Atmospheric concentrations of the major greenhouse gases, carbon dioxide, methane and nitrous oxide, continued to increase in 2020 and 2021. The growth rate of all three greenhouse gases in 2020 was above the average for the last decade despite a 5.6% drop in fossil fuel CO2 emissions in 2020 due to restrictions related to the COVID-19 pandemic.
Global mean temperature in 2021 (January to September) is around 1.08 ±0.13 °C above the 1850-1900 pre-industrial average and the year is likely to be between the 5th and 7th warmest year on record. 2021 is cooler than recent years owing to La Niña conditions early in the year.
The rate of global sea level rise has increased since satellite altimeter measurements began in 1993, reaching 4.4 mm/yr between 2013 and 2021. Global mean sea level reached a new record high in 2021.
Ocean heat content reached new record highs in 2019 and then 2020, the latest year for which a comprehensive analysis is available. Ocean warming rates show a particularly strong increase in the past two decades.
Changes in the global cryosphere in 2021 were consistent with recent multi-decadal trends, with below-normal Northern Hemisphere spring snow cover and end-of-summer Arctic sea ice area, negative mass balances on mountain glaciers and the Greenland and Antarctic Ice Sheets, and near-normal Antarctic sea ice cover.
The summer heat wave in western North America took a toll on the region's mountain glaciers, with exceptional mass losses in the Cascade, southern Coast, and Rocky Mountains. Mass loss at some glaciers in southwestern British Columbia was the greatest in the instrumental record (1965-2021).
Greenland experienced an exceptional mid-August melt event which included temperatures above 0 °C and rainfall at Summit Station, the highest point on the ice sheet. This is the first time that rain has been observed at Summit, and marks the third time in the last nine years that the Summit has experienced melting conditions. Ice core records indicate that only one such melt event occurred in the 20th century.
Exceptional heatwaves affected western North America on several occasions during June and July. Lytton, in south-central British Columbia, reached 49.6 °C on 29 June, breaking the previous Canadian national record by 4.6 °C. 569 heat-related deaths were reported in British Columbia alone between 20 June and 29 July.
Death Valley, California reached 54.4 °C on 9 July, equalling a similar 2020 value as the highest recorded in the world since at least the 1930s.
Extreme heat affected the broader Mediterranean region on several occasions during the second half of the Northern Hemisphere summer. The most exceptional heat was in the second week of August. On 11 August, an agrometeorological station near Syracuse in Sicily reached 48.8 °C, a provisional European record.
The most significant hurricane of the North Atlantic season was Ida. Ida made landfall in Louisiana on 29 August with sustained 1-minute winds of 240 km/h, the equal-strongest landfall on record for the state, with major wind damage and storm surge inundation. The system continued on a northeast track over land with significant flooding, especially in the New York City area. In total, 72 direct and 43 indirect deaths were attributed to Ida in the United States and Venezuela, with economic losses in the United States estimated at US$63.8 billion.
Extreme rainfall hit Henan Province of China from 17 to 21 July. On 20 July, the city of Zhengzhou received 201.9 mm of rainfall in one hour (a Chinese national record), 382 mm in 6 hours, and 720 mm for the event as a whole, more than its annual average. The city experienced extreme flash flooding with many buildings, roads and subways inundated. 302 deaths were attributed to the flooding, and economic losses of US$17.7 billion were reported.
Western Europe experienced some of its most severe flooding on record in mid-July. The worst-affected area was western Germany and eastern Belgium, where 100 to 150 mm fell over a wide area on 14-15 July over wet ground. The highest daily rainfall was 162.4 mm at Wipperfürth-Gardenau (Germany). Numerous rivers experienced extreme flooding, with several towns inundated, and there were also several landslides. 179 deaths were reported in Germany and 36 in Belgium, with economic losses in Germany exceeding US$20 billion.