According to a recent report from the World Meteorological Organization (WMO), four key climate change indicators — greenhouse gas concentrations, sea level rise, ocean heat and ocean acidification — set new records in 2021.

The WMO State of the Global Climate 2021 report confirms that the past seven years have been the warmest seven years on record and documents new high levels for greenhouse gas concentrations, ocean heat, sea level rise and ocean acidification. The average global temperature in 2021 was about 1.11° C (± 0.13) above the 1850 to 1900 pre-industrial average.

Greenhouse gas concentrations reached a new global high in 2020, when the concentration of carbon dioxide (CO₂) reached 413.2 ppm globally, or 149% of the pre-industrial level. These concentrationsSource: WMO continued to increase in 2021 and early 2022, with monthly average CO₂ at Mauna Loa in Hawaii reaching 416.45 ppm in April 2020, 419.05 ppm in April 2021 and 420.23 ppm in April 2022.

The upper 2,000 m depth of the ocean continued to warm in 2021; data point to a strong increase in ocean warming rates in the past two decades. The warmth is penetrating to ever deeper levels and much of the ocean experienced at least one pronounced marine heatwave in 2021.

The ocean absorbs around 23% of the annual emissions of anthropogenic CO₂ to the atmosphere. The resulting ocean acidification threatens marine ecosystems 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 open ocean surface pH is now judged to be at its lowest level in the last 26,000 years.

Global mean sea level reached a new record high in 2021 after increasing at an average 4.5 mm per year during 2013 to 2021. This is more than double the rate recorded between 1993 and 2002 and is largely attributed 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.

The report complements the UN Intergovernmental Panel on Climate Change Sixth Assessment report, which includes data up to 2019. The new WMO report is accompanied by a story map and provides information and practical examples for policymakers of climate change trends.