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Upper Ocean Temperatures Hit Record Highs in 2020

Ocean surface temperatures reached a new high in 2020, portending dangerous consequences as scientists urge officials to implement environmental protections and push for clean energy.

Ocean surface temperatures reached a new high in 2020, portending dangerous consequences as scientists urge officials to implement environmental protections and push for clean energy.

Fishing boats amidst "Arctic sea smoke" near Qingdao, China on Jan. 7. Arctic sea smoke is a result of frigid air passing over relatively warm water; the phenomenon is rare, even in the Arctic. (Photo by Shaoqing Wang)

(CN) — Climate change did not skip a beat in 2020, according to a new study, as the ocean experienced record warming and surface temperatures reached levels not seen in decades.

The study, published Wednesday in the journal Advances in Atmospheric Sciences, was conducted by a team of international scientists who hope that their latest evidence on oceanic conditions can be enough to persuade policymakers and contributors to implement drastic change before the damage becomes irreversible.

"Over 90% of the excess heat due to global warming is absorbed by the oceans, so ocean warming is a direct indicator of global warming — the warming we have measured paints a picture of long-term global warming," said lead author Lijing Cheng, associate professor with the International Center for Climate and Environmental Sciences at the Institute of Atmospheric Physics of the Chinese Academy of Sciences.

"However, due to the ocean's delayed response to global warming, the trends of ocean change will persist at least for several decades, so societies need to adapt to the now unavoidable consequences of our unabated warming. But there is still time to take action and reduce our emissions of greenhouse gases,” Cheng continued.

Due to government restrictions put in place to slow the spread of Covid-19, global greenhouse gas emissions saw a 7% decrease from the lack of transportation activity last year, the most significant decline ever seen. Studies show that April 2020 experienced a 17% drop in emissions, but since then they have risen and are almost back to 2019 levels. Now scientists are urging officials to put environmental protections in place and enforce the push towards clean energy consumption as we recover from the pandemic.

By looking at all available data on oceanic conditions within the World Ocean Database and combining it with an IAP/CAS based method, the team saw that despite the drop in emissions in 2020, the uppermost 2,000 meters of the ocean absorbed 20 more zettajoules of heat than in 2019. To put that figure in perspective, the authors say that amount of heat could boil 1.3 billion kettles of water.

"Why is the ocean not boiling?" Cheng asked. "Because the ocean is vast. We can imagine how much energy the ocean can absorb and contain, and, when it's released slowly, how big the impact is."

Furthermore, as the upper layer becomes increasingly warm, its salinity is altered which creates a barrier between the fresher water above and the saltier water below. The stratification makes it more difficult for oxygen to permeate to the deep ocean, creating a problem for deep-sea dwellers and posing a risk for increased acidification.

"The fresh gets fresher; the salty gets saltier," Cheng said. "The ocean takes a large amount of global warming heat, buffering global warming. However, the associated ocean changes also pose a severe risk to human and natural systems."

Risks of the ocean changes include sea level rise, a drop in biodiversity, food scarcity and other dangerous consequences.

One such consequence has already occurred in the Great Barrier Reef, where scientists found in a separate study released this week that baby sharks cannot survive in the coming ocean temperatures. According to doctoral candidate Carolyn Wheeler at the ARC Centre of Excellence for Coral Reef Studies at James Cook University and the University of Massachusetts, warmer ocean temperatures cause baby epaulette sharks to hatch far too early, significantly decreasing their chances for survival. They hatch much smaller than normal, with less strength and a far larger appetite.

"The hotter the conditions, the faster everything happened, which could be a problem for the sharks. The embryos grew faster and used their yolk sac quicker, which is their only source of food as they develop in the egg case. This led to them hatching earlier than usual," Wheeler said.

In warmer waters, shark embryos grew faster and used their yolk sac quicker, which is their only source of food as they develop in the egg case. This led to them hatching earlier than usual. (Photo by M. Johnson)

This is especially concerning as sharks are the apex predators of the sea and are vital to maintaining ocean health. Without sharks, the population of its prey would explode and in turn could throw off the balance of the food chain and available resources for marine life. These predators are already close to making the threatened species list, and since they repopulate and reach maturity slower than other ocean species, it is important to protect them to adulthood.

"The epaulette shark is known for its resilience to change, even to ocean acidification," Jodie Rummer, co-author of the study published in Scientific Reports, said. "So, if this species can't cope with warming waters then how will other, less tolerant species fare?"

Another consequence of unhealthy oceans is the increased risk of natural disasters on land, which has already been seen over the years. Cheng noted the devastating fires seen throughout 2020 that caused unmitigated damage to parts of Australia, the Amazon and the American West.

"Warmer oceans and a warmer atmosphere and also promote more intense rainfalls in all storms, and especially hurricanes, increasing the risk of flooding," Cheng said. "Extreme fires like those witnessed in 2020 will become even more common in the future. Warmer oceans also make storms more powerful, particularly typhoons and hurricanes."

"As more countries pledge to achieve 'carbon neutrality' or 'zero carbon' in the coming decades, special attention should be paid to the ocean," Cheng said. "Any activities or agreements to address global warming must be coupled with the understanding that the ocean has already absorbed an immense amount of heat and will continue to absorb excess energy in the Earth's system until atmospheric carbon levels are significantly lowered."

Categories / Environment, Science

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