Monday, December 01, 2008

No Quick Fix to Greenhouse CO2 levels.

The surface layers of the oceans are becoming saturated with CO2, and less able to absorb more of it; hence, policies to curb carbon emissions will not have an immediate impact, and it may take hundreds of thousands of years for the natural (pre-industrial) balance of the gas to be restored. I have tried to keep an open mind about the facts of Anthropogenic global warming and climate change, whereby it is assumed that our profligate use of fossil fuels has contributed to an excess of CO2 in the atmosphere, which will cause the planet to heat-up, with concomitant climate change that will prove detrimental to life on Earth. The general consensus is that we should reduce our use of fossil-fuels, in the hope that the planet will recover its equilibrium, through natural absorption processes. Around 40% of the carbon burned from fossil fuels since 1950 has been absorbed, while the remainder has accumulated in the atmospheric burden of CO2.

More proactive measures are proposed too: for instance the growth of plants, to absorb CO2 from the atmosphere through photosynthesis, which are then pyrolysed in the absence of oxygen to form various gaseous and liquid products that might feed markets for fuel and organic chemicals, leaving a residue of carbon ("biochar") which could be dug into soil, both to improve its fertility and to bury some of that miscreant greenhouse carbon. The latter would pose a considerable undertaking, however, and to restore CO2 levels to those of the pre-industrial era would require pyrolysing most of the world's biomass for the next 40 years, and burying its thermal residue of biochar.

Lesser scale operations could pull-down enough CO2 from the atmosphere to restrain it from the putative 450 ppm tipping-point, beyond which the climate runs out of control. The level is around 390 ppm now. However, a new study offers little cheer that even such gargantuan feats of political cooperation and engineering might save us, even if they could really be done. The findings contradict prevailing views that CO2 will be cleaned-out of the atmosphere during the next century or so by natural forces, if we simply curb our emissions by around 80% by 2050, as Britain has pledged to do, by switching over to carbon-free sources of energy. Now this is a massive imperative in its own right, and I wonder as to the viability or veracity of such a policy.

Enter, Professor David Archer of the University of Chicago, who is quoted as saying: "the climatic effects of releasing fossil fuel carbon dioxide into the atmosphere will last longer than Stonehenge, longer than time capsules, far longer than the age of human civilization so far. Ultimate recovery takes place on timescales of hundreds of thousands of years, a geologic longevity typically associated with public perceptions of nuclear waste."

Most of the CO2 that is removed from the atmosphere is absorbed by the oceans, but the process is becoming slower. The ocean waters to a depth of around 100 metres, which is where CO2 is principally and initially dissolved are becoming saturated with the gas, which increases their acidity, and discourages further uptake. In order to re-activate the solvent power of the surface layers of water, fresh seawater from lower depths needs to recycle upward, but this process takes "centuries or a millennium." If the surface waters are becoming warmer too, the process is slowed-down yet further.

In a forthcoming paper (to be published in Annual Reviews of Earth and Planetary Sciences) the additional posit is made that the recycling process per se is insufficient to absorb all the unwanted CO2 from the atmosphere, and the snail-pace weathering of rocks which locks-up CO2 as solid limestone will be required, taking thousands of years to be accomplished. Professor Ken Caldeira, a co-author of the report, raises his game still. He concludes that even after the "pollution" by CO2 stops, the mean temperature of the Earth will settle at a new higher level, rather than falling.

This makes sense, if the heating effect of CO2 is as severe as climate-models indicate, and the concentration of the gas remains steady and relatively high over long periods. James Hansen, director of the NASA Goddard Institute of Space Studies, concludes that the "long lifetime of CO2 emitted by fossil fuel burning" means that simply reducing emissions does not provide a solution, and that some of these fuels must "be left in the ground" forever, and that gas must actually be removed from the air. Now that latter point does sound potentially like the biochar strategy.

What Hansen in fact proposes is removing CO2 by growing trees (you'd need an awful lot of them!), and then burning them to produce electricity and capturing the CO2 before it is emitted. Interesting that BP have just pulled out of the carbon capture game. He also thinks that there should be no more coal-fired power plants built.

Growing trees, other biomass, algae etc. is probably the only way we can withdraw significant amounts of CO2 from the atmosphere. The question is what do we do with that carbon-rich material once we have it? Pyrolyse it and bury the carbon biochar, or burn it and bury the carbon dioxide? Leaving more of the fossil fuels in the ground (i.e. not using them) makes a lot of sense, and seems to point to some combined strategy of energy efficiency and curbing inefficient oil-based transportation. We will need to do these things anyway, as fossil and other resources run expensive and eventually short, but if these scientists are right, it just won't do much to alleviate global warming and climate change.

If the predictions prove true, then we are stuck with the consequences of our actions and will need to weather climatic shocks and changes of various kinds. That noted, it is the instance of running-out of plentiful oil and then natural gas that will impact most immediately on human life and indeed all life, along with limiting supplies of clean water. Testing the theoretical models of scientists may be a luxury for future generations. Our practical actions now will contribute to how that future may unfold, and whether it contains civilisation as we have come to know it.

Related Reading.
"Greenhouse gases will heat up planet 'for ever'."


André Sautou said...

Hi Chris

I have just read your article with great (intellectual) interest, as usual.

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energybalance said...

Hi Andre',

mmmm... makes me think that maybe coal would make a good investment??

I see oil has dropped to $49 a barrel and all the markets have fallen once again and vastly. The £ is now worth only $1.48!