A range of technologies — loosely defined as 'geoengineering' — are being explored as responses to climate change. Yet their effectiveness, and whether they should be implemented at all, is debated among scientists.
Australia's bushfires have brought the devastating consequences of a warming world into sharp relief. And with modelling pointing to temperature increases of between three and four degrees Celcius by 2100 in a business-as-usual scenario, predictions suggest such extreme events are set to become more frequent.
What if we could reverse the warming that is fueling drought and causing flooding around the world?
That is exactly what organizations like the US-based non-profit Foundation for Climate Restoration (F4CR), are proposing. The group wants to restore carbon dioxide levels in the atmosphere to under 300 parts per million, as was the case in the pre-fossil fuel age. Today, the global average measures more than 400 parts per million.
"I'm very interested in leaving [behind] a world where our children can survive," Pieter Fiekowsky, an MIT-trained physicist who founded F4CR in 2015, told DW. To him, "that clearly requires getting CO2 back to safe levels.”
According to the foundation, achieving that involves "climate restoration," that is, making sure we're collectively removing more greenhouse gases from the atmosphere than we produce. The foundation believes around a trillion tons of carbon dioxide needs to be extracted.
That would require large-scale implementation of nature-based or artificial technologies to suck vast quantities of greenhouse gases out of the atmosphere to cool the planet — strategies that fall under the loose definition of "geoengineering." However, which technologies are best suited, and whether to implement them at all, is hotly debated among scientists.
Rob Jackson, an earth systems scientist at Stanford University, believes that restoring the climate to what it once was is a better goal than merely stabilizing Earth's temperatures.
"We need a new story, a new narrative around climate change," says Jackson, who argues this should involve ambitions that go beyond merely limiting the damage of climate change. "[Climate restoration] will bring climate benefits. It will save lives by reducing air pollution. It will provide a host of other benefits."
One solution proposed by F4CR in a last year entails restoring marine habitats that store carbon, such as underwater kelp forests. Another is a form of concrete that binds carbon as it's made, which was used recently to build a new terminal at San Francisco airport.
There are sectors where certain emissions are hard to remove entirely, such as methane — a greenhouse gas more potent than carbon dioxide — in the agricultural sector, says Jackson. He recently proposed a technology to remove methane from the air by oxidizing it to carbon dioxide, which although stays around longer has less heat-trapping capacity.
Climate scientists have included some geoengineering solutions, such as bioenergy with carbon capture and storage (BECCS) — the process of extracting carbon from crops and storing it underground — in the majority of pathways modelled in the Paris Climate Agreement to limit global warming to below 2 degrees Celsius compared to pre-industrial levels.
A form of concrete that binds carbon as it's made was used recently to build a new terminal at San Francisco airport
"It is actually not possible to limit global warming to 2 or 1.5 degrees Celsius, without [removal of greenhouse gases]," Avit Bhowmik, an assistant professor of risk and environmental studies at Sweden's Karlstad University, told DW. "Just stopping the increase of atmospheric concentrations of carbon dioxide and greenhouse gasses wouldn't be enough — we have to sequester them."
No silver bullet
Still, Jackson notes some geoengineering proposals, such as releasing large quantities of iron into the ocean to stimulate the growth of phytoplankton—providing food for fish and thereby rebuilding carbon-sequestering fisheries — are still at the experimental stage.
More research is needed both into scaling up such ideas and into the ecological impacts, says Jackson.
Even technologies like BECCS are still in testing. Many experts believe they also distract from the urgency of ceasing greenhouse gas emissions.
"I think these long-term goals [of climate restoration] take away focus from the really important challenge that we have today of bending the emissions curve downward," says Joeri Rogelj, a climate scientist at Imperial College London.
There is also concern that geoengineering technologies could create a false sense of security that increased emissions could be removed. Rogelj says ecosystems unable to adapt to current warming are not likely to return even if temperatures decrease.
"Climate restoration doesn't mean that the Earth will look the same [as it did before the pre-industrial era]," Rogelj adds.
A middle ground?
Bhowmik believes it should be possible to achieve a net decline in greenhouse gases without resorting to the most radical geoengineering approaches. The Exponential Roadmap report published in 2019, in which Bhowmik led the modelling work, lays out a strategy focused heavily on nature-based solutions.
To follow that roadmap, the world would need to halve global greenhouse gas emissions every decade from 2020 onwards, improve agricultural practices so farmland absorbs rather than emits carbon, restore large areas of forest and protect carbon-storing ecosystems like peatlands.
"If you follow that route, it would actually be possible by the end of this century to have a substantial reduction in the atmosphere greenhouse gas concentrations. And soon thereafter we will reach the level that was in the preindustrial period," Bhowmik believes.
Climate restoration got a boost in September 2019 when F4CR joined scientists, venture capitalists and youth activists at a UN Forum aiming to spur investment for a range of nascent technologies to reverse global warming.
Even though there's disagreement on what — if any — form climate restoration should take, most scientists do agree that it shouldn't be a replacement for mitigating climate change or helping communities around the world cope with the impacts of rising tempertures.
That includes F4CR. "Climate restoration is a critical third pillar,” says Rick Parnell, CEO of the organization. “[It’s] a third leg of the stool, along with mitigation and adaptation."
This is an updated version of a previous article.