Global Warming increases Marine heatwaves

marine heatwavesLand based heatwaves rather obviously involve an increase in air temperature, but since most of the planet is covered by water then we also have something similar in the world’s oceans – marine heatwaves. The concept recently entered the public’s social consciousness when the following was tweeted …

Scripps researchers have been taking sea surface temperature and salinity readings at the pier since 1916. In 1925, they began taking seafloor water temperature measurements as well, and so the above reading is the highest they have ever measured since they started doing that.

Phys.Org has more details

There they report …

The region off Southern California has been experiencing anomalously warm temperatures for the past week and other observational networks farther off the coast have reported record or near-record temperatures as well.

Researchers said that the record warmth is consistent with similar records for high temperatures set on land as well as a torrent of extreme weather in 2018. This is how global warming will play out, said Scripps scientists: Records related to heat and intense weather will become easier to break having been given a boost from anthropogenic climate change that has added about 1 degrees C to ocean temperatures over the past century.

“Like other climate change trends, background warming enhances the probability and magnitude of extreme events,” said Scripps oceanographer and Shore Stations principal investigator Reinhard Flick.

Physical oceanographer Dan Rudnick runs a Scripps program that employs underwater gliders to make ocean temperature profiles to points about 200 miles off the California coast as well as in other regions around the world. He has noticed a similar warming throughout Southern California coastal waters.

Rudnick is one of several Scripps researchers who has tracked an uptick in ocean temperatures related to El Niño, a phenomenon characterized by the movement of warm waters to the eastern equatorial Pacific Ocean, which often affects water temperatures off California. The rise began in 2014 during a marine heatwave, then an intense El Niño bore down on the West Coast the following year. In times past, the pattern would have been for ocean water temperatures to return to historical averages following the event but that hasn’t been the case.

“It looks like we took a step up during 2014-2016 from which we have not completely recovered,” said Rudnick.

Recent Studies concerning the impact of Marine Heatwaves

Ecosystem Impact

Ecosystem restructuring along the Great Barrier Reef following mass coral bleaching – Nature – July 25th 2018

It reviews the details of the extensive ecosystem impact upon the Great Barrier Reef by the 2016 bleaching event but highlights that sea temperature change and not just coral loss is a huge issue…

Here we use data from before and after the 2016 mass bleaching event to evaluate ecological changes in corals, algae, fishes and mobile invertebrates at 186 sites along the full latitudinal span of the Great Barrier Reef and western Coral Sea. One year after the bleaching event, reductions in live coral cover of up to 51% were observed on surveyed reefs that experienced extreme temperatures; however, regional patterns of coral mortality were patchy. Consistent declines in coral-feeding fishes were evident at the most heavily affected reefs, whereas few other short-term responses of reef fishes and invertebrates could be attributed directly to changes in coral cover. Nevertheless, substantial region-wide ecological changes occurred that were mostly independent of coral loss, and instead appeared to be linked directly to sea temperatures.

Let’s be a bit more specific about what the study discovered. There are fish that eat algae and so remove it from coral surfaces. This helps the coral to recover after a bleaching. Because of the sea temperature change these fish have declined, and that has impacted coral recovery.

Global Warming is a factor that is in play

Marine Heatwaves under global warming – Nature – Aug 15th 2018

This study reveals that Marine Heatwaves are increasing in both intensity and also frequency.

They used satellite observations and a suite of Earth system model simulations to show that marine heatwaves have already become longer-lasting and more frequent, extensive and intense in the past few decades, and that this trend will accelerate under further global warming. Between 1982 and 2016, they detected a doubling in the number of marine heatwaves days, and this number is projected to further increase on average by a factor of 16 for global warming of 1.5 degrees Celsius relative to preindustrial levels and by a factor of 23 for global warming of 2.0 degrees Celsius.

A Realistic Projected Impact

Right now the current policies in place for the reduction of global carbon emissions are predicted to result in global warming of about 3.5 degrees Celsius by the end of the twenty-first century. The study on the impact of Global Warming on Marine Heatwaves reveals that if that does happen then the average increase in the probability of marine heatwaves will be by a factor of 41.

  • At this level of warming, marine heatwaves have an average spatial extent that is 21 times bigger than in preindustrial times
  • They would also last on average 112 days and reach maximum sea surface temperature anomaly intensities of 2.5 degrees Celsius.

Has it always been as it is now?

No. Today about 87% of the observed marine heatwaves is attributable to human-induced warming.

As things play out they will become even more frequent and intense.

That will probably push marine organisms and ecosystems to the limits of their resilience and even beyond. We are on the cusp of  irreversible changes.

How big a deal is this?


Marine heatwave may also affect the ocean’s ability to soak up greenhouse gases.

To date, oceans have absorbed more than 90 percent of the extra heat generated by manmade climate change. Without that sea-water sponge, air temperatures would be tens of degrees Celsius higher.

Further Reading

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