James Hansen warns of global warming in the pipeline
The renowned climate scientist James E. Hansen, along with a slew of colleagues, have gone and done it again.
Publication yesterday of their study, Global Warming in the Pipeline, will require responsible policymakers and the informed public to consider the threat presented by unarrested climate change quite a bit differently.
For purposes of full disclosure, I should note that Dr. Hansen serves on the CPR Initiative Board of Advisers, and further, I have long served as his legal and policy adviser. Nonetheless, my brief statement here about Dr. Hansen’s new study is entirely my own.
First, we should define a couple of terms. Equilibrium Climate Sensitivity (ECS) is “the eventual global temperature change caused by doubled CO2 if ice sheets, vegetation and [other] long lived GHGs are fixed.” Earth System Sensitivity (ESS), in turn, is the planet’s estimated eventual temperature that more fully accounts for slow feedbacks, including ice sheet size.
Utilizing multiple lines of evidence (including paleoclimate estimates and actual measurements) the Hansen team finds that both ECS and ESS have been underestimated to date, and that “eventual Earth system response” [ESS] to today’s level of GHG forcing “is about 10oC.” If, however, human-made aerosols are held constant at current levels, “then equilibrium warming for today’s atmosphere is reduced to 8oC.” Still, as they observe, “[e]ither 10oC or 8oC dwarfs observed global warming of 1.2oC to date.”
The Hansen team’s study was published in Oxford Open Climate Change. That journal’s editor, Eelco Rohling, along with a colleague, produced an accompanying editorial that itself is well worth reading. It observes that the Hansen team’s use of climate sensitivity estimates derived from paleoclimate studies “indicate larger implications of modern climate change than we had estimated before. This elevates ‘high impact, low probability’ impacts toward the ‘high impact, high probability’ level, and this is enough reason to publish the new estimates. It should make everyone sit up and take notice.” [Emphasis added.]
We will have further occasion to “sit up and take notice” in this space in coming weeks.