The pace of global heating has been significantly underestimated, according to renowned climate scientist Prof James Hansen, who said the international 2˚C limit is “dead”.
A new analysis by Hansen and colleagues concludes that both the impact of recent cuts in sun-blocking shipping pollution, which has raised temperatures, and the sensitivity of the climate to increasing fossil fuels emissions are greater than thought.
The new analysis said global heating is likely to reach 2˚C by 2045, unless solar geoengineering is deployed.
The world has seen extraordinary temperatures over the last two years. The primary cause is the relentless rise in CO2 emissions from the burning of fossil fuels. The peak of the El Niño climate cycle in 2024 added an extra temperature boost. However, these two factors do not fully explain the extreme temperatures, or their persistence after the El Niño ended in mid-2024.
A key focus has been on emissions from shipping. For decades, the sulphate particles produced by ships burning fuel have blocked some sunlight from reaching the Earth’s surface, suppressing temperatures. But in 2020, new anti-pollution regulations came into force, sharply cutting the level of the aerosol particles. This led to more heat from the sun reaching the surface.
The new study also argues that the planet’s climate sensitivity to rising carbon emissions has been underestimated, partly because of the underestimation of the impact of reduced shipping emissions.
Climate sensitivity is defined by scientists as the temperature rise that would result from a doubling of CO2 levels in the atmosphere.
The IPCC, a collaboration of the world’s climate scientists, found that the computer models that best reproduce past temperatures have a climate sensitivity of 2.5˚C to 4˚C. Hansen’s team took a simpler approach, calculating the potential range in temperature rises for a doubling of CO2 and then using data on how much heat the Earth has trapped to estimate the most likely climate sensitivity. Their estimate is 4.5˚C. Cloud formation, which is affected by global heating and aerosol pollution, is a key source of the uncertainties.
Hansen’s group also argues that the accelerated global heating they predict will increase ice melting in the Arctic. “As a result, shutdown of the Atlantic Meridional Overturning Circulation (AMOC) is likely within the next 20-30 years, unless actions are taken to reduce global warming – in contradiction to conclusions of IPCC.
“If AMOC is allowed to shut down, it will lock in major problems including sea level rise of several metres – thus, we describe AMOC shutdown as the ‘point of no return’.”
The central estimate of another recent study on the timing of an AMOC collapse was 2050. However, Hansen said the point of no return could be avoided, based on the growing conviction of young people that they should follow the science. He called for a carbon fee and dividend policy, where all fossil fuels are taxed and the revenue returned to the public.
“The basic problem is that the waste products of fossil fuels are still dumped in the air free of charge,” he said.