Still Baffled by BERN, but a little wiser

About a year ago, I professed myself “baffled” by the BERN carbon cycle model.  Since then, I’ve finally twigged how the oceans will behave over the next century or so.  This post aims to further clarify my current understanding.

In particular, I remain convinced that the concept of an airborne fraction (AF) of carbon emissions is entirely erroneous; it is unsafe to base policy on the idea that chemical processes and ecosystems will take up a fixed proportion of annual carbon emissions.

As well as my last blog entry (and the two previous discussions it references), I have been engaged in an extended email dialogue with the Climate Philosopher, who has added a question to my original post on the BERN model:

“Do you think all of the processes depend on the level in the atmosphere dCO2(Outflow)/dt = a(CO2 – p) where a & p are constants. This would be my simple understanding.
- ie is BERN *completely* wrong?

Or are there some processes that are BERN-like e.g. equilibrium with the upper oceans so that dCO2(Outflow)/dt = a1(CO2 -p) + b(dCO2(Inflow)/dt)

I’d like it that the simple model (that bern is completely wrong) was the valid one.”

The answer to the question posed in the second paragraph is “yes”, although the “or” beginning the sentence is logically incomplete and, in this case, misplaced – we cannot categorise “all” carbon uptake processes in any single way.

Here’s a numerical summary of what I think is happening (based on IPCC AR4 data, all figures very approx.):

• “Surface water” is (by definition) in eq’m with atmosphere.  According to the IPCC (Fig. 7.3), such water holds 18GtC more than the pre-industrial level. i.e. approx. 0.16GtC per ppm increase in atmospheric CO2 (that is ~18GtC divided by the 110ppm increase – from 280ppm to 390ppm – in atmospheric CO2 levels).

• This process of “uptake by re-equilibration” (the Climate Philosopher’s b(dCO2(Inflow)/dt) ) is therefore weak – accounting for ~0.3GtC per year (0.16GtC/ppm from above times an annual increase in atmospheric CO2 of a bit under 2ppm) increase in CO2 held in surface waters.

• But there is a turnover of ~10% of ocean surface water p.a. This accounts for the Climate Philosopher’s other term: a(CO2 -p).

• In this process the ocean exchanges carbon between surface and the deep ocean.  Even though, this process releases carbon (because there is more in the deep ocean than the surface waters), it releases less now than before industrialisation, because the descending waters hold more carbon than before.

• By the overturning process, the deep ocean therefore currently takes up 1.8GtC p.a. more than before industrialisation.

• The total extra carbon uptake of 1.8 (from overturning) + 0.3 (because of 2ppm/yr increase) = 2.1GtC/yr, a good fit with published data based on observations.

• Sanity check: a letter to Nature by Peter Cox (I can’t access more than the synopsis either) suggests the ocean *could* take up 5GtC/yr under BAU by 2100 implying that by then there will be 50GtC more than the pre-industrial level in surface water.  The CO2 in the atmosphere would therefore be 280ppm + 50/0.15 = 280+330 = ~600ppm.  Sounds about right.

And the consequences are…

1. It’s hands-up time.  The idea in my original post that “it appears that removal by the oceans is indeed saturated (AR4, p.26 & elsewhere)” is wrong (and too pessimistic).  The AR4 reference is to the data on ocean uptake over the last 25 years which has increased from about 1.8 to 2.2GtC/year (although these figures are very rough estimates).  The point is that, whilst annual emissions have increased significantly since 1980, the atmospheric level, which is dominant in determining the ocean uptake rate, has not increased so much.

2. The idea that a fixed proportion of annual anthropogenic carbon emissions remains in the atmosphere (i.e. that the AF remains constant) is also false.  My original post is correct on this point, if a little pessimistic on the ability of the ocean to take up CO2.  Curiously, whilst trying to find a bit more information about the BERN model, I came across this recent paper by Terenzi and Khatiwala (pdf). I have to say I’m rather disappointed there’s no reference to my original post, since I noted from a bit of ad hoc modelling that the AF only remains roughly constant “while CO2 emissions and atmospheric levels are increasing at a fairly steady rate.”  Terenzi and Khatiwala note that:

“Specifically, our results suggest that both the quasi-constancy of AF over the past half-century, and its particular numerical value of ~50%, are essentially a consequence of exponentially growing emissions with a nearly-constant growth rate of 1/40th per year.”

So basically, as T&K point out, policies assuming a constant AF are quite possibly misguided! Both T&K (loads of equations) and myself (back of an envelope) reach the conclusion that the “constant” AF is an artefact, entirely data-dependent, a mere coincidence!!

