Looking to the climate-change road less traveled

by Bill Chameides | February 22nd, 2012
posted by Erica Rowell (Editor)

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Tropospheric ozone, a component of smog (shown here over Los Angeles), is one pollutant that is being targeted to help reduce global warming while we await policies to curb carbon dioxide emissions. (Gene Daniels)
Tropospheric ozone, a component of smog (shown here over Los Angeles), is one pollutant that is being targeted to help reduce global warming while we await policies to curb carbon dioxide emissions. (Gene Daniels)

Congressional deadlock and new scientific insights force new heading.

The news on the avoid-dangerous-climate-change front seems to get ever bleaker.

On the policy side, little to no progress

The probability of a U.S. policy to curb greenhouse gas emissions any time soon is as close to zero as you can get — President Obama said as much in his State of the Union address. Internationally the news is not that much better: from the latest climate talks in Durban, it appears that, if all goes according to plan, 2020 is the soonest we can expect a new international agreement to go into effect.

On the science side, too little, too late for CO2-related policies

It’s looking ever more apparent that the time to prevent carbon dioxide (CO2) concentrations from rising above 450 parts per million (ppm) — the line-in-the-sand threshold that’s been nominally identified to avoid dangerous climate change — is all but gone.

Durban’s target date might be 2020, but if the International Energy Agency’s 2011 energy projections [pdf] are accurate, waiting that long to seriously start cutting emissions will make keeping CO2 concentrations below 450 ppm virtually impossible.

Things look even bleaker if non-CO2 greenhouse warmers are figured into the projections. For example, in a recent project out of Stanford University’s Energy Modeling Forum, a suite of coupled climate-economic models was used to estimate what it would take to keep the total equivalent CO2  concentration below 450 ppm, 550 ppm, and 650 ppm. Most of the study’s models were unable to find any scenario capable of meeting the 450-ppm-equivalents threshold [pdf] without maintaining high concentrations of polluting and life-threatening aerosols.

And while much is being made of natural gas serving as a bridge fuel between coal-fired power and some future carbon-free energy system, Nathan Myhrvold of Intellectual Ventures and Ken Caldeira of the Carnegie Institution argue in the journal Environmental Research Letters that such a strategy will do little to nothing to reduce global warming in this century. To have any impact in that time period, they write, coal-fired power will need to be replaced by “conservation, wind, solar, nuclear power, and possibly carbon capture and storage.”

Non-CO2 strategies getting a serious look

So what’s a global-warming mitigator to do? Look for alternatives. And fortunately, it looks like one can at least buy us time.

Despite two important caveats — namely that CO2 is the largest single greenhouse warmer we add to the atmosphere, and there is no long-term global-warming solution that doesn’t involve major cuts in its emissions — the non-CO2 greenhouse warmers are not irrelevant. Collectively, they’re responsible for about 30-40 percent of global warming. Key among them are

  • methane, which comes from such sources as agriculture, landfills and natural-gas leakage;
  • black carbon (a k a soot), which comes from using low-tech cookstoves and burning biomass; and
  • lower-atmospheric ozone, a product of photochemical smog largely generated from automobile and power-plant pollution.

Importantly, their temporal characteristics are very different CO2’s. CO2 emissions largely come from energy generation; the infrastructure and technologies needed for this energy have decades of useful lifetimes, and so change is difficult and slow unless you’re willing to abandon investments already made. Moreover, because CO2 has a long atmospheric lifetime, slowing CO2 emissions enough to have a substantial effect on its concentration takes time — were CO2 emissions held constant today, its concentration would continue to rise for centuries.

Greenhouse warmers such as methane, black carbon and ozone are quite different. Lowering their emissions would not require huge investments or a retooling of our energy infrastructure; on the contrary, in most cases lowering their emissions would involve making current technologies cleaner and more efficient. Plus, their atmospheric lifetimes are relatively short — about 10 years for methane, weeks to a month for ozone, and about a week for black carbon. Cutting these emissions would reduce their concentrations much more quickly than cutting CO2, and have a more immediate effect on slowing global warming.

