“[T]here is growing evidence of much smaller climate sensitivity to CO2; and even if these drastic emissions reductions occurred, we see little impact on the climate in the 21st century (even if you believe the climate models).”
“It seems rather futile to make token emissions reductions at substantial cost. Deciding that all this is impractical or infeasible seems like a rational response to me.”
– Judith Curry, “A Roadmap for Meeting Paris Emissions Reduction Goals.” Climate Etc., March 25, 2017.
Numerous posts at MasterResource have summarized the thinking of climate scientist and straight shooter Judith Curry. Bravely, and with intellectual vigor, she has personified the adage: “One plus the truth equals a majority.”
Curry has not only documented the fact that estimations of climate sensitivity to the enhanced greenhouse effect have been coming down, and tie-in’s of climate forcing and extreme weather events remain unproven. She has also explained why the large majority of climate scientists have cut intellectual corners to be activists in a cause that is futile politically and economically unattractive (these two are tied).
Curry’s evolution away from the alarmist side (another story) took another step, in my view, with her latest commentary on what would be required for the climate goals of the Paris Agreement on Climate Change to be met. Her views (see below) regard a new paper in Science, “A Roadmap for Rapid Decarbonization” (by Johann Rockstrom, Owen Gaffney et al.). The Abstract of that paper states:
Although the Paris Agreement’s goals are aligned with science and can, in principle, be technically and economically achieved, alarming inconsistencies remain between science-based targets and national commitments.
Forced energy transformation, the authors state, would require a carbon tax that begins at $50 per metric ton–worldwide–that would increase past $400 per ton by 2050. Government R&D would increase by “an order of magnitude between now and 2030,” and so on. (Also see the Vox summary of the proposal that Curry references.)
For more than a decade, climate scientist/activist James Hansen has been clear on the daunting math of CO2 reduction. He first stated that the world had ten years to reverse course on fossil-fuel reliance, a prediction made in 2006 in The New York Review of Books.
When that prediction came due, Hansen floated the need to go emissions-negative. Wow! Then, just a couple of months later, he recanted to say that we still have time to turn things around. (“The ponderous response of the climate system also means that we don’t need to instantaneously reduce GHG amounts.”) Lots of confusion, to say the least, from the father of climate alarmism.
Back to the new Science article, Curry goes over the mitigation math. She then ties the implications of the paper with the latest climate science to reach these profound conclusions.
Apart from the issues raised in this paper, there are several other elephants in this room: there is growing evidence of much smaller climate sensitivity to CO2; and even if these drastic emissions reductions occurred, we see little impact on the climate in the 21st century (even if you believe the climate models).
I think that what this paper has done is important: laying out what it would actually take to make such drastic emissions reductions. Even if we solve the electric power problem, there is still the problem of transportation, not to mention land use. Even if all this was technically possible, the cost would almost certainly be infeasible.
As Oliver Geden states, its time to ask policy makers whether they are going to attempt do this or not. It seems rather futile to make token emissions reductions at substantial cost. 
Deciding that all this is impractical or infeasible seems like a rational response to me. The feasible responses are going with nuclear power or undertaking a massive R&D effort to develop new emission free energy technologies. Independent of all this, we an reduce vulnerability from extreme weather events (whether or not they are exacerbated by AGW) and the slow creep of sea level rise.
The implications of the Bad Mitigation Math (BMM: let this become an acronym in the debate) go further.
What is very bad today for mitigation is becoming worse by the day as fossil fuels continue their dominance in the energy sphere. Total demand is growing, and renewable-energy subsidies are under increasing assault around the world; it is quite possible that the market share of natural gas, coal, and oil will expand in the next decades from today’s 80 percent (+) market share.
Profoundly, the US’s about-face on climate activism, and a weakening of the paper promises of countries worldwide, could permanently ruin the math of mitigation from the activists own viewpoint. There might still be activism, but it will be increasingly seen as token and futile. Adaptation will be the only game, which points to a free market strategy of global freedom of movement for goods, services, and people.
“It’s all over but the shouting” may be the case for climate alarmists/mitigationists, but the public policy imperative is to end government taxing-and-spending in the name of climate change, and pressure private foundations/civil society to stop funding climate activism and address here-and-now human needs.
That job awaits a lot of us.
 Curry begins her post with this quotation from Oliver Geden: “I think this should be the way forward, translating [overarching climate goals] into ‘policy portfolios’ and then asking policymakers if they are going to do it or not.”