Uncharted Territory

November 18, 2009

The Guardian on Chinese Coal (including the Strangely Deserted City of Ordos) and the Airborne Fraction, plus some more comments on the Ocean Circulation

Filed under: Coal, Energy, Global warming, Science — Tim Joslin @ 8:08 pm

The Guardian’s been running some pretty hardcore articles on global warming lately, in the run-up to Copenhagen. On Monday, Jonathan Watts reported on China’s coal industry from Ordos in Inner Mongolia. The name “Ordos” leapt out of the page, since I’d just seen the place mentioned in a scare story about China’s over-production by the inimitable Ambrose Evans-Pritchard of the Telegraph:

“Once you know that Hunan authorities have torn down two miles of modern flyway so that they can soak up stimulus by building it again, or that the newly-built city of Ordos is sitting empty in Inner Mongolia, you know what must come next.”

Watts doesn’t mention the population of Ordos, but does claim to have seen a coal liquefaction plant there. Scary stuff. Deserted town, black liquids… all very X-Files!

It’s a miner point but Watts’ article did leave me slightly confused over how far China has progressed carbon capture and sequestration (CCS). He notes that “almost none” of China’s coal plants “remove carbon dioxide”, but then, towards the end, implies that their pilot sequestration project will begin next year. Is “almost none” in fact a face-saving way of saying “none”? Even more worryingly, Watts concludes:

“Beijing’s policymakers are doubtful. They believe dumping carbon underground is expensive and risky for local environments. But under foreign pressure, they have identified more than 100 sites for potential storage.

Ordos will lead the way, but it remains to be seen whether its scientists will be as successful with carbon storage as they have been with coal liquefaction.”

Seems to me that if their heart’s not in it, it just ain’t gonna happen…

One small gripe with the Guardian’s spread on Monday was that they included a figure showing that we’ve emitted 500bn tonnes of carbon (GtC) so far and that the 750GtC mark – and a 75% chance of avoiding a 2C temperature rise – will be reached around 2030 “unless emissions are curbed”, noting that “[c]urrent global emissions are close to 10bn tonnes a year”. My beef is with the last bit which says that “[a]t current rates the trillion tonne mark will be reached before 2050.” No it won’t. What they mean is that we’ll get to the trillion tonne mark by 2050 assuming the current rate of increase in annual emissions, or under so-called “business as usual” (BAU) emission scenarios.

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Today’s Guardian spread (print edition version is edited from Alok Jha’s online piece I’ve linked to) covered the vexed question of whether the Earth’s natural carbon sinks are becoming less efficient.

And the Guardian had a good stab at explaining the issue, even if they did include some diagrams (not in the online version) denominating emissions in, not GtC, gigatonnes of carbon, not even the equivalent PgC, petagrams of carbon, but “trillion grams of carbon per year”, so that the amounts had to be denominated in 1000s! Pity the poor reader!

Anyway, the Guardian reported a timely study published in Nature Geoscience:

“By studying 50 years of data on carbon emissions and combining with estimates of human carbon emissions and other sources such as volcanoes, the team was able to estimate how much CO2 is being absorbed naturally by forests, oceans and soil. The team conclude in the journal Nature Geoscience that those natural sinks are becoming less efficient, absorbing 55% of the carbon now, compared with 60% half a century ago. The drop in the amount absorbed [annually] is equivalent to 405m tonnes of carbon or around 60 times the annual output of Drax coal-fired power station, which is the largest in the UK.”

In other words, the study found that the “airborne fraction” (AF) of CO2 emissions has increased from 40% to 45%.

This would only be a surprise if there was a theoretical basis for the AF remaining constant in the first place. But there is not.

Consider some important natural sinks:
(1) Dissolution of CO2 in the surface waters of the ocean.
(2) Uptake of CO2 by marine organisms, which transport it to the bottom of the ocean as organic debris (the “biological pump”).
(3) Overturning circulation of the oceans.
(4) Uptake of carbon by plants on land.

Of these, only (1) is proportional to the annual increase in atmospheric CO2.

(2), (3) and (4) all likely depend on the level of atmospheric CO2, among other factors. Just to be crystal, the level of atmospheric CO2 depends on the sum of emissions over time, not the level of emissions in any given year.

Plants on land, for example, simply do not “know” about our annual emissions. They only respond to the level of CO2 in the atmosphere. Obviously.

The idea that the AF should be constant is an embarrassment for global warming science. It simply has no theoretical basis. It’s nonsense to say “carbon sinks are becoming less efficient”, because they never were “efficient” in terms of their uptake of annual emissions. Last time I looked into this I cited a paper by Terenzi and Khatiwala. At least there’s some sanity out there.

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It turns out that in fact sink (1), dissolution of CO2, the only one that clearly does depend on the annual increase in atmospheric CO2 (because the surface ocean simply acts as an extension of the atmosphere) is a weak process compared to the others. And since we can control what happens on land, the critical process, the one we ought to be worrying ourselves sick about, is the ocean circulation, which brings CO2 to the surface from the deep ocean. Where there’s a vast amount of it.

I was much taken by the Weatherwatch column in this Monday’s Guardian. Unfortunately the column doesn’t seem to be being put online any more, but the article described the Little Ice Age and how “[o]ne Inuit paddled down the river Don in Aberdeen.”

Surely only changes in the ocean circulation are powerful enough to explain the Little Ice Age (LIA) and the Medieval Warm Period (MWP) that preceded it? Certainly not this nonsense about the effect of the solar cycle on cosmic rays.

Maybe what happened was something like: warming at high (northern) latitudes caused by a strong ocean circulation during the MWP gradually reduced ice cover, causing further warming by the albedo positive feedback effect. This eventually weakened the driver of the ocean’s circulation, the temperature difference between low and high latitudes. But when the Gulf Stream weakened and stopped bringing so much warm water north, the temperature dropped again. After a time lag – the LIA – the circulation strengthened again. Just a thought.

Maybe the process is reinforced at certain points in the cycle by the effect of the circulation on atmospheric CO2 levels. For example, a stronger circulation during the MWP would release more CO2, causing more warming (with a disproportionate amount of extra heat captured at low latitudes), strengthening the circulation further, until the heat transported north reduced ice cover and hence the temperature difference between high and low latitudes… And the reverse in the LIA.

The difference now, though, is that because of the vast increase in GHG levels, we’re capturing much more heat in tropical regions, so warming at high latitudes might not in itself weaken the circulation. Not for a while, anyway.

OK, maybe this is getting way too speculative, but I’d really like to see the results of some modelling of what will happen to the ocean circulation as we cook the planet…

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