I’ve been following James Hansen‘s work for decades, and his latest paper demands our attention. Hansen and his team have just released “Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed?” It’s the third of three planned papers examining the causes and implications of the dramatic acceleration in global warming we’ve observed in recent years. While the paper itself is lengthy and highly technical, Hansen has provided an invaluable summary of the key scientific findings in his latest commentary (which he regularly produces every two to three months).
The bottom line is startling: Hansen’s team argues that mainstream climate science, as reflected in the IPCC’s reports, underestimates climate sensitivity to CO2 by about 50 percent. Their research suggests that the “short-term”—century time scale—equilibrium warming from a doubling of CO2e should be 4.5 degrees C, not the standard estimate of 3 degrees.
The reason for this error, in the view of Hansen and his team, is that conventional climate science, which is almost wholly wedded to climate models, has miscalculated the past impact of aerosols on warming trends. Now that shipping aerosols have declined dramatically across the north Pacific and Atlantic, that extra climate forcing is being revealed—ergo the acceleration. Paleoclimatic data, they argue, also support a substantially higher estimate of climate sensitivity.
These findings have predictably ruffled feathers in the climate science community. Scientists like Michael Mann find these claims particularly irksome. However, Hansen’s paper directly addresses the standard rebuttals that Mann and others have recently put forward in widely reported critiques.
While Hansen and his team have long been outliers in their interpretation of warming causes and trends, we can’t ignore Hansen’s track record of being substantially right over the decades and consistently ahead of the curve. Though scientific consensus typically deserves our respect, in this case, there’s reason to believe that fears of being labeled “climate doomsters” or “alarmists” may have led the mainstream climate science community to underestimate both the amount and rate of future warming.
These findings have implications that stretch across all sectors concerned with climate change, suggesting we need to radically rethink our timelines and response strategies.
— Cascade Institute Executive Director Thomas Homer-Dixon
Related read: The most important scientific article of the last decade