have been retreating over the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey reports that over 68 percent of the world's freshwater supplies are locked in icecaps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 27: The Perito Moreno glacier stands in Los Glaciares National Park, part of the Southern Patagonian Ice Field, the third largest ice field in the world, on November 27, 2015 in Santa Cruz Province, Argentina. Certain areas of glacial ice take on a blueish hue due to light refraction. The majority of the almost fifty large glaciers in the park have been retreating over the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey (USGS) reports that over 68 percent of the world's freshwater supplies are locked in icecaps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 28: Runoff cascades from the edge of Heim glacier in Los Glaciares National Park, part of the Southern Patagonian Ice Field, the third largest ice field in the world, on November 28, 2015 in Santa Cruz Province, Argentina. The majority of the almost fifty large glaciers in the park have been retreating over the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey reports that over 68 percent of the world's freshwater supplies are locked in icecaps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 27: The Perito Moreno glacier stands in Los Glaciares National Park, part of the Southern Patagonian Ice Field, the third largest ice field in the world, on November 27, 2015 in Santa Cruz Province, Argentina. The majority of the almost fifty large glaciers in the park have been retreating over the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey (USGS) reports that over 68 percent of the world's freshwater supplies are locked in icecaps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 29: The Perito Moreno glacier stands in Los Glaciares National Park, part of the Southern Patagonian Ice Field, on November 29, 2015 in Santa Cruz Province, Argentina. Certain areas of glacial ice take on a bluish hue due to light refraction. The Southern Patagonian Ice Field is the third largest ice field in the world. The majority of the almost 50 large glaciers in Los Glaciares National Park have been retreating during the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey (USGS) reports that over 68 percent of the world's freshwater supplies are locked in ice caps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 28: An iceberg broken off from a melting glacier floats in Lake Argentino, which holds runoff water from the Southern Patagonian Ice Field, the third largest ice field in the world, on November 28, 2015 in Santa Cruz Province, Argentina. The majority of the almost fifty large glaciers in the surrounding Los Glaciares National Park have been retreating over the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey reports that over 68 percent of the world's freshwater supplies are locked in icecaps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 29: Melting glacial ice floats in Los Glaciares National Park, part of the Southern Patagonian Ice Field, on November 29, 2015 in Santa Cruz Province, Argentina. Certain areas of glacial ice take on a bluish hue due to light refraction. The Southern Patagonian Ice Field is the third largest ice field in the world. The majority of the almost 50 large glaciers in Los Glaciares National Park have been retreating during the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey (USGS) reports that over 68 percent of the world's freshwater supplies are locked in ice caps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 28: An iceberg broken off from a melting glacier floats in Lake Argentino, which holds runoff water from the Southern Patagonian Ice Field, the third largest ice field in the world, on November 28, 2015 in Santa Cruz Province, Argentina. Certain areas of glacial ice take on a blueish hue due to light refraction. The majority of the almost fifty large glaciers in the surrounding Los Glaciares National Park have been retreating over the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey reports that over 68 percent of the world's freshwater supplies are locked in icecaps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 29: Melted glacial ice floats in Los Glaciares National Park, part of the Southern Patagonian Ice Field, on November 29, 2015 in Santa Cruz Province, Argentina. Certain areas of glacial ice take on a bluish hue due to light refraction. The Southern Patagonian Ice Field is the third largest ice field in the world. The majority of the almost 50 large glaciers in Los Glaciares National Park have been retreating during the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey (USGS) reports that over 68 percent of the world's freshwater supplies are locked in ice caps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 29: The Perito Moreno glacier stands in Los Glaciares National Park, part of the Southern Patagonian Ice Field, on November 29, 2015 in Santa Cruz Province, Argentina. Certain areas of glacial ice take on a bluish hue due to light refraction. The Southern Patagonian Ice Field is the third largest ice field in the world. The majority of the almost 50 large glaciers in Los Glaciares National Park have been retreating during the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey (USGS) reports that over 68 percent of the world's freshwater supplies are locked in ice caps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
SANTA CRUZ PROVINCE, ARGENTINA - NOVEMBER 28: Runoff cascades from the edge of Heim glacier in Los Glaciares National Park, part of the Southern Patagonian Ice Field, the third largest ice field in the world, on November 28, 2015 in Santa Cruz Province, Argentina. The majority of the almost fifty large glaciers in the park have been retreating over the past fifty years due to warming temperatures, according to the European Space Agency (ESA). The United States Geological Survey reports that over 68 percent of the world's freshwater supplies are locked in icecaps and glaciers. The United Nations climate change conference begins November 30 in Paris. (Photo by Mario Tama/Getty Images)
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"If the circulation changes are caused by anthropogenic greenhouse warming (or other human or natural external forcings such as ozone depletion, aerosol emissions, or solar activity) this pattern of atmospheric change should emerge as a clear signature when averaging together many climate model simulations of this period," Neil Swart, a Research Scientist with Environment and Climate Change Canada who wasn't involved in the new study, wrote in an accompanying article.

But when Ding averaged the climate models together, the air circulation changes canceled each other out—like a balanced equation. They only data that remained in the models was responding to external forcings, like greenhouse gas emissions. In other words, Ding found that between 30-50 percent of the arctic melting is due to these unforced, or non-climate change caused variations—and that with this factored in, the climate models were generally accurate. The increased rapidity of Arctic melting was due to natural variations outside of the scope of the climate change models.

Ding is quick to point out that this doesn't mean that climate change isn't real. He equates these natural variations to putting a blanket on the sea ice, while climate change is turning up the thermostat. And as anyone who has huddled under a blanket in a toasty house knows, the end result is a whole lotta sweat.

