Scientists claim that 2023 and 2024 were the hottest years on record (MARIO TAMA)
MARIO TAMA/GETTY IMAGES NORTH AMERICA/Getty Images via AFP
By AFP - Agence France Presse
Scientists struggle to explain the record increase in global heat
Nick Perry
The world has been getting warmer for decades, but a sudden and extraordinary increase in heat has taken the climate into uncharted territory - and scientists are still trying to figure out why.
Over the past two years, temperature records have been repeatedly shattered by a wave so persistent and intriguing that it has tested the best available scientific predictions about how the climate works.
Scientists are unanimous that the burning of fossil fuels has been largely responsible for long-term global warming and that natural climate variability can also influence temperatures from one year to the next.
But they are still debating what may have contributed to this particularly exceptional heatwave.
Experts believe that changes in cloud patterns, atmospheric pollution, and the Earth's capacity to store carbon could be factors, but it will take another year or two for a clearer picture to emerge.
“The warming in 2023 was much greater than in any other year, and 2024 will be too,” said Gavin Schmidt, director of NASA's Goddard Institute for Space Studies, in November.
“I wish I knew why, but I don't,” he added.
“We're still in the process of assessing what happened and whether we're seeing a change in the way the climate system operates.”
- Uncharted territory
When burned, fossil fuels emit greenhouse gases such as carbon dioxide, which trap heat close to the Earth's surface.
With fossil fuel emissions rising to record levels in 2023, average sea surface and air temperatures have risen in a consistent, decades-long warming trend.
But in an unprecedented run between June 2023 and September 2024, global temperatures were unlike anything ever seen before, according to the World Meteorological Organization - and sometimes by a considerable margin.
The heat was so extreme that it was enough to make 2023 - and then 2024 - the hottest years in history.
“The record global heat of the last two years has taken the planet into uncharted territory,” Richard Allan, a climate scientist at the University of Reading in the UK, told AFP.
What happened was “at the limit of what we could expect based on existing climate models,” Sonia Seneviratne, a climatologist at ETH Zurich in Switzerland, told AFP.
“But the general long-term warming trend is not unexpected,” given the amount of fossil fuels being burned, she added.
- Difficult to explain
The scientists said that climate variability could go some way to explaining what happened.
The year 2023 was preceded by a rare three-year La Nina phenomenon, which had a strong cooling effect on the planet, pushing excess heat into the depths of the oceans.
This energy was released back to the surface when an opposite, warming El Nino event took over in mid-2023, increasing global temperatures.
But the heat persisted even after the El Nino reached its peak in January.
Temperatures didn't fall as quickly as they rose, and November was still the second warmest on record.
“It's difficult to explain this at the moment,” said Robert Vautard, a member of the UN's expert panel on climate, the IPCC. “We lack a bit of perspective.
“If temperatures don't fall more sharply by 2025, we will have to ask ourselves about the cause,” he told AFP.
- The jury is out -
Scientists are looking elsewhere for clues.
One theory is that the global switch to cleaner fuels in 2020 accelerated warming by reducing sulfur emissions that make clouds more mirror-like and reflective of sunlight.
In December, another peer-reviewed article analyzed whether the reduction in low clouds had allowed more heat to reach the Earth's surface.
At the American Geophysical Union conference this month, Schmidt brought scientists together to explore these and other theories, including whether solar cycles or volcanic activity offer any clues.
There are concerns that, without a more complete picture, scientists could be missing even more profound and transformative changes in the climate.
“We can't rule out the possibility that other factors have also pushed temperatures even higher... the verdict is still out,” said Seneviratne.
This year, scientists warned that the Earth's carbon sinks - such as the forests and oceans that suck CO2 out of the atmosphere - would suffer an “unprecedented weakening” by 2023.
This month, the US National Oceanic and Atmospheric Administration said that the Arctic tundra, after blocking CO2 for millennia, was becoming a net source of emissions.
The oceans, which have acted as a huge carbon sink and climate regulator, are warming at a rate that scientists “can't fully explain,” said Johan Rockstrom from the Potsdam Institute for Climate Impact Research.
“Could this be the first sign that the planet is beginning to show a loss of resilience? We can't rule it out,” he said last month.
np-bl/jj/rsc
Comments