Climate change: Even La Niña’s cooling effect could not temper 2021, one of the seven warmest years on record

Last year, the global average temperature was about 1.11 °C above pre-industrial levels (1850-1900). The seven warmest years have all occurred since 2015, with 2016, 2019 and 2020 taking the top three places in the rankings. We are dangerously close to the lower limit of the Paris Agreement to curb global warming.

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La Niña episodes between 2020 and 2022 brought a temporary reduction in global average temperatures, but despite this, 2021 became one of the seven warmest years on record, according to six major international datasets consolidated by the World Meteorological Organization (WMO).

La Niña is a phenomenon that produces large-scale cooling of ocean surface temperatures in the central and eastern parts of the equatorial Pacific, in addition to other changes in tropical atmospheric circulation. Its effects on weather and climate are usually the opposite of those of El Niño. La Niña exerts a transient cooling effect on a global scale, which is usually strongest in the second year of the episode.

Last year, the global average temperature was about 1.11 (±0.13) °C above pre-industrial levels (1850-1900). Thus, 2021 is the seventh consecutive year (2015-2021) in which global temperature has exceeded pre-industrial levels by more than 1 °C.

With the new record in 2021, global warming, as well as other long-term climate change trends, looks set to continue as a result of unprecedented levels of heat-trapping greenhouse gases in the atmosphere.

There is definite evidence that global warming is approaching the lower limit of the temperature increase envisaged in the Paris Agreement, which is to try to limit that increase to 1.5°C above pre-industrial levels.

The seven warmest years have all occurred since 2015, with the top three in the rankings being 2016, 2019 and 2020. The exceptionally strong El Niño event in 2016 contributed to unprecedented global average warming.

Following the new data, the Secretary-General of the World Meteorological Organization, Professor Petteri Taalas, said that “long-term global warming from increased greenhouse gas concentrations is now much larger than the inter-annual variability of global average temperatures caused by naturally occurring climate forcing”.

Records to remember
“The year 2021 will be remembered for record temperatures of nearly 50°C in Canada (comparable to those seen in the hot Saharan desert of Algeria), exceptional rainfall and deadly floods in Asia and Europe, as well as drought in parts of Africa and South America. The impacts of climate change and climate-related hazards had devastating effects that disrupted the lives of communities on all continents,” he added.

According to scientific criteria, the place each particular year occupies in the global ranking must be interpreted from a long-term perspective, especially as the differences between specific years are sometimes minimal. Since the 1980s, each new decade has been warmer than the previous one, and this trend is expected to continue.

Temperature is only one indicator of climate change, to which can be added greenhouse gas concentrations, ocean heat content, ocean pH, global mean sea level, glacier mass and sea ice extent.