CAMBRIDGE, Mass.--A group of academics on Friday considered the ultimate engineering challenge: building machines to stabilize the earth's climate.
The Massachusetts Institute of Technology convened a symposium here to discuss the potential benefits and pitfalls of geoengineering, also called climate engineering. Everything from shooting light-blocking particles into the atmosphere to "artificial trees" is being seriously studied, despite trepidation among researchers and opposition from others.
During talks Friday morning, academics said climate engineering techniques are not well understood and, because of the complexity of the global climate system, individual approaches are pockmarked with uncertainties.
Still, speakers at the event said it's time to step up research in geoengineering to sort out which approaches are worth serious consideration. But they cautioned against expecting easy fixes or abandoning efforts to ratchet down the growth of greenhouse gas emissions in the atmosphere.
"At this point the fear is that if we talk about this, people will stop cutting emissions, which is a rational fear. But the idea that we shouldn't have a research program would be a real mistake," said David Keith, the director of the ISEEE Energy and Environmental Systems Group at the University of Calgary during his talk the symposium, which was called Engineering a Cooler Planet.
Speakers said each climate engineering approach needs to be viewed with an associated cost and risk. For example, one relatively inexpensive idea is to shoot particles, called aerosols, into the air in order to block the amount of heat from the sun that reaches the earth's surface.
The cooling effect from aerosols, such as sulfur dioxide, in the atmosphere is rapid--measured in days or years. But they also impact the planet's water cycle. Early models show that large-scale efforts to inject aerosols in the atmosphere would likely make certain areas drier and affect the monsoons in India and Asia, said Joyce Penner, a professor of atmosopheric sciences at the University of Michigan.
Even with the risks and uncertainties of climate engineering, speakers said that there is risk with the so-called business-as-usual scenario where the concentration of greenhouse emissions continues to increase at its current pace.
These heat-trapping gases in the atmosphere are forecast to raise average global temperatures, speakers said. But there are a number of regional impacts from global warming, which will likely spur more research in planet-level engineering, said Thomas Karl, the director of NOAA's National Climatic Data Center.
For example, higher temperatures directly affect water and agriculture. The productivity and ability to reproduce of common crops goes down after certain temperature levels, Karl noted. Pests have a longer time to populate and weeds grow better with more carbon dioxide, too, he said. The west of the U.S. is already feeling the impact of droughts, which will continue if mountain snowpack decreases.
"It's an important choice to make even if we don't do a thing--that's a choice itself," said Karl. "The consequences of not studying this are enormous--understanding the physical, ecosystem, and societal impacts."
Engineering for a cooler planet
There are two general approaches to engineering for a cooler planet: reflecting sunlight back into space or removing carbon dioxide from the air and storing it.
Injecting sulfur-based aerosols in the atmosphere have a known cooling effect observed in volcanic eruptions, including Mount Pinatubo in 1991. The approach is more practical than, say, placing mirrors in space. But there still isn't suitable understanding of how the entire climate system would react, including potential changes to ocean circulation, ocean ecosystems, and land precipitation, said Penner.
Also, blocking sunlight from space does not address the problems caused by higher concentrations of carbon dioxide on earth, notably ocean acidification which makes it more difficult for marine animals with shells or corals to grow, speakers noted.
Other approaches for reflecting heat back into space include spraying sea salt from special-purpose boats to enhance the reflectivity of clouds or installing white roofs on buildings to bounce more sunlight back into space.
Land-based approaches to reducing greenhouse gas concentrations include growing algae-based fuels at massive scale, storing carbon dioxide in underground geological formations, and making charcoal with plants to create a soil amendment called biochar.
There have also been 12 tests to stimulate plankton growth by "fertilizing" the ocean with iron. The goal is to create a rapid "plankton bloom" which will remove carbon dioxide and sequester it in the ocean. But this technique is difficult to verify and risks transforming the existing ocean ecosystems, said Tim Lenton, professor of earth system science at the University of East Anglia.
Because of the risk and uncertainly, Lenton said he is not convinced that climate engineering proposals to block solar radiation makes sense. On the other hand, land-based approaches create competition with other uses of land, notably agriculture.
One area that clearly needs further research is the life-cycle analysis of different climate engineering idea, Lenton said. For example, dumping iron into the ocean to grow plankton has an associated carbon footprint.
"You'll find out when you do the full calculation, it's very difficult to make it carbon negative," he said. "Because of the emissions in simply deploying the technology, it will veto a number of options."
The computational models to simulate the regional impact of climate changes need to be improved as well, said David Battisti, a professor of atmospheric sciences at the University of Washington. In research he presented on Friday, Battisti found that once models took into account ice and ocean effects from aerosol injection, there was a significant variation on the projected impact on temperatures and precipitation.
The symposium at MIT is not the first meeting of scientists to consider geoengineering--the idea has been discussed for decades. But some of the academics on Friday said the current trajectory of climate change argues in favor of at least doing research on climate engineering techniques, even if these projects are ultimately never launched.
There is also a uncertainty around climate policy and how effective policies will be at cutting emissions, noted Keith. "It doesn't mean that we have to do it. But it means that you do need to have the capability to do it," he said.
In the near term, research in the field should be focused on ranking different proposals, addressing both scientific and political issues, said Philip Boyd, a professor of ocean biochemistry from the University of Otago in New Zealand.
Boyd has created a model that ranks geoengineering schemes in terms of efficacy, affordability, safety, speed of implementation, and the ability to stop a project. Societal and political factors need to be considered because conflicts over use of land, water, and the ocean creates a "geopolitical mess."
"We pump up the potential for conflict," he said. "It's just a minefield in terms of teasing these apart."