Quite frequently in discussions on climate change, projections are given out to some time period like “by 2100” or by some useful metric like “a doubling of CO2.”
Global Warming Art
These are perfectly acceptable for talking about how much warming we’d get in a specified amount of time, or at a certain level of CO2, etc. but often people lose sight of the fact that all of these lines are still going up. The world does not end when we hit the first doubling of 560 ppm, or when we hit 2100. Even in discusing climate sensitivity, if we suppose that the sensitivity is on the low end of the IPCC projections, there is still nothing to stop us from tripling or quadrupling CO2 if continue on business as usual for centuries. The real issue here is coal, which is much larger than what is left from oil and gas. I can imagine how year 2200 or 2300 seems like such a long time away, but imagine if the ancient Greeks or Romans were faced with the issues we have today– how would they have left the world, and would we like it?
Geo-engineering has been following me a bit this week. Earlier today I heard someone talking about injecting sulphate aerosols into the atmosphere to offset the warming effect due to rising CO2 concentrations. It doesn’t seem like one of the more practical options out there, and is not exactly at the forefront of “solutions” to the climate problem. Still, it is brought up quite a bit in “what if” thought experiments, it’s probably something we should know out there, and a lot of people still take it seriously. I have my concerns over playing games with an incompletely understood climate system by trying to balance the energy balance of the planet with a higher albedo. I have concerns with short-term mitigation options as a whole though.
Climate Change is both a short-term and a long-term problem. When we inject a pulse of CO2 in the atmosphere, it has a different variety of “fates.” About three-quarters of the drawdown of the excess CO2 takes place in centuries by dissolving in the oceans. There is still some left over CO2 that becomes becomes neutralized by reactions with calcium carbonate and then igneous rock, but these processes take much longer. If there was just air and water and no rocks this tail end would basically stay there forever. So essentially our excess CO2 will effect climate for thousands to tens of thousands of years. In fact, using up the entire coal reservoir could prevent another glaciation for half a million years or longer. So if we offset rising CO2 with sulphate aerosols, we’d have to commit to that for thousands of years, which is absurd. If we were to stop, then the aerosol effect would disappear rather quickly, while CO2 was still very high. Talk about an abrupt climate change!
It is still feasible to keep atmospheric CO2 from exceeding about 450 ppmv by 2100 (which has been argued in the peer-review to be a threshold for “dangerous” interference with the climate system), if emissions from coal and unconventional fossil fuels are constrained. Coal-fired plants need to be phased out within decades, raising prices on carbon emissions helps, and a stronger backbone for alternative energy development needs to be put in place. None of these things are impossible nor impractical with technology or economics; we simply need the will. Continued discussion of short-term “offsetting global warming solutions” could work in sync with longer term strategies, but by themselves they are pointless.