Earth's oceans have reached the hottest and most acidic levels on record, UN says

Oceans reached their hottest and most acidic levels on record last year, the World Meteorological Organization said Wednesday, marking a major consequence of climate change from human-induced greenhouse gas emissions.

The findings were part of a broader annual report that detailed how four primary measures of climate change — greenhouse gas concentrations, sea level rise, ocean temperatures and ocean acidification — hit record highs in 2021.

"Our climate is changing before our eyes," WMO Secretary General Petteri Taalas said in a statement. "The heat trapped by human-induced greenhouse gases will warm the planet for many generations to come."

Oceans have been hit particularly hard by rising greenhouse gas emissions and temperatures. In fact, much of the ocean experienced at least one "strong" marine heatwave at some point last year, the report found.

Such heat extremes have put critical marine ecosystems such as coral reefs, seagrass meadows and kelp forests at risk of collapse. Rapid ocean warming has also triggered a drop in global fish populations.

The WMO also confirmed that pH levels in the oceans have reached the lowest point in at least 26,000 years. As oceans grow more acidic, their capacity to absorb carbon dioxide from the atmosphere declines.

Sea levels also hit record highs last year after rising an average of 4.5 mm every year in roughly the last decade, the WMO said. That's more than double the rate seen between 1993 and 2002 and is mainly due to the accelerated loss of ice mass from melting ice sheets. The sea level rise puts hundreds of millions of coastal dwellers at risk of more intense and frequent storms and floods, the WMO warned.

"Sea level rise, ocean heat and acidification will continue for hundreds of years unless means to remove carbon from the atmosphere are invented," Taalas said.

Scientists have warned the world has already warmed roughly 1.1 degrees Celsius above preindustrial levels and is set to see global temperatures rise 2.4 degrees Celsius by 2100. The past seven years have been the warmest seven years on record.

U.N. Secretary-General António Guterres in a statement criticized the "the dismal litany of humanity's failure to tackle climate disruption" and called for urgent action to grab the "low-hanging fruit" of shifting energy systems away from planet-warming fossil fuels to renewable energy.