Rapid thinning of the sea ice in the Beaufort Sea indicates that there is virtually no latent heat buffer left to consume further heat flowing from the Atlantic Ocean and the Pacific Ocean into the Arctic Ocean.
|[ feedback #14: Latent Heat ]|
Above image shows a number of feedbacks that are accelerating warming in the Arctic. Feedback #14 refers to the heat that is (less and less) going into melting the sea ice. The reason this heat is called latent (hidden) heat, is that it doesn’t raise the temperature of the water, but instead gets consumed in the process of melting the ice.
Thinner Sea Ice
Heat is melting Arctic sea ice from below, as it enters the Arctic Ocean from the Atlantic Ocean and the Pacific Ocean. This is a self-reinforcing feedback loop, i.e. as the sea ice gets thinner every year, an increasing proportion of this heat is no longer consumed by melting the ice the next year, but will instead get absorbed by the water and thus contribute to accelerated warming of the water of the Arctic Ocean.
As illustrated by above combination image, the thickness of the sea ice is now substantially less than it used to be. The image compares June 1, 2021 (left), with June 1, 2015 (right).
The navy.mil animation below was run on September 15, 2020, and shows Arctic sea ice thickness over 30 days (last 8 frames are forecasts for September 16 – September 23, 2020).
As long as there is sea ice in the water, this sea ice will keep absorbing heat as it melts, so the temperature will not rise at the sea surface and remain at zero°C. The amount of energy that is consumed in the process of melting the ice is as much as it takes to heat an equivalent mass of water from zero°C to 80°C.
|[ from the post Arctic Ocean invaded by hot, salty water ]|
As the Latent Heat Tipping Point gets crossed, there will still be a thin layer of ice at the surface, at least as long as air tempartures are low enough to keep it frozen. This thin layer of ice will still consume some heat below the surface, but at the same time it acts as a seal, preventing heat from the Arctic Ocean to enter the atmosphere. Once the tipping point is crossed, the bulk of the heat from the influx of warm water will go into heating up the water of the Arctic Ocean, including the deeper parts of the water, and each year this will occur earlier in the year.
Methane Hydrates Tipping Point
As discussed in a 2020 post, loss of subsurface sea ice is only one of multiple tipping points hitting the Arctic. Once this Latent Heat Tipping Point is crossed and as the temperature of the oceans keeps rising, more heat will reach sediments that are located at the seafloor of the Arctic Ocean and that contain vast amounts of methane, as discussed in this page and this post. The danger is that further heat will destabilize hydrates in these sediments, resulting in huge eruptions of methane both from the destabilizing hydrates and from methane that is present in the form of free gas underneath the hydrates.
The methane hydrates tipping point is estimated to get crossed as ocean temperature anomalies on the Northern Hemisphere become higher than 1.35°C above the 20th century average, as the image further above indicates.