33 PHOTOS
Surfing in the arctic circle
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Surfing in the arctic circle
A man looks for a remote surfing spot in a fjord near Flakstad, near Ramberg, in Lofoten archipelago, Arctic Circle, on March 14, 2016. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Northern lights ( aurora borealis ) illuminate the sky over the snow covered Fjord of Flakstad, on Lofoten Islands, Arctic Circle, on March 14, 2016. Surfers from all over the world come to Lofoten islands to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A girl goes out the water at the snowy beach of Flackstad, in Lofoten archipelago, Arctic Circle, on March 13, 2016 Surfers from all over the world come to Lofoten islands to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
People arrive to go surfing at the snowy beach of Flackstad, near Ramberg, in Lofoten archipelago, Arctic Circle, on March 13, 2016. Surfers from all over the world come to Lofoten islands to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A car passes under a cloudy sky at the snowy beach of Flackstad, in Lofoten archipelago, Arctic Circle, on March 13, 2016. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Surfers ride a wave at night time at the snowy beach of Flackstad, in Lofoten Islands, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten islands to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Surfers ride a wave at night time at the snowy beach of Flackstad, in Lofoten Islands, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten islands to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Northern lights ( aurora borealis ) illuminate the sky over the snow covered beach of Flakstad, on Lofoten Islands, Arctic Circle, on March 14, 2016. Surfers from all over the world come to Lofoten island to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A young couple gets prepared to go surfing at the snowy beach of Flackstad, near Ramberg, in Lofoten archipelago, Arctic Circle, on March 13, 2016. Surfers from all over the world come to Lofoten islands to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Surfers ride a wave at night time at the snowy beach of Flackstad, in Lofoten Islands, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten islands to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A girl goes to surf at the snowy beach of Flackstad, near Ramberg, in Lofoten archipelago, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten islands to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A surfer looks at the Northern lights ( aurora borealis ) illuminating the sky over the snow covered beach of Unstad, on Lofoten Islands, Arctic Circle, on March 14, 2016. Surfers from all over the world come to Lofoten island to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Northern lights ( aurora borealis ) illuminate the sky over the snow covered beach of Flakstad, on Lofoten Islands, Arctic Circle, on March 14, 2016. Surfers from all over the world come to Lofoten island to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A girl goes to surf at the snowy beach of Flackstad, near Ramberg, in Lofoten archipelago, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten islands to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A man goes to surf at the snowy beach of Flackstad, near Ramberg, in Lofoten archipelago, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten islands to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Surfers walk on the snow covered beach of Flakstad, near Rambeg, as they have a break during a surf session on the Lofoten Island, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten island to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A surfer rides a wave at the snow covered beach of Flackstad, near Ramberg, on Lofoten Island, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten island to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Surfers sit on their board as they have a break during a surf session at the snow covered beach of Flackstad, on Lofoten Island, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten island to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Vidar, a Norwegian surf instructor, waxes his board before going to the water to surf at the snow covered beach Unstad in Lofoten Island, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten island to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Young Swedish surfers go to the water at the end of afternoon, after spending the night under a tent at the snow covered beach Unstad in Lofoten Island, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten island to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Young Swedish surfers go to the water at the end of afternoon, after spending the night under a tent at the snow covered beach Unstad in Lofoten Island, Arctic Circle, on March 12, 2016. Surfers from all over the world come to Lofoten island to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
The beach of Unstad is photographed, in Lofoten archipelago, Arctic Circle, on March 10, 2016. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
The snowy filed of Unstad is photographed, in Lofoten archipelago, Arctic Circle, on March 10, 2016. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
The beach of Unstad is photographed under a strong wind at the end of afternoon, in Lofoten archipelago, Arctic Circle, on March 10, 2016. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Northern lights ( aurora borealis ) illuminated the sky over the snow covered beach of Unstad, on Lofoten Island, Arctic Circle, on March 10, 2016. Surfers from all over the world come to Lofoten island to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A surfer walks with his board after leaving the snowy beach of Unstad after a surfing session, in Lofoten Island, Arctic Circle, on March 10, 2016. Surfers from all over the world comes to Lofoten island to surf in extrem conditions. Ocean temperature is 6-7 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Surfing swell is photographed at snowy beach of Unstad, Norway on Lofoten Island, Arctic Circle, on March 9, 2016. Surfers from all over the world comes to Lofoten island to surf in extrem conditions. Ocean temperature is 6-7 °C, air temperature around 0°C in spite of very unstable weather. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
Surfers leave the snowy beach of Unstad after surfing, in Lofoten Island, Arctic Circle, on March 10, 2016. Surfers from all over the world comes to Lofoten island to surf in extrem conditions. Ocean temperature is 6-7 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A surfer rides a wave at the snowy beach of Unstad, in Lofoten Island, Arctic Circle, on March 10, 2016. Surfers from all over the world come to Lofoten island to surf in extrem conditions. Ocean temperature is 6-7 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A surfer rides a wave at the snowy beach of Unstad, in Lofoten Island, Arctic Circle, on March 09, 2016. Surfers from all over the world comes to Lofoten island to surf in extrem conditions. Ocean temperature is 6-7 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
A surfer leaves the snowy beach of Unstad after a surfing, in Lofoten Island, Arctic Circle, on March 09, 2016. Surfers from all over the world comes to Lofoten island to surf in extrem conditions. Ocean temperature is 6-7 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
TOPSHOT - A surfer stands by northern lights ( aurora borealis ) on the snow covered beach of Unstad, on Lofoten Island, Arctic Circle, on March 10, 2016. Surfers from all over the world comes to Lofoten island to surf in extrem conditions. Ocean temperature is 5-6 °C, air temperature around 0°C in spite of a weather very unstable. / AFP / OLIVIER MORIN (Photo credit should read OLIVIER MORIN/AFP/Getty Images)
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