This announcement, the first revision to these rules in 40 years, is welcome and overdue. SO2 emissions from industry and vehicles is a major ambient pollutant, contributing to asthma, bronchitis and premature deaths. In many parts of the US, the communities downwind of the smokestacks tend to be composed disproportionately of poor people and people of color. The EPA estimates that implementing the new rules will prevent between 2,900 and 5,900 premature deaths and 54,000 asthma attacks.
And of course, SO2 is a precursor to acid rain.
European countries have also been steadily tightening their air pollution laws to reduce the amount of SO2 entering the atmosphere.
This is good news for the environment and people, but why am I writing about it on Carbon Clear's climate change blog?
SO2 particles are just the right size to block certain wavelengths of light. Scattered in the atmosphere, millions of tonnes of these particulates block a fraction of the sun's light and provide a planetary cooling effect. These effects are so significant that the Intergovernmental Panel on Climate Change incorporates assumptions of industrial SO2 emissions in their long-range climate models. More specifically, they assume that SO2 emissions will continue to diminish over time as more stingent pollution controls are enacted and we switch away from fossil fueled power generation.
And that means we will no longer be able to hide behind the cooling effects of industrial pollution. It's ironic that cleaning up a pollutant that causes such misery on a local and regional level means we have to work even harder to prevent a warming climate.
This may not be the last we hear of SO2, however. Given its strong cooling influence and relatively low cost of production, an increasing number of scientists believe SO2 may provide a last-ditch defense against catastrophic climate change. Faced with abrupt and runaway warming, governments might choose to inject large volumes of SO2 into the stratosphere to simulate the cooling effects of a major volcanic eruption.
While these geoengineering measures might provide short term relief from warming, they are not without their own challenges. First, the effects on regional climates have not been modelled thoroughly - changing rainfall and temperature patterns may create winners and losers. Second is the fact that SO2 injection would mask the warming effects of climage change, but would not actually address the cause - greenhouse gases in the atmosphere, nor would it do anything to counter CO2's acidifying effects on the world's oceans. What is more, SO2 only stays in the atmosphere for a few months or years, at most, while CO2 stays in the atmosphere for hundreds of years. That means that, once we start injecting SO2 into the atmosphere, we have to keep doing it unless we want to see a dramatic and devastating rebound to higher temperatures. And of course, geoengineering does not provide the benefits that accrue from decarbonising our energy and transportation infrastructure.
It is clear, then, that geoengineering with SO2 is not a measure to be undertaken lightly. As countries around the world impose much needed regulation to continue reducing ambient air pollution levels, we will be running a mini-geoengineering experiment, in reverse. I anticipate that climate scientists will be observing the resulting changes and incorporating them into their models. It would be a tragedy if we were panicked into adopting geoengineering measures without fully understanding the likely impacts.
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