Arctic News: Extreme Heat Risk

Friday, August 8, 2025

Extreme Heat Risk

The above image, adapted from NOAA National Weather Service, shows extreme heat risk for multiple areas in the U.S., with a location near Imperial, California highlighted with details.
Details for the forecast for this location are:

- Wet bulb globe temperature: 93°F or 34°C
- Temperature: 102°F or 39°C
- Apparent Temperature: 117°F or 47°C
- Dew Point: 77°F or 25°C
- Relative Humidity: 46%
- Forecast for: August 9, 2025 21:00 UTC

On the above image, this extreme risk area is located at a latitude of 33.22° North. What is remarkable is that on the map there is also a high risk area that extends all the way from the southern border of the U.S. with Mexico to the northern border of the U.S. with Canada, with extreme risk areas showing up at latitudes North higher than for Toronto, Canada.

The image below, adapted from the heat risk page at the NOAA National Weather Service, shows a forecast for August 9, 2025, updated 10.49 AM EST. The map shows high and extreme risk areas, including an extreme risk area centered around Grand Rapid, Michigan, which is located at a latitude of about 43° North.

The images illustrate that extreme weather events that come with extreme, even fatal heat stress risk conditions can now increasingly occur almost anywhere in the U.S.

The image below, adapted from Climate Reanalyzer, shows a three-day forecast of maximum temperatures run on August 8, 2025.

The image below, also adapted from Climate Reanalyzer, shows the one-day average sea surface temperature anomaly (from 1971-2000) for August 7, 2025.

Speeding up Arctic sea ice demise

[ click on images to enlarge ]

The above image shows very high sea surface temperature anomalies around and inside the Arctic Ocean. These anomalies are getting higher by the day, due to Earth Energy Imbalance and the change of seasons.

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 5, 2025.

The image on the right underneath shows North Atlantic sea surface temperatures as high as 32.8°C on August 5, 2025.

[ from earlier post, click to enlarge ]

The image shows heat moving up along the path of the Gulf Stream toward the Arctic, threatening to accelerate 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.

There are also buffers and once they are overwhelmed or disappear, the temperature rise will speed up rapidly. One example is the latent heat buffer. Arctic sea ice is getting thinner over the years, so the amount of heat that can be absorbed in the process of melting is getting smaller over time.

As the latent heat buffer decreases, the heat that was previously absorbed by the phase change from ice to water, will therefore instead get absorbed by the water, further raising the temperature of the water. As the sea ice thickness decreases over the years, less incoming ocean heat can therefore be consumed by melting the remaining sea ice.

More freshwater temporarily slows down melting of Arctic sea ice

[ 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 temperature 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 strongly, 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 has created a temporary slowdown in the decline of the sea ice, a buffer of 2°C (as depicted by the image below on the right).

Freshwater buffer looks set to be overwhelmed soon

[ Saltier water, less sea ice, from earlier post ]

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).

This slowdown in the melting of Arctic sea ice 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.

The above image shows Arctic sea ice concentration on August 9, 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, giving the sea ice a buffer that temporarily slows down the melting of the sea ice. 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.

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 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.

The slowdown in the melting of Arctic sea ice 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.

The net result is illustrated by the image below, showing that the global sea ice area anomaly was 2.69 million km² below the 1981-2010 mean on August 9, 2025, a standard deviation of -5.22σ from 1981-2010.

What makes the dire state of the sea ice even more significant is that there currently are no El Niño conditions. The ENSO outlook favors borderline La Niña during the Northern Hemisphere fall and early winter 2025-2026, as discussed in a recent 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.