This article was originally published on The conversation.
The Earth is about 1.1℃ warmer than it was at the start of the industrial revolution. This warming has not been uniform, with some regions warming at a much faster 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 that the Arctic is on average about 3℃ warmer than it was in 1980.
This is alarming, as the Arctic contains sensitive and delicately balanced climate components which, if pushed too hard, will react with global consequences.
Why is the Arctic warming up so much faster?
Much of the explanation concerns the pack ice. It is a thin layer (usually one to five meters thick) of seawater that freezes in winter and partially melts in summer.
The pack ice is covered with a layer of shiny snow that reflects about 85% of incident solar radiation back into space. The opposite occurs in the open sea. As the darkest natural surface on the planet, the ocean absorbs 90% of solar radiation.
When covered in sea ice, the Arctic Ocean acts as a large reflective blanket, reducing the absorption of solar radiation. As sea ice melts, absorption rates increase, resulting in a positive feedback loop in which the rapid rate of ocean warming further amplifies sea ice melt, contributing to even faster global warming. oceans.
This feedback loop is largely responsible for what is known as Arctic amplification and explains why the Arctic is warming much more than the rest of the planet.
Is arctic amplification underestimated?
Numerical climate models were used to quantify the magnitude of Arctic amplification. They generally estimate the amplification rate to be around 2.5, which means 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 around four.
Rarely do climate models obtain such high values. This suggests that the models may not fully capture the full feedback loops responsible for Arctic amplification and may, therefore, be underestimating future Arctic warming and potential accompanying consequences. .
How concerned should we be?
In addition to sea ice, the Arctic contains other climatic components that are extremely sensitive to warming. If pushed too hard, they will also have global consequences.
One such element is permafrost, a (now not so) permanently frozen layer of the Earth’s surface. As temperatures rise in the Arctic, the active layer, the top layer of soil that thaws 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 average global temperatures by more than 3℃. If permafrost melt accelerates, there is potential for a runaway positive feedback process, often referred to as the permafrost carbon time bomb. The release of previously stored carbon dioxide and methane will contribute to further warming of the Arctic, subsequently accelerating future permafrost thaw.
The Greenland Ice Sheet is a second arctic element vulnerable to temperature increase. As the largest mass of ice in the Northern Hemisphere, it contains enough frozen ice to raise global sea levels by 7.4 meters if it melted completely.
When the amount of melt on the surface of an ice cap exceeds the rate of winter snow accumulation, it loses mass faster than it gains. When this threshold is exceeded, its surface area decreases. This will accelerate the rate of melting, as temperatures are higher at lower elevations.
This feedback loop is often referred to as the Little Ice Sheet instability. Previous research places the temperature increase required around Greenland for this threshold to be exceeded at around 4.5℃ above pre-industrial levels. Given the exceptional rate of warming in the Arctic, exceeding this critical threshold quickly becomes probable.
Although there are some regional differences in the magnitude of Arctic amplification, the observed rate of Arctic warming is much higher than models imply. This brings us dangerously close to key climate thresholds which, if exceeded, will have global consequences. As anyone working on these issues knows, what happens in the Arctic doesn’t stay in the Arctic.
Jonathan Bamber receives funding from the UK Natural Environment Research Council and the EC European Research Council and the H2020 program.