Dangerously large Arctic sea ice extent
Arctic sea ice extent was 5.88 million km² on August 21, 2022, larger in extent than in any of the years from 2010 through 2021 at this time of year, as illustrated by the image below.
At first glance, one might think that this relatively large extent was a sign of healthy sea ice. After all, the larger the sea ice, the more sunlight gets reflected back into space. At the same time, however, the situation is very dangerous, as there is a growing risk that large eruptions of methane will occur from the seafloor of the Arctic Ocean.
Ocean stratification is increasing globally, as ocean warming is stronger for upper layers versus the deep ocean. Stratification increased from 1960 to 2018 by 5.3% for the upper 2000m and by as much as 18% for the upper 150m, while salinity changes also play an important role locally, a 2020 study finds.
As temperatures in the Arctic are rising faster than in the rest of the world, the Jet stream is getting deformed, and this can, at times strongly, increase precipitation over the North Atlantic and increase runoff from land (including from melting glaciers) that both contribute to growth of a relatively cold, freshwater lid at the surface of the North Atlantic.
The navy.mil combination image below has three panels. The left panel shows the sea ice on August 30, 2012, the center panel shows the sea ice on August 30, 201, and the right panel shows a forecast for the sea ice for August 21, 2022, run on August 20, 2022.
Sea ice acts as a buffer that absorbs heat, while keeping the temperature at zero degrees Celsius. As long as there is sea ice in the water, this sea ice will keep absorbing heat, so the temperature doesn’t rise at the sea surface. The amount of energy absorbed by melting ice is as much as it takes to heat an equivalent mass of water from zero to 80°C.
This ice has meanwhile all but disappeared, so without this latent heat buffer further incoming heat must go elsewhere, i.e. the heat will further raise the temperature of the water of the Arctic Ocean.
The danger is that, as more salty, warm water keeps arriving in the Arctic Ocean while the latent heat buffer has largely disappeared and while sea ice extent is relatively large, this will raise the temperatures and salinity levels at the bottom of the Arctic Ocean enough to destabilize hydrates in sediment at the seafloor of the Arctic Ocean, resulting in methane eruptions both from these hydrates and from free gas underneath these hydrates.
Methane releases from the seafloor of the Arctic Ocean are very dangerous because there is very little hydroxyl in the atmosphere over the Arctic to break down the methane.
The MetOp satellite image underneath shows a mean for methane of 1971 ppb (marked by the red oval) at 293 mb on the morning of August 18, 2022 am. An abrupt release as large as the methane currently in the atmosphere could raise the mean twice as high, to 3942 ppb and when using a 1-year GWP of 200, this translates into 788.4 ppm CO₂e.
In other words, a large eruption of methane from the seafloor of the Arctic Ocean could abruptly cause the joint CO₂e of just two greenhouse gases, i.e. methane and CO₂, to cross the 1200 ppm clouds tipping point globally and trigger a further 8°C global temperature rise, due to the clouds feedback alone.
In conclusion, there is a growing risk that methane will erupt from the seafloor of the Arctic Ocean and cause a dramatic rise in temperature.
Even without such eruption of methane from the seafloor of the Arctic Ocean, temperatures look set to rise strongly soon, as we move into an El Niño and face a peak in sunspots.
This makes it in many respects rather futile to speculate about what will happen beyond 2026. At the same time, the right thing to do now is to help avoid the worst things from happening, through comprehensive and effective action as described in the Climate Plan.
• Increasing ocean stratification over the past half-century – by Guancheng Li et al.
https://www.nature.com/articles/s41558-020-00918-2• The ocean has become more stratified with global warming – news release
• Cold freshwater lid on North Atlantic
• NOAA – Monthly Temperature Anomalies Versus El Niño
• University of Bremen
• NSIDC – Arctic sea ice concentration
• NSIDC – Chartic, interactive sea ice graph
• NOAA – Trends in Atmospheric Methane