The image below, adapted from
Climate Reanalyzer, shows the one-day average sea surface temperature anomaly (from 1971-2000) on August 7, 2025.
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| [ click on images to enlarge ] |
Speeding up Arctic sea ice demise
Arctic sea ice declines due to rising ocean heat. The above image shows very high sea surface temperature anomalies around and inside the Arctic Ocean. These anomalies go up and down with the change in seasons, but they are getting higher over time due to rising Earth Energy Imbalance.
The image on the right, from an earlier post, illustrates the huge amounts of heat that have accumulated in the ocean, showing equivalent ocean heat content on August 9, 2025.
The image on the right underneath shows North Atlantic sea surface temperatures as high as 32.8°C on August 5, 2025. The image shows heat moving up along the path of the Gulf Stream toward the Arctic, threatening to cause more loss of sea ice and permafrost.
Arctic sea ice also declines due to the sunlight heating up the sea ice. Where sea ice disappears, the water heats up rapidly. Arctic sea ice decline comes with feedbacks such as the albedo feedback, i.e. less sunlight getting reflected by sea ice means more heat is getting absorbed, further accelerating the temperature rise. More algae and soot settling on the sea ice can further contribute to albedo loss.
Feedbacks of the temperature rise can manifest as changes in heat sinks and buffers, with rapid impact on the temperature rise. Oceans constitute a huge buffer that has taken up huge amounts of heat. The capacity of oceans to take up heat threatens to diminish, e,g, due to stratification and changes in ocean currents, as discussed in earlier post such as
this one.
Another buffer is the latent heat buffer that consumes heat in the process of melting snow and ice. Arctic sea ice is getting thinner over the years, and the amount of heat that can be absorbed in the process of melting is getting smaller over time. As the latent heat buffer diminishes, heat that was previously absorbed by the phase change from snow and ice to water, will therefore instead get absorbed by the water, further raising the temperature of the water. As sea ice thickness decreases over the years, less incoming ocean heat can be consumed by melting the remaining sea ice.
More freshwater temporarily slows down melting of Arctic sea ice
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| [ Bering Strait ] |
Furthermore, Arctic sea ice decline is due to heat that is moving with the flow of rivers into the Arctic Ocean. The image on the right shows sea surface temperatures as high as 20.3°C in the Bering Strait on August 7, 2025.
Extreme weather events are getting more severe and are occurring more frequently, including heatwaves and thunderstorms on land that can extend over the Arctic Ocean. Rain falling on sea ice can speed up its demise. Heatwaves and storms over land can furthermore heat up the water of rivers and increase their flow, thus increasing the heat flowing into the Arctic Ocean.
Also, more evaporation of sea water takes place over the North Atlantic, with more precipitation falling further down the track of the Gulf Stream and its extension north. This also adds more freshwater in the Arctic.
Water from melting sea ice, from rivers and from precipitation is all freshwater, i.e. it contains no salt. The increase in freshwater at the surface of the Arctic Ocean has resulted in a temporary slowdown in the retreat of Arctic sea ice extent, due to a buffer that spans a maximum of 2°C (as depicted by image below on the right).
Freshwater buffer looks set to be overwhelmed soon
The higher the water's salt content, the lower its melting point. Seawater typically has a salinity of about 3.5% (35 grams of salt per liter of water).
Sea ice starts melting when the temperature rises to about -2°C (28.4°F). By contrast, freshwater remains frozen as long as the temperature remains below 0°C (32°F).
As said, the increase in freshwater at the surface of the Arctic Ocean slows down the retreat of Arctic sea ice extent, but this is only a temporary slowdown. Given the speed at which the temperature of the water of the Arctic Ocean keeps rising, this temporary slowdown looks set to be overwhelmed soon and rapid melting of sea ice looks set to return with a vengeance.
The above image shows Arctic sea ice concentration on August 14, 2025.
Arctic and Antarctic - two different situations
The image below, by
Eliot Jacobson, illustrates the rise of precipitable water (total column) over the years.
Over the past two months (June-July 2025), the temperature over the Arctic Ocean has been slightly lower than 1951-1980, as illustrated by the image below. By contrast, areas with very high anomalies are visible between 60°S and 90°S. What's happening?
The image below shows that the precipitable water anomaly can be very high at both the North Pole and the South Pole. The image depicts the situation on August 9, 2025 18Z.
In the Northern Hemisphere, water evaporates from the sea surface of the North Atlantic and the North Pacific. Prevailing winds carry much water vapor in the direction of the Arctic. Precipitation over the Arctic Ocean freshens the surface, forming a buffer that temporarily slows down the decline of the sea ice extent. Similarly, much of the precipitation over land is carried by rivers into the Arctic Ocean, also freshening the surface of the Arctic Ocean. And of course, heavy melting of Arctic sea ice in June and July 2025 has added further freshwater to the surface of the Arctic Ocean.
The slowdown of AMOC can also create a buffer by delaying the transport of ocean heat toward the Arctic Ocean, but given the increase of Earth's Energy Imbalance and the additional heat that is instead accumulating in the north Pacific and the North Atlantic, more heat looks set to eventually reach the Arctic Ocean, overwhelming such buffers.
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| [ Precipitable water anomalies over Antarctica ] |
In the Southern Hemisphere, water evaporates from the Southern Ocean and part of it falls on the Antarctic ice sheet, thickening the snow layer, as illustrated by the image on the right, showing a forecast of high precipitable water anomalies over Antarctica on August 20, 2025.
As a result, the Southern Ocean surface is getting more salty. As discussed in an
earlier post, saltier surface waters sink more readily, allowing heat from the deep to rise, which can melt Antarctic sea ice from below, even during winter, making it harder for ice to reform. This vertical circulation also draws up more salt from deeper layers, reinforcing the cycle.
In conclusion, geographic differences result in different precipitation outcomes and this in turn causes salinity differences that are behind these temperature anomaly differences.
As said, the slowdown in the decline of Arctic sea ice extent that results from the increase in freshwater is temporary. Given the speed at which the temperature of the water of the Arctic Ocean keeps rising, this temporary slowdown looks set to be overwhelmed soon and rapid melting of sea ice looks set to return with a vengeance.
By contrast, the dramatic decrease in sea ice around Antarctica looks set to continue long-term, as a feedback that is amplified by albedo loss, lower emissivity, loss of the sea ice's latent heat buffer, ocean current changes and salinity changes.
Dire state of sea ice
The net result is illustrated by the image below. The global sea ice area anomaly was 2.62 million km² below the 1981-2010 mean on August 13, 2025, a standard deviation of -4.13σ from 1981-2010. The image shows that the global sea ice area anomaly was well below 1981-2010 in the years 2023, 2024 and 2025, which is remarkable, since there was a La Niña early in 2025. The year 2016 is also marked, since 2016 was a strong El Niño year.
The image below shows Arctic sea ice volume through August 11, 2025, when volume was at a record daily low, as it has been for more than a year.
, the ENSO outlook (CFSv2 ensemble mean, black dashed line) favors borderline La Niña conditions during the Northern Hemisphere fall and early winter 2025-2026, which suppresses temperatures.
