Multiple climate change indicators reached record levels in 2020 and 2021, according to a World Meteorological Organization report published May 18.
Sea level rise, ocean heat and ocean acidification, as well as greenhouse gas concentrations, all reached record levels in the past two years.
In terms of global temperature, 2021 saw a 1.11- (plus or minus 0.13) degree Celsius global mean temperature. This was a slight reduction from the 1.2-degree Celsius GMT in 2020.
Last year’s GMT was “between the fifth and seventh warmest year on record,” which ends a seven-year trend of each year’s global mean temperature being the highest on record.
A key factor in this slight decline was the La Niña events that bookended 2021, the report explained, as these La Niña conditions temporarily cool global temperatures.
Carbon dioxide concentration in 2020 was 149% above pre-industrial levels, while methane was 262% above and nitrous oxide was 123% above. Preliminary data for 2021 indicates that the rise seen in 2020 has continued.
Both ocean heat and acidification levels reached all-time highs in 2021, which is directly tied to greenhouse gas concentration.
Excess energy from greenhouse gases is absorbed by the ocean, raising ocean temperatures (and, by extension, raising sea levels due to melting ice) and causing acidification (“lowering the average pH of the water”), the report explained.
“The upper 2,000m 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 timescales,” the report said.
Despite the La Niña events, global mean sea levels still rose in 2021 – contrasting the three previous period with similar cooling events when sea levels did not rise. From 1993 to 2002, GMSL rose an average of 2.11 millimeters per year. From 2003 to 2012, GMSL increased 2.9 mm per year on average, and 4.5 mm per year from 2013 to 2022.
In 2021, ocean pH levels were the lowest they have been in 26,000 years. Acidification reduces the amount of excess carbon dioxide that the oceans can absorb. It also negatively impacts oceanic ecosystems, which, in turn, threatens “food security, tourism and coastal protection.”
“It is just a matter of time before we see another warmest year on record,” said WMO Secretary-General Prof. Petteri Taalas, in a press release announcing the report’s publication. “Our climate is changing before our eyes. The heat trapped by human-induced greenhouse gases will warm the planet for many generations to come.
The full report is available here.