A panel of scientists from the United States is calling for more research into tools for intentionally altering components of Earth's climate system as a way to forestall or blunt the worst effects of global warming.
Neither of the two broad approaches that the National Research Council (NRC) panel examined in a pair of reports released Tuesday is ready for prime time. But of the two, removing carbon dioxide from the atmosphere is far enough along to benefit from dedicated research-and-development efforts to scale up the techniques and cut their costs.
The other, altering the amount of sunlight that Earth's surface receives, carries too many unknown, hard-to-quantify risks for it to be more than a topic of additional research – at least for now.
The 16-member panel, operating under the auspices of the National Academy of Sciences, was asked to review what's known about the techniques and recommend additional steps to give the public and politicians the information needed to decide whether such tools should be used to tackle global warming, and to explore some of the ethical and policy issues that should be addressed.
The effort comes at a time when greenhouse-gas emissions, mainly carbon dioxide, from burning fossils fuels and from land-use changes continue to rise – reaching levels not seen in the climate system for more than 800,000 years.
Meanwhile, global talks aimed at producing a new climate treaty that embraces all nations, not just the industrial countries, are heading to what negotiators hope will be approval in Paris at the end of the year. But the pledges that countries have made so far to tackle emissions fall short of what researchers say is needed in the near term to stand even a 50-50 chance of holding the increase in global average temperatures to about 2 degrees C (3.6 degrees F.) above preindustrial levels by the end of the century.
Like the concept of adaptation to global warming before it, the notion of intentionally altering aspects of the climate system to forestall or reduce the more harmful effects of global warming has been around in the research community for decades. Now it is getting a fresh look in the policy arena.
As one gauge of interest, the Congressional Research Service and the Government Accountability Office in Washington both have taken up the topic in recent years, as have other policy groups, in addition to position statements and studies from scientific groups such as the NRC, the American Meteorological Society, and Britain's Royal Society.
Indeed, "the real challenge for geoengineering, writ large, is going to be on the public front," says Benjamin Hale, an associate professor in philosophy and in environmental studies at the University of Colorado at Boulder, as people sort through the ethical issues behind the choices they will face.
Debates over the Keystone XL pipeline will pale in comparison with debates over whether to deploy climate modification tools that in some cases can have vast unintended consequences for billions of people, he says.
For the panel's part, cutting emissions and adapting to changes already in the pipeline are paramount.
"Our efforts to address climate change should continue to focus most heavily on mitigating greenhouse-gas emissions in combination with adaptation to the impacts of climate change," noted Marcia McNutt, former head of the US Geological Survey and now editor of the journal Science, during a briefing Tuesday outlining the group's findings.
Even so, the climate-science community has reached "a level of maturation" that is allowing it "to think through all possibilities, even if they're very, very distasteful," added David Titley, director of the Center for Solutions to Weather and Climate Risk at Penn State University in University Park. He and Dr. McNutt served on the panel producing two volumes released Tuesday, each covering an approach.
The broad approach closest at hand involves either removing the additional CO2 that human activities are adding to the atmosphere or preventing it from reaching the atmosphere in the first place. Specific tools range from restoring forests or changing land-use and farming practices to enhance carbon storage in the ground to burning biomass to generate electricity while scrubbing CO2 from the smokestack and piping it deep underground.
According to the Intergovernmental Panel on Climate Change, this bioenergy carbon capture and storage (BECCS) has the potential to yield negative CO2 emissions, since growing the next batch of fuel takes up CO2 from the atmosphere that will then be kept from the atmosphere through underground sequestration. Indeed, most of the modeling that the IPCC relied on to identify pathways to a 2-degree global average temperature increase required BECCS to get there.
On the plus side, approaches to removing CO2 from the atmosphere deal with the greenhouse gas cited as the main cause of global warming. It introduces no novel planet-wide risks. And the ethical issues it raises are more locally focused and so potentially easier to address. But in general, the techniques currently are expensive, and their effects are slow to take hold and require coordinated action by all major emitters to have maximum impact.
In many ways, these approaches carry the least ethical baggage, suggests Dr. Hale. "What you're doing is cleaning up your mess," he says, rather than "polluting."
The one glaring exception is trying to fertilize ocean plankton with iron or other nutrients so they soak up more CO2 – a marine version of replanting forests. But this approach, known as ocean fertilization, carries its own set of unknown or unquantified risks to marine ecosystems, the NRC panel notes.
Still, issues such as siting a repository for CO2 or shifting land-use patterns will involve trade-offs that call for inclusive, transparent decisionmaking, ethicists say.
Of greater concern is the second of the two categories – altering the amount of sunlight reaching Earth's surface. Two widely discussed approaches involve pumping tiny particles called aerosols into low-level clouds over the ocean to increase the number of cloud droplets, thickening the clouds to reflect more sunlight back into space or delivering large quantities of aerosols to the stratosphere.
Altering the planet's reflectivity, or albedo, can be done quickly with virtually immediate effects – as witnessed after powerful or long-lasting volcanic eruptions. And compared with emissions reductions, the approach is cheap. But it merely masks the problem by cooling the planet while allowing CO2 to continue to build up in the atmosphere.
Similarly, the temperature changes averaged over the planet, as well as changes to rainfall, can mask significant departures from the average in particular regions. Moreover, the approach would have to be maintained indefinitely, since a sudden stop would allow temperatures to warm again, driven by the additional CO2 that would have been pumped into the air during the cool period.
Albedo modification may cool Kansas, leaving Kansans happy with the technique, McNutt said. "But the Congo may not be happy because of changes in rainfall."
Albedo modification exposes a much wider ethical mine field than does carbon removal because of its global reach. The issues range from how such approaches should be governed to how to respond to the actions of an individual nation or even person who decides, based on local or regional interests, to dim the sunlight for a spell.
Anticipating an eventual move from modeling studies to field experiments, the NRC panel notes that before this happens, the proposed work needs careful outside approval and oversight in an inclusive, transparent manner.
The NRC panel's two volumes touch on these and related issues.
They represent a "big step" in focusing attention on climate interventions as an arrow in the quiver for dealing with global warming, says Rafe Pomerance, former deputy assistant secretary of State for environment and development and a member of the National Academy of Sciences' Polar Research Board.
"The risks that are presented by climate change make it necessary to have this research – not to deploy it, but to know whether there's a tool" available, he says.
Beyond technique-specific issues, however, work on approaches to climate intervention faces a broader challenge: avoid what University of Montana environmental ethicist Christopher Preston calls technological lock-in.
"You get vested interests – people who put money into this and invest research careers in this. Once you get institutional momentum towards something, there's the potential for decisionmaking to be slightly biased," he says. "Or you might move more quickly into something than you would otherwise."
"People get very excited about exciting-sounding technologies, especially when you've got a problem that's as vexing as climate change," cautions Dr. Preston, noting that embracing a technological solution to something that otherwise requires a change in behavior can be seductive.
"If climate intervention becomes necessary, it would be regrettable. It would demonstrate a moral failure" to make the required changes, he says. "Hopefully, it would be something that would be a brief intervention."