Inside Climate News: New Research Led by James Hansen Documents Global Warming Acceleration

New research by an international team of climate scientists documents a surge of global warming during the past 15 years that risks shutting down a key ocean current by 2050.

During a webinar Tuesday discussing the study, the authors said the rate of global warming since 2010 has increased by more than 50 percent over the rate of warming in the preceding four decades, surging more than 0.7 degrees Fahrenheit (0.4 degrees Celsius) in just the past two years.

At the current rate, the Paris Agreement goal of limiting global warming to somewhere between 2.7 degrees and 3.6 degrees Fahrenheit (1.5-2 degrees Celsius) is pretty much dead, said James Hansen, a former NASA climate scientist who led the team and whose 1988 testimony to Congress was one of the early public warnings about the risks of greenhouse gas emissions.

The increased rate of warming will intensify already deadly heatwaves and worsen both drought and flooding extremes, as well as speed up the spread of deadly diseases associated with warmer temperatures.

The shutdown of the Atlantic Meridional Overturning Current (AMOC) discussed in the new paper would lead to a sudden surge of sea level rise along the East Coast, and bring crop-threatening climate extremes to parts of Europe, according to a 2024 study.

Scientists expected the global average temperature to start dropping this winter because parts of the tropical Pacific Ocean are in La Niña conditions, the cool phase of a cycle that can reduce the annual global average temperature by up to 0.36 degrees Fahrenheit.

Instead, temperatures continued to surge into 2025 with the warmest January on record—3.13 degrees Fahrenheit (1.74 degrees Celsius) above the pre-industrial baseline. Researchers have noted how the sustained warmth is unexpected.

As in other papers he published recently, Hansen said the new findings affirm that a key driver of the warming is the reduction of sulfate aerosol pollution over Northern Hemisphere oceans. That change, due to stricter shipping fuel regulations, has the effect of dimming the reflectivity of clouds and allowing more heat to reach the surface of the Earth.

Other research looking at the remarkable 0.7-degree Fahrenheit rise of the past two years found that the spike could be attributed to a combination of causes in addition to aerosol reductions, including a Pacific Ocean warm phase and decadal shifts of large-scale pressure patterns.

AMOC Shutdown?

Global warming is most pronounced in the Arctic, and that is melting a lot more ice and sending more freshwater into the North Atlantic than currently estimated by most climate models, Hansen said. That inflow of water could have dire consequences, particularly for the ocean current that warms much of Western Europe.

A “shutdown of the Atlantic Meridional Overturning Circulation (AMOC) is likely within the next 20-30 years, unless actions are taken to reduce global warming,” the researchers wrote. Their warning about AMOC contradicts the conclusions of the Intergovernmental Panel on Climate Change (IPCC), they added.

The IPCC is the United Nations entity charged with assessing climate science and exploring policy options, and its most recent global assessment, in 2021, concluded that the AMOC will slow in a warming climate, but did not find it likely the current would shut down this century.

The AMOC is “the ocean conveyor that carries a huge amount of heat into the Northern Hemisphere,” Hansen said Tuesday. “If it shuts down, the heat stays in the Southern Hemisphere and will lock in many meters of sea level rise.”

“We can adapt to more extreme heat waves, droughts, storms and floods, and minimize their impact,” he said. “But the main issue is the sleeping giant, the point of no return, the danger of an AMOC shutdown and large sea level rise.”

The IPCC fell short of adequately warning the public about this “point of no return” by ruling that an AMOC shutdown is not likely this century, Hansen said. The panel rejected a 2015 paper with an AMOC shutdown warning, he noted, because it showed too much freshwater from melted Arctic ice flowing into the Atlantic.

“But now, surely, ice melt will accelerate,” he said. “Warmer Pacific water is beginning to flow over the Aleutian shelf into the Arctic Ocean surface layer. And in the North Atlantic, warmer water is invading under the sea ice and under Greenland ice shelves.”

Earth history shows that such ocean warming can lead to rapid loss of sea ice at both poles, he said, and sea level can rise several meters within a century during times of rapid warming.

“We must understand this situation better,” he said. “Models used by the IPCC are not realistic.”

“The main issue is the sleeping giant, the point of no return, the danger of an AMOC shutdown and large sea level rise.”

— James Hansen

Andrej Mahecic, head of media and communications with the IPCC, said the panel doesn’t comment on individual studies.

“The IPCC assesses the science that has been published on climate change,” he said. “For each report, there are cut-off dates for publications to be considered in an assessment.”

Other scientists, who say they generally respect Hansen’s work, disagree with his conclusions on aerosols and the acceleration of global warming.

Bob Kopp, a climate and sea level researcher at Rutgers University, posted Tuesday on Bluesky that Hansen is “just flat wrong” to make sea level rise projections based on the assumption that we’re already in an era of exponentially rising polar ice loss. The most current calculations of ice mass loss don’t support those projections, he said.

And climate scientist Michael Mann, director of the Center for Science, Sustainability & the Media at the University of Pennsylvania, responded to previous research by Hansen about the reduction of aerosol pollution accelerating warming of the oceans by noting that the recent two-year global temperature increase is within the range of warming projected by models…

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