Tiny air pollution particles known as black carbon (or soot) form in the air when fuels like coal, wood, and diesel are burned. Because they absorb heat from sunlight, these airborne pollutants add to global warming. This animation shows how soot was dispersed around the Himalayas in 2009. Scientists and policy makers are looking to black carbon, among other targets, to help mitigate global warming as a stopgap measure. (Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio)

So how effective would a strategy focused on non-CO2 warmers be? Drew Shindell of NASA’s Goddard Institute for Space Studies and colleagues recently addressed that question in a paper published last month in the journal Science. The authors identified 14 measures (see table below) — seven that reduced methane emissions and seven that addressed black carbon — that collectively could reduce net global warming by 2050 by almost one degree Fahrenheit. Not enough to solve the problem, but enough to buy us time to get our act together on CO2 emissions.

14 Measures Addressing Methane Emissions and Black Carbons

Measure / Gas Sector
Methane measures
Mitigation of methane from coal mines Fossil fuels
Recovery of leaked methane from oil and gas production
Reducing gas leakage during pipeline transmission
Landfill gas collection and mitigation of biodegradable waste Waste management
Including gas recovery at wastewater treatment plants
Control of methane emissions from manure Agriculture
Intermittent aeration of continuously flooded rice paddies
Black Carbon measures
Filters for diesel vehicles Transportation
Elimination of highest-emitting vehicles
Introduce clean-burning biomass stoves in developing countries Residential
Substitution of clean-burning cookstoves using modern fuels (liquid petroleum gas or biogas) for traditional biomass cook stoves in developing countries
Replace traditional brick kilns Industrial
Replace traditional coke stoves
Ban open burning of agricultural waste Agricultural

After Shindell et al, Science magazine, 2012

State department gets into the act

A common refrain in international policy circles is that the United States should take a leadership role on climate change. But with the U.S. political climate currently what it is, that’s a tall order. Rather than tilting at the windmill, the State Department (and by extension the administration) has decided to take a different tack: the recently announced international voluntary program called the Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants. Launched by six countries and the United Nations, the initiative targets black carbon, shorter-lived hydrofluorocarbons, and methane to achieve “concrete benefits on climate, health, food and energy resulting from reducing short-lived climate pollutants.” In addition to potentially reducing net global temperatures by almost one degree Fahrenheit by 2050, the 14 measures could avoid the annual loss of more than 30 million tons of crops and millions of premature deaths.*

A few mild barbs have been lobbed at the program. For example the World Wildlife Fund cautions that this should not be allowed to obfuscate the real imperative to cut CO2 emissions, and worries about its tendency to shift the burden from developed nations to developing economies where black-carbon emissions and ozone-producing gases are largest. Eileen Claussen, president of the Center for Climate and Energy Solutions, expressed similar sentiments.

The criticisms notwithstanding, I think the State Department is on to something here. The time for just focusing on CO2 emissions is past — that train left the station years ago.



In a related initiative the U.S. Environmental Protection Agency announced a program to address black carbon emissions in the Russian Arctic.


filed under: carbon dioxide emissions, climate change, energy, faculty, fossil fuels, global warming, methane, natural gas, policy, politics, pollution
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1 Comment

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  1. Hank Roberts
    Mar 11, 2012

    You write: > black carbon (a k a soot), which comes from > using low-tech cookstoves and burning biomass I think I recall — can you check? — that half of black carbon is from diesel (trucks, ships, trains, other big engines). I’ve seen the ‘cookstove’ source emphasized in publications from the petroleum industry, while not mentioning the diesel. Odd, that. Why not go after these larger point sources rather than after individual household stoves? I haven’t seen health effects compared from diesel small particle pollution vs. cookstove pollution,

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