James Hansen is an 83-year-old climate research scientist that became known in the 1980s for making accurate predictions about global temperature increases. Now, he forecasts that warming is happening even faster than he expected.
Will policymakers listen to Hansen this time?
His latest paper, a 33-page peer-reviewed report that was published in November 2023, covers a myriad of related topics about climate change, including possible remedial actions to stop the worst impacts.
But a key conclusion of the paper – “Global Warming in the Pipeline” -- is his (and his co-authors) bold claim that the current rate of change in the amount of carbon dioxide in the atmosphere could cause temperatures to increase by about 4.8 degrees Celsius after CO2 doubles. That degree of warming would change the planet in a dramatic way, as it makes it possible that both of the large ice sheets, Antarctica and Greenland, could partially or completely melt, leading to sea level increases of 50 meters or more. The title “Warming in the Pipeline” hints that a large amount of warming is already likely even if immediate action to limit emissions is taken.
You can access the paper at Oxford Academic.
The Earth’s Energy Imbalance (EEI) causes warming as the earth absorbs more energy from the Sun than it radiates out to space. The earth will keep getting hotter until that imbalance is resolved. About 90 percent of the excess warming has gone into the ocean so far.
And the idea that 4.8 degrees is “baked in the cake” comes from the analysis of periods when large changes in atmospheric CO2 occurred, going back in geological time over the last 66 million years -- the Cenozoic era after the extinction of the large dinosaurs.
The recent CO2 increase has been very substantial in comparison to previous cycles and has occurred 100-200 times faster than during any previous era. These gains have happened since the industrial era began in England in 1800 when coal burning was introduced for industrial applications. CO2 levels at that time were about 280 ppm (parts per million) and today are measured at an observatory in Hawaii at 425 ppm, an increase of about 50 percent.
Hansen is now saying that 1.5 degrees of warming will arrive this decade, and that 2 degrees is expected before 2050.
The Intergovernmental Panel on Climate Change (IPCC) forecasts a temperature change of 3 degrees Celsius after a doubling of CO2 and doesn’t believe that would cause drastic changes. That panel completes a comprehensive scientific assessment every 6 to 7 years. The Fifth Assessment in 2014 provided the basis for the Paris Agreement and the target of limiting warming to 1.5 degrees.
The public and politicians are likely to accept the more conservative predictions from the IPCC.
As Hansen states, “A climate characterized by delayed response and amplifying feedbacks is especially dangerous because the public and policymakers are unlikely to make fundamental changes … until they see visible evidence of the threat.”
Hilliard MacBeth
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