Arctic sea ice has been melting at a slower rate for the past 20 years, despite human-induced global warming.
This comes at a time of record warming, debates about whether global warming is accelerating and decades of enhanced Arctic warming relative to the rest of the globe.
Climate modelling evidence suggests the finding is the result of 'natural climate variations' off-setting the human-driven loss of sea ice.
Scientists say this is a temporary slowdown that may continue for a further five to 10 years and, when it ends, is likely to be followed by faster-than-average sea ice decline.
In a new study, they investigated changes in observed Arctic sea ice cover, using two datasets collected with satellite measurements from 1979 to the present day.
Focusing on September, when ice cover is at its annual minimum, the researchers found sea ice between 2005 and 2024 declined by 0.35 and 0.29 million km2 per decade respectively.
The longer-term rate of decline for the period 1979-2024 was 0.78 and 0.79 million km2 per decade (depending on which dataset used), making the slowdown a 55% and 63% reduction.
This was the slowest rate of loss for any 20-year period since the start of satellite records in 1979, and four to five times slower than the peak 20-year period of 1993-2012.
A similar feature was observed by measuring the volume of ice lost, which for 2010-2024 was 0.4 million km3 per decade - seven times smaller than the long-term loss of 2.9 million km3 per decade for the period 1979-2024.
The slowdown in sea ice loss was evident for every single month of the year, so not confined to the summer or winter months.
To investigate whether such slowdowns are rare, the researchers searched the CMIP5 and CMIP6 archives for climate models that exhibit ice loss slowdowns.
They found that nearly all models can simulate these pauses in the loss of September Arctic cover, suggesting that the slowdown in the Arctic is not a rare event.
The researchers estimate the current slowdown to have a one in two chance of persisting for a further five years, and a one in four chance of lasting a further 10 years.
However, this slowdown will not last forever, with climate models indicating that when this current slowdown ends, the pace of Arctic sea ice loss could be 0.6 million km2 per decade faster than the broader long-term decline.
The modelling evidence is not conclusive in determining whether human actions were the cause of this slowdown, however it is likely that 'internal climate variability', the naturally occurring variations in climate due to interactions between components of the Earth system, played an important role.
Dr Mark England, who led the study while at the University of Exeter and is now at UC Irvine, said: "Summer sea ice conditions in the Arctic are at least 33% lower than they were at the beginning of the satellite record nearly 50 years ago.
"Given this - and the indisputable fact of human-driven climate change - it may seem surprising to find a temporary slowdown in Arctic sea ice loss.
"It is, however, entirely consistent with climate model simulations and is likely due to natural climate variability superimposed on the human-driven long-term trend. This is only a 'temporary reprieve' and before long the rate of sea ice decline will catch up with the longer term rate of sea ice loss.
"It's like the analogy of a ball bouncing down a hill where the hill is climate change, given by Professor Ed Hawkins. The ball continues going down the hill but as it meets obstacles in its path, the ball can temporarily fly upwards or sideways and not seem to be travelling down at all - that trajectory is not always smooth but we know that at some point the ball will careen towards the bottom of the hill."
