Monday, May 20, 2024

Ocean Heat, Acidification, Sea Level Rise Set New Records in 2021


Sea level rise, ocean heat and ocean acidification set new records in 2021, yet another clear sign that human activities are causing planetary scale changes in the ocean, on land and in the atmosphere, according to a new report issued this week by the World Meteorological Organization (WMO).

Ocean heat was at a record high, WMO’s report found:

“The upper 2000m depth of the ocean continued to warm in 2021 and it is expected that it will continue to warm in the future – a change which is irreversible on centennial to millennial time scales. All data sets agree that ocean warming rates show a particularly strong increase in the past two decades. The warmth is penetrating to ever deeper levels. Much of the ocean experienced at least one ‘strong’ marine heatwave at some point in 2021.”

Ocean acidification also saw increases:

“The ocean absorbs around 23% of the annual emissions of anthropogenic CO2 to the atmosphere. This reacts with seawater and leads to ocean acidification, which threatens organisms and ecosystem services, and hence food security, tourism and coastal protection. As the pH of the ocean decreases, its capacity to absorb CO2 from the atmosphere also declines. The IPCC concluded that ‘there is very high confidence that open ocean surface pH is now the lowest it has been for at least 26,000 years and current rates of pH change are unprecedented since at least that time.'”

Additionally, global mean sea level reached a new record high in 2021, after increasing at an average 4.5mm per year over the period 2013-2021, according to WMO:

“This is more than double the rate of between 1993 and 2002 and is mainly due to the accelerated loss of ice mass from the ice sheets. This has major implications for hundreds of millions of coastal dwellers and increases vulnerability to tropical cyclones.”

Even for glaciers, while they saw less melting in 2020-2021 than in recent years, “there is a clear trend towards an acceleration of mass loss on multi-decadal timescales,” according to the report:

“On average, the world’s reference glaciers have thinned by 33.5 meters (ice-equivalent) since 1950, with 76% of this thinning since 1980. 2021 was a particularly punishing year for glaciers in Canada and the US Northwest with record ice mass loss as a result of heatwaves and fires in June and July. Greenland experienced an exceptional mid-August melt event and the first-ever recorded rainfall at Summit Station, the highest point on the ice sheet at an altitude of 3,216m.”

Check out the WMO’s full report here.

John Liang
John Liang
John Liang is the News Editor at He first got the diving bug while in High School in Cairo, Egypt, where he earned his PADI Open Water Diver certification in the Red Sea off the Sinai Peninsula. Since then, John has dived in a volcanic lake in Guatemala, among white-tipped sharks off the Pacific Coast of Costa Rica, and other places including a pool in Las Vegas helping to break the world record for the largest underwater press conference.