Greenhouse gases other than CO2

Rusty metal pipes

A recent Newsweek article discussing Al Gore’s new book made reference to recently published work on how different gases are contributing to anthropogenic climate change: Improved Attribution of Climate Forcing to Emissions, written by scientists from NASA’s Goddard Institute including Drew Shindell and Gavin Schmidt.

Two especially notable points are made. Firstly, the researchers estimate that carbon dioxide (CO2) is ‘only’ responsible for 43% of observed warming, once interactions between gases and aerosols were taken into account. At the same time, methane accounts for 27% of warming, halocarbons 8%, black carbon 12%, and carbon monoxide and volatile organics 7%. Secondly, there are the policy implications that flow from this. Preventing CO2 emissions basically requires reducing deforestation and the burning of fossil fuels – with the latter being an especially challenging thing to do in a world as promiscuous with energy as ours. Reducing methane, by contrast, may be as simple as capturing and burning gases from landfills, and adopting other comparatively low-cost and low-sacrifice strategies. The authors conclude that strategies that incorporate all greenhouse gases (GHGs) are “likely to be much more cost-effective than CO2-only strategies.”

There are other complications involving GHGs, including atmospheric lifetime. CO2 is removed by various means, across different timescales. Methane doesn’t last as long, but does cause more warming than CO2 when present and often breaks down into it later. Black carbon is washed out of the atmosphere quite quickly, meaning that eliminating its production could yield reduced radiative forcing relatively quickly.

The greater importance of non-CO2 gases described in this study is potentially good news for climate change mitigation, given how challenging it has been to convince governments to accept even very minor costs in order to reduce the risks associated with climate change. Developing an improved understanding of exactly how much various GHGs alter the climate should also allow for more efficient carbon pricing, where the incentives to reduce the most harmful GHGs are the strongest.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here.

11 thoughts on “Greenhouse gases other than CO2”

  1. This just goes to show how complex climate science is: even the relative weighting of GHGs is potentially subject to revision.

    That said, it is good news that cutting non-CO2 gasses could have so much of an effect.

  2. On the surface, this is a very hopeful idea. But, if not just relative reductions – but absolute reductions of Co2 emissions are required, then this is only a small incremental shift in how difficult “saving the world” will be.

  3. What we need is to stop the composition of the atmosphere from changing the amount of radiative forcing occurring (and thus prevent temperature change).

    CO2 isn’t the only gas we need to be concerned about, and if it is cheaper to cut other gasses first, there is every reason to start there.

  4. As discussed in this blog post, many gasses of concern. Some of them are a lot more short-lived than CO2 (like black carbon), some are much more powerful in terms of their warming effect (like PFCs), and some eventually break down into CO2 (like methane).

    It would be good to see an updated version of the WRI flowchart, with the data from this latest study.

  5. With methane, there are two pretty different mitigation approaches. You can burn methane that would otherwise be released, either to make power (as with landfill gas) or just prevent emissions (as with flaring at oil wells far from gas markets).

  6. Interactions with aerosols boost warming potential of some gases

    For decades, climate scientists have worked to identify and measure key substances — notably greenhouse gases and aerosol particles — that affect Earth’s climate. And they’ve been aided by ever more sophisticated computer models that make estimating the relative impact of each type of pollutant more reliable. Yet the complexity of nature — and the models used to quantify it — continues to serve up surprises. The most recent? Certain gases that cause warming are so closely linked with the production of aerosols that the emissions of one type of pollutant can indirectly affect the quantity of the other. And for two key gases that cause warming, these so-called “gas-aerosol interactions” can amplify their impact.

    “We’ve known for years that methane and carbon monoxide have a warming effect,” said Drew Shindell, a climate scientist at the NASA Goddard Institute for Space Studies (GISS) in New York and lead author of a study published this week in Science. “But our new findings suggest these gases have a significantly more powerful warming impact than previously thought.”

    Human activity is a major source of sulfate aerosols, but smokestacks don’t emit sulfate particles directly. Rather, coal power production and other industrial processes release sulfur dioxide — the same gas that billows from volcanoes — that later reacts with atmospheric molecules called hydroxyl radicals to produce sulfates as a byproduct. Hydroxyl is so reactive scientists consider it an atmospheric “detergent” or “scrubber” because it cleanses the atmosphere of many types of pollution.

    In the chemical soup of the lower atmosphere, however, sulfur dioxide isn’t the only substance interacting with hydroxyl. Similar reactions influence the creation of nitrate aerosols. And hydroxyls drive long chains of reactions involving other common gases, including ozone.

