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Weather | Marine heat wave

Marine heat waves behind balmy summer weather in U.S.

Dr. Mario Picazo
Meteorologist, PhD

Sunday, August 19, 2018, 18:15 - The summer of 2018 will be remembered for the warm balmy weather experienced across a great portion of Europe and North America.

Over the past two months, many areas accustomed to milder summer weather like the U.S. West Coast or much of northwest Europe, have been living in a more tropical-like environment, and much of it has to do with ongoing frequent and prolonged marine heat waves.

What is a marine heat wave?

Marine heat waves are different than terrestrial heat waves in that they can last longer, sometimes weeks, since oceans take in and give away heat at a much slower rate than air. They can also affect vast extensions of water, much greater in size than land heat waves, and can have a tremendous impact both on temperature and water vapor content of the air.

SST anomalies Atlantic -- July 2018

The situation we have been experiencing across many areas of Europe and North America is a consequence of a loop-like effect. 

As warmer air affects an area, it also has a greater capacity to retain water vapor. More water vapor means the air can trap more outgoing longwave radiation, especially at night when the Earth's surface is expected to cool down. This is one of the reasons why overnight lows near or at many coastal areas of both continents have been exceptionally high during the summer months. 

Tropical nights (when low temperatures remain above 68oF) have been more common, and minimum temperatures have remained in the 70s for many areas. During these balmy nights, it is more difficult for the human body to cool down, especially the elderly and sick people.

SST anomalies East Pacific -- August 2018

Scientists have used satellite data to determine that between 1982 and 2016, the number of marine heat wave days doubled, and that they normally last longer than in previous decades. This is probably no surprise for those who have traveled to southern California this summer in search of cool coastal Pacific sea breezes. 

This summer a tropical-like environment is dominating much of the west coast, and cities like San Diego and Los Angeles have been on the balmy side week after week, with exceptionally high minimum temperatures and high dew point temperatures overall.

This summer Sea Surface Temperature anomalies (SSTa) along the coast of southern California and much of northern Baja California in Mexico have skyrocketed and are well above average, with some values reaching 5 to 6oF. This excess ocean energy is not only affecting human comfort conditions, but also marine fauna and ecosystems in the region.

Will marine heat waves be more frequent in the future?

A study conducted by Dr. Thomas Frölicher from the Physics Institute at the University of Bern, Switzerland, shows ocean heat waves will be more common in the future.

If average global temperatures increase to 3.5°C above pre-industrial levels by the end of the century as researchers currently project, the frequency of ocean heat waves could increase by a factor of 41.

Nightime temperature anomalies -- Aug. 2, 2018

He adds that these changes are already well outside what could be expected on the basis of natural swings in Earth's climate. The study’s analysis determined that 87 per cent of heat waves in the ocean are the result of human-induced global warming.

Whales, sharks, squid: Spectacular marine hot spot found

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