Our top climate scientist has sent out a really, really long email (where does he find the time?), mostly discussing comments on his recent email essay on coal. I think Hansen is the clearest thinker on climate among the top scientists in the field, so I will reprint the email, breaking it up into several postings. The first one addresses “Coal-CO2 versus Oil-CO2” (a query that was also raised by a commenter here)
My statement that releasing a coal-CO2 molecule into the air is more harmful than setting free an oil-CO2 molecule caused puzzlement. Of course the molecules are identical. What I want people to recognize is a way of framing the climate problem that makes clear what action is required to avert disaster. Only two aspects of the physics must be understood:
(1) CO2 “lifetime”. A substantial fraction of the CO2 released to the air in burning fossil fuels will stay there for a very long time (about one-quarter is still there after 500 years).
(2) Fossil fuel reservoir sizes. There is enough CO2 in readily accessible oil and gas reserves to take atmospheric CO2 close to, and probably somewhat beyond, the “dangerous” level. The coal reservoir, not to mention unconventional fossil fuels such as tar shale, can take CO2 far beyond the dangerous level, producing, indeed, “a different planet”.
One other reality, albeit not physics, must be recognized: we can not (successfully) demand that countries such as Saudi Arabia and Russia not mine and sell their oil. And it hardly matters how fast they mine it. We can conserve energy and oil to beat the band, but the readily available oil is still going to be mined in coming decades, not 500 years from now. So, there is just one way we can keep CO2 within, or at least within hailing distance of, the dangerous limit. Indeed, it is a sensible, doable proposition: we must agree to use coal only in (truly) clean-coal power plants at which the CO2 is captured and sequestered. By phasing out existing old-fashioned dirty coal plants over the next few decades, we can keep CO2 below 450 ppm, cf. our “peak oil” paper: http://pubs.giss.nasa.gov/abstracts/submitted/Kharecha_Hansen.html
Would other countries agree to this? It is the only way to avoid mutual self destruction. Developing countries have the most to lose by failing to halt coal pollution and the most to gain by succeeding. Present dirty-coal uses are, among other things, polluting world oceans with mercury and other bad stuff, making the air in some countries almost unbreathable (killing more than one million people per year), and damaging crops (reducing agricultural productivity in India and China by about 30%). Surely developing countries can be convinced to phase out dirty-coal power, but not while the West is still building dirty-coal plants. And developed countries will need to help developing countries with the technology for carbon sequestration.
Is this “no-CO2-from-coal” strategy (phase out of coal use, except at power plants that capture CO2) so difficult to accomplish? Compare it to the effort and cost that went into World War II. Yet this simple “coal” strategy is the primary action needed to solve the purportedly “unsolvable” global warming problem. As described below (“Two Plus Two Solution” [I will post this later]), only one other significant action is needed, plus two rather easy “tweaks”.
In summary, there is a difference between coal-CO2 molecules and oil-CO2 molecules. The oil-CO2 molecules, at least those in large readily extractable deposits, will get into the air anyhow. The coal-CO2 molecules need not get into the air. Once CO2 molecules get into the air, they are practically beyond our reach; they will stay there “an eternity”. It is a tragedy if we continue to release coal-CO2 molecules prior to development of capture and sequestration technology, because these CO2 molecules are the ones that will push climate change into the “dangerous” range. (Refinements to this overview, discussed below [which I'll post later], e.g., actions to “draw down” atmospheric CO2 and the effects of a rising carbon price on the economics of mining fossil fuels in remote locations or extreme environments, do not alter the essence of this story.