Broecker believes the carbon pie approach would make it easier to cut emissions by setting an upper limit to the total amount of carbon added by humans to the atmosphere.
Right now humans burn and release about four gigatons of carbon into the air each year. Another four gigatons is released by wildfires. That raises the carbon dioxide concentration in the atmosphere by about one part per million (ppm) every year.
If a carbon dioxide cap were set at 560 ppm worldwide — twice the pre-industrial levels — there would be a carbon pie of 720 gigatons to divvy up. A lower ppm goal, about 450 ppm, would reduce carbon dioxide even further and shrink the carbon emissions pie to 280 gigatons.
But such a reduction would be possible only with successful efforts to actively take more carbon out of the atmosphere, said Broecker. That means new technologies to suck up the carbon dioxide, which can then be pumped into the ground.
"The hardest thing is direct capture" of carbon dioxide, said climate researcher David Keith of the University of Calgary. Research into the matter is very preliminary, he said, and ultimately comes down to the problem of making it cost-effective.
"Air capture is certainly technically possible," said Keith. "But can you do it at a reasonable cost?"
As for whether Broecker's carbon pie strategy will ever be implemented, that's a political question, Keith said.
"We don't know the politics yet," said Keith. "It may take a hundred years to figure this out."
