New James Hansen paper links accelerating climate change to new aerosol regulations for ships 

A new paper claims that average temperatures have shifted permanently above 1.5C as a result of an obscure factor: recent regulations on shipping.A recent study led by legendary climatologist James Hansen presents compelling evidence that new International Maritime Organization (IMO) regulations on ship emissions have contributed significantly to the rapid acceleration of global warming observed since 2010.These regulations, aimed at reducing sulfur dioxide (SO2) emissions to improve air quality, have also had an unintended consequence: the loss of cooling effects from sulfate aerosols that previously offset some greenhouse gas (GHG) warming.Is global warming accelerating?Hansen’s paper highlights that since 2010, the rate of global warming has increased by more than 50% compared to the 1970–2010 warming rate of 0.18°C per decade. This trend has caused Earth’s temperature to reach levels not seen in at least 120,000 years, comparable to the extreme warm Eemian interglacial period. The rapid warming observed during the recent El Niño event further emphasizes the severity of this trend, with global temperatures increasing by 0.4°C—far exceeding previous El Niño-driven warming events.How do aerosols influence radiative forcing?For decades, climate scientists have recognized the dual role of human-made pollutants: while greenhouse gases trap heat and drive warming, aerosols—tiny particles emitted from burning fossil fuels and biofuels—reflect sunlight back into space, cooling the planet. Charlson et al. (1992) initially demonstrated that aerosol cooling was comparable in magnitude to GHG warming, effectively masking the full extent of anthropogenic climate change.However, this was a “Faustian bargain,” as aerosol pollution also contributes to millions of deaths annually due to respiratory and cardiovascular diseases. As a result, regulatory efforts to improve air quality—such as the IMO’s strict sulfur limits on ship fuels—have inadvertently led to a rapid reduction in aerosol-driven cooling, revealing the full force of GHG warming.
Global dimming: how tackling air quality exacerbates global warming 
In a painful irony, improving global air quality through regulation and decarbonising could actually raise average surface temperatures by counteracting a phenomenon called ‘global dimming’…. Read MoreWhat does this mean for estimations of climate sensitivity?Hansen’s research challenges previous estimates by the Intergovernmental Panel on Climate Change (IPCC), suggesting that aerosol climate forcing has been underestimated. The paper argues that:IPCC’s reliance on climate models led to a systematic underestimation of both aerosol forcing and climate sensitivity.
The sudden reduction in ship aerosol emissions in 2020 has likely contributed an additional +0.5 W/m² of climate forcing, far exceeding the IPCC’s estimated +0.079 W/m².
This discrepancy helps explain the une