Scientists struggle to explain record rise in global heat 17/12/2024

Scientists claim that 2023 and 2024 were the warmest years on record (MARIO TAMA)

MARIO TAMA/GETTY IMAGES NORTH AMERICA/Getty Images via AFP

By AFP - Agence France Presse

Scientists struggle to explain record rise in global heat

Nick Perry

The world has been warming for decades, but a sudden and extraordinary spike in heat has pushed 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 surge so sustained and intriguing that it has tested the best available scientific predictions about how the climate works.

Scientists agree that fossil fuel burning is largely to blame for long-term global warming, and that natural climate variations can also affect temperatures from one year to the next.

But they are still debating what may have contributed to this particularly extraordinary heat wave.

Experts believe that changes in cloud patterns, air pollution and the Earth's ability to store carbon could be factors, but it will take another year or two before a clearer picture emerges.

“Warming in 2023 was much stronger than 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 know,” he added.

“We are still in the process of evaluating what happened and whether the climate system has changed.

- Unknown territory

The burning of fossil fuels releases greenhouse gases, such as carbon dioxide, which trap heat near the Earth's surface.

Since fossil fuel emissions reached record levels in 2023, average ocean surface and air temperatures have been on a steady warming trend for decades.

But in an unprecedented streak between June 2023 and September 2024, global temperatures were as high as ever, and sometimes even significantly higher, according to the World Meteorological Organization.

The heat was so extreme that it was enough to make 2023 - and then 2024 - the hottest years in history.

“The record-breaking global heat of the last two years has pushed 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,” she added, considering the amount of fossil fuels burned.

- Difficult to explain

Scientists said that climate variability could provide an explanation for the events.

The year 2023 was preceded by a rare three-year La Nina phenomenon, which had a strong cooling effect on the planet and pushed excess heat into the depths of the oceans.

That energy was released back to the surface when an opposite, warming El Niño event hit in mid-2023, pushing global temperatures higher.

But even after the El Niño peaked in January, the heat persisted.

Temperatures did not drop 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 panel of climate experts, the IPCC. ”We lack a little perspective.

“If temperatures don't drop more sharply by 2025, we really need to ask ourselves what caused this,” he told AFP.

- The jury is still out.

Scientists are looking for clues elsewhere.

One theory is that the global switch to cleaner fuels in 2020 accelerated warming by reducing sulfur emissions, which make clouds more reflective and reflective of sunlight.

In December, another peer-reviewed article examined whether the reduction in low-hanging clouds has caused more heat to reach the Earth's surface.

At the American Geophysical Union conference this month, Schmidt brought together scientists to explore these and other theories, including whether solar cycles or volcanic activity offer clues.

Without a more complete picture, scientists fear they could miss even deeper and more disruptive changes to the climate.

“We can't rule out the possibility that other factors may have pushed temperatures even higher... the jury is still out,” Seneviratne said.

This year, scientists warned that the Earth's carbon sinks – such as the forests and oceans that remove CO2 from the atmosphere – would suffer an ‘unprecedented weakening’ by 2023.

This month, the US National Oceanic and Atmospheric Administration said that after blocking CO2 for millennia, the Arctic tundra is becoming a net source of emissions.

The oceans, which have acted as a giant carbon sink and climate regulator, are warming at a rate that scientists “can't fully explain,” said Johan Rockstrom of the Potsdam Institute for Climate Impact Research.

“Could this be the first sign that the planet is losing resilience? We can't rule it out,” he said last month.

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