She Swallowed the Spider to Catch the Fly

by Michael Tobis     Department: Earth

There are a variety of ways to look at the climate change problem. One of them is the Luddite view, that we must stop living our modern lifestyle and revert to a preindustrial way of living. The problem with this point of view is that it is hopelessly unrealistic. The human population has exploded as a direct result of modernization. If we outlaw technology, a famine will ensue immediately. While the future will be different from the present in very substantial ways, it will also be equally different from the past.

At the opposite extreme to the back-to-nature idea, which we can call technophobia is what we can call technophilia. At its most extreme (you often here this from less actually technically adept folks) it's just an idea that we can do whatever we like, "they" will figure out something in the end. As one of the "them" in question, this is a pretty terrifying position.

Some people, though, are technophiles with specific ideas. They propose large scale deliberate alterations of the earth system to balance out the accidental ones that we are already doing. This approach is sometimes called "geoengineering". 

Some geoengineering advocates note that certain large volcanoes (most recently, Pinatubo in summer of 1991) , effectively cool the earth quite substantially. Indeed there was a year in the 19^th century called the "year without a summer"  in which crops failed at northern latitudes worldwide because of a volcanic cooling episode.

Public domain image by D. Harlow, U.S. Geological Survey, via Wikipedia

Some people see in this event a possible solution to our global warming problem. It appears feasible to deliberately emit sufficient quantities of sulfur dioxide into the upper atmosphere to cool the surface of the earth enough to cancel global warming.

There are many problems with this, but the one which always bothered me most is that "global warming" isn't really the problem. What affects us as individuals on one corner of the earth or another is rapid climate change, change that is fast enough that we or our infrastructures, or our natural environment will have trouble coping. Canceling out changes in the global average to ever-increasing changes (greenhouse forcing is cumulative) doesn't mean individual regions will stop changing. My intuition is that we won't be that lucky.

Recently, people have addressed this idea using climate models, and my intuition was borne out at an AGU session devoted to the matter. Sulfur dioxide cooling cools the tropics far more than it does the poles. This is really a showstopper, as the biggest hit that climate change will deliver in the near future, the one tipping point we need most to attend to, is the potential of very large sea level rise from melting ice sheets. Cooling the tropics and warming the poles will not help this. Also, if we treat this as a final solution, the ever-increasing accumulation of CO2 being cancelled by ever -increasing sulfur emissions will still amount to accelerating climate change. It doesn't get us off the hook at all.

There are other ideas about how to cool the world's average temperature; for instance spraying salt into the lower atmosphere to encourage the formation of low cloud decks in the tropics. There's some discussion of that AGU session up on RealClimate that is worth a look.

Again, these ideas are not too effective, because they address the average temperature of the earth, not its climate. It's climate change that is the problem. Global warming is only a symptom. Though it's the most predictable symptom, we simply can't settle for symptomatic relief. We have to limit the rate at which climate changes to something comparable to what appears in nature. In fact we are starting to cross that limit, and things look only to get worse before they get better.

In other words such ideas fail because they address symptoms, not the fundamental problem. There are geoengineering methods that address the disease, and not the symptoms, methods which address the chemistry of the atmosphere and not its thermodynamics. These are harder to dismiss, and I'll take them up in a subsequent article.

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