Greenhouse gas concentrations continued to increase. Global temperature, the ozone hole and sea ice extent were comparable to previous years.
Atmospheric CO2 concentration increased by 2.5 ppm – 6% faster than the previous year and 11% faster than the average 2000–2020 growth rate. This was in part due to economic recovery from COVID-19 pandemic conditions. Average CO2 concentration reached 416 ppm; a 31% increase from 1960.
Global average air temperature in 2021 was 0.14 °C lower than the previous year but was still 0.82 °C above the twentieth-century average and the sixth warmest year on record.
The ozone hole remained stable compared to the previous year and very close to the 2000–2020 average.
Sea ice extent increased slightly in the Arctic. Ice extent on both hemispheres combined was 1.4% greater than the previous year, but still 2.1% lower than the 2000–2020 average.
Global mean air temperature (difference from 1901-2000 average) (NOAA)