Cold freshwater lid on North Atlantic

At least ten tipping points look set to hit the Arctic hard, as described in an earlier post. Tipping points are abrupt climate changes that typically occur as self-reinforcing feedback loops start to kick in. Such tipping points can coincide and they are in many ways interrelated, making that the danger is compounded by the domino effect of multiple tipping points hitting one another. 

One feedback that is rarely-mentioned is the cold freshwater lid that is forming at the surface of the North Atlantic. 


Arctic is heating up faster than the rest of world.
Temperatures in the Arctic are rising faster than elsewhere in the world, as illustrated by the image on the right. As a result, the temperature difference between the North Pole and the Equator narrows and this slows down the overall speed at which the jet stream circumnavigates Earth.

It also widens the band within which the jet stream travels, so at times the jet stream will fan out widely or become much more wavy.

This distorted Jet Stream can cause more hot air to travel from the Atlantic Ocean and Pacific Ocean into the Arctic, as well as more cold air to travel out of the Arctic and descend over Europe, Asia and North America. Furthermore, high sea surface temperatures strengthen the wind over oceans, in turn increasing the speed of ocean currents and wave height.  

The image below, from an earlier post, shows the situation in September 6, 2020, when high sea surface temperatures on the Northern Hemisphere and a narrow difference between the Equator and the North Pole distorted the Jet Stream, making it cross the Arctic Ocean, form circular wind patterns and reach high speeds over the North Atlantic. The globe on the right shows that the Gulf Stream off the North American coast reached speeds of 8 km/h or 5 mph (at green circle).

[ click on images to enlarge ] 
Emissions by people heat up the air, which heats up oceans and makes winds stronger, in turn speeding up global ocean currents. A 2020 study by Hu et al. found increased kinetic energy in about 76% of the upper 2,000 meters of global oceans, as a result of intensification of surface winds since the 1990s. Wind speed increases especially during Winter on the Northern Hemisphere, when there are large temperature differences between the oceans and continents on the Northern Hemisphere. 

Below follow a number of images showing wind speed at different pressure levels, i.e. 850 hPa and 250 hPa (Jet Stream), wave height, sea surface temperature anomalies and 3-hour precipitation accumulation, all on December 12, 2020. 

The first image below shows that, on December 12, 2020, waves as high as 12.95 m or 42.5 ft (green circle) were recorded in the North Atlantic, and wind speed was 139 km/h or 86 mph (at 850 hPa) at that location.


The next image (below) shows that, on December 12, 2020, sea surface temperatures were very high off the east coasts of Asia and North America, where ocean currents carry hot water to the north-east. As the image shows, the sea surface temperature was 14°C or 25.1°F higher than 1981-2011 at the green circle. 


High sea surface temperatures are causing winds over oceans to get much stronger than they used to be at this time of year. The image below shows that, on December 12, 2020, the jet stream reached speeds as high as 324 km/h or 201 mph (at the green circle), while instantaneous wind power density at 250 hPa (jet stream) was 141.1 kW/m².


These strong winds then collide at high speed with the air in front that is moving at a slower speed. This collision occurs with an even greater force due to the lower overall speed at which the jet stream circumnavigates Earth, and especially in Winter on the Northern Hemisphere, when temperatures over land (i.e. North America, Europe and Asia) are low. Where such collisions occur, the air gets strongly pushed aside toward the Arctic and the Equator. The images show the Jet Stream crisscrossing the Equator and moving high up in the Arctic. 


Above image shows 3-hour precipitation accumulation as high as 94 mm or 3.7 in (at the green circle) on December 12, 2020. 

At times, the Jet Stream can reach even higher speeds. The image on the right shows that on December 20, 2020, the Jet Stream reached a speed of 406 km/h or 252 mph at the green circle, while the Jet Stream crosses the Equator in the south and, in the north, wind forms a circular pattern over the Arctic Ocean. As described in an earlier post, the Jet Stream was as fast as 411 km/h or 255 mph south of Greenland (at the green circle), before crossing the Arctic Ocean on November 4, 2020.

As said, as ocean heat increases, the temperature difference between land and oceans increases in Winter on the Northern Hemisphere, when land is cold. 

The temperature difference increases even more at times when cold air descends from the Arctic over North America and over Europe and Asia. 

This larger temperature difference results in stronger winds that can carry more warm, moist air farther down the track of the Gulf Stream, as illustrated by image on the right that shows precipitation in mm per hour. 

Stronger ocean stratification, in combination with higher sea surface temperatures and distortions of the Jet Stream, can cause a sudden strengthening of the wind, and this can push a lot of warm, moist air all the way from the Atlantic Ocean into the Arctic Ocean. 

[ click on images to enlarge ]
As oceans heat up, more water evaporates from the sea surface. This evaporation will cool the sea surface somewhat, so the sea surface can be colder than the water just underneath the sea surface. 

Much of the moisture that evaporates from the sea surface will get blown farther along the path of the Gulf Stream in the direction toward the Arctic before precipitating, thus contributing - along with meltwater - to the formation of a cold freshwater lid at the surface of the Atlantic Ocean. 

The image on the right shows a wavy Jet Stream pushing precipitation north over the Atlantic Ocean, with 0.9 mm or 0.04 in of precipitration (3-hour accumulation) reaching the North Pole on December 24, 2020. 

Stronger winds along the path of the Gulf Stream can speed up sea currents that travel underneath this cold freshwater lid over the North Atlantic. As a result, huge amounts of warm, salty water can travel from the AtlanticOcean toward the Arctic Ocean, pushing up temperatures and salinity levels at the bottom of the Arctic Ocean and threatening to destabilize methane hydrates that are contained in sediments at the seafloor of the Arctic Ocean.

As the image on the right shows, sea surface temperatures off the east coast of North America were very high on January, 2021, as much as 15.4°C or 27.7°F higher than 1981-2011 at the green circle.

In summary, the danger is that stronger winds will trigger huge eruptions of methane, as more hot and salty water will reach the shallow parts of the Arctic Ocean that contain huge amounts of methane in the form of hydrates and free gas in sediments at the seafloor, resulting in huge eruptions of methane. 

On its own, this could within years cause the 1200 ppm CO₂e cloud feedback tipping point to be crossed, which in turn can cause global temperatures to rise by 8°C, as discussed in an earlier post.

Latent heat loss, feedback #14 on the Feedbacks page

More methane over the Arctic will push up temperatures locally over the Arctic Ocean as well as over the permafrost on land. A 2020 study by Turetsky et al. found that Arctic permafrost thaw plays a greater role in climate change than previously estimated. 


Links

• Earth nullschool.net

• Climate Reanalyzer

• Carbon release through abrupt permafrost thaw - by Merritt Turetsky et al.

• Deep-reaching acceleration of global mean ocean circulation over the past two decades - by Shijian Hu et al. 

• 2020: Hottest Year On Record 

• Temperatures threaten to become unbearable

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