A new commentary piece in Nature Climate Change continues to make significant errors and propagates a mistaken core assumption too many in the climate community make: that with enough [insert: political will or technological breakthroughs], 2C warming is still an achievable goal.
I have disagreed with this assumption and therefore its conclusion for six years – ever since establishment Democrats decided to waste valuable political capital on a right-wing insurance bill with a vague promise that climate legislation would come someday. That decision essentially assured that, absent a global economic collapse or catastrophic geologic events, our species would easily push the planet past 2C warming.
The following graphic shows global historical emissions in solid black. The green curve represents the fantasy projection of an emissions pathway that leads to <2C global warming. As you can see, emissions have to start declining this year in the assumed scenario. The yellow curve represents what is likely to happen if climate action is delayed for 8 years and this year’s emissions remain constant during those 8 years. It gets increasingly difficult to achieve the same long-term warming cap because of that 8 year delay.
The red curve builds on the yellow curve projection by keeping the next 8 year’s emissions constant but reducing federal money to research decarbonization technology. This is the linchpin to any emissions pathway that could potentially put us on a pathway to a less warm climate. Decarbonization technology has to not only be fully researched but fully deployed on a planetary scale for the 2C pathway to happen. It’s hard to see on this graph, but global emissions have to go net negative for us to achieve <2C warming. While the yellow curve has a harder time achieving that than the green curve, the red curve doesn’t get there one century from now. But the red curve isn’t the most likely pathway – it wasn’t in 2010 and it isn’t today.
The most likely pathway is the solid black curve out to 2125. It assumes the same things as the red curve and adds an important component of reality: emissions are likely to increase in the near-term due to continued increased fossil fuel use. Natural gas and coal plants continue to be built – any assumption otherwise might be interesting academically but has no place in the real world. By assuming otherwise, scientists make themselves a target of future policy makers because the latter won’t pay attention to the nuanced arguments the scientists will make once it’s clear we’re hurtling past 2C. Once we burn increasing amounts of fossil fuels during the next 8 years (as we did the 8 years before that and so on), it is harder still to cut emissions fast enough to try to keep global warming <2C. The reasons should be obvious: the emitted GHGs will radiatively warm the planet so long as they’re in the atmosphere and it will take even more technological breakthroughs to achieve the level of carbon removal necessary to keep warming below some level.
The authors recognize this challenge:
[…]to remain within a carbon budget for 2 °C in the baseline scenario considered, peak reduction rates of CO2 emissions around 2.4% per year are needed starting mitigation now. A global delay of mitigation action of eight years increases that to 4.2% per year (black dashed in Fig. 1a) — extremely challenging both economically and technically. The only alternative would be an overshoot in temperature and negative emissions thereafter. Research in negative emissions should therefore be a priority, but near term policy should work under the assumption that such technology would not be available at large scale and low cost soon.
I disagree with the author’s conclusion:
Society is at a crossroad, and the decisions made in the US and elsewhere over the next 4–8 years may well determine if it is possible to limit climate change to levels agreed in Paris.
We passed the crossroad already. It really doesn’t matter when, the fact is we passed it. I think it is a waste of time to examine low-end emission scenarios for policy purposes. They serve some scientific use. Policy makers need relevant scientific advice and 2C scenarios don’t do that. They perpetuate a myth and therefore pose a real danger to society. The so-called reality-based community needs to critically self-examine what they’re doing and why they’re doing it. We’re headed for >3C warming and we need to come to terms with what that means.
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