Scientist Jim Hansen and some scientist and non-scientist co-authors are throwing cold water on the hot conventional wisdom that things will be fine if only the world can hold global temperature increases to no more than 3.6 degrees Fahrenheit, 2 degrees Centigrade.

Image of Hansen
A photo from Jim Hansen’s website shows him with some members of his ‘future generations’ often at the heart of his climate concerns.

Forget about that threshold, and think more along the lines of a 1 degree C increase, they urge, saying an increase of 2 degrees C would lead to “disastrous consequences.” They recommend in a new paper, as Hansen often does, substantial cuts in carbon emissions “to protect young people, future generations, and nature.”

Published in PLOS One, an open-source online journal, the former NASA lead climate scientist, now leading a policy program at Columbia University’s Earth Institute, partnered on the piece not only with other respected climate scientists, but also with economists and policy experts. The Hansen initiative appears to reflect a more gloves-off and activist policy approach than even he was taking as a civil servant and federal agency scientist. It’s indeed one of the objectives Hansen pointed to in announcing his retirement from NASA in April 2013.

Hansen ‘Speaking Truth to Power’

The Hansen paper, posted online December 3, comes just a week before he is to make at least one major presentation before what is likely to be an overflow large audience as part of the fall conference of the American Geophysical Union in San Francisco. Among other likely presentations, he is scheduled to deliver the AGU “Frontiers of Geophysics Lecture” from 12:30 to 1:30 p.m. on December 10. In promoting his presentation, the AGU website says Hansen “is recognized for speaking truth to power, for identifying ineffectual policies as greenwash, and for outlining actions that the public must take to protect the future of young people and other life on our planet.”

That pretty much describes what Hansen and his co-authors set out to do in their no-holds-barred December 3 posting for which he is the principal author:

A cumulative industrial-era limit of ~500 GtC fossil fuel emissions and 100 GtC storage in the biosphere and soil would keep climate close to the Holocene range to which humanity and other species are adapted. Cumulative emissions of ~1000 GtC, sometimes associated with 2 degrees C global warming, would spur “slow” feedbacks and eventual warming of 3-4 degrees C with disastrous consequences. Rapid emissions reduction is required to restore Earth’s energy balance and avoid ocean heat uptake that would practically guarantee irreversible effects. Continuation of high fossil fuel emissions, given current knowledge of the consequences, would be an act of extraordinary witting intergenerational injustice.

Somewhat mirroring, but going beyond, remarks made that same day about abrupt climate change impacts (see related story posted December 5) as part of a National Research Council new report, Hansen and his authors warn in their paper that “Climate impacts accompanying global warming of 2 degrees C or more would be highly deleterious. Already there are numerous indications of substantial effects in response to warming of the past few decades.”

Their paper explores what they see as climate change impacts associated with sea-level rise; shifting coastal zones; human extermination of species; coral reef ecosystems; climate extremes; human health, and ecological and environmental issues. The authors caution that reaching a 2 degrees C increase inevitably would lead to further global temperature increases as a result of more gradual warming “feedbacks.”

While not published in one of the high-visibility peer-reviewed journals such as Science, Nature, or the Proceedings of the National Academy of Science, the new Hansen paper is likely to generate lots of attention and interest. The reception it receives by media, fellow scientists and policy professionals, and the broader public may help address questions and concerns about whether Hansen, in having given up his federal agency high-visibility perch at NASA, can retain his bully pulpit and megaphone.

Those knowing him over his long career as a climate scientist, communicator, and activist aren’t inclined to doubt that he may well do so. His newest study is certain to attract barbs from all the usual Hansen critics, but the real test may involve how it is received by his erstwhile and present scientific colleagues in academia and public service. The AGU presentations will likely provide insights on those issues.

Bud Ward was editor of Yale Climate Connections from 2007-2022. He started his environmental journalism career in 1974. He later served as assistant director of the U.S. Congress's National Commission...