After an astonishing rise in 2023, sea surface temperature anomalies fell for six months in the Northern Hemisphere, but they are rising again, threatening to cause dramatic sea ice loss over the next few months and destabilize sediments at the seafloor, resulting in huge amounts of methane erupting and abruptly entering the atmosphere.

NSIDC explains the difference between extent and area: A simplified way to think of extent versus area is to imagine a slice of Swiss cheese. Extent would be a measure of the edges of the slice of cheese and all of the space inside it. Area would be the measure of where there is cheese only, not including the holes. Therefore, if you compare extent and area in the same time period, extent is always bigger.

Another measure is concentration. The image on the right, from NSIDC, shows Arctic sea ice concentration on June 18, 2024. 

Volume is another measure. The image below is adapted from the Danish Meteorological Institute and shows that Arctic sea ice volume is at a record low for the time of year, as it has been for most of the year.  

Volume is calculated by multiplying thickness with concentration and with area, which implies that Arctic sea ice is very thin, as also indicated by the image below, adapted from the University of Bremen, which is combined with a NASA satellite image for comparison. 

The image below measures thickness by using both the brightness temperature data from ESA’s Soil Moisture and Ocean Salinity (SMOS) satellite and NASA’s Soil Moisture Active Passive (SMAP) satellite.

Lack of sea ice in the Kara Sea and the Laptev Sea (at top of the above images) is worrying, since these are shallow seas that hold huge amounts of carbon in sediments at the seafloor. Heat can penetrate these sediments and destabilize hydrates, resulting in eruption of huge amounts of methane.

Loss of sea ice comes with numerous further feedbacks that accelerate the temperature rise, and just the temperature rise itself comes with feedbacks such as more water vapor in the atmosphere. 

Surface precipitable water reached a record high of 27.139 kg/m² in July 2023, as illustrated by the image below, adapted from NOAA. Worryingly, a value of 26.138 kg/m² was reached in May 2024, much higher than the 25.378 kg/m² in May 2023, which raises fears that surface precipitable water will reach an even higher peak in 2024 than was reached in 2023.

Thawing permafrost can cause huge emissions of carbon dioxide, methane and nitrous oxide. Ominously, the image below shows high methane levels over Scandinavia, which could be the result of higher temperatures. 

As illustrated by the image below, adapted from Climate Reanalyzer, the temperature anomaly in Scandinavia was high in May 2024. 

Studies such as by Hubau (2020) warn that the uptake of carbon into Earth’s intact tropical forests peaked in the 1990s. Studies now warn that the Arctic has also changed from sink to source. 

A study by Del Vecchi et al. (2024) suggests that a gradual thawing of Arctic permafrost could release between 22 billion and 432 billion tons of carbon dioxide by 2100 if current greenhouse gas emissions are reined in — and as much as 550 billion tons if they are not.

An analysis by Ramage et al. (2024) concludes that Arctic terrestrial permafrost now emits more greenhouse gases than it stores, and the trend is likely to accelerate as temperatures keep rising in the Arctic. The highest carbon dioxide emissions over the 2000-2020 period came from inland rivers and wildfires. The non-permafrost wetlands exhaled the most methane, and dry tundra released the most nitrous oxide.

The prospect of further releases looks dire. The analysis gives estimates that the upper three meters of permafrost region soils store 1,000 Gt of soil organic carbon, while deeper deposits could store an additional amount of as much as 1,000 Gt C. The analysis concludes that the permafrost region is the largest terrestrial carbon and nitrogen pool on Earth.

Note that the joint CO₂e of emissions in this analysis only covers part of global emissions, e.g. the analysis excludes emissions from Arctic subsea permafrost and from oceans in general, from many mountain areas and from the Southern Hemisphere. The study also appears to have excluded emissions caused by anthropogenic disturbances such as clear-cutting, logging and fracking activities in the region, while calculations typically use a low global warming potential (GWP) for methane (100-year horizon).  

Miesner et al. (2023) warn that an additional 2822 Gt of organic carbon is stored in subsea Arctic shelf permafrost and Huang et al. (2024) warn that the top two meters of soil globally holds about 2300 Gt of inorganic carbon, which has been left out of environmental models, and 23 Gt of this carbon may be released over the next 30 years.

The transition from sink to source of the region is an important feedback of the temperature rise that is not fully reflected in many climate models. According to the IPCC, 14–175 Gt CO₂e (in carbon dioxide and methane) gets released per 1°C of global warming, which is likely to underestimate the situation by downplaying many feedbacks. Despite the dire situation, the IPCC keeps promoting less effective policies such as support for biofuel and tighter fuel efficiency standards, as discussed in earlier posts such as this 2022 one.