The Earth is about 1.1℃ hotter than at the start of the Industrial Revolution. That warming has not been uniform, with some regions warming at a far greater rate. One such region is the Arctic.
A new study shows that the Arctic has warmed nearly four times faster than the rest of the world over the past 43 years. This means the Arctic is on average about 3℃ warmer than in 1980.
This is worrying, as the Arctic has sensitive and delicately balanced climate components that, if pushed too hard, will react with global consequences.
Why is Arctic warming so fast?
A large part of the explanation relates to sea ice. It is a thin layer of sea water (usually one meter to five meters thick) that freezes in winter and partially melts in summer.
Sea ice is covered in a shiny layer of ice that reflects about 85 percent of the solar radiation that falls back into space. The opposite happens in the open ocean. As the deepest natural surface on the planet, the ocean absorbs 90 percent of solar radiation.
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When covered by sea ice, the Arctic Ocean acts like a large reflective blanket, reducing the absorption of solar radiation. As sea ice melts, absorption rates increase, resulting in a positive feedback loop, where sea ice melts at a faster rate than ocean warming, which also accelerates ocean warming.
This feedback loop is largely known as Arctic amplification, and is the explanation for why the Arctic is warming so much more than the rest of the planet.
Is Arctic amplification underestimated?
Numerical climate models have been used to measure the magnitude of Arctic amplification. They generally estimate the amplification ratio to be around 2.5, meaning the Arctic is warming 2.5 times faster than the global average. Based on observational records of surface temperatures over the past 43 years, the new study estimates the Arctic amplification rate to be about four.
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Rarely do climate models achieve such high values. This suggests that the models may not fully capture the full feedback loop responsible for Arctic amplification and, as a result, may underestimate future Arctic warming and the potential consequences that may accompany it.
How worried should we be?
In addition to sea ice, the Arctic contains other climate components that are extremely sensitive to warming. If pushed too hard, they will have global consequences as well.
One of those elements is permafrost, a (no longer so) permanently frozen layer of the Earth’s surface. As temperatures rise in the Arctic, the active layer, the top layer of soil that melts each summer, deepens. This, in turn, increases biological activity in the active layer resulting in the release of carbon into the atmosphere.
Arctic permafrost contains enough carbon to raise the global average temperature by more than 3℃. Should the thawing of permafrost be accelerated, a runaway positive feedback process is likely, often referred to as the permafrost carbon time bomb. The release of previously stored carbon dioxide and methane would contribute to further Arctic warming, subsequently accelerating future permafrost thaw.
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The second Arctic component sensitive to temperature rise is the Greenland ice sheet. As the largest ice mass in the Northern Hemisphere, it contains enough frozen ice to raise global sea levels by 7.4 meters when completely melted.
When the amount of melting at the surface of the ice cap exceeds the rate at which ice accumulates in winter, it will lose mass faster than any gain. When this limit is exceeded, its surface decreases. This will speed up melting, as the temperature is higher at lower altitudes.
This feedback loop is often called small ice cap instability. Prior research places the required temperature rise around Greenland to pass about 4.5℃ above pre-industrial levels. Given the extraordinary pace of Arctic warming, crossing this critical threshold is likely to happen rapidly.
Although there are some regional differences in the magnitude of Arctic amplification, the observed pace of Arctic warming is far greater than the implied models. This brings us dangerously close to critical climate limits that if passed will have global consequences. As anyone who has worked on these problems knows, what happens in the Arctic does not stay in the Arctic.
This article is republished from The Conversation. Read the original article.