In the race to slow global warming, science has been exploring ways to manipulate the climate, but until recently the conversations have been confined to laboratories.
While the growing field of geoengineering offers promise, it also comes with all kinds of potential pitfalls, and that's what experts and policy-makers are discussing at a conference in Berlin this week.
Geoengineering can be as simple as planting trees to remove CO2 from the air or as complicated as trying to use giant mirrors to reflect the sun into space or using wind-powered pumps to refreeze parts of the Arctic that have been impacted by global warming.
The thinking is that simply reducing CO2 emissions may not be enough to slow climate change so there should be supplementary approaches researched and ready to deploy.
"I'm extremely frustrated by how slow it's been to get real action on cutting emissions," said Canadian scientist David Keith, who is an expert in solar geoengineering.
The idea behind his research is that fine particles scattered in the upper stratosphere could reflect some of the sun's rays and reduce or maintain global temperatures.
It's a concept that's similar to how big volcanic eruptions are able to lower global temperatures, such as the 1991 eruption of Mount Pinatubo in the Phillippines, says Keith, a professor of applied physics and public policy at Harvard University.
"If you reduce the solar input a little bit — we're talking one per cent or less than one per cent — you might reduce some of the climate risks, like global warming, like extreme storms, that come from the accumulated carbon dioxide," he said.
'We don't live in a risk-free world'
Finding ways to hit the global temperature targets set by the Paris climate accord is a significant challenge.
"We have the risk of accumulated carbon dioxide in the atmosphere, we can't wish that away … even if we eliminated all emissions tomorrow, it's still there," Keith said. "We don't live in a risk-free world."
The risks are exactly what others are worried about.
Once you begin a solar geoengineering process, can you stop it? What happens if things don't go as planned? And what about the repercussions of CO2 emissions not related to global temperatures, such as ocean acidification?
Pat Mooney is concerned not only about the unforeseen impacts of geoengineering but also about the potentially reckless way governments and big businesses might leverage technology like Keith's solar interventions.
"These governments haven't done what they should have done for the last 40 years," said Mooney, of Ottawa-based ETC Group, a non-profit that looks at the impacts of emerging technology. "We're just giving them another reason not to do it. So, I don't see the plus side of that. I don't see the logic of letting them off the hook."
Maximize benefit, minimize risk
In New York, the Carnegie Climate Geoengineering Governance Initiative (C2G2) is trying to bring governments and policy-makers into the conversation.
"It's too important to leave to scientists alone," says Cynthia Scharf, senior strategy director with C2G2. "There are huge implications for almost any endeavour in society by using geoengineering."
She says those implications range from land use to ethical and religious concerns to debates about who should bear the brunt of the unintended consequences of climate manipulation. Leaders, from heads of states right down to local politicians, need to be part of conversations addressing those issues, she said.
"They need to be aware that these things are coming and look specifically at what it will take to maximize benefits — but, more importantly, minimize risks," said Scharf.
Those conversations are underway now at the second Climate Engineering Conference, where 250 experts have gathered to discuss, among other topics, a code of conduct for research, international rules governing the field and how climate policy should deal with fake news.
Keith says he recognizes the science of solar geoengineering is unproven, and it might not yet be the time to use it. But he is in favour of researching its potential.
"It's nonsense to claim we have to do it," he says. "But I think knowing more about something that is potentially really useful for reducing climate risks is very important."