The melting of sea ice in the Arctic has slowed dramatically in the past 20 years, scientists have reported, with no statistically significant decline in its extent since 2005.
The finding is surprising, the researchers say, given that carbon emissions from fossil fuel burning have continued to rise and trap ever more heat over that time.
They said natural variations in ocean currents that limit ice melting had probably balanced out the continuing rise in global temperatures. However, they said this was only a temporary reprieve and melting was highly likely to start again at about double the long-term rate at some point in the next five to 10 years.
The findings do not mean Arctic sea ice is rebounding. Sea ice area in September, when it reaches its annual minimum, has halved since 1979, when satellite measurements began. The climate crisis remains “unequivocally real”, the scientists said, and the need for urgent action to avoid the worst impacts remains unchanged.
The natural variation causing the slowdown is probably the multi-decadal fluctuations in currents in the Atlantic and Pacific oceans, which change the amount of warmed water flowing into the Arctic. The Arctic is still expected to see ice-free conditions later in the century, harming people and wildlife in the region and boosting global heating by exposing the dark, heat-absorbing ocean.
Dr Mark England, who led the study while at the University of Exeter, said: “It is surprising, when there is a current debate about whether global warming is accelerating, that we’re talking about a slowdown.
“The good news is that 10 to 15 years ago when sea ice loss was accelerating, some people were talking about an ice-free Arctic before 2020. But now the [natural] variability has switched to largely cancelling out sea ice loss. It has bought us a bit more time but it is a temporary reprieve – when it ends, it isn’t good news.”
The research, published in the journal Geophysical Research Letters, used two different datasets of Arctic sea ice levels from 1979 to the present day. The scientists analysed the sea ice area for every month of the year and the slowdown was seen in all cases.
To see if such a slowdown could be a result of natural variation, they examined the results of thousands of climate model runs. “This is not an extremely rare event – over a century, it should happen a couple of times,” said England, now at the University of California, Irvine. Furthermore, all the simulations showed sea ice loss accelerating again after the slowdown.
Prof Julienne Stroeve, of University College London, said: “We know climate records, be it in global temperatures or sea ice, can remain the same for several years in a row as a result of internal climate variability.”
Stroeve’s analysis of the long-term trend from 1979 to 2024 shows that about 2.5 sq metres of September ice is lost for every tonne of CO2 emitted.
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Prof Andrew Shepherd, of Northumbria University, said: “We know that the Arctic sea ice pack is also thinning, and so even if the area was not reducing, the volume still is. Our data show that since 2010 the average October thickness has fallen by 0.6cm per year.”
The rate of the rise in global surface temperature has also slowed down in the past, before resuming a rapid rise. A major El Niño event in 1998 was followed by a decade or so of similar global temperatures, which was nicknamed “the pause”. However, the planet continued to accumulate heat throughout and global temperatures have since risen rapidly.
England rejected any suggestion the sea ice slowdown suggested climate change was not real. “Climate change is unequivocally real, human-driven, and continues to pose serious threats. The fundamental science and urgency for climate action remain unchanged,” he said.
“It is good to explain to people that [the slowdown] is happening, else they are going to hear it from someone who is trying to use it in bad faith as a way to undermine our very solid understanding of what’s happening with climate change.”
