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No excuses: Cut carbon dioxide emissions now, scientists urge

Image of geese flying past a smokestack.
In this file photo, a flock of geese fly past a smokestack at the Jeffery Energy Center coal power plant near Emmitt, Kan.Charlie Riedel / AP file

Recently, several scientific studies have concluded that the global climate is less sensitive to the greenhouse gas carbon dioxide than previously believed. Other studies also found that cuts to short-lived pollutants such as soot could temporarily slow the pace of warming.

Neither, however, are reasons to delay weaning the world off fossil fuels in a bid to curb global warming, according to a pair of perspective papers released Thursday.

"Both of these (findings) have been quoted as reasons why the case for reducing CO2 emissions may be less urgent than previously thought," Myles Allen, a climate scientist at Oxford University in the United Kingdom, told NBC News. "These papers are addressing that misconception."

Allen is an author on both of the papers published Thursday in the journal Nature Climate Change. The papers come as policymakers negotiate a new international deal to combat global warming, and on the heels of a report from the Intergovernmental Panel on Climate Change that shows the world has already emitted more than half the carbon allowed if it aims to limit warming to 3.6 degrees Fahrenheit. 

"I am hoping that message is getting through," Allen said. "I am worried it may not be."

Climate sensitivity
Allen is also an author of a recent study in Nature Geoscience that showed the global climate is likely to warm about 25 percent to 30 percent less than previously thought from a doubling of carbon dioxide over pre-industrial levels, a measure known as climate sensitivity.

The popular science journalist and author Matt Ridley cited the revised estimates on climate sensitivity as a reason to avoid implementing policies that raise the price of fossil fuels and convert forests and crops into biofuel. Such policies, he explained, would damage the global economy and disproportionately impact the world's poor — all in an effort to curb warming that isn't all that bad.

"Even if we reached doubled carbon dioxide in just 50 years, we can expect the world to be about two-thirds of a degree warmer than it is now, maybe a bit more if other greenhouse gases increase too," Ridley wrote on his blog, Rational Optimist. "That is to say, up until my teenage children reach retirement age, they will have experienced further warming at about the same rate as I have experienced since I was at school."

Ridley added that with ongoing advances in nuclear and solar technology "there is now a good chance we will have decarbonized the economy before any net harm is done."

Allen cited Ridley's blog post as one of the misconceptions addressed by the new papers in Nature Climate Change. He agrees that a technological fix to the carbon conundrum "would be great. But nobody has really come up with that." 

Allen and his colleagues assume that procrastination doesn't beget a technological fix or bigger cuts when action gets under way. Rather, the longer the world twiddles its thumbs, the more peak warming it commits itself to. "If emissions are going up at 2 percent a year, then peak warming is going up at 2 percent a year," he explained. 

That means avoiding warming above the internationally agreed limit of 3.6 degrees Fahrenheit gets harder and harder the longer the world waits to take action.

Cutting soot not a long-term fix
The second paper refutes the notion that reductions in so-called "short-lived" climate pollutants such as soot from cook stoves and kerosene lanterns buy the world time to cut carbon dioxide, which is a long-lived climate pollutant. "Unless carbon dioxide emissions are falling, cuts in short-lived climate pollutants won't make any difference to peak warming," Allen said.

That point, the paper noted, is well understood in the scientific community, but is "often overlooked in policy discourse." 

Drew Shindell, a climate scientist at the NASA Goddard Institute for Space Studies in New York, made the same point in a paper on the benefit of cutting short-lived pollutants, published last year in the journal Science. "Action on SLCPs (short-lived climate pollutants) doesn't take the pressure off the need to limit CO2 emissions — it does not 'buy time' for reducing CO2," he said in an email to NBC News.

However, Shindell added, there are benefits "over the next several decades" to a reduction in these short-lived pollutants, including curbing the impacts of climate change on agriculture, snow and ice melt, and storm intensity. 

"I think reducing those impacts is a very worthy societal goal alongside trying to keep peak temperatures in the most distant future from getting too high," he said. "The latter is the only point addressed in the two perspectives, and while a worthy goal, it's not the only one. ... I continue to believe that there is convincing evidence that societies need to reduce both."

In addition to Allen, the paper on the impact of a delay in reducing carbon dioxide emissions was co-authored by Thomas Stocker of the University of Bern in Switzerland. The paper on role of short-lived pollutants was co-authored by Niel Bowerman at the University of Oxford; David Frame at Victoria University of Wellington in New Zealand; Chris Huntingford at the Center for Ecology and Hydrology in Wallingford, United Kingdom; Jason Lowe at the Met Office in the United Kingdom; and Stephen Smith with the Committee on Climate Change in London.

John Roach is a contributing writer for NBC News. To learn more about him, visit his website