Global warming has accelerated. The debate among scientists is not whether that is true — it is how fast, and why.
Earth warmed at roughly 0.18°C per decade until the 2010s. Then temperatures began climbing faster. 2023 became the hottest year on record by a margin of 0.17°C, more than existing models predicted. 2024 was hotter still, exceeding 1.5°C above pre-industrial levels for the first time. Temperatures stayed nearly as high into 2025, when heatwaves killed thousands in Europe and cyclones struck South-East Asia and Jamaica.
James Hansen at Columbia University published a widely discussed paper arguing the warming rate had reached 0.32°C per decade after 2010. That figure is higher than the 0.24°C estimated by the UN Intergovernmental Panel on Climate Change and the 0.29°C average from the latest generation of climate models.
Hansen’s paper pointed to aerosol pollution as the central mechanism. Sulphur aerosols from fossil fuel burning reflect sunlight and seed reflective clouds, partially masking CO₂-driven warming for decades. As countries reduce that pollution, the masking effect fades and suppressed warming re-emerges.
The Aerosol Shift
Global sulphur dioxide emissions have fallen 40 per cent since the mid-2000s, according to the report. Two actions drove most of that drop. China launched a pollution crackdown around the 2008 Beijing Olympics and has since cut its sulphur aerosol output by at least 75 per cent. The International Maritime Organization separately tightened limits on sulphur emissions from ships, reducing the cloud trails that typically form in vessel wakes. Because the air above oceans was already less polluted than over land, even modest reductions there produced outsized effects on cloud cover. “The atmosphere is cleaner, so more solar radiation is coming in,” said Samantha Burgess at the European Union’s Copernicus Climate Change Service.
Most scientists accept that declining aerosols have contributed to accelerated warming. The disagreement is over magnitude.
Natural Noise in the Signal
Three separate natural events have complicated the picture. A strong peak in the roughly 11-year solar cycle arrived in 2020, increasing the amount of sunlight reaching Earth. In 2022, an underwater volcano near Tonga in the South Pacific erupted, sending 146 million tonnes of water vapour — a greenhouse gas — into the stratosphere, while also ejecting sulphur aerosols that temporarily cooled the atmosphere. Then 2023 and 2024 brought a strong El Niño, a natural pattern in which weakening trade winds push warm Pacific water eastward, raising global surface temperatures.
Some researchers argue these overlapping natural fluctuations account for much of the recent temperature spike and will fade. Others say the underlying human-caused acceleration is real and steeper than models show.
“Ultimately, this is a question of how bad climate change is going to be,” said Zeke Hausfather at Berkeley Earth.
Photo by Gasper Pogacar on Pexels
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