The world's oceans in 2021 grew to their warmest and most acidic levels on record, while melting ice sheets helped push sea levels to new heights, the World Meteorological Organization (WMO) said on Wednesday.
Oceans saw the most striking extremes as the WMO detailed a range of turmoil wrought by climate change in its annual "State of the Global Climate" report.
"Our climate is changing before our eyes. The heat trapped by human-induced greenhouse gases will warm the planet for many generations to come," said WMO Secretary-General Petteri Taalas in a statement.
The WMO report follows on the latest United Nations climate assessment, which warned that humanity must drastically cut its greenhouse gas emissions or face increasingly catastrophic changes to the world's climate.
The levels of climate-warming carbon dioxide and methane in the atmosphere in 2021 surpassed previous records, the WMO said.
Globally, the average temperature last year was 1.11 degrees Celsius above the preindustrial average - as the world inches closer to the 1.5 C threshold beyond which the effects of warming are expected to become drastic.
Last year's temperatures were tempered slightly compared to 2020 because of the cooling effects of La Nina in the Pacific, though the year was still among the top seven hottest years on record.
"It is just a matter of time before we see another warmest year on record," Taalas said.
Oceans bear much of the brunt of the warming and emissions. The bodies of water absorb around 90% of the Earth's accumulated heat and 23% of the carbon dioxide emissions from human activity.
The ocean has warmed markedly faster in the last 20 years, hitting a new high in 2021, and is expected to become even warmer, the report said. That change would likely take centuries or millennia to reverse, it noted.
The ocean is also now its most acidic in at least 26,000 years as it absorbs and reacts with more carbon dioxide in the atmosphere.
Sea level has risen 4.5 centimeters (1.8 inches) in the last decade, with the annual increase from 2013 to 2021 more than double what it was from 1993 to 2002.
The WMO also listed individual extreme heatwaves, wildfires, floods and other climate linked disasters around the world, noting reports of more than $100 billion in damages.
The continental United States saw its hottest-ever summer, with hundreds of heat-related deaths recorded. The Dixie fire burned 3,900 square kilometers (1,500 square miles), making it California's largest ever wildfire.