Last year was the fifth hottest on Earth on record, European scientists said on Monday. But the fact that the global average temperature has not broken the record is no reason to stop worrying about the grip of global warming on the planet, they said.
Not when the United States and Europe had their hottest summers on the books. Not when warmer temperatures around the Arctic first brought rain to the normally freezing top of the Greenland ice sheet.
And certainly not when the hottest seven years on record were, by far, the last seven.
The events of 2021 “are a stark reminder of the need to change our habits, to take decisive and effective measures towards a sustainable society and to work towards the reduction of net carbon emissions”, said Carlo Buontempo, director of Copernicus Climate Change Service, the European Union. program that conducted the analysis released on Monday.
Last year, the global average temperature was 1.1 to 1.2 degrees Celsius (2 to 2.2 degrees Fahrenheit) higher than it was before industrialization led humans to start pump large amounts of carbon dioxide into the air.
The year was the fifth hottest with a slight margin from 2015 and 2018, according to Copernicus’ ranking. The hottest years on record are 2016 and 2020, in a virtual tie.
Constant warming corresponds to the scientific consensus that increasing levels of greenhouse gases in the atmosphere are causing lasting changes in the global climate. Copernicus said its preliminary analysis of satellite measurements found that concentrations of heat-trapping gases continued to rise last year, aided by 1,850 megatonnes of carbon emissions from forest fires around the world.
One of the main reasons for the 2021 average temperature drop was the presence at the start of the year of La Niña conditions, a recurring climate pattern characterized by lower surface temperatures in the Pacific Ocean. (La Niña has returned in recent months, which could portend a drier winter in the southern United States but wetter conditions in the Pacific Northwest.)
However, these effects were offset in the 2021 average by warmer temperatures in many parts of the world between June and October, Copernicus said.
“When we think of climate change, it’s not just a progression, year after year being the hottest,” said Robert Rohde, senior scientist at Berkeley Earth, an independent environmental research group.
“The preponderance of evidence – which comes from examining ocean temperatures, Earth temperatures, higher air temperatures, melting glaciers, changes in sea ice – tells us a cohesive story about changes in the system. Earth that indicates global warming, ”Dr Rohde mentioned. “Slight variations up or down, a year or two at a time, don’t change that picture. “
Berkeley Earth is expected to release its own analysis of 2021 temperatures this month, as are two U.S. government agencies: NASA and the National Oceanic and Atmospheric Administration.
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Unlike these groups, Copernicus uses a method called reanalysis, which produces a portrait of global weather conditions using a computer model that fills in the gaps between the temperature readings. Even so, the findings of different groups generally align quite closely.
As always, higher average temperatures were not observed uniformly across the planet over the past year. Most of Australia and parts of Antarctica experienced below normal temperatures in 2021, as did parts of Western Siberia.
Last year’s European summer was the hottest on record, although 2010 and 2018 were not far behind, according to Copernicus. Heavy rains and flooding caused destruction and deaths in Belgium, Germany, Luxembourg and the Netherlands. The heat and drought set the stage for the forest fires that ravaged Greece and other places around the Mediterranean.
The western part of North America experienced extreme heat, drought and wildfires last summer. Canada’s maximum temperature record was broken in June when the mercury in a small town in British Columbia hit 121.3 degrees Fahrenheit, or 49.6 degrees Celsius.
Scientists concluded that the heat wave on the Pacific coast would have been next to impossible in a world without human-induced warming. The question is whether the event fits into current meteorological understanding, albeit unprecedented, or if it is a sign that the climate is changing in ways that scientists do not fully grasp.
“From where I’m sitting right now, I would tend to think that this was probably still a very rare event, even in the modern climate,” Dr Rohde said. “But there is a certain degree of waiting and seeing.”
If the planet does not experience heat episodes of similar intensity over the next several decades, scientists will likely look back and view 2021 as an extreme fluke, he said. “If we do, it tells us that something has changed in a more fundamental way. “