My RSS news feeds are simply bursting at the seams with the news that scientists have figured out that by concentrating on non-CO2 greenhouse-effect emissions we can get a pretty big and speedy bang for the buck. Can we slow down the victory parade for just a moment and think about this?
A pretty representative article on the development comes from Andrew Freedman at Climate Central, Groundbreaking New Study Shows How to Reduce Near-Term Global Warming:
Let’s face it — the prospects for containing global climate change by slashing emissions of greenhouse gases, such as carbon dioxide, are looking rather bleak these days. International treaty talks are proceeding at a snail’s pace, and after dipping during the global recession, emissions of carbon dioxide (CO2) — the most important greenhouse gas — from the energy sector climbed to record levels this year, and studies show that the effects of climate change, such as sea level rise, are now expected to be much worse than previously thought.
Now what if I told you that we could slash the rate of global warming nearly in half during the next several decades, while saving as many as 4.7 million lives a year and boosting crop yields, by addressing non-CO2 global warming agents? And, that we wouldn’t need endless rounds of United Nations climate negotiations in order to do it? You’d probably think it sounds too good to be true, like some sort of late night global warming infomercial.
According to a group of 13 scientists from the U.S., Europe, Africa and Asia, these goals are actually well within reach, and could be accomplished by tackling emissions of short-lived global warming agents such as soot and methane, a precursor to low-level ozone formation and a greenhouse gas in its own right.
The short-lived global warming pollutants are distinct from CO2, which has hogged the limelight of global climate policy efforts for decades, since they remain in the atmosphere for a relatively short period. Whereas CO2 emitted today can remain in the atmosphere for centuries, the atmospheric lifetimes of pollutants such as soot (technically known as black carbon), as well as methane (a powerful greenhouse gas), are far shorter. Soot, for example, only stays in the air for several hours to a couple of weeks before precipitation rinses it out or chemical processes break it down.
So, as the study demonstrates, while cutting emissions of CO2 won’t have a tangible impact on global warming for another several decades, if we were to target the short-lived pollutants, we could counter some portion of global warming in the near-term. And, since methane contributes to low level ozone pollution that damage crops and human health, and soot also aggravates respiratory and cardiovascular illness, we could make dramatic gains in other areas as well.
Perhaps the biggest advantage to pursuing cuts in methane, black carbon and other short-lived pollutants is that they don’t require that an agreement be reached through the cumbersome United Nations climate negotiations. Instead, policies can be implemented at national, regional, and local levels, Zaelke said.
Let me be clear that Freedman and people he quotes are unwavering in their conviction that whether or not we pursue cutting methane and black carbon emissions, we still have to get far more aggressive about curtailing our CO2 emissions. This is probably the most important single point in this entire news story, and one that I don’t think is getting sufficient attention, particularly from headline writers. As Ray Pierrehumbert said on RealClimate in a must-read post from December 2010 (Losing time, not buying time):
Let’s suppose, however, that we decide to go all-out on methane, and not do anything serious about CO2 for another 30 years. To keep the example simple, we’ll think of a world in which methane and CO2 are the only anthropogenic climate forcing agents. Suppose we are outrageously successful, and knock down anthropogenic methane emissions to zero, which would knock back atmospheric methane to a pre-industrial concentration of around 0.8 ppm. This yields a one-time reduction of radiative forcing of about 0.9W/m2. Because we’re dealing with fairly short-term influences which haven’t had time to involve the deep ocean, we translate this into a cooling using the median transient climate sensitivity from Table 3.1 in the NRC Climate Stabilization Targets report, rather than the higher equilibrium sensitivity. This gives us a one-time cooling of 0.4ºC. The notion of “buying time” comes from the idea that by taking out this increment of warming, you can go on emitting CO2 for longer before hitting a 2 degree danger threshold. The problem is that, once you hit that threshold with CO2, you are stuck there essentially forever, since you can’t “unemit” the CO2 with any known scalable economically feasible technology.
