Rare "sea smoke" is seen over waters off the coastal city of Qingdao, East China's Shandong Province, on January 7. Photo:Wang Shaoqing

Despite the small dip in global carbon emissions due to restrictions on travel and other activities due to the COVID-19 pandemic, global ocean temperatures continued breaking records in 2020, with a recent study reporting the highest ocean temperatures since 1955 from surface level to a depth of 2,000 meters.

Ocean temperatures will continue to rise this century and will prompt more extreme weather events such as intensive rainfall and hurricanes globally, and in China, rising global sea levels together with extreme weather may cause seawater to flood China's coastal areas and even inundate some regions, researchers from the study warned. 

The paper, authored by 20 scientists from 14 institutes around the world, found that in 2020, the upper 2,000 meters of the world's oceans absorbed 20 Zettajoules more than in 2019. 

The paper was published by the international journal Advances in Atmospheric Sciences on Wednesday. 

That amount of heat could boil 1.3 billion kettles, each containing 1.5 liters of water, Cheng Lijing, the lead author and associate professor with the International Center for Climate and Environmental Sciences at the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences (CAS), told the Global Times on Wednesday. 

Over 90 percent of the excess heat due to global warming is absorbed by oceans, which means ocean warming is a direct indicator of global warming, according to Cheng.

Due to the ocean's delayed response to global warming, the trend of ocean temperatures rising will persist for at least eight decades, and ocean temperatures will rise three times as much in the next 80 years as they did in the last 60 years even after fulfilling the Paris climate agreement of limiting the global temperature increase this century to 2 degrees Celsius, Cheng said.

Using a method developed at IAP/CAS, the researchers calculated temperatures and salinity of the oceans down to 2,000 meters with data taken from the World Ocean Database.

"Warmer oceans will promote more intense rainfalls in storms, and especially hurricanes, increasing the risk of flooding, and extreme fires like those witnessed in 2020 will become even more common in the future," Cheng said.

Chinese coastal regions are among the most vulnerable areas in the world to rises in sea level, and the increasing ocean temperature will lead to rising sea levels which will erode and, in extreme situations, inundate land, forcing people in coastal regions to relocate, Cheng said.

Rare "sea smoke" was seen over waters off the coastal city of Qingdao, East China's Shandong Province, on January 7. 

The phenomenon was created by current sub-zero winds in Qingdao combining with the relatively warm water.