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Four key measures of climate change set records in 2021

Greenhouse gas concentrations, sea level rise, ocean temperatures and ocean acidification all hit their highest recorded levels, a U.N. report found.
Scorching Heat In Delhi-NCR
A man pours water over his face during an extreme heatwave in New Delhi on May 14, 2022. Hindustan Times / via Getty Images

Four key measures of climate change hit record highs last year, the United Nations said Wednesday. 

Greenhouse gas concentrations, sea level rise, ocean temperatures and ocean acidification all hit their highest recorded levels in 2021, leading to “harmful and long-lasting ramifications” for humans and nature, according to the World Meteorological Organization.

It said extreme weather supercharged by climate change last year had led to billions of dollars in economic losses and triggered shocks to global food and water supplies that were reverberating into 2022. 

The WMO State of the Global Climate report found that the past seven years were the seven hottest on record and that temperatures in 2021 were 1.11 Celsius (2 Farenheit) above pre-industrial baseline levels. 

U.N. Secretary General António Guterres said the assessment showed “the dismal litany of humanity’s failure to tackle climate disruption” and called for governments to accelerate their transition away from planet-warming fossil fuels. 

Guterres said countries needed to make genuine progress towards decarbonizing their economies this century in order to stave off the worst impacts of climate change and limit heating to 1.5C. That is the most ambitious temperature goal of the 2015 Paris Agreement.

Despite a record drop in greenhouse gas emissions in 2020 due to lockdowns and other restrictions linked to Covid, the WMO said that concentrations of carbon dioxide, methane and nitrous oxide all hit record levels.

Atmospheric CO2 levels reached 413.2 parts per million (ppm) globally, or 149 percent of pre-industrial levels. It said it expected concentrations to continue upward, with the Mona Loa observatory in Hawaii measuring 420.23 ppm in April 2022.

Oceans absorb up to a quarter of the CO2 emitted by human activity and play a vital role in regulating global weather patterns. The WMO said that the upper 2,000 meters of ocean had continued to warm, breaking the 2020 temperature record.

It warned that this impact would be "irreversible on centennial to millennial time scales."

CO2 reacting with seawater leads to ocean acidification, which poses a threat to sealife, coastal areas and to the food and tourism industries reliant on health seas.

The WMO concurred with a recent U.N. climate science panel report that warned pH levels in the world's oceans were now at their lowest in at least 26,000 years.

Sea levels hit record levels in 2021, after rising an average of 4.5 mm each year since 2013, largely driven by melting ice sheets. The WMO warned that sea-level rise posed a threat for "hundreds of millions of coastal dwellers," putting them at risk of more powerful and frequent floods and storms.

2021 was a particularly punishing year for Earth's frozen spaces, with the Greenland ice sheet, which contains enough frozen water to raise sea levels some six metres, undergoing "an exceptional melt event" in August and the first ever recorded rainfall at Summit Station, at an altitude of 3,216 m.  

Some inland glaciers, upon which around two billion people rely as the main source of drinking water, have already reached the point of no return, the assessment showed.

While 2021 itself was not the hottest year on record (2020 and 2016 are currently tied as the warmest) this was due to the mild cooling boought by the La Nina weather event at the star of the year.

WMO Secretary General Petteri Taalas said it was "just a matter of time" before Earth witnessed another record hottest year.

"Our climate is changing before our eyes. The heat trapped by human-induced greenhouse gases will warm the planet for many generations to come," he said.

CORRECTION (May 18, 2022, 6:00 a.m. ET): A previous verison of this article misstated the depth of the ocean that continues to warm. It is the top 2,000 meters, not 200.