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maltatoday | SUNDAY • 14 AUGUST 2022 12 OPINION Arctic is warming nearly four times faster than the rest of the world THE Earth is approximate- ly 1.1 o C warmer than it was at the start of the industrial rev- olution. That warming has not been uniform, with some regions warming at a far greater pace. 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 av- erage around 3 o C warmer than it was in 1980. This is alarming, because the Arctic contains sensitive and delicately balanced climate components that, if pushed too hard, will respond with global consequences. Why is the Arctic warming so much faster? A large part of the explanation relates to sea ice. This is a thin layer (typically one metre to five metres thick) of sea water that freezes in winter and partially melts in the summer. The sea ice is covered in a bright layer of snow which re- flects around 85% of incom- ing solar radiation back out to space. The opposite occurs in the open ocean. As the darkest natural surface on the planet, the ocean absorbs 90% of solar radiation. When covered with sea ice, the Arctic Ocean acts like a large reflective blanket, reducing the absorption of solar radiation. As the sea ice melts, absorp- tion rates increase, resulting in a positive feedback loop where the rapid pace of ocean warm- ing further amplifies sea ice melt, contributing to even faster ocean warming. This feedback loop is largely responsible for what is 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 underes- timated? Numerical climate models have been used to quantify the magnitude of Arctic amplifica- tion. They typically estimate the amplification ratio to be about 2.5, meaning the Arctic is warming 2.5 times faster than the global average. Based on the observational record of surface temperatures over the last 43 years, the new study estimates the Arctic amplification rate to be about four. Rarely do the climate models obtain values as high that. This suggests the models may not fully capture the complete feed- back loops responsible for Arc- tic amplification and may, as a consequence, underestimate future Arctic warming and the potential consequences that ac- company that. How concerned should we be? Besides sea ice, the Arctic con- tains other climate components that are extremely sensitive to warming. If pushed too hard, they will also have global conse- quences. One of those elements is per- mafrost, a (now not so) per- manently frozen layer of the Earth's surface. As tempera- tures rise across the Arctic, the active layer, the topmost 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 glob- al mean temperatures by more than 3 o C. Should permafrost thawing accelerate, there is the potential for a runaway positive feedback process, often referred to as the permafrost carbon time bomb. The release of pre- viously stored carbon dioxide and methane will contribute to further Arctic warming, subse- quently accelerating future per- mafrost thaw. A second Arctic component vulnerable 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 lev- els by 7.4 metres if melted com- pletely. When the amount of melting at the surface of an ice cap ex- ceeds the rate of winter snow accumulation, it will lose mass faster than it gains any. When this threshold is exceeded, its surface lowers. This will quick- en the pace of melting, because temperatures are higher at low- er elevations. This feedback loop is often called the small ice cap instabil- ity. Prior research puts the re- quired temperature rise around Greenland for this threshold to be passed at around 4.5 o C above pre-industrial levels. Given the exceptional pace of Arctic warming, passing this critical threshold is rapidly becoming likely. Although there are some re- gional differences in the mag- nitude of Arctic amplification, the observed pace of Arctic warming is far higher than the models implied. This brings us perilously close to key cli- mate thresholds that if passed will have global consequences. As anyone who works on these problems knows, what happens in the Arctic doesn't stay in the Arctic. Prof. Jonathan Bamber Jonathan Bamber is Professor of Physical Geography, University of Bristol As temperatures rise across the Arctic, the active layer, the topmost layer of soil that thaws each summer, deepens