Records broken for four climate change indicators

Four key climate change indicators — greenhouse gas concentrations, sea level rise, ocean heat and ocean acidification — set new records in 2021, in another clear sign that human activities are causing planetary-scale changes on land, in the ocean and in the atmosphere.

That’s according to the World Meteorological Organization (WMO)’s State of the Global Climate 2021 report, which also confirmed that the past seven years have been the warmest seven years on record. The report also finds that 2021 was ‘only’ one of the seven warmest because of a La Niña event at the start and end of the year, which had a temporary cooling effect but did not reverse the overall trend of rising temperatures. The average global temperature in 2021 was about 1.11 (± 0.13)°C above the pre-industrial level.

Released shortly after the WMO’s latest Global Annual to Decadal Climate Update, the State of the Global Climate report complements the IPCC’s Sixth Assessment Report, which includes data up to 2019. The new WMO report provides information and practical examples for policymakers on how the climate change indicators outlined in the IPCC reports played out during recent years globally and how the associated implications on extremes have been felt at national and regional level in 2021. Dozens of experts contributed to the report.

“It is just a matter of time before we see another warmest year on record,” said WMO Secretary-General Professor Petteri Taalas. “Our climate is changing before our eyes. The heat trapped by human-induced greenhouse gases will warm the planet for many generations to come. Sea level rise, ocean heat and acidification will continue for hundreds of years unless means to remove carbon from the atmosphere are invented. Some glaciers have reached the point of no return and this will have long-term repercussions in a world in which more than 2 billion people already experience water stress.”

Other key messages from the report are as follows:

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. Data from specific locations indicate that they continued to increase in 2021 and early 2022, with monthly average CO₂ at Mona 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 2000 m depth of the ocean continued to warm in 2021 and it is expected that it will continue to warm in the future — a change that is irreversible on centennial to millennial time scales. All datasets agree that ocean warming rates show a particularly strong increase in the past two decades. The warmth is penetrating to ever deeper levels, and much of the ocean experienced at least one ‘strong’ marine heatwave at some point in 2021.

Ocean acidification owing to CO₂ absorption threatens organisms and ecosystem services, 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 IPCC concluded that “there is very high confidence that open ocean surface pH is now the lowest it has been for at least 26,000 years and current rates of pH change are unprecedented since at least that time”.

Global mean sea level reached a new record high in 2021, after increasing at an average 4.5 mm per year over the period 2013–2021. This is more than double the rate of between 1993 and 2002 and is mainly due 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.

Although the glaciological year 2020–2021 saw less melting than in recent years, there is a clear trend towards an acceleration of mass loss on multi-decadal timescales. 2021 was a particularly punishing year for glaciers in Canada and the US Northwest, with record ice mass loss as a result of heatwaves and fires in June and July. Greenland experienced an exceptional mid-August melt event and the first-ever recorded rainfall at Summit Station, the highest point on the ice sheet at an altitude of 3216 m.

Heatwaves broke records across western North America and the Mediterranean. California’s Death Valley reached 54.4°C on 9 July, equalling a similar 2020 value as the highest recorded in the world since at least the 1930s, and Syracuse in Sicily reached 48.8°C. British Columbia reached 49.6°C on 29 June, and this contributed to more than 500 reported heat-related deaths and fuelled devastating wildfires which, in turn, worsened the impacts of flooding in November.

Flooding induced economic losses of US$17.7 billion in Henan province of China, and Western Europe experienced some of its most severe flooding on record in mid-July associated with economic losses in Germany exceeding US$20 billion. There was also heavy loss of life.

Drought affected many parts of the world, including the Horn of Africa, Canada, the western United States, Iran, Afghanistan, Pakistan and Turkey. In sub-tropical South America, drought caused big agricultural losses and disrupted energy production and river transport. Eastern Africa is meanwhile facing the prospect that the rains will fail for a fourth consecutive season, placing Ethiopia, Kenya and Somalia into a drought of a length not experienced in the last 40 years.

Hurricane Ida was the most significant of the North Atlantic season, making landfall in Louisiana on 29 August, with economic losses in the United States estimated at US$75 billion.

The ozone hole over the Antarctic was unusually large and deep, reaching its maximum area of 24.8 million km² (the size of Africa) as a result of a strong and stable polar vortex and colder than average conditions in the lower stratosphere.

Hydrometeorological hazards continued to contribute to internal displacement. The countries with the highest numbers of displacements recorded as of October 2021 were China (more than 1.4 million), the Philippines (more than 386,000) and Vietnam (more than 664,000).

Image credit: ©stock.adobe.com/au/bilderstoeckchen

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