3. I still can’t relate the BERN carbon cycle model to the real world.  It appears to assume atmospheric carbon will return asymptotically to equilibrium following the emission of a pulse of carbon.  Deriving an AF in this way makes little sense for several reasons:

• Different feedbacks have different effects over different time periods.  For example: after some centuries elevated levels of dissolved CO2 in the oceans will affect the oceanic ability to take up more CO2; warming of the land (fast) and oceans (slow) will at some point affect CO2 uptake; etc.  I haven’t even considered uptake of carbon by the biosphere, but the response will likely not resemble a chemical equilibrium, since secondary ecosystem responses will modulate carbon uptake. The process will also differ considerably between the oceans and land.
• The natural carbon cycle is not in equilibrium.  Rather, because of the different time-periods of various feedbacks, it oscillates, giving us the ice age cycle (in resonant response to Milankovitch forcings).
• You simply can’t model individual years’ carbon emissions according to the BERN model, since we’re already out of equilibrium, by more and more each year.  This observation, in itself, casts considerable doubt on the “constant AF” conception.

It does rather seem to me that the idea that “if industrial emissions ceased tomorrow” atmospheric carbon would progressively decline to approach an equilibrium level is entirely suspect.  Furthermore, when we consider possible scenarios of future annual carbon emissions we have a more complex situation, perhaps more of a bifurcation: if our emissions continue to increase rapidly, the AF will increase, even without positive carbon cycle feedbacks (only the relatively tiny amount of carbon taken up by re-equilibration of the ocean surface waters is proportionate to emissions; other carbon uptake processes are proportionate, at best, to the difference between current and pre-industrial CO2 levels); whereas, if we decrease our annual emissions, natural processes will help us, and the AF will actually decrease – or even go negative.

Ocean Carbon Uptake: Further Reflections

In my previous 2 posts, The Sea, The Sea and How To Freeze A Mammoth, I have argued – nay, stronger than that, pointed out – that the 2GtC/yr of carbon that the oceans are helpfully taking up from the atmosphere is due largely to a reduction in the amount of carbon released annually as currents exchange deep with surface water.  The deep sea has a higher carbon content than the surface waters because of the “biological pump” whereby organic material (krill poo, dead whales etc) descends through the water column.

Towards the end of my last blog entry, I discovered that the quantification I had previously sought in vain in the 1000 odd pages of the IPCC’s latest Science report does in fact exist in their carbon cycle diagram, Fig. 7.3 on p.515.  These figures broadly support the guesstimates I made towards the end of my initial blog entry of the series.

In case you don’t have a copy of the IPCC report to hand, let me explain what Fig. 7.3 tells us.  It notes that, of total anthropogenic carbon emissions during the industrial era, 18Gt remains in the surface waters and 100Gt is now in the intermediate and deep ocean.  The diagram even includes a flow of 1.6GtC/yr from the surface to the deeper ocean.

The ocean “surface” is that part which, moreorless by definition (perhaps the scientists could make this explicit sometime), is in equilibrium with the atmosphere.  Now, CO2 in the atmosphere is at roughly 390ppm, against a preindustrial level of 280ppm.  1 ppm ~= 2GtC (~ means approx.).  So, the surface layers of the ocean represent an “extension” of the atmosphere for the purposes of holding carbon dioxide, of, according to the IPCC, only 18/220, i.e. very ~ 10%.

That is, as we increase the atmospheric CO2 by 2ppm/year, 4GtC, the part of the ocean in equilibrium with the atmosphere is helping us out by dissolving an additional 0.4GtC.

Add 0.4GtC to the 1.6GtC “removed” annually by turnover of the surface waters (and, I suppose, diffusion) – though in fact only removed in the sense that the turnover of the surface waters results in the emission to the atmosphere of 1.6GtC/yr less carbon than would be the case without the elevated atmospheric level of CO2 caused by industrial carbon emissions – and we get the observed 2GtC/yr total net uptake by the oceans compared to the rough equilibrium between the atmosphere and the oceans in the few thousand years prior to the industrial era.

Until changing conditions (e.g. rising temperatures) affect the relevant processes, the consequences are:

1. The oceans will continue to reduce any increase (or increase any reduction) in atmospheric CO2 by about 10% due to the reasonably fast process of chemical equilibration.

