The rate at which the Earth is warming has reached a record level in 2023, with 92% of last year’s heat records caused by humans, top scientists have calculated.
The group of 57 scientists from around the world used United Nations (UN)-approved methods to examine the causes of last year’s deadly heatwave. They said that although warming was accelerating, they did not see evidence of a significant acceleration of human-caused climate change beyond increased burning of fossil fuels.
Last year’s record temperatures were so unusual that scientists questioned what caused the jump and wondered whether climate change was accelerating or whether other factors were at play.
“If you think the world is accelerating or going through a tipping point, that’s not the case,” said the study’s lead author, Piers Forster, a climate scientist at the University of Leeds. Things are heating up and getting worse exactly as we predicted. »
This phenomenon is largely explained by the accumulation of carbon dioxide due to the increase in the use of fossil fuels, according to him and one of his co-authors.
Last year, the rate of warming reached 0.26°C per decade, up from 0.25°C the year before. It’s not a significant difference, but this year’s rate is the highest ever, Forster said.
Act on the climate
However, outside scientists said the report highlighted an increasingly alarming situation.
“The choice to act on climate has become a political talking point, but this report should remind people that it is fundamentally a choice to save human lives,” said Andrea Dutton, a climate scientist at University of Wisconsin who was not part of the international study team. To me, this is something worth fighting for. »
The team of authors ― assembled to provide annual scientific updates between major United Nations scientific assessments that occur every seven to eight years ― determined that last year was 1.43° warmer C than the average from 1850 to 1900, of which 1.31°C is due to human activity. The remaining 8% is primarily due to El Niño, the natural, temporary warming of the central Pacific that changes weather patterns around the world, as well as exceptional warming along the Atlantic and other random weather phenomena .
Over a broader ten-year period, which scientists prefer to individual years, the world has warmed by about 1.19°C since the pre-industrial era, according to the report published in the journal Earth System Science Data.
1.5°C threshold
The report also says that if the world continues to use coal, oil and natural gas, the Earth will likely reach the point in 4.5 years where it can no longer avoid crossing the internationally accepted warming threshold of 1.5 °C.
These figures are consistent with previous studies that predicted the Earth would be on track or stuck toward warming of at least 1.5°C by early 2029 if emissions trajectories do not change. The 1.5°C threshold could be reached years later, but it would be unavoidable if all the carbon was used, Forster warned.
It’s not the end of the world or humanity if temperatures rise above the 1.5C limit, but it will be quite serious, scientists say.
Previous UN studies show that massive changes to the Earth’s ecosystem are more likely to occur between 1.5 and 2°C of warming, including the possible loss of the planet’s coral reefs, sea ice, Arctic sea, species of plants and animals, as well as more dangerous extreme weather events that kill people.
“Staggering” rise in temperatures
Last year’s rise in temperatures wasn’t just a small jump. It was particularly unusual in September, recalled Sonia Seneviratne, co-author of the study and head of land-climate dynamics at ETH Zurich, a Swiss university.
The year fell within the forecast range, although it was at the upper end of the range, Ms. Seneviratne said.
“The acceleration, if it were to happen, would be even worse, like if we reached a global tipping point, that would probably be the worst scenario,” Ms. Seneviratne said. But what is happening is already extremely serious and is already having major repercussions. We are in the middle of a crisis. »
Jonathan Overpeck, University of Michigan dean of environment, and Zeke Hausfather, a climate scientist at Berkeley Earth, who were not involved in the study, said they still see an acceleration. Hausfather pointed out that the rate of warming is considerably higher than the 0.18°C per decade of warming observed between 1970 and 2010.
Scientists have put forward several hypotheses to explain the massive increase in temperatures in September, which Hausfather called “staggering.” Wednesday’s report did not find enough warming for other potential causes. The report says reductions in sulfur pollution from shipping, which helped cool the atmosphere, were outpaced last year by carbon particles released into the air from Canada’s wildfires .
The report also says that an undersea volcano that injected massive amounts of heat-trapping water vapor into the atmosphere also released cooling particles, with the two forces virtually canceling each other out.
Katharine Hayhoe, Texas Tech climate scientist and Nature Conservancy chief scientist, said “the future is in our hands. It is we ― not physics, but humans ― who will determine how quickly and to what extent the world warms.”