Arctic News: BOE

Showing posts with label BOE. Show all posts

Monday, March 17, 2025

Arctic Blue Ocean Event 2025?

Arctic sea ice area

Arctic sea ice area has been at a record daily low since the start of February 2025.

Arctic sea ice area was 1.28 million km² lower on March 5, 2025, compared to March 5, 2012. The comparison with the year 2012 is important, since Arctic sea ice area reached its lowest minimum in 2012. Arctic sea ice area was only 2.24 million km² on September 12, 2012.

The size of the sea ice can be measured either in extent or in area. What is the difference between sea ice area and extent? Extent is the total region with at least 15% sea ice cover. Extent can include holes or cracks in the sea ice and melt ponds on top of the ice, all having a darker color than ice. Sea ice area is the total region covered by ice alone.

Blue Ocean Event (BOE)

A Blue Ocean Event (BOE) occurs when the size of the sea ice falls to 1 million km² or less, which could occur in Summer 2025 in the Northern Hemisphere for Arctic sea ice. If the difference between 2012 and 2025 continues to be as large as it is now, there will be a Blue Ocean Event in September 2025.

A BOE is often defined as crossing a tipping point that is crossed when sea ice reaches or falls below 1 million km² in extent. However, it make more sense to look at sea ice area, rather than at sea ice extent, since sea ice area is a more critical measure in regard to albedo. Loss of sea ice area (and thus of albedo) is a self-reinforcing feedback that causes the temperature to rise, resulting in further melting of sea ice and thus further accelerating the temperature rise.

A BOE occurs when the size of the sea ice falls to 1 million km² or less, which could occur in Summer 2025 in the Northern Hemisphere for Arctic sea ice. Arctic sea ice area was only 1.24 million km² above a BOE on September 12, 2012. If the difference between 2012 and 2025 continues to be as large as it is now, there will be a BOE in September 2025.

Arctic sea ice volume and thickness

Volume and thickness are two further measures to assess the health of Arctic sea ice, and they are critical in regard to the latent heat buffer, which decreases as sea ice, permafrost and glaciers disappear.

Latent heat is energy associated with a phase change, such as the energy consumed when ice turns into water. During a phase change, the temperature remains constant. As long as there is ice, additional heat will be absorbed by the process of ice turning into water, so the temperature doesn't rise at the surface.

[ from Albedo, latent heat, insolation and more ]

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. The energy required to melt a volume of ice can raise the temperature of the same volume of rock by as much as 150ºC.

Warmer water flowing into the Arctic Ocean causes Arctic sea ice to lose thickness and thus volume, diminishing its capacity to act as a buffer that consumes ocean heat entering the Arctic Ocean from the North Atlantic. This means that - as sea ice thickness decreases - a lot of incoming ocean heat can no longer be consumed by melting the sea ice from below, and the heat will therefore contribute to higher temperatures of the water of the Arctic Ocean. Similarly, there is a point beyond which thawing of permafrost on land and melting of glaciers can no longer consume heat, and all further heat will instead warm up the surface.

[ from earlier post ]

[ Arctic sea ice volume, click to enlarge ]

Abrupt seafloor methane eruptions

Further incoming heat therefore threatens to instead reach the seafloor of the Arctic Ocean and destabilize methane hydrates contained in sediments at the seafloor, resulting in eruptions of huge amounts of methane, in turn threatening increased loss of permafrost, resulting in additional emissions, as illustrated by the above image.

The image on the right shows that Arctic sea ice volume has been at a record daily low for more than a year.

Loss of the latent heat buffer constitutes a tipping point. Beyond a certain point, further ocean heat arriving in the Arctic Ocean from the Atlantic Ocean and the Pacific Ocean will no longer be able to be consumed by melting sea ice from below.

The danger is especially large in the East Siberian Arctic Shelf (ESAS), which contains huge amounts of methane and which is hit strongly by the temperature rise. The image below shows that high February 2025 sea surface temperature anomalies are present in the Arctic Ocean, including over ESAS.

The bathymetry map in the right panel of above image shows how shallow seas in the Arctic Ocean can be. The water over the ESAS is quite shallow, making that the water can warm up very quickly during summer heat peaks and heat can reach the seafloor, which comes with the risk that heat will penetrate cracks in sediments at the seafloor. Melting of ice in such cracks can lead to abrupt destabilization of methane hydrates contained in sediments.

[ from earlier post, click on images to enlarge ]

Large abrupt methane releases will quickly deplete the oxygen in shallow waters, making it harder for microbes to break down the methane, while methane rising through waters that are shallow can enter the atmosphere very quickly.

The situation is extremely dangerous, given the vast amounts of methane present in sediments in the ESAS, given the high global warming potential (GWP) of methane immediately following its release and given that over the Arctic there is very little hydroxyl in the air to break down the methane.

[ from earlier post ]

As illustrated by the image below, very high temperature anomalies are forecast over the Arctic Ocean for October 2025.

[ from earlier post ]

Climate Emergency Declaration

The situation is dire and the precautionary principle calls for rapid, comprehensive and effective action to reduce the damage and to improve the situation, as described in this 2022 post, where needed in combination with a Climate Emergency Declaration, as discussed at this group.