Every decade since the 1980s has been warmer than the previous one.
On the 19th, the World Meteorological Organization (WMO) released the latest integrated six major international data sets, showing that although the global average temperature has temporarily cooled due to the La Niña event in 2020-2022, 2021 is still one of the warmest seven years on record. Global warming and other long-term climate change trends are expected to continue as endothermic greenhouse gases in the atmosphere reach record levels.
"The La Niña incident has followed, and the warming in 2021 is relatively less significant than in recent years. Even so, 2021 is still warmer than previous years affected by La Niña. The overall long-term warming caused by the increase in greenhouse gases is now much larger than the annual variation in global average temperature due to natural climate drivers. WMO Secretary General Taras explained.
The seven warmest vintages all appeared after 2015
La Niña refers to a large-scale cooling of surface temperatures in the central and eastern equatorial Pacific Oceans, accompanied by changes in tropical atmospheric circulation. Its effects on weather and climate are often the opposite of El Niño, which has a temporary global cooling effect, usually strongest in the second year of the event.
The data shows that the global average temperature in 2021 is about 1.11 (0.13) degrees Celsius higher than the pre-industrial ± (1850-1900) level, and 2021 is the seventh consecutive year (2015-2021) when global temperatures are above pre-industrial levels of more than 1 degree Celsius.
In fact, the seven warmest years began in 2015, with 2016, 2019 and 2020 in the top three. An unusually intense El Niño event occurred in 2016, which also contributed to a record increase in global average warming.
WMO notes that rankings for individual years should be looked at in a long-term context, especially since the differences between years are sometimes small. What can be seen, however, is that each decade since the 1980s has been warmer than the previous, and this is expected to continue.
The Paris Agreement seeks to limit the increase in global average temperature to well below 2 degrees Celsius above pre-industrial levels, while striving to limit the rise to 1.5 degrees Celsius above pre-industrial levels. The average global temperature in 2021 is 1.11 degrees Celsius higher than pre-industrial (1850-1900) levels, approaching the lower limit of warming that the Paris Agreement seeks to avoid.
Taras said 2021 will be remembered for Canada's record temperatures of nearly 50 degrees Celsius (comparable to those reported in the hot Sahara Desert region of Algeria), unusual rainfall and deadly flooding in Asia and Europe, and droughts in parts of Africa and South America. "The effects of climate change and weather-related hazards are changing the lives of communities on every continent, with devastating effects." Taras said.
WMO is using datasets developed and maintained by the National Oceanic and Atmospheric Administration (NOAA), NASA's Goddard Institute for Space Research (NASA GISS), the MET Office's Hadley Centre and the University of East Anglia's Climate Research Laboratory (HadCRUT), Berkeley Earth, the European Medium Range Weather Forecast Centre and its Copernican Climate Change Service and the Japan Meteorological Agency (JMA).
The reason WMO used the six international datasets was to ensure that WMO's temperature assessments were the most comprehensive and authoritative. The same data will be used in its annual State of The Climate report, which aims to inform the international community of global climate indicators.
Among them, data from the Copernicus Climate Change Service, which was released earlier, estimates that 2021 is the fifth warmest year on record, but the temperature is only slightly higher than in 2015 and 2018.
NOAA and The Berkeley Earth Organization consider 2021 to be the sixth warmest year in name. NASA GISTEMP and HadCRUT consider 2021 to effectively be tied for the sixth warmest year. The Japan Meteorological Agency (JMA) re-analysis data ranks 2021 as the seventh warmest year in nominal terms. Small differences between these datasets show the margin of error for calculating the global average temperature.
These temperature values will be included in WMO's final report on the state of the climate in 2021, to be released in April 2022. The report will include information such as all key climate indicators and excerpts on climate impacts.
It should be noted that temperature is only one of the indicators of climate change, and other important indicators include greenhouse gas concentration, ocean heat content, ocean pH, global average sea level, glacier quality, and sea ice range.
For example, in the case of ocean heat content, about 90% of the accumulated heat in the Earth system is stored in the ocean, which can be measured by the heat content of the ocean. In 2019, the 2,000-meter depth area of the upper ocean continued to heat up, reaching a record high. The results of WMO's preliminary analysis of it based on a global dataset show that it exceeded that record in 2020. All datasets consistently show that the rate of ocean warming has shown particularly strong growth over the past 20 years, and the ocean is expected to continue to warm in the future.
Most of the oceans experienced at least one "strong" ocean heat wave sometime in 2021, with the exception of the eastern equatorial Pacific Ocean (due to the effects of La Niña) and much of the Southern Ocean. Between January and April 2021, the Lapouteve and Beaufort Seas in the Arctic experienced "severe" and "extreme" marine heat waves.
The oceans absorb about 23 percent of the carbon dioxide that humans emit into the atmosphere each year and are therefore becoming more acidified. The global open ocean surface pH has declined over the past 40 years and is now at least 26,000 years old. The current rate of change in pH is at least unprecedented since then. As the ocean's pH declines, so does the ocean's ability to absorb carbon dioxide from the atmosphere.