更敏感的北极海冰：温室气体排放导致消失速度加快

Nature Communications, 6 June 2023

This study, calibrating latest models from the IPCC with actual observations, found greenhouse gases as the main driver of Arctic sea ice loss over the past four decades; and in a new finding, also the leading cause of the ice loss now occurring during all seasons/every month of the year. Researchers used ten climate models from the IPCC Sixth Assessment (AR6) to better capture the faster rates of sea ice decline actually observed during this period by satellite. Using these same models, they then projected forward to find that with moderate or high emissions (and current emissions continue to follow a high trajectory), the Arctic becomes ice-free during much of the summer; with the first instance of an ice-free Arctic Ocean possible already in the 2030s. This is a decade earlier than predicted in the latest IPCC AR6 Report, released in March of this year; and is yet another example of the rapidly-evolving nature of cryosphere science.

These re-calibrated models concur with the earlier IPCC AR6 finding that at least one ice-free instance is inevitable before 2050 even with very low emissions (the pathway known as SSP1). However, higher greenhouse gas emissions emissions dramatically extend the length of committed ice-free periods; whereas in the very low emissions pathway — which remains within reach with sufficient action by major emitters during this decade, also according to the latest IPCC Report as well as an evaluation released by Climate Analytics at the UNFCCC meetings in Bonn this week — sea ice loss stabilizes later this century above ice-free conditions.

Otherwise, Arctic sea ice will continue its steep decline, with ice-free conditions likely throughout August-October before the 2080s even with moderate emissions. While some shipping and extractive industries in the region applaud the new markets this would open, an ice-free Arctic Ocean for such a lengthy summer period is projected to have highly destructive impacts in the Arctic region and throughout lower latitudes, with feedbacks reverberating for decades to centuries in the global climate system. These may include even more severe periods of drought, extreme weather and wildfires in North America and Russia; faster melt and related global sea-level rise from the Greenland Ice sheet; increased thawing of permafrost and resulting methane and CO2 emissions; disturbance of key ocean currents such as the AMOC; and loss of many Arctic species dependent on a consistent sea ice cover.

These changes will result in extensive loss and damage by global populations, yet experienced first by Arctic Indigenous and other high-latitude communities and economies, such as Norway’s cod industry and the crab fisheries off Alaska, where decreases already seem to be occurring. A very low emissions pathway however offers some hope of stability in these ecosystems and economies by the time today’s children reach mid-adulthood.

https://www.nature.com/articles/s41467-023-38511-8