When the Paris Agreement set an ambitious goal of limiting the global temperature rise to 1.5 degrees Celsius above pre-industrial levels, the negotiators put climate engineering on the table, says Simon Nicholson, professor at American University, in this week’s episode of Backdraft. Once the purview of science fiction, a majority of the models run by the Intergovernmental Panel on Climate Change (IPCC) required large-scale use of climate engineering technologies to keep additional warming below 2 degrees.

“Nobody who was arguing for that 1.5 degree target at Paris was thinking in their heads we should start shooting sulfate particles into the atmosphere,” says Nicholson. They were looking at the science and recognizing that without aggressive action a lot of people will suffer. But, says Nicholson, it’s not clear that the target is attainable through traditional mitigation alone. “The entire conversation is in some ways an unintended consequence of not doing enough. Very few people want to talk about doing climate engineering. The reason you get a growing number of scientists and policymakers [discussing climate engineering], is because the situation is getting pretty desperate.”

There are two types of climate engineering technologies – solar radiation management and carbon dioxide removal. While carbon dioxide removal tends to be slow-acting and expensive, solar radiation management is fast-acting and seemingly cheap. “One thing to really pay attention to is that each of the technologies has its own risk profile,” says Nicholson, the co-founder of the Forum for Climate Engineering Assessment. “We have to parse them out and discuss them one by one.”

Both technologies have significant environmental, political and social, and existential implications. For example, bio-energy with carbon capture and storage (BECCS), a carbon dioxide removal technology used in the IPCC modeling, would require an immense industrial infrastructure to capture carbon and move it to storage. There would be massive changes in land use, which could generate political and social conflicts. Determining who gets a voice in the decision-making process will be extremely complicated and could increase the vulnerability of already vulnerable communities, says Nicholson.

While faster-acting and less expensive than carbon removal technologies like BECCS, solar radiation management technologies, like stratospheric aerosol injection, could have devastating environmental consequences. “Even if we get it right, there is potential for downsides,” says Nicholson.

“The biggest problem is the social and political transformation that’s needed so that long-term human beings and the way that we live are compatible with ecological realities,” says Nicholson. “Solar radiation is not a fix… And yet, one could imagine politicians and other actors try to sell it as a fix.”

Currently, there is no formal governance system overseeing climate engineering, and Nicholson suggests that this may be an even bigger hurdle than even the environmental impacts. A successful climate intervention would require at least a couple hundred years to achieve a significant decrease in temperature, and stopping an intervention prematurely could lead to a spike in warming. “How do you build a system of governance that lasts across multiple centuries?” he asks. “It might not be the technological challenges that sink something like stratospheric aerosol injection; it may be that the political conversation is just too tough. We just can’t find a way to put together a governance arrangement that’s robust enough that the world community buys it.”

“Although negotiators didn’t intend for this to be the case, now we’re kind of locked into a conversation where climate engineering is on the table,” says Nicholson. “If these [technologies] do start to come onto the table, then they can’t be used as cover for inaction. And that is perhaps the biggest political challenge in this space.”

For more on climate engineering technologies, listen to the podcast postscript: