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Sea Ice

High evidence, high agreement

It is beyond question that Arctic sea ice extent is declining in response to warming, and that considerable changes are happening in the Arctic climate system.

For other Arctic processes (ice thickness, velocity, snow, coastal erosion, ecosystem effects), the overall confidence is medium (medium evidence, high agreement) reflecting the need for more accurate observational data throughout the year.

For impacts in mid-latitudes (including UK) the overall confidence is low (medium evidence, low agreement) related to current theoretical understanding, and a lack of robust observed responses when compared with substantial natural variability.

What could happen in the future?
  • It is virtually certain that Arctic sea ice will continue to decline in response to global warming caused by rising atmospheric CO2 concentrations.
  • It is likely that the Arctic will become practically ice-free at the seasonal minimum at least once before 2050, regardless of the future emission scenarios. This loss is not irreversible and Arctic summer sea ice should recover if Arctic temperatures reduce.
  • Changes in the timing of sea ice formation and melt are likely to further increase total primary production in the Arctic Ocean. This is likely to cause a mismatch in demand for food and habitat for marine species, with potential impacts on Arctic fisheries.
  • It is virtually certain that the Arctic will continue to warm faster than the rest of the globe. The resulting reduction in the equator-to-pole temperature gradient has the potential to affect mid-latitude (UK) climate, including via possible changes in the jet stream.
  • These rapid changes in the Arctic have the potential to cause rapid and unexpected changes in the midlatitude North Atlantic via the outflow of fresh, cold, polar water from the Arctic into the subpolar North Atlantic.

High evidence, high agreement

Despite model uncertainties around future emission scenarios and internal variability, all climate models agree on the downward trend in sea ice extent.

For other Arctic processes (ice-free Arctic date, ice thickness, snow cover, MIZ expansion, coastal erosion, ecosystems), the overall confidence is medium (medium evidence, high agreement) with new observations, expected improvements in model physics, resolution and coupling likely to increase our understanding of the Arctic climate system today, and how it may change in the future.

For impacts in mid-latitudes (including UK) the overall confidence is low (low evidence, medium agreement). Although the emergence of a larger climate change signal in future model projections increases agreement, the absence of observations means the amount of evidence is lower.

Key Challenges and Emerging Issues
  • There is evidence that Arctic sea ice loss could affect weather and climate in north-west Europe, however knowledge of the nature and size of these effects are imprecise. A better understanding is required of the involved mechanisms, their pathways to lower latitudes, and their fidelity in models.
  • Assess risks associated with Arctic shipping and offshore operations (e.g. contaminant spills; damage to ships and offshore structures caused by waves, sea ice floes, and icing spray), and land-based infrastructure (e.g. coastal erosion and permafrost decay).
  • Comprehensive assessments of ocean biogeochemistry for the ecosystem-based management of rapidly changing Arctic marine systems, including monitoring and knowledge building upon the following areas: life form responses across trophic levels (from microbial life to marine mammals); food security for Indigenous peoples; the impact of increasing terrigenous inputs (inc. rapid carbon discharge and associated changes in nutrients or contaminants)