Oceans Are Warming 40 Percent Faster Than Previously Estimated

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In the past several years, many studies and individual researchers have been warning that the official  Intergovernmental Panel on Climate Change (IPCC) assessments are underestimating the pace of global warming.  This is proving to be especially true for the oceans, who are absorbing about 93 percent of additional heat created by human carbon emissions – the so-called increased ocean heat content (OHC). 

Scientists now agree that Earth’s seas are warming faster than previously thought. A review of available studies, published in Science in January 2019, has revealed that the rate of ocean warming is as much as 40% faster than that suggested by IPCC. The team stated that “multiple lines of evidence from four independent groups thus now suggest a stronger observed [OCH] warming.”

Another 2019 study called “Global reconstruction of historical ocean heat storage and transport” also suggests that the oceans are taking up at least 90 percent of excess atmospheric heat and that they have been warming at least since the 1800s. 

Map of ocean heat content in the upper ocean (from the sea surface to a depth of 700 meters, or 2,300 feet) for 2017 relative to the 1993–2017 baseline. Source: NASA.
Map of ocean heat content in the upper ocean (from the sea surface to a depth of 700 meters, or 2,300 feet) for 2017 relative to the 1993–2017 baseline. Source: NASA.

Why is Ocean Warming Important?

Although anomalous land warming often gets the most publicity, understanding the dynamics of ocean warming is very important for several reasons. 

  • A precise understanding of ocean warming is crucial for the scientific understanding of the global warming phenomenon as a whole.
  • The pattern of ocean currents is thought to depend on ocean temperatures as well as by the changes in the warming atmosphere; it is possible that drastic temperature changes will cause disruptions in the current global current patterns.
  • The warmth of the ocean directly affects the melting of sea ice and, consequently, the pace of the global sea-level rise.
  • The ocean ecosystem supports the entire biosphere in various ways – and that includes the human societies. 

Influence on Ocean Currents and Sea Level Rise

As for the second and third reasons listed above, the latter study found that in recent decades there has been a noticeable change in the large-scale circulations patterns. It suggests that about half of the extra heat stored in the mid-latitude regions of the Atlantic in the second half of the 20th century was transported there from other parts of the oceans by the unusual currents. That means that the sea-level rise in this part of the ocean is being influenced by the changing circulation patterns.

The pattern change may be influenced by rising ocean temperatures, and also by atmospheric patterns and winds that are likewise changing under the influence of global warming. 

The authors of the study point out that “Future changes in ocean transport could have severe consequences for regional sea-level rise and the risk of coastal flooding.” 

Influence On Marine Life

To illustrate how ocean warming extremes affect ocean life, a new study sheds light on a notorious die-off event that happened a few years ago. 

From 2015 to 2016, about 62,000 common murres (Uria aalge) washed onto the shores from Southern California to Alaska – starved, dying or already dead. At the same time and shortly after, the reproductive season in the murres’ colonies failed on a massive scale. A study estimated that 10 to 20 percent of the region’s total population was lost in this unfortunate event.

Survey of murres population along the west coasts between May 2015 and April 2016.  Gold circles indicates numbers of monthly dead or moribund murres.  Red circles indicates opportunistic beach surveys and rehab captures.  Map: Piatt et al., 2020.
Survey of murres population along the west coasts between May 2015 and April 2016. Gold circles indicates numbers of monthly dead or moribund murres. Red circles indicates opportunistic beach surveys and rehab captures. Map: Piatt et al., 2020.

The mechanisms that affected this well-adapted seabird’s demise were widely researched and debated. The most recent 2020 study by John F. Piatt and his team labels the main suspect as “The Blob” – a Northern Pacific ocean heatwave, extreme both in strength and in duration. The Blob had managed to disrupt the ocean food web by changing the range and the diversity of plankton and increasing the metabolic demands of fish. As a consequence, the species on the top of the food chain – the murres – suffered greatly. 

Future climate disruption may cause even greater shifts in ocean stability. Monitoring these changes diligently could help predict which parts of the ocean will warm and expand rapidly in the future, and possibly to predict a range of consequences these changes will have. 

Also, the alarming new estimate of ocean take-up of the excess anthropogenic heat, with all its consequences, is another call to action on reducing emissions and mitigating climate change.


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Resources

The Studies:

Lijing Cheng et al. (2019). How fast are the oceans warming? Science 11 Jan 2019: Vol. 363, Issue 6423, pp. 128-129. DOI: 10.1126/science.aav7619

Zanna, L. et al. (2019) Global reconstruction of historical ocean heat storage and transport. PNAS January 22, 2019 116 (4) 1126-1131; https://doi.org/10.1073/pnas.1808838115

Piatt, J.F. et al. (2020). Extreme mortality and reproductive failure of common murres resulting from the northeast Pacific marine heatwave of 2014-2016. PLOS ONE. January 15, 2020. https://doi.org/10.1371/journal.pone.0226087

The Articles:

Harvey, C. “Oceans Are Warming Faster Than Predicted”. Scientific American E&E News. January 11, 2019. https://www.scientificamerican.com/article/oceans-are-warming-faster-than-predicted/

Lambert, J. “The ‘Blob,’ a massive marine heat wave, led to an unprecedented seabird die-off. Science News. January 15, 2020. https://www.sciencenews.org/article/massive-marine-heat-wave-blob-unprecedented-seabird-die-off

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