2. The oceans will continue to take up around 1.6GtC/yr whilst atmospheric CO2 levels remain at their current elevated level.  This level of uptake will only increase slowly if our annual CO2 emissions continue to increase – i.e. as I discussed some time ago, in this scenario, the oceans will take up a declining proportion of our annual emissions and more will remain in the atmosphere.   In fact, there’s no direct relation between our annual emissions and the airborne fraction (AF).  It is daft to suppose there would be.

2A. On the other hand, if our annual emissions decline, we will still get the benefit of the 1.6GtC net removal from the atmosphere attributable to oceanic circulation.

3. Ocean CO2 uptake is not very sensitive to geo-engineering interventions to increase the amount of CO2 that dissolves in it, e.g. by dumping calcium carbonate in the sea (though this might eventually be worth doing – expensive though it would be because of the mass that would have to be transported – in order to preserve shelled creatures, corals etc).  The problem is that the surface waters only turn over about once every ~10 years on average (18Gt extra carbon held in total divided by 1.6Gt transported to the depths each year – my previous guesstimate was once every 20 years).

4. Ocean CO2 uptake is very sensitive to changes in the circulation of the oceans. Since such circulation is more likely to lessen than to increase, we really are getting ourselves in deep water!
[Note (12/6/09): this is a potentially misleading throwaway comment - as explained previously a reduction in the rate of oceanic circulation would, assuming the biological pump is unaffected and atmospheric CO2 levels remain elevated, lead to a reduction in the rate of release of carbon by the oceans, i.e. overall the oceans would take up even more atmospheric carbon].

5. Ocean CO2 uptake is very sensitive to changes in the biological pump, which removes 11GtC (according to Fig.7.3) each year.

I hardly ever keep my promises for future blog entries, but in the unlikely event that I do on this occasion, next time I’ll discuss what factors could affect the biological pump…

How to Freeze a Mammoth, or, Has the IPCC Got it Wrong?

My previous post attempted to answer the question as to whether the oceans would continue to take up CO2 if the level of the gas in the atmosphere started to decrease.  To sum up, I concluded that, in fact, the oceans would continue to help us out.  The reason is that different mechanisms dominate the exchange of CO2 between the sea and the air over different timescales:

• over short timescales – years – the surface layers of the oceans are in equilibrium with the atmosphere.  The oceans (to a limited degree) buffer changes in atmospheric CO2.
• over intermediate timescales – decades to centuries – the turnover of the surface waters of the oceans dominates the chemical equilibrium of the surface waters with the atmosphere.  The ocean will continue to remove carbon whilst the level in the atmosphere declines over decadal timecales, whilst this level remains greater than the equilibrium with the oceans as a whole, that is (arguably) while it is greater than around 280ppm.  Over time, though, this equilibrium point will shift (upwards) as ocean warming and acidification reduce the capacity of the processes controlling the net annual removal of CO2, notably the “solubility pump”.  [I've now noticed that the IPCC implicitly support this conclusion - in their carbon cycle diagram (Fig 7.3, p.515), they show that 18Gt of anthropogenic carbon has ended up in the "surface ocean", available to bubble back out if the atmosphere level of CO2 decreases suddenly, but 100GtC has ended up in the "intermediate and deep ocean", from where it can't easily be re-released.  The proportions are roughly what I assumed in my previous post, too].
• over very long timescales – millennia – the entire ocean is in equilibrium with the atmosphere.  Though the effect on this equilibrium of relatively small changes in the processes driving the exchange of CO2 is very high.  In particular, the “biological pump” removes 10GtC/yr (I explain below where this figure comes from).  A 10% change in efficacy, sustained for a millennium, therefore represents around 1000GtC, somewhat more than is present in the atmosphere.

Whilst writing the previous post, I came across what appears at first glance to be a bit of a howler by the IPCC.  In section 7.3.4.5.1 Robust findings (no less), and elsewhere, they claim that:

“A potential slowing down of the ocean circulation and the decrease of seawater buffering with rising CO2 concentration will suppress oceanic uptake of anthropogenic CO2.” (my emphasis).

I beg to differ.  I don’t understand how a “slowing down of the ocean circulation” would have this effect.

Here’s a carbon cycle diagram, quite similar to (though rather simpler than) the one the IPCC include as Fig. 7.3 on p.515 (this one’s thanks to NASA via Wikipedia and has no copyright restrictions, though the IPCC stuff might not have any either).  Blue numbers represent annual carbon flows, black ones carbon stores:

Now, what’s important is that the “solubility pump” returns an annual net 100 – 91.6 = 8.4GtC to the atmosphere from the oceans.  The solubility pump would be directly affected by a slowing of the oceanic circulation.

