Global climate context in 2020
Concentrations of the major greenhouse gases (GHGs) – carbon dioxide (CO2 ), methane (CH4) and nitrous oxide (N2O) – continued to increase in 2019 and 2020.5 Despite the La Niña conditions in the latter part of the year, the global mean temperature in 2020 was one of the three warmest on record (Figure 1), at about 1.2 °C above pre-industrial levels. The past six years, including 2020, have been the six warmest years on record. Global mean sea level has risen throughout the altimeter record, but recently it has been rising at a faster rate partly due to increased melting of the Greenland and Antarctic ice sheets.
The goal of the Paris Agreement6 is to hold the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels. Progress towards this global goal is measured relative to pre-industrial conditions (1850–1900). There are no separate limits for temperatures at a regional scale. In fact, it is impossible to calculate a reliable pre-industrial baseline for many regional time series owing to a lack of data for much of the Earth from the late nineteenth century. Consequently, 1981–2010 is used as a temperature baseline in this report.