Thursday, December 9, 2010

Short-term Mitigation

Going into the Cancun talks, there was widespread consensus that it was unlikely that a legally-binding international agreement could be reached. With only two days to go in the conference this forecast is unlikely to change. That does not mean that meaningful steps could not be taken now to stall for time. There has been quite a bit of discussion and reference to the idea that short-term mitigation may provide a temporary way in which to decrease the mechanisms in the atmosphere leading to higher temperatures.

The idea behind short-term mitigation is to concentrate on drastically reducing some of the other gases and aerosols in the atmosphere that are easier to address than CO2. As Todd Stern, the U.S. negotiator indicated, it's not a long term solution but it is something that we can do now. You may remember that we talked about this very issue last year in the blog as well but nothing coordinated was done about it.

Methane (CH4), for example, is an incredibly effective greenhouse gas but it has a relatively short life cycle in the atmosphere. That is, once it is released into the atmosphere, it doesn't remain for nearly as long as carbon dioxide. So a net reduction in the amount of methane released into the atmosphere could have a significant impact as it will quickly cycle out of the atmosphere.

Two of the aerosols referred to are mundane substances that are familiar to us all: soot and dust. The good news is that cleaning up these aerosols is also an exercise in cleaning up air quality which is a major health risk, especially in the developing world. Soot, or black carbon, is produced from the inefficient burning of fuels such as coal or wood. It is the airborne component of the stuff that is left in the fireplace after you have a fire. It can come from burning forests, cooking and heating fuels, and diesel engines. Black carbon is very effective at absorbing sunlight which increases temperatures. This can happen in the atmosphere when the soot is airborne or on the ground when it coats the surface of the ground as it settles out of the air.

If you have ever had the experience in wintertime of seeing beautiful white snow turned gray and black from dust or grime accumulating on top of it, you have seen what is happening around the world with soot and dust. As the surface darkens in color, the reflectivity of the snow starts to decrease. The more sunlight that is absorbed at the surface of the dirty snow, the more heat accumulates and the higher the temperatures become. As you might expect, this effect will be greater in the high latitudes (closer to the poles) and also high altitudes (higher up in the mountains) where there is more snow and ice cover that would normally be very reflective. As these are the areas of the world that are likely to experience the greatest overall shift in temperatures by the end of the century, this is no small thing.

Ozone in the lower levels of the atmosphere can also play a role in short-term mitigation of climate warming. We should say that this has nothing to do with the hole in the Ozone layer, which is much further up in the atmosphere and works differently. Ground-level ozone is a greenhouse gas and a pollutant that directly heats the atmosphere by absorbing radiative energy and also by causing damage to vegetation. It is produced by chemical reactions of other pollutants such as hydrocarbons and nitrous oxide (NOx).

Ground-level ozone alerts are all too common in cities especially during hot summer days. Like the aerosols mentioned earlier, they also lead to severe health problems such as childhood asthma and respiratory distress among the elderly. Ground level ozone has also been found to lower plant productivity. This is not only important because we need plants (crops) to survive, but they also act to scrub the atmosphere by taking out carbon dioxide and storing it as biomass as they grow. The slower they grow, the less efficient they are at removing CO2 from the atmosphere.

Clearly, short-term mitigation is no replacement for some coherent means to reduce the amount of carbon dioxide in the atmosphere. But it is something that can be done now under the auspices of reducing significant air pollution and improving human health in the absence of a broad international agreement. It can reduce the rate of warming occurring globally in the short-term. It is something. It is the low-hanging fruit.

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