Cap and Trade Worked for Acid Rain, Why Not for Climate Change?

May 12, 2009 | Jesse Jenkins,

One of the most often-repeated assumptions in the climate policy debate is that cap and trade, the preferred mechanism for reducing greenhouse gas emissions, worked for SO2 and acid rain, so it will work for GHGs. Sounds good. Until you take a second to think about the comparison.

Dealing with GHGs is a challenge of an order of magnitude greater scale and complexity. To see why, see the two graphics below:

First, here's a graphical representation of the Acid Rain cap and trade challenge:


Below the fold, you'll see a graphic representation of the global flow of greenhouse gas emissions, the challenge we have to deal with to avert potentially catastrophic climate change...

(click to enlarge).

As you can see, the global climate challenge is obviously not as simple as the SO2 challenge, or indeed, any pollution reduction challenge we've faced to date. It won't be as easy as adding scrubbers or catalytic converters to smokestacks and tailpipes or burning low-sulfur coal and gasoline with new additives instead of lead. Those transitions we're relatively easy, required no major innovation, and allowed business-as-usual to continue in the electricity and transportation sectors in all meaningful ways (essentially same energy sources, same technologies, same consumption practices).

In contrast, what we're talking about today is fundamentally different: a full-scale transformation of our entire global energy system, consumption habits and more (agriculture, international deforestation, etc.). It's both an order of magnitude larger and more complex a challenge.

In fact, there is truly no parallel for this kind of transition in the history of pollution regulation. There may be no real parallel at all, but if there is, it will look more like major technological transformations in agriculture, telecommunications, or the transitions between major primary energy sources (wood/dung to coal to oil etc.) or transportation methods. None of those transformations were driven by taxes or regulations on incumbent techs. They were driven by innovation and the emergence of better/cheaper technologies, as well as major public investments in technology R&D, deployment, infrastructure and education. For more on historic examples of this kind of challenge, see our recent report Case Studies in American Innovation: A New Look at Government Involvement in Technological Development

It's long past time we put this comparison between acid rain and global climate change to rest.


Another big part of the acid rain story that generally doesn't get told was the deregulation of the railroads (starting with the 1976 Railroad Revitalization and Regulatory Reform Act), which made it much cheaper to ship low-sulfur coal from Western coal fields. That meant that by the time the 1990 Clean Air Act Amendments established the SO2 emissions trading system to stop Acid Rain, fuel-switching to low-sulfur coal was economically feasible, even for coal plants in the East, and compliance with the regulations was easy. While Natural Gas may provide some low-cost fuel switching, there's simply no analogous way forward to the completely transformed, low-carbon global energy system necessary to stop global climate change.

By Jesse Jenkins on 2009 06 30

Flue gas scrubbing was only part of the acid rain solution. The cap on SOx pushed manufacturing offshore, and low-sulfur sub-bituminous coal, like Powder River Basin, substituted for bituminous coal from the heartland. So the Rust Belt and the heartland took a hit for the environment, whether they volunteered or not. Let's remember that as the CO2 debate goes forward.

Otherwise, acid rain and global climate change are as different as an ant and an elephant. The problem is that people can't comprehend the scale of the CO2 emissions. Each metric ton of CO2 is as big as a house, and a 500 MW (typical) coal-fired power plant emits 3 million tons of CO2 each year. That's about 2 cubic kilometers each year from each plant in the fleet.

Also, the chemical scrubbing that worked for SO2 or for natural gas sweetening and IGCC won't work for the CO2 in flue gas. SO2 is only a trace constituent in flue gas, unlike CO2, which is on the order of 15%, so the amount of sorbent required for CO2 chemical capture is enormous compared to SO2. And for post-combustion capture out of flue gas, where there is also a 75% nitrogen ballast hiding the CO2 targets, even more sorbent is necessary than in IGCC, natural gas sweetening, and other easy applications.

SO2 scrubbing uses as a sorbent lime or limestone, which are cheap and which make gypsum and are therefore not regenerated. The sorbent for CO2 scrubbing is expensive amine or, alternatively, chilled ammonia. The amine sorbent must be regenerated by heating to release the CO2, and the heat exchange surfaces scale with heat-stable salts (from residual SOx making sulfuric acid and combining with the amine sorbent) and are gummed up with fly ash sludge. Each ton of coal burned to produce the energy to do the scrubbing adds another 3 tons of CO2 to the scrubbing task, and if you need to burn a ton of coal to scrub 3 tons of CO2 you are just running in place and not producing any power.

Post-combustion carbon capture, from the emissions of coal-fired power plants, is what the world needs urgently, and post-combustion chemical carbon capture is a dry hole. Here is an alternative solution for carbon capture:

By Wilmot McCutchen on 2009 05 27