Chilly Mystery
Climate Change Daily Earth Science Repost

A chilly mystery in the North Atlantic

Temperatures in Siberia, above the Arctic circle, soared to over 100 degrees Fahrenheit (F) recently. The planet has warmed by nearly 2 degrees F since 1900, and the Arctic and Antarctic are warming several times faster than the rest of the globe. But far from land, in the open seas of the North Atlantic Ocean, something strange is happening. A vast area of the ocean to the south of Greenland is cooling almost as fast as the rest of the planet warms.

Understanding global warming first requires grasping the scope of ocean warming. But don’t just think about warming in terms of rising temperatures. Instead, think of it in terms of increasing heat content. More than 90 percent of the extra heat absorbed by the earth over the past 50 years ended up in the oceans. So, the oceans are the primary heat sink for our warming planet. 

The general effect of this marine heating is a rise in average ocean surface temperatures and a corresponding rise in atmospheric temperatures over the past 120 years. However, the North Atlantic did not receive the message and bucked the global trend, cooling by about 1.6 degrees F and presenting a chilly mystery.  

Ocean circuitry

Solar radiation is the primary source of heat for the earth, and the tropics are hot because they receive more solar heat than the polar regions. Ocean currents are one of the ways that this heat redistributes from the tropics to higher latitudes.  These currents form the planetary circuitry of heat dissipation, but global warming is causing the oceans to rewire themselves in ways that interrupt existing circulation patterns.

One of the North Atlantic’s critical circulation systems is the Atlantic Meridional Overturning Circulation (AMOC). This system drives the famous Gulf Stream, which carries warm water from the Caribbean and Gulf of Mexico into the North Atlantic. Thus, Europe owes its mild winters to the heat from the Gulf Stream.

The critical enabler of the Gulf Stream is thermohaline circulation. When cold salty water from the Arctic flows into the North Atlantic, it is denser than the surrounding waters and sinks to the ocean bottom. This sinking water then creates a void, and warm water from the tropics flows in to fill that void. So, the real driver for the Gulf Stream is dense Arctic water. If less Arctic water sinks, then less tropical water can flow in from the south.

Researchers believe that the chilly mystery of cooling in the North Atlantic may be related to a weakening AMOC, and hence a weakening Gulf Stream.

Too much freshwater

This incident is not the first time in recorded history that unexplained cooling occurred over the North Atlantic. Between the years 1300 and 1850, Europe experienced a general cooling of its climate. The average temperatures in Europe dropped by about 3.6°F. The name given to this period is the ‘Little Ice Age.’

Visible effects of this cooling were noted all across Europe. The Baltic Sea froze over in winters, along with rivers and lakes across Europe. Also, winters were bitterly cold, and the summers were cool. Because of the colder climate, crop failure was prevalent, leading to famine, population decline, and social unrest. Mountain snowlines dropped to lower elevations, and glaciers expanded, wiping out villages and farms. Additionally, the Arctic Ocean ice packs extended southward, making winter shipping impossible in some areas. Multiple theories for causes of the Little Ice Age, including changes in solar activity, increased volcanism, and weakening of the AMOC.

Many researchers believe that freshwater is the culprit in this chilly mystery we have today. Extra fresh water in the North Atlantic dilutes the dense, salty Arctic water, making it more buoyant and less likely to sink. Researchers tie the increase in freshwater to melting ice in Greenland.

The Greenland Ice Sheet has lost an estimated 3.8 trillion tons of ice since 1992, according to a study from NASA and the European Space Agency (ESA). Massive volumes freshwater flowing into the North Atlantic lower the salinity, and hence the density, of surface waters. So with less water sinking to the ocean bottom, the Gulf stream slows down and thus carries less heat to the North Atlantic. With less heat, the ocean cools, solving the puzzle of why this area of the North Atlantic is chilling as the rest of the planet heats up.


ArcheanWeb:

Gulf Stream and the Little Ice Age (Source: ArcheanWeb) – https://archeanweb.com/2019/12/30/gulf-stream-and-the-little-ice-age/  Also:

Thermohaline circulation (Source: ArcheanWeb) – https://archeanweb.com/2020/04/03/thermohaline-circulation/  Also:

Riding the global conveyor belt (Source:ArcheanWeb) – https://archeanweb.com/2020/04/06/riding-the-global-conveyor-belt/  Also:

Ocean warming dwarfs atmospheric warming (Source: ArcheanWeb) – https://archeanweb.com/2020/01/21/ocean-warming-dwarfs-atmospheric-warming/  Also:


Sources:

If you doubt that the AMOC has weakened, read this (Source: RealClimate) – http://www.realclimate.org/index.php/archives/2018/05/if-you-doubt-that-the-amoc-has-weakened-read-this/  Also:

Why Earth has a stubborn spot that’s cooling (By MARK KAUFMAN; Mashable) – https://mashable.com/article/cold-blob-atlantic-ocean-climate-change/  Also:

Greenland’s Rapid Melt Will Mean More Flooding (Source: NASA) – https://www.jpl.nasa.gov/news/news.php?feature=7556  Also:

Feature Image: Giant Ocean Wave (Modified) – By Unknown author – [1], CC0, https://commons.wikimedia.org/w/index.php?curid=88819036  

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.