A new study in the journal Nature Climate Change is breaking new ground in the debate about how to limit average global warming to 1.5°C, suggesting for the first time that the target may be achievable with little or no reliance on a controversial and unproven “negative emission” technique, Bioenergy with Carbon Capture and Storage (BECCS).
“I do believe getting rid of negative emissions totally is not possible—but minimizing them might be attractive,” said lead author Prof. Detlef von Vuuren, senior researcher with the Netherlands Environmental Assessment Agency. “Negative emissions are not necessarily bad, but it means that one does accept certain risks.”
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The new scenario assumes “ambitious but not unrealistic” deployment of renewable electricity, high levels of energy and materials efficiency, agricultural intensification, and reduction of greenhouse gases other than carbon dioxide “using the best-available technologies and further technological progress,” Carbon Brief reports.
It shows improved access to education accelerating a trend toward reduced fertility, so that today’s world population of 7.0 billion peaks at 8.4 billion in 2050, before falling to 6.9 billion in 2100. The majority of the world’s population adopts “sustainable lifestyles”, with less air travel and private automobile use, more walking and cycling, and pretty much everyone adopting healthier diets with less meat consumption.
The paper departs from most 1.5°C scenarios by emphasizing options that “have tended to be excluded from the conversation, because they are hard for scientists to model,” Carbon Brief notes.
The 1.5°C pathways developed until now “have relied on negative emissions from BECCS to suck excess CO2 out of the atmosphere later this century,” writes Deputy Editor Simon Evans. “In part, this reflects the assumption that inertia in the global energy system makes it hard to peak and then eliminate CO2.”
The integrated assessment models (IAMs) at the heart of most low-carbon pathways “select technologies on the basis of relative costs,” the new report states, so that “they normally concentrate on reduction measures for which reasonable estimates of future performance and costs can be made. This implies that some possible response strategies receive less attention, as their future performance is more speculative or their introduction would be based on drivers other than cost, such as lifestyle change or more rapid electrification.”
As well, “existing studies hardly look into more aggressive implementation of options, such as rapid implementation of the best available technologies or deep reduction of non-CO2 [greenhouse gases]. Technology development could also be more rapid than typically assumed in IAM model runs.”
Those factors help explain “why BECCS has become so dominant in the 1.5°C scenarios, even though its widespread deployment faces daunting sociopolitical barriers,” Evans explains. “In contrast, alternative solutions have often been ignored because it is hard to estimate their performance or cost.”
In the new study, “combining all of the mitigation options together effectively eliminates the need for BECCS to stay within a 1.5°C limit,” Carbon Brief notes. “This frees up significant areas of agricultural land in the model, some of which is reforested, resulting in ‘natural’ CO2 removal.”
Carbon Brief describes van Vuuren as “a key figure in the early use of BECCS within climate models” who now considers it “unfortunate” the technology has to come to dominate scenario work on 1.5°C. The more common approach has raised apprehension across the climate community that is likely to reach a crescendo later this year, with the Intergovernmental Panel on Climate Change due to release a special report  on 1.5°C pathways ahead of the UN climate conference this December in Katowice, Poland.
“There are major concerns about the sustainability of large-scale deployment of CO2 removal (CDR) technologies, especially in relation to BECCS, but also for large-scale afforestation,” said Dr. Alexander Popp, head of the land-use management group at the Potsdam Institute for Climate Impact Research.
While the new study points to a different path, research scholar Dr. Joeri Rogeli at the International Institute for Applied Systems Analysis said the fundamental issue for policy-makers is unchanged.
“The core of the mitigation challenge remains the same: global CO2 emissions need to be reduced to zero,” he told Carbon Brief. “What policy-makers should take from this entire body of research on 1.5°C scenarios is that there is a variety of avenues one can pursue to limit CO2 emissions, and that these different avenues or strategies allow to limit the contribution of potentially undesirable technologies like BECCS.”