It sounds like something from B-movie lore. Scientists working to avert global catastrophe invent a terrible technical instrument that could affect the fundamental way that the planet operates. The question is not whether they should use it, but whether they have a choice. In both academic and privately funded laboratories, such techniques are being considered, mostly in response to global warming. Geoengineering, or "ecohacking" - using science to change the environment on a vast scale - could become a reality faster than you think.
There are roughly 385 parts per million (ppm) of carbon in the atmosphere today, and that's making scientists already concerned about global warming unhappy. "I think it's a good goal to not go over 450ppm," says Alan Robock, a professor in the department of environmental sciences at Rutgers University. Many in his field consider that figure to be a tipping point, when global warming could run out of control. "The solution is mitigation," he warns.
But how to mitigate? Paul Crutzen doesn't think we're moving fast enough with reductions in carbon emissions. The professor emeritus at Utrecht University's Institute for Marine and Atmospheric Sciences became one of the most famous geoengineering advocates for his idea of copying the Pinatubo volcano.
Its 1991 eruption sent 10m tonnes of sulphur (which became sulphur dioxide) into the atmosphere, reducing the global temperature by 0.5C the next year. Crutzen suggested a project to produce a similar effect, using balloons or artillery shells to put 1.9m tonnes of sulphur into the atmosphere to cool the Earth.
He wasn't the first would-be ecohacker. As far back as the 1970s, Russian climatologist Mikhail Budyko suggested putting reflective aerosols in the atmosphere. "And the first time that a US president was informed that there might be a global warming problem from carbon dioxide was in 1965," says Ken Caldeira, a scientist at the Carnegie Institution's department of global ecology. "President Johnson's advisors gave him a report that suggested we might put reflective materials across the surface of the ocean." The idea was that these would reflect large amounts of sunlight back into space and mitigate the effects of global warming.
Even in the early 19th century, US meteorologist James Espy advocated burning huge areas of forest in the hope of making rain by affecting the thermal dynamics of the atmosphere, says meterological historian and professor of science, technology, and society at Colby College James R Fleming.
When leading US meterologist Harry Wexler predicted ecohacking in a 1962 lecture, the first weather satellite had been up for three years. "He pointed out that any intervention with the Earth's heat budget could cause a change in the downstream flow and the climactic systems and weather patterns," says Fleming. "He gave serious lectures about the possible inadvertent damage we might do."
As climate change becomes an increasing concern, geoengineering is making a comeback. Scientists are looking at the atmosphere, the ocean, the land and even space to create a variety of effects, including helping to reduce the effect of sunlight on the Earth and sequestering carbon.
Seeding the ocean
US firm Climos plans to seed the ocean with iron particles. This will encourage the development of phytoplankton, it says, which carry large amounts of carbon to the ocean floor when they die. The company hopes to turn a profit by selling carbon credits.
Others are hoping to achieve a similar effect by bringing things up from underneath the ocean, rather than dropping things in from the surface. Atmocean plans to put large tubes in the ocean which will move vertically with the waves, pumping cool water to the surface from 200 metres down, says chief executive Phil Kithil. This will bring more nutrients with it, encouraging the phytoplankton to grow, he hopes.
Kithil adds that there's another benefit: "You're also reducing hurricane intensity by cooling the upper ocean." He argues that deploying these pumps over a roughly 60 x 60km area at one every 500 metres would bring enough cool water to the surface to reduce the intensity of a hurricane or perhaps even divert it, but ultimately he thinks the tubes could cover 80% of the ocean's surface for CO2 sequestration purposes.
Peter Flynn has oceanographic ideas of his own. The professor of mechanical engineering at Canada's University of Alberta cites worries about the Gulf Stream, which cycles warm water from the south Atlantic to the north, and sends cooler water back again. Salty water in the north sinks to the ocean floor and keeps the cycle moving. Should melting fresh water from the Arctic north shut down the pump, the results could be catastrophic, and Europe could be plunged into an ice age. Flynn proposed re-icing the Arctic using 8,000 giant floating platforms that would draw salty water from the ocean and spray it on to winter ice, dramatically increasing its thickness. It would continue to do this in the summer, which would then melt the ice and send tonnes of salty water plunging into the Gulf Stream.
Looking to the stars
Roger Angel, director of the Centre for Astronomical Adaptive Optics at the University of Arizona, is looking to the stars rather than the sea. He wants to put a mesh of tiny light refractors into space to sit between the Earth and the sun. The material would bend some of the sun's rays away from the planet.
"It's probably the most expensive and the cleanest," says Angel, who would need 16 trillion gossamer-light spacecraft, each sitting about a kilometre apart. Roughly 5m tonnes of material would be shot into space by a large magnetic railgun seated at the top of a mountain near the equator. Other than the $1tn (£500bn) launch cost, the other downside would be the 30 years needed to get them up there.
One of the upsides of the project is that it is reversible. Control craft would be needed to keep the others in exact position (using energy harvested from the solar light that they would be diverting). The control craft could move the array of reflectors out of the earth's orbit. In theory, the solar rays that contribute to climate change could be dialed up and down. "But whose hand is on that knob?" asks Caldeira. Whoever controlled the technology would be in a position of significant power. Getting everyone in the world to agree on climactic issues was difficult enough in Kyoto. And things could get even stormier when climactic, technological, and political fronts collide.
"Let's say Europe and North America don't reduce their carbon emissions, and China has a decade-long drought," Caldeira says. "It could say, 'You guys wrecked our climate, and we're going to engineer our own climate to repair things'."
One of the biggest worries for Robock is that such tinkering could produce complicated outcomes. For example, spraying sulphur into the atmosphere might reduce the sunlight by 2%, he argues, but what will it do to the rain? "You might reduce precipitation," he says. "Preliminary results from calculations suggest that the Asian monsoon would be affected, which provides food for billions in Asia."
Some would-be ecohackers such as Espy may have been over-optimistic, but most of today's geoengineers are more cautious in their studies. Flynn says that his system would only be useful if we reached a tipping point.
Angel proposes amortising the cost of his project over 50 years. "You could say that a minimum of 100 million people would have their way of life ruined," says Flynn, musing about a gulf-stream shutdown. The $50bn that he'd need to mitigate the problem seems like a drop in the ocean when you consider that the money currently spent on the wars in Afghanistan and Iraq would pay for it in just over three months.
But hopefully we're not in B-movie territory yet. "The simplest thing is to stop putting in the gases that cause the warming," says Robock. When it comes to preventing the conditions that might make governments take geoengineering projects seriously, we all have our hands on the climate dial.