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In a stark warning to the world, renowned climate scientist Professor James Hansen has declared that the international target of limiting global warming to 2°C above preindustrial levels is no longer achievable. Hansen, a leading figure in climate science who first sounded the alarm on climate change in a landmark 1988 testimony to the U.S. Congress, now warns that the pace of global heating has been significantly underestimated, with dire consequences for the planet.
A new analysis by Hansen and his colleagues, published in the journal *Environment: Science and Policy for Sustainable Development*, reveals that recent cuts in sun-blocking shipping pollution and the climate’s sensitivity to rising fossil fuel emissions are greater than previously thought. These findings suggest that global temperatures could reach 2°C by 2045, far sooner than anticipated, unless drastic measures are taken.
A Grim Forecast for the Planet
The 2°C target, established by the Paris Agreement in 2015, was intended to prevent the worst impacts of climate change. However, Hansen’s analysis suggests that this goal is now out of reach due to rising global energy consumption and the underestimated effects of reduced shipping emissions. The study also warns of an increased risk of passing critical global tipping points, such as the collapse of the Atlantic Meridional Overturning Circulation (Amoc), a key ocean current system that regulates climate.
“The Intergovernmental Panel on Climate Change (IPCC) defined a scenario which gives a 50% chance to keep warming under 2°C – that scenario is now impossible,” Hansen said. “The 2°C target is dead, because global energy use is rising, and it will continue to rise.”
The Role of Shipping Emissions and Climate Sensitivity
One of the key factors driving accelerated warming is the reduction of sulphate aerosols from shipping emissions. For decades, these particles blocked sunlight, temporarily suppressing global temperatures. However, new anti-pollution regulations introduced in 2020 have sharply reduced these emissions, allowing more solar heat to reach the Earth’s surface. Hansen’s team estimates this change has added 0.5 watts per square metre (W/m²) of heat, a figure significantly higher than other recent studies.
The study also argues that the climate’s sensitivity to carbon emissions has been underestimated. While the IPCC estimates that a doubling of CO₂ levels would lead to a temperature rise of 2.5°C to 4°C, Hansen’s team calculates a higher sensitivity of 4.5°C. This discrepancy stems from differing methodologies, with Hansen’s approach relying more on historical climate data and observations rather than computer models.
Extreme Weather and Tipping Points
The world has already experienced devastating impacts from climate change, with global temperatures currently 1.3°C above preindustrial levels. Extreme weather events, from heatwaves to floods, have become more frequent and severe, causing widespread destruction. Hansen warns that reaching 2°C would exacerbate these impacts, with potentially catastrophic consequences.
One of the most alarming predictions in the study is the potential collapse of the Amoc within the next 20 to 30 years. Such an event could lead to a sea level rise of several metres and disrupt weather patterns globally.
References:
https://www.tandfonline.com/doi/full/10.1080/00139157.2025.2434494
https://www.un.org/en/climatechange/paris-agreement
https://oceanservice.noaa.gov/facts/amoc.html
Banner Image: Photo by Jacek Dylag on Unsplash
