Sucking Carbon From Sky May Be Necessary to Cool Planet, UN Says

Image: Senators Speak Through Night on Climate Change in DC

The dome of the U.S. Capitol is seen behind the smokestacks of the Capitol Power Plant, the only coal-burning power plant in the nation's capitol, in Washington, D.C., on March 10. JIM LO SCALZO / EPA

International efforts to combat global warming are so broken that it's come to this: hoovering massive amounts of carbon dioxide out of the sky.

A body of scientists convened under the auspices of the United Nations is giving more weight to the idea that vacuuming vast stores of CO2 from the skies and burying it in the ground may be necessary to limit the temperature rise to the internationally agreed safe level of 3.6 degrees Fahrenheit above pre-industrial levels. The plan's not quite like a giant thermostat for the whole globe, but the metaphor's not completely off either.

While the Intergovernmental Panel on Climate Change has touched on so-called geoengineering approaches in the past, the increased discussion of removing carbon dioxide from the atmosphere reflects a sense in academic climate policy circles that "it is more okay" to do so, said David Keith, a climate scientist and expert on geoengineering at Harvard University in Massachusetts.

Keith has participated in previous reports released by the climate science body, but dropped out of the process about a year ago. In a report released Sunday, the group said the world must swiftly enact a suite of economic and behavioral changes that cut global greenhouse gas emissions by 40 to 70 percent by the middle of this century and to near zero by its end to avoid a dangerous temperature rise.

"What comes out very clearly in this report is the fact that the high-speed mitigation train would need to leave the station soon and all of global society would have to get on board," Rajenda Pachuari, chairman of the panel, said Sunday during a press briefing when the report was released.

The report is the last of three from the climate science panel. The first, released in September 2013, found with 95 percent certainty that human activity is the primary driver of global climate change. The second, released in March, noted that climate changes are already reverberating around the world and are likely to accelerate in the decades to come.

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The latest report essentially explores scenarios on how to prevent a climate catastrophe, many of which co-chair Ottmar Edenhofer, a German economist, noted in the press briefing "strongly depend on the ability to remove large amounts of carbon dioxide from the atmosphere."

Shift to carbon sucking technology

The report's discussion of technology to remove carbon dioxide from the atmosphere comes as the climate science body's earlier assumptions about how easily the world would gravitate to technologies with lower emissions have been proven wrong, according to Steve Rayner, the co-director of the Oxford Geoengineering Program at the University of Oxford in England.

"They seem to have abandoned such assumptions, only to substitute the assumption that carbon dioxide removal from the ambient air will do much the same job," he told NBC News in an email. "There has been no comprehensive assessment of the feasibility of taking such technologies to scale in terms of costs, skills and materials requirements, or incentives, regulation and financing."

Indeed, the panel noted in its summary that "the availability and scale of these … technologies and methods are uncertain and … to varying degrees, associated with challenges and risks."

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Spotlight on biofuels

The term geoengineering encompasses a broad range of technologies that bring about a cooling of the planet. Some focus on blocking sunlight through means such as filling the skies with sulfate particles to mimic the cooling effect of a massive volcanic eruption. Others focus on ways to capture carbon dioxide from power plant smokestacks or the air and store it underground.

The climate change panel has focused its discussion on the carbon capture and storage approach, in particular one associated with burning wood chips or other crops grown for energy. Edenhofer, co-chair of the climate mitigation report, co-authored a May 2013 paper in the journal Climatic Change on the benefits of the technology, known as bioenergy carbon capture and storage.

The approach's promise stems from the use of plants, which absorb carbon via photosynthesis as they grow, as the fuel source for power plants instead of fossil fuels such as coal. When the plants are burned, the carbon emissions are captured and buried underground. The net result is negative emissions, at least on paper.

The technology is largely untested outside of projects that capture carbon dioxide streams from ethanol refineries. The gas is then pumped into the ground to enhance the recovery of oil, "which means it is being used to access more oil," Rachel Smolker, co-director of BiofuelWatch, an advocacy group that opposes scaling up biofuels, told NBC News in an email. "That is hardly reducing emissions."

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Other concerns include increased competition between crops grown for biofuel and food and the potential for leaks and earthquakes associated with burying carbon dioxide underground. Furthermore, scaling up any approach to remove carbon dioxide from the atmosphere "would take many decades and vast expenditures to build sufficient capacity to reverse engineer a century and a half of the fossil fuel industry," noted Rayner.

Sunlight blocking a 'political hot potato'

More technically feasible, he added, would be an approach that would block sunlight with a method such as pumping tiny particles that reflect sunlight into the air from ships or planes. That place could also come with large environmental and social costs. For example, several recent modeling studies have suggested that an aggressive campaign to block sunlight could dramatically change precipitation patterns around the world with adverse impacts on agricultural productivity.

"Although it seems technically nearest to being able to be implemented, it would be likely to be very difficult to do so without some kind of international agreement to do so — and we all know how good we are at getting those for climate change," Rayner said. The approach, he added, "is still too much of a political hot potato for the IPCC to be able to address it in any consensual way."

The reluctance of the panel to take up sunlight blocking in a serious manner is a failure for a body that is supposed to help policymakers make decisions, according to Keith. "There are lots of good reasons why we might not want to do it," he said. "But to me it is of first-order importance to how we think about climate policy over the next century."