Every kid who’s ever played with a bucket and a garden hose knows that the bucket will overflow and make a mess unless the water gets shut off in time.
The global bucket of carbon dioxide is now two-thirds full, according to a new study published in Nature Geoscience. And we’re running out of time to cut that carbon flow to limit global temperature increases to 2 degrees Celsius above preindustrial levels to prevent catastrophic climate change.
The report was released as more than 310,000 people marched in Manhattan on Sunday to demand action on climate change while world leaders prepare to gather in New York City for Tuesday’s United Nations Climate Summit.
To achieve the 2-degree target, that bucket’s maximum capacity is 3,200 billion metric tons of carbon dioxide, said Pierre Friedlingstein, a climate and carbon cycle modeler at the University of Exeter in the United Kingdom. We can only emit another 1,200 billion tons of carbon dioxide after 2015 if we want to remain on track.
Friedlingstein prefers to think of the remaining quota as a piece of cake. Now that we’ve eaten two-thirds of the cake, we have to cut slivers off the remaining piece, he said. At current rates, that slice of cake will be exhausted in 30 years—equivalent to one generation. The calculation is a new approach to determining when we might hit specific temperature thresholds.
But slashing greenhouse emissions won’t be a piece of cake.
Carbon dioxide emissions continue to grow, year after year. In 2013, more than 36 billion tons of carbon dioxide were released into the atmosphere from the burning of fossil fuels and cement production, a 2.3 percent increase over the previous years, according to the report.
The authors project that carbon dioxide output will rise to 37 billion tons for 2014 and to 43.2 billion tons by 2019.
To keep temperatures below the 2-degree threshold, we must reduce global emissions by 5 percent to 7 percent annually, said Glen Peters, a climate policy analyst at the Center for International Climate and Environmental Research in Oslo, Norway.
“That’s something that has never been seen before, and it has to happen globally for the rest of the century,” said Peters, who contributed to the research.
Furthermore, no single country has met that target on its own.
“Theoretically it’s possible, but it’s difficult in practice,” he said.
Restricting carbon dioxide emissions from transportation and power plants and putting a price on carbon could slow emissions. The capture and storage of fossil-fuel power-plant emissions could also help, but the technology remains expensive and undeveloped.
Any delays in reducing carbon emissions mean the 2-degree mark will hit even sooner. “If we don’t do anything until 2020, then we’ll only have 22 years,” said Friedlingstein.
In a second study, published in Nature Climate Change, researchers looked at how this remaining quota could be distributed nationally or regionally.
Sharing the pain of cutting emissions by dividing the cake among countries based on their population won’t work, argued Peters. Doing so would be “easier for the big emitters but makes it harder for the developing countries,” he said.
A better option would allow developing countries to grow their economies and give large emitters reasonable targets to shoot for.
“In some way the quota will be shared,” said Peters. “All the countries need to make contributions.”