While we are “buying” (or frittering away) time dealing with methane, fossil-fuel CO2 emission rate, and hence cumulative emissions, continue rising at the rate of 3% per year, as they have done since 1900. By 2040, we have put another 573 gigatonnes of carbon into the atmosphere, bringing the cumulative fossil fuel total up to 965 gigatonnes. By controlling methane you have indeed kept the warming in 2040 from broaching the 2C limit, but what happens then? In order to keep the cumulative emissions below the 1 trillion tonne limit, you are faced with the daunting task of bringing the emissions rate (which by 2040 has grown to 22 gigatonnes per year) all the way to zero almost immediately. That wasn’t very helpful, was it? At that point, you’d probably like to return the time you bought and get a refund (but sorry, no refunds on sale items). More realistically, by the time you managed to halt emissions growth and bring it down to nearly zero, another half trillion tonnes or so would have accumulated in the atmosphere, committing the Earth to a yet higher level of long-term warming.
In a follow-up piece (Covering the Coverage: Scientists Propose Cuts in Methane, Soot Emissions), Freedman re-visits that last point I quoted from him above, saying: “One of the attractive aspects of focusing on non-CO2 global warming agents is that it offers the prospect of progress despite the global stalemate in international climate talks.”
Forgive me if I’m missing something obvious, but why would a worldwide reduction in methane and black carbon emissions be easier than a worldwide reduction in CO2 emissions? Is there some secret, pent-up desire to curb methane and black carbon that’s somehow being restrained? Making such changes might be presumed to be politically easier because there’s no immense, well funded effort to stop them, as there is with CO2, but getting worldwide cooperation on any such agreement would be a major feat of international diplomacy. As one might expect, Freedman notes in the second article that no one should underestimate the difficulty of getting 3 billion people in developing countries to switch to cleaner type of cooking stove to reduce black carbon emissions. I agree.
It’s worth pointing out that a lot of methane emissions are not easily targeted. Yes, there are leaks from natural gas lines, mines, and landfills, but there is also a considerable amount of methane emitted as part of agriculture. (I have yet to see the paper in question, so I don’t how the authors deal with this point.) According to the EPA’s 2011 U.S. Greenhouse Gas Inventory Report report (Table ES-2, page ES-5), the top seven sources of US methane emissions in 2009, representing 95% of the total were (values are millions of tons of CO2 equivalent):
- Natural gas systems: 221.2
- Enteric fermentation: 139.8
- Landfills: 117.5
- Coal mining: 71.0
- Manure management: 49.5
- Petroleum systems: 30.9
- Wastewater treatment: 24.5
Enteric fermentation (i.e. farm animal belches and flatulence), manure management, and wastewater treatment all present challenging scenarios, to put it mildly.
And let us not forget that we have the two crazy uncles of such discussions to contend with: Economics and politics. How much money and how much political capital will it take to significantly reduce worldwide methane and black carbon emissions? (Please remember that political capital is not infinite, even if it is renewable in the face of political successes; waging a fight to curb non-CO2 emissions will consume all manner of resources needed to restrict our CO2 emissions.) Given the tone of discussion about environmental issues in the Republican party in the US, can you imagine the uproar and political backlash if anyone suggested we pass laws or a sufficiently high carbon price to effect the desired reductions in the energy and farming sectors? Just how high would a carbon price have to be, and what economic effect would it have? (If only there was some plan, some mechanism, whereby we could look at the carbon emissions of the entire country, put a limit (a “cap”?) on that total number and then let businesses trade emissions credits amongst themselves so the entire economy would do what it does best and allocate resources and seek the optimal price level. I know, it’s a wild fantasy that no one would ever seriously consider. Forgive me for even bringing it up.)
I think the most accurate thing we can say about this study and the discussion it has triggered is that it doesn’t change anything. We’ve known for a long time that methane and black carbon were significant contributors to global warming and that reducing those emissions would provide a much quicker payback than would cutting CO2. Now we have the first attempt (as far as I know) to quantify what we could achieve with a focused and successful effort to curtail them, an undeniably good thing. But we shouldn’t take our eye off the big goal.