Ocean Temperature In 2019 Was The Warmest In Recorded Human History

Earth's oceans absorb most of the excess heat from greenhouse gas emissions, which leads to a rise in ocean temperatures. Jiang Zhu

Our oceans are more than just a means of fluid transport and habitat for seafood, they are also heat stores, with more than 90 percent of the excess heat from human-emitted greenhouse gases accumulated within our seas. By measuring the increase in warmth, scientists can reveal more about our planet's rate of global warming. 

"The world’s oceans (especially at upper 2,000 meters) in 2019 were the warmest in recorded human history," write an international team from 11 institutes worldwide in the journal Advances in Atmospheric Sciences.

Last year’s ocean temperature was about 0.075°C (0.14°F) above the 1981-2010 average. That means the ocean took in 228 Zetta Joules above the 1981-2010 average and 25 Zetta Joules above 2018. Zetta is 21 zeros to that number to make it 228,000,000,000,000,000,000,000 Joules of heat.

The figure is a lot to handle, so lead author Lijing Cheng compared the heat to the Hiroshima atom-bomb, which exploded with a blast energy of about 63,000,000,000,000 Joules. Around 3.6 billion Hiroshima atom-bomb explosions have been added to the world’s ocean in the past quarter-century.

"Our data shows that global warming is accelerating. In fact, the heating rate now is about 500 percent greater than it was in the 1980s and before. This is a problem that will not get better on its own. We need to work on solutions now," co-author John Abraham, professor of mechanical engineering at the University of St. Thomas in the United States, told IFLScience.

Ocean warming threatens food security and people's livelihoods. Jiang Zhu

"When the Sun’s energy reaches the Earth, some of it is reflected back to space and the rest is absorbed and re-radiated by greenhouse gases such as carbon dioxide. This is called greenhouse effect that keeps our Earth warm," Cheng, from the International Center for Climate and Environmental Sciences at the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences (CAS), told IFLScience.

The heat was distributed throughout Earth’s oceans, with the Atlantic Ocean and Southern Ocean showing one of the largest warming trends compared to most other basins. Since the 1970s, it's been known the Southern Ocean is a focal point of rising heat, with 35 to 43 percent of the increase in global ocean heat content relegated to the ocean south of 30°S between 1970 and 2017.

"The overall ocean warming means the natural variability creates hot spots and marine heat waves," said Cheng. "The Blob was a notable one in 2014 and led to major consequences for all of marine ecosystems, from plankton to fish to marine mammals and birds. Over 100 million cod were lost.
A substantial marine heat wave with similar consequences for marine life occurred in the south Tasman Sea in 2015."

The researchers obtained their values from the Institute of Atmospheric Physics (IAP) ocean analysis, which uses a method to account for sparse data and updates in the instruments used to measure ocean temperature. They managed to calculate ocean temperatures down to 2,000 meters (6,500 feet) using observations from a variety of measurement devices from the World Ocean Database of the National Oceanic and Atmospheric Administration (NOAA).

"The warming oceans are indisputable proof that the Earth is warming. There is no natural alternative to explain this (I wish there were). This isn’t just a 'natural cycle'. This is human caused," said Abraham.

"Ocean warming and its consequences have long been overlooked," Cheng said.

"It has lots of consequences: melting ice sheets from the bottom because of ocean warming, bleaching coral reefs, rising sea level (because warming water expands), fueling the storms (super-charge typhoons and hurricanes), reducing the ocean dissolved oxygen (because of warmer water has less capability to dissolve oxygen), increase extremes such as marine heat waves etc. These stresses caused by ocean environmental changes clearly pose high risks to biodiversity and fisheries, and cause economic losses."

The team say it is important to note that ocean warming will continue even if surface air temperature is kept at or below 2°C (3.6°F). Changes in ocean temperature driven by greenhouse gas emissions are slow to respond and equilibrate. However, the rates will be smaller with lower greenhouse gas emissions and "the rate of increase can be reduced by appropriate human actions that lead to rapid reductions in GHG emissions, thereby reducing the risks to humans and other life on Earth."

The paper was scheduled for a late evening embargo but broke early yesterday due to a Springer contract company “now bracing for the possible full eruption of Taal volcano just 61km from its workplace.” Not wanting to endanger anyone, the paper was released early.

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