The 8.4GtC is counterbalanced by 10GtC removed from the atmosphere by “marine biota”.  This “biological pump” would not be directly affected by a slowing of the oceanic circulation (though might be affected indirectly, by a reduction in available nutrients).

The IPCC seems to think that blocking a process – the solubility pump – with the net effect of adding carbon to the atmosphere will “suppress oceanic uptake of anthropogenic CO2″.  This conclusion seems more than a little fishy to me!

At first glance the IPCC seem to be confused by their deltas.  They have analysed the solubility pump in terms of the difference between the pre-industrial state and the present, with lots of nice diagrams showing where the “anthropogenic carbon” has ended up.  The pump is, it seems, putting 2GtC less carbon into the atmosphere than before.  But the solubility pump used to be balanced by the biological pump, which takes carbon out of the atmosphere.  If we stop the solubility pump, we’ll still be left with the biological pump!  If this happened (and it’s quite a big “if”), more carbon would be removed from the atmosphere each year!!

Why is this important?

Well, I think it would be a good idea to really understand the ice age cycle before trying to predict what will happen to the carbon cycle over the next century or two as we warm the planet.  The point is that the carbon cycle plays a large part in reinforcing the Milankovitch cycles which change the pattern of warming of the Earth over thousands of years.

One puzzle that it seems to me should be resolved is why the planet does not just keep on warming as it comes out of an ice age.  It was warmer than it is now during the last interglacial 120,000 years ago (120 kya) and at the end of the last ice age 10 to 5 kya (IPCC p.460 ff) (though unless we act now, in 50 to 100 years it will be significantly warmer than during those periods).  Warming during an interglacial is fast: strong positive feedbacks are in play – warming causes increased CO2 release from the oceans (see previous post) which causes more warming.

We need some negative feedbacks!  The obvious one is that in a wetter and warmer world, land uptake of CO2 starts to exceed oceanic release (which is why it might be a good idea to allow reforestation so that nature can help solve the problem for us).  Another negative feedback, I suggest, may be a slowing of the oceanic circulation – driven as it is by the cooling of poleward currents (IPCC Box 5.1, p.397).  Since the poles warm faster than equatorial regions this switch-off of ocean circulation is likely to happen as the world warms, as often discussed in the media, such as the film The Day After Tomorrow. (Though real life would be nowhere near as dramatic!).

Such a sudden cessation of warming could help explain how mammoths are found so well-preserved in permafrost!  More to the point, it could help explain how CO2 stops rising at the end of interglacials.   The situation is complex, since instability is produced, as cooling caused by slowing of the ocean circulation would tend to cause the circulation to restart.   Not only that, the sudden cooling would reduce CO2 uptake in high northern latitudes in particular (by inhibiting plant growth).  [This points to a problem with a mechanism that just relies on slow cooling to explain the turning point in the ice age cycle - the land (taking up carbon at this point) cools faster than the oceans (which are releasing carbon).  This would surely cause a net increase in CO2, tending to reverse the cooling.].

I therefore speculatively hypothesise that the peak warming in (natural) interglacials is caused by a reversal of rising CO2 caused by a stop-start sequence in the ocean circulation.  This may act together with the Milankovitch cycles to tip the Earth back into a cooling phase leading to the next ice age.  Also, of course, if the cooling freezes the vast northern wetlands (which we’re now melting), e.g. in Siberia, it very quickly removes a large source of methane, which, because methane breaks down in the atmosphere relatively quickly to less powerfully warming CO2, would very quickly produce more cooling.

Has the IPCC got it wrong?  And missed part of the explanation for the ice age cycle?

Afterword: It occurs to me that some people might think that increased CO2 uptake due to a slowing of the ocean circulation might represent something of  a get out of jail card.  On the contrary.  It would surely result in even worse climate instability than we’re already heading for.  We need to reduce GHG levels before we get to The Day After Tomorrow point.

The Sea, The Sea

About a week ago I was browsing David MacKay’s excellent resource, “Sustainable Energy – without the hot air“. This, and a brief conversation earlier the same evening, had started me pondering (again) on the thorny topic of CO2 uptake by the oceans. Specifically, I wanted to make some progress towards answering the question:

“If we reduce the level of CO2 in the atmosphere from its present 390ppm or an even higher level in future, will the oceans release CO2 they are currently absorbing (about 2GtC/year)? And, if so, over what timescale?”

Professor MacKay includes a chