No magic bullet -- study challenges perception that CO2 reduction can be delayed by other actions

Earth water levels rise pursuant to global warming
CC BY 2.0 Andrea Della Adriano

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

--climatologist Raymond Pierrehumbert of the University of Chicago

Reducing carbon dioxide, CO2, qualifies as the hottest of political hot potatoes. The proof lies in the absolute lack of traction on the Kyoto protocol, in spite of almost universal scientific consensus that we are already passing the point of no return in climate effects.

Is methane to blame?

Here, we are not asking if methane and other global warming gases (such as hydrofluorocarbons, black carbon soot, ozone, or nitrous oxide) should shoulder the blame for global warming. The question raised by professor Pierrehumbert is whether methane has served as an expedient straw-man for politicians and companies claiming progress on global warming.

It works like this: chemicals are assigned a Global Warming Potential (GWP) factor that serves as an indicator of the chemical's relative contribution to global warming effects. The GWP calculated for methane, based on a 100-year time span, is 21. That is, methane is 21 times worse than CO2 for global warming effects. In shorter terms, like 20 years, methane's relative contributions to global warming could be 86 times higher than carbon dioxide.

So who can be blamed for jumping on the bandwagon to reduce this obvious warming target -- a target that often can be reduced with good management practices and improved technology, much less threatening to the energy supplies upon which our economies rely.

Pollutant trading schemes use these GWP factors as well, giving more credit to reductions of methane or other shorter-term actors, and even allowing CO2 emissions to rise while showing on paper an overall reduction in greenhouse gas potential.

No magic bullet

Professor Pierrehumbert uses the acronym SLCP for short-lived climate pollutants like methane. His study compares our current course of action -- progress on SLCPs while CO2 remains in political limbo -- with the outcome of policies prioritizing CO2 reductions and delaying SLCP action.

The problem with ongoing emissions of CO2 is that they stick around in the atmosphere for generations. So reduction of SLCPs works like a one-time benefit while the CO2 reduction delivers cumulative effects. Think of this like comparing a retirement plan based on sticking extra cash under your mattress versus investing those savings in the bank or the stock market. The mattress plan is better than nothing, but it results in savings only equivalent to what you stick away. The invested money grows, and that growth further increases the investment, with well-publicized results.

Imagine reading one of those articles about the amount of money you will have at 60 if you start investing at a young age. Now imagine that miracle of growth turned on its head: we effectively "investing" in climate change with every emission of CO2 we make.

This means that reducing methane is no magic bullet against climate change. There is only one way to save ourselves from the costs and pain of climate change: reduce carbon dioxide. Starting now. It will be a hard pill to swallow. But in the words of Pierrehumbert:

If you're serious about protecting climate, it's the CO2 you've got to deal with first.

The study is published in the Annual Review of Earth and Planetary Sciences.

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