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Machines dig for coal near a power plant outside the city of Grevenbroich in western Germany. The IPCC report on Sunday is expected to outline how to reduce harmful emissions from power generation and other industries.



Battle Plan for Climate Change: How to Cut Greenhouse Gases

An upcoming climate change "mitigation" report offers methods to stave off the worst effects.

Trust in technology: That seems to be the underlying message of a coming report from the world's top panel on climate change. (Related: "Can Coal Ever Be Clean?")

Scheduled for release on Sunday in Berlin, Germany, the new Intergovernmental Panel on Climate Change (IPCC) report will point to many possible ways—from burying greenhouse gases to going nuclear to encouraging biofuel production—to save humanity from the ravages of climate change.

"We are at a critical juncture," IPCC chair Rajendra Pachauri said in a statement kicking off the final review of the report on Monday. The document is still in draft form and will be revised before its release this Sunday. The final report matters, he emphasized, because it will define the issues and outline options for policymakers at next year's international climate summit in Paris.

There, world leaders—if they have the political backbone—will face the climate challenges they left unresolved at the 2008 climate meeting in Copenhagen, Denmark.

An earlier IPCC report in 2013 found that more than half of the global warming observed since 1950 was caused by humans. The biggest culprit has been emissions from the burning of fossil fuels such as coal. (Related: "Clean Coal Test: Power Plants Prepare to Capture Carbon.") And the warming looks "virtually certain" to continue unless those emissions are cut.

"I think we will see that there are a wide number of paths we can take to get to the mountaintop we want to reach," says economist James Edmonds of the Joint Global Change Research Institute in College Park, Maryland. (Edmonds participated in drafting the latest IPCC report, but he emphasized that his comments to National Geographic represented his personal views.) "We just have to pick what mountaintop we all want, in terms of a temperature goal for the climate. And we have to decide to climb there."

Some critics, such as political scientist Steven Cohen of the Earth Institute at Columbia University in New York City, think it's unlikely that the IPCC report will spur political action. It should be seen more as a guide "to point to ways to transition to renewable energy," he says. "Ingenuity is more likely to help us than a treaty."

A Hard Climb

A 1992 United Nations agreement broadly obligated the world to limit global temperature increases to 3.6 degrees Fahrenheit (2 degrees Celsius) over preindustrial levels. Some studies have noted significant dangers—chiefly, lower farm production—if the planet warms beyond that point.

"The most interesting and useful thing the new report could do would be in simply laying out all the paths we could take to not breach that limit," says MIT economist John Reilly. "Most people think it's very unlikely we are going to stay within that [3.6-degree] limit."

The IPCC Working Group 3 report, based on six years of economic and technology studies, will lay out innovations and reforms in power generation, industry, transportation, farming, and other fields that might help nations to reduce emissions. Yet many of the scenarios examined in the report also look at what the world might do if the 3.6-degree limit is passed and temperatures rise still higher.

"Based on the studies that are already out there, I think we can say the sooner emissions are reduced, the easier it becomes to reach those goals," Edmonds says.

Written by 235 scientists from 53 nations over four years, the report on climate change mitigation is the third in a series released in the past year. The IPCC has released such reports in groups every six to seven years since 1990.

IPCC reports synthesize scientific studies to present policy options to government leaders. The two earlier reports enumerated the near-certain evidence that greenhouse gas emissions are responsible for increasing temperatures worldwide over the last century, and detailed the impacts on people, wildlife, and the environment.

"The IPCC is not going to solve the political problem that is at the bottom of things," Reilly cautioned. "A lot of the studies [considered] in the report started from the premise that we already were doing something about carbon reduction. That didn't happen."

Big Surprise

One surprise that will likely appear in the final version of the report is that some technologies appear to have more potential than they did in 2007 to remove carbon from the air.

The final IPCC document is still being edited and reviewed, but recent news reports have suggested that it will tout power plants that burn agricultural waste, farmed trees, or algae as fuel, then capture the carbon dioxide emissions and store them underground. The technology is called "bioenergy with carbon capture and storage" (BECCS).

"Is atmospheric carbon dioxide removal a game changer for climate change mitigation?" was the title of a recent Climatic Change journal report on BECCS co-authored by the chief author of the IPCC study, Ottmar Edenhofer of Germany's Potsdam Institute for Climate Impact Research.

Such methods are expensive and face skepticism, however. "The technology only works ... if you store the carbon and you put some kind of price on carbon to make it economically feasible," Edmonds says, adding that all carbon-cutting technologies should be available for policymakers to consider.

"The more bullets you have to shoot, the more likely you are to hit your target," he says.

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