Long argued that events would ultimately force the collective global hand. "People will begin feeling climate stress, such as in heatwaves, and asking, 'What can we do?' People are going to be making interventions on local and then regional, and then ever-growing scales until what they are doing does begin affecting the global climate."
Deciding whether to pursue geoengineering as a factor in addressing climate change will, suggested MacMartin, require addressing and answering difficult and uncomfortable questions.
"It's absolutely true that we could cool the planet by introducing particles into the stratosphere," he said. "Just because we could, doesn't mean we should. But there's a plausible argument that there's less risk in doing that than in allowing the planet to heat by 3 to 4 degrees."
The prospect of a potential climate solution involving some tough calls was a theme underlined by Long.
"Don't forget that the sulfur dioxide being put into the air by power plants, which is horrible for human health, is cooling the Earth," she said. "This is complicated. It's very, very complicated."