Professor Darin Toohey of the University of Colorado at Boulder has prepared a guest weblog for today.
When I opened my local newspaper today, and read the Associated Press interview with John Holdren, it was refreshing to see that the Obama administration is actually considering geoengineering as a potential emergency option to deal with global warming. What’s refreshing isn’t the detailed schemes Holdren mentioned, so much, as the notion that we have a White House that is in tune with the issue enough to be willing to say in public that it’s considering such options. If nothing else, it’s an admission that this is a problem that the US is now taking very seriously.
You can’t be serious about a problem if you do not look into all the possible solutions and geoengineering is, if still poorly understood, a possible solution to out-of-control GHG emissions.
But with some geoengineering schemes, there could be nasty side effects. It’s one thing to pull carbon dioxide out of the air and bury it. It may not be easy, but it makes sense if CO2 is the big problem. It’s something wildly different to inject particles into the stratosphere or to launch mirrors or giant solar power satellites into space. The problem is that stuff called “ozone”- it used to be really important. In fact, it was so important that in order to protect it from even a few percent loss (thereby saving hundreds of thousands of people from life-threatening UV-related skin cancers), we have the only successful international policy to protect the environment that this world has ever seen; it’s called the Montreal Protocol.
Now, it turns out the particles people are considering injecting into the stratosphere act as surfaces for chemical reactions that accelerate ozone-destroying reactions of chlorine and bromine that are present in the stratosphere both from man-made and natural sources. Rocket emissions (and I assuming here that the best way to get payloads into orbit is to launch them on conventional rockets) destroy ozone by directly adding additional particles for these heterogeneous reactions (alumina, in the case of solid rocket motors, and soot, in the case of kerosene fueled engines) or by influencing the abundances of trace gases like water and nitric acid that produce particles, particularly in the polar regions. The stratosphere is relatively safe from the sort of global launch activity that we see today but to scale this up to a geoengineering scheme to save the planet from runaway global warming will pit ozone depletion against climate change. Which would you rather have? How would you know?
There is a new publication in the journal Astropolitics of which I am a co-author;
Ross, M., D. Toohey, M. Peinemann, and P. Ross, 2009: Limits on the Space Launch Market Related to Stratospheric Ozone Depletion Astropolitics, 7, 50-82, doi:10.1080/14777620902768867
that makes the case that if we don’t start thinking about how to deal with the ozone-depletion caused by rockets, we may be in for a rough ride when the main source of ozone depletion in the stratosphere is from rocket emissions, and not from chlorofluorocarbons (CFCs), sometime in about 20-30 years. That’s probably around the time that geoengineering schemes will no longer be interesting after-AGU dinner conversation. On the other hand, the rocket industry is real; there are a few launches worldwide every week. Just about every aspect of our personal and professional lives depends on launching more and larger satellites for communication and remote sensing.
Currently, the amount of ozone-depleting material deposited in the stratosphere by a few space shuttle launches is comparable to the amount of propellants released from 50 million metered dose inhalers (MDIs) each year in the US. This past December, CFCs were banned from those MDIs. But rocket launches aren’t regulated at all. The Astropolitics paper doesn’t make the case that we should immediately start regulating rocket launches. What is says is that the space launch industry is in a unique position when it comes to ozone-depleting practices, because the amount of ozone depletion caused by rockets has been minuscule compared to that caused by CFCs. But as CFCs are purged from the atmosphere, and as space launch activities increase as forecast, something will eventually have to be done; either propellants will be altered to mitigate ozone losses or the number of launches will need to be restricted. We can be certain that solid propellant rockets are worse for the ozone layer than liquid propellants but we do not know if they are a factor of 10 or 100 times worse. No matter from which angle you look at it, add to the mix geoengineering schemes that require large rockets, launched often, and we’ll be stuck between a rock and a hard place.