Ecosystems that will have begun to adapt to higher global temperatures as the world warms may struggle to adjust to the global cooling that peak and decline envisions. Scientists haven’t done much research on what the effects might be, Field said.
Sanderson said that peak and decline is unlikely within this century, but much more likely in the next century or beyond because changes in the climate system are hard to turn around even as atmospheric carbon concentrations decline.
The paper says that massive deployments of negative emissions technologies might work, but if they don’t, “future generations may be stuck with substantial climate change impacts, large mitigation costs, and unacceptable tradeoffs.”
Field said that when all the unknowns about negative emissions are considered, the best strategy to solve the climate crisis is to both develop carbon removal technology and work as quickly as possible to cut emissions today.
The paper generated a range of responses from negative emissions experts.
Klaus Lackner, director of the Center for Negative Carbon Emissions at Arizona State University and one of the world’s leading experts on carbon removal, said that he agrees with most of the paper’s conclusions, but it implies that climate change can be mitigated if emissions are drawn down quickly today.
“Yes, we should reduce emissions and move away from fossil fuels, but we will overshoot acceptable CO2 concentrations — indeed, we may already have overshot,” Lackner said, adding that no matter how much emissions are cut today, failure to develop negative emissions technologies will seriously damage the planet.
He said cutting carbon emissions gets more and more difficult the more they are reduced. Carbon removal is necessary to prevent atmospheric carbon dioxide concentrations from growing further.
Glen Peters, a scientist at the Norway-based climate research organization CICERO whose 2016 paper called focusing on negative emissions technology a “moral hazard,” said he agrees with the paper’s conclusion that countries need to both radically cut greenhouse gas emissions while also upscaling negative emissions technology.
Peters said he isn’t worried about the consequences of peak and decline because paleontological records suggest there are few catastrophic consequences of small declines in the earth’s average temperature over a period of decades.
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Sanderson said the questions the paper raises about the degree to which negative emissions technologies should be developed may be best solved by a putting a price on carbon.
“A well designed carbon market would find the optimal combination of emissions reductions and carbon removal,” he said. “This rather breaks the deadlock for decision makers today — they don’t have to decide whether to reduce emissions or invest in reduction technologies, all they need to do is put a price on carbon.”
John DeCicco, a professor at the University of Michigan-Ann Arbor Energy Institute, called the paper “excellent and thoughtful,” but it does not sufficiently recognize that the global carbon cycle already includes carbon removal processes. He said the paper doesn’t sufficiently factor in ways forests and soils could be managed to store more carbon than they do naturally.
DeCicco said that he agrees with the paper’s conclusion that it’s unwise for countries to automatically assume that technology will be developed to bring atmospheric carbon concentrations and global temperatures down to tolerable levels eventually.
“Hoping that future generations might somehow figure out an atmospheric CO2 decline in a way that undoes climate catastrophe is just foolish,” he said, adding that it’s critical for humanity to pursue both emissions cuts and carbon removal technology as quickly as possible.
“We can’t wait for some sort of technological deus ex machina to save us from ourselves," DeCicco said.
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