Negative Emissions Key to Meeting 2°C Threshold

Humans will have to not only stop emitting greenhouse gases by 2085, but also develop technology that will result in negative emissions — the removal of 15 billion tons of carbon dioxide from the atmosphere each year by the end of the century —  in order to prevent global warming from exceeding 2°C (3.6°F), according to a new study.

Human greenhouse gas emissions, including methane and carbon dioxide, have already warmed the globe more than 1°C (1.8°F) compared to pre-industrial levels.  The Paris Climate Agreement negotiated last year seeks to cap warming to below 2°C, while at the same time pursuing an even more ambitious goal of limiting warming to 1.5°C.

But according to a new National Center for Atmospheric Research study, just cutting emissions under the Paris agreement may not be enough to keep global warming from blasting past 2°C, said Benjamin Sanderson, the study’s lead author.

Meeting the Paris agreement as written will require a long-term commitment to negative emissions in the last two decades of the century, he said.

Countries have agreed to cut total annual global greenhouse gas emissions from about 60 billion metric tons of carbon dioxide-equivalent today to about 54 billion tons in 2030.  Without steeper emissions cuts sooner, about 15 billion tons of carbon dioxide will have to be removed from the atmosphere every year by the end of the century in order to keep within 2°C of warming, he said.

Sabine Fuss, a negative emissions researcher at the Mercator Research Institute on Global Commons and Climate Change in Berlin, said the NCAR research confirms that individual countries’ emissions cuts pledges under the Paris agreement are insufficient to meet the pact’s global warming goals.

The study is in line with earlier research supporting negative emissions and its approach gives scientists a better understanding of when emissions cuts and carbon removal are necessary to keep global warming in check, she said.

Negative emissions aren’t a new idea.  The Intergovernmental Panel on Climate Change included negative emissions in some of its climate stabilization scenarios in its Fifth Assessment Report in 2014.  The IPCC warned that the feasibility of removing carbon from the atmosphere is highly uncertain, however, in part because the technology remains unproven and scientists haven’t assessed any risks carbon removal may pose.

Negative emissions technology isn’t being used anywhere in a significant way today, and the best options for carbon removal have major land and environmental impacts, Fuss said.

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