    Methane and carbon monoxide use up hydroxyl that would otherwise produce sulfate, thereby reducing the concentration of sulfate aerosols. It’s a seemingly minor change, but it makes a difference to the climate. “More methane means less hydroxyl, less sulfate, and more warming,” Shindell explained.

    His team’s modeling experiment, one of the first to rigorously quantify the impact of gas-aerosol interactions on both climate and air quality, showed that increases in global methane emissions have caused a 26 percent decrease in hydroxyl and an 11 percent decrease in the number concentration of sulfate particles. Reducing sulfate unmasks methane’s warming by 20 to 40 percent over current estimates, but also helps reduce negative health effects from sulfate aerosols.

    In comparison, the model calculated that global carbon monoxide emissions have caused a 13 percent reduction in hydroxyl and 9 percent reduction in sulfate aerosols.

  7. It’s all about me (thane)!
    — gavin @ 12 November 2009

    Well, it’s not really all about me. But methane has figured strongly in a couple of stories recently and gets an apparently-larger-than-before shout-out in Al Gore’s new book as well. Since a part of the recent discussion is based on a paper I co-authored in Science, it is probably incumbent on me to provide a little context.

    First off, these latest results are being strongly misrepresented in certain quarters. It should be obvious, but still bears emphasizing, that redistributing the historic forcings between various short-lived species and CH4 is mainly an accounting exercise and doesn’t impact the absolute effect attributed to CO2 (except for a tiny impact of fossil-derived CH4 on the fossil-derived CO2). The headlines that stated that our work shows a bigger role for CH4 should have made it clear that this is at the expense of other short-lived species, not CO2. Indeed, the attribution of historical forcings to CO2 that we made back in 2006 is basically the same as it is now.

    As is well known, methane (CH4) is the greenhouse gas whose anthropogenic increase comes second only to CO2 in its 20th Century effect on climate. It is often stated that methane is ‘roughly 20 times more powerful’ as a greenhouse gas than CO2 and this can refer to one of two (very different) metrics. If you calculate the instantaneous forcing for an equivalent amount of CO2 and CH4 (i.e. for a 1 ppmv increase in both), you find that the global forcing for CH4 is about 23-24 times as large (depending slightly on the background assumed). Separately, if you look up the Global Warming Potential (GWP) of CH4 in IPCC AR4 (the integrated forcing of a kg of CH4 compared to kg of CO2 over a 100 year period), you get a value of about 25. GWP is used to compare the effects of emissions today on climate in the future. The numbers are only coincidentally similar since the GWP incorporates both the weight ratio and the ratio of effective lifetimes in the atmosphere which roughly cancel for a 100 year time-horizon.

  8. Levin,I., Naegler,T., Heinz,R. et al. 2010. The global SF6 source inferred from long-term high precision atmospheric measurements and its comparison with emission inventories. Atmos. Chem. Phys. 10:2655-2662.

    Analysis of observational data indicates that countries are significantly underreporting their emissions of SF 6 .
    Sulphur hexaflouride (SF6) is a very potent greenhouse gas, with an atmospheric lifetime of some 3200 years. Therefore, it is included as one of the key greenhouse gases within the UNFCCC. Furthermore, since there are no significant natural sources of SF6, changes in atmospheric concentrations of this gas over time provide a good proxy record of global emissions. New analyses of records of SF6 atmospheric concentrations show that global emissions decreased briefly between 1995 and 1998, but increased again during the past decade. More importantly, the observations indicate that the collective emissions as reported by Annex I countries are only about 20-30% of that actually released on a global scale. Authors of the study argue that there is clearly a need for a much better independent auditing of emissions reported by Annex I countries under the UNFCCC.

    Summary courtesy of Environment Canada

  9. Impatient with the slow pace of international climate change negotiations, a small group of countries led by the United States is starting a program to reduce emissions of common pollutants that contribute to rapid climate change and widespread health problems.

    Secretary of State Hillary Rodham Clinton plans to announce the initiative at the State Department on Thursday accompanied by officials from Bangladesh, Canada, Ghana, Mexico, Sweden and the United Nations Environment Program.

    The plan will address short-lived pollutants like soot (also referred to as black carbon), methane and hydrofluorocarbons that have an outsize influence on global warming, accounting for 30 to 40 percent of global warming. Soot from diesel exhausts and the burning of wood, agricultural waste and dung for heating and cooking causes an estimated two million premature deaths a year, particularly in the poorest countries.

    Scientists say that concerted action on these substances can reduce global temperatures by 0.5 degrees Celsius by 2050 and prevent millions of cases of lung and heart disease by 2030.

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