As carbon dioxide (CO2) in America has declined, environmentalists and the federal government have begun to focus on the energy that got us CO2 emissions back at early 1990s levels - natural gas.

What was once the preferred solution of environmentally conscious people became worse than coal and methane, they began to claim, would make CO2 irrelevant if natural gas were not banned. That was a claim so crazy even the National Resources Defense Council disavowed it, though it got a prominent place, bolstered by lots of anonymous sources, in the New York Times.

Don't buy into the latest fad, says University of Chicago climatologist Raymond Pierrehumbert. CO2 remains the longest-lived greenhouse gas, with effects on climate that extend thousands of years after emissions cease. Other, shorter-lived gases, such as methane, hydrofluorocarbons, and nitrous oxide, and particulates such as soot and black carbon, all contribute to warming but they are going to be a pointless distraction.  

"Until we do something about CO2, nothing we do about methane or these other things is going to matter much for climate," Pierrehumbert
says.




Raymond Pierrehumbert. Credit: Robert Kozloff/University of Chicago

The basic physics of climate pollutants has been well known for a long time. The warming effect of methane and other short-lived climate pollutants disappears quite quickly after the pollutants are removed from the atmosphere.  If we banned natural gas, we would get a one-time-only, lump-sum benefit. Since there is no nuclear energy option that Democrats will support, that would leave coal and its CO2. CO2 lingers in the atmosphere. If you are still emitting CO2 while you are reducing methane and other gaes, that additional CO2 continues to affect the climate for thousands of years.

 Why do activists think they can pay lobbyists to get rid of natural gas and think things will be okay? Part of the problem is that the statistical tool used to compare the climate effect of gases is badly flawed. That measure, called Global Warming Potential (GWP), has been used since 1990 despite its well-known defects, and was incorporated into the Kyoto Protocols in the climate-trading schemes implemented by Europe. GWP predicts the effect on climate by comparing the emission rate of carbon dioxide with the emission rate of methane. But a one-ton-per-year reduction in the amount of methane emitted translates into a single lowering of the global thermostat, while a one-ton-per-year reduction in CO2 yields a climate benefit that increases over time. That's because each extra ton of CO2 that would have been emitted would have irreversibly ratcheted up the global thermostat by an additional increment.  


Pierrehumbert proposes a different metric, which looks at the climate effect of reducing CO2 emission by a fixed number of tons and then finds the rate by which you have to reduce methane emissions to get the same effect.   

Pierrehumbert hopes that his work will help lead policymakers to abandon Kyoto-style multi-gas trading schemes, which treat greenhouse gases equivalently, and put the emphasis on CO2 for the next 50 years or so. "I see puncturing the excessive enthusiasm about short-lived climate pollution control as a step in the right direction," he said, "because it takes away one of the grounds for procrastination on CO2. If you're serious about protecting climate, it's the CO2 you've got to deal with first." 


The New York Times is cleaning house of its bloggers and asking journalists to get back to doing journalism, which means fewer chances of making climate stars out of marine ecologists who use ancient Soviet data to claim methane will ruin the world.


Published in Annual Review of Earth and Planetary Sciences.
Source: University of Chicago