by Judith Curry
“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.” — Oliver Geden
A provocative paper has been published in Science:
A roadmap for rapid decarbonization
Johann Rockstrom, Owen Gaffney et al.
Abstract. 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. Despite progress during the 2016 Marrakech climate negotiations, long-term goals can be trumped by political short-termism. Following the Agreement, which became international law earlier than expected, several countries published mid-century decarbonization strategies, with more due soon. Model-based decarbonization assessments and scenarios often struggle to capture transformative change and the dynamics associated with it: disruption, innovation, and nonlinear change in human behavior. For example, in just 2 years, China’s coal use swung from 3.7% growth in 2013 to a decline of 3.7% in 2015. To harness these dynamics and to calibrate for short-term realpolitik, we propose framing the decarbonization challenge in terms of a global decadal roadmap based on a simple heuristic—a “carbon law”—of halving gross anthropogenic carbon-dioxide (CO2) emissions every decade. Complemented by immediately instigated, scalable carbon removal and efforts to ramp down land-use CO2 emissions, this can lead to net-zero emissions around mid-century, a path necessary to limit warming to well below 2°C.
[Link] to abstract.
It’s behind paywall (of course). Brad Plumer at Vox has a good summary entitled: Scientists made a detailed roadmap for meeting Paris climate goals. It’s eye opening. Excerpts:
To hit the Paris climate goals without geoengineering, the world has to do three broad (and incredibly ambitious) things:
1) Global CO2 emissions from energy and industry have to fall in half each decade. That is, in the 2020s, the world cuts emissions in half. Then we do it again in the 2030s. Then we do it again in the 2040s. They dub this a “carbon law.” Lead author Johan Rockström told me they were thinking of an analogy to Moore’s law for transistors; we’ll see why.
2) Net emissions from land use — i.e., from agriculture and deforestation — have to fall steadily to zero by 2050. This would need to happen even as the world population grows and we’re feeding ever more people.
3) Technologies to suck carbon dioxide out of the atmosphere have to start scaling up massively, until we’re artificially pulling 5 gigatons of CO2 per year out of the atmosphere by 2050 — nearly double what all the world’s trees and soils already do.
“It’s way more than adding solar or wind,” says Rockström. “It’s rapid decarbonization, plus a revolution in food production, plus a sustainability revolution, plus a massive engineering scale-up [for carbon removal].”
So, uh, how do we cut CO2 emissions in half, then half again, then half again? Here, the authors lay out a sample “roadmap” of what specific actions the world would have to take each decade, based on current research. This isn’t the only path for making big CO2 cuts, but it gives a sense of the sheer scale and speed required.
It’d be entirely understandable to look at this all and say, “That’s insane.” Phasing out sales of combustion engine vehicles by 2030? Carbon-neutral air travel within two decades? Cities going entirely fossil fuel–free in the next 13 years? Come on.
And fair enough. None of this is easy. It might well prove impossible. But this is roughly what staying well below 2°C entails — at least without large-scale geoengineering to filter out sunlight and cool the planet (a risky step). This is what world governments implicitly agreed to when they all signed on to the Paris accord.
Rockström and his colleagues argue that future UN climate talks should strive to create a much more detailed decade-by-decade road map along the lines of their Science paper, in order to gain much more clarity on what needs to happen to stay below 2°C.
Of course, it’s possible that if policymakers really grappled with what staying below 2°C entails, they might come away thinking it’s impractical or undesirable. They might decide that maybe we should aim to stay below 2.5°C or 3°C, and just try to deal with the severe risks of a hotter planet, from higher sea level rise droughts to crop failures, that come with it.
But something has to force that conversation. If this 2°C climate goal is going to loom over every international climate meeting, every white paper and discussion, then the least people can do is take it seriously.
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 would 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 can reduce vulnerability from extreme weather events (whether or not they are exacerbated by AGW) and the slow creep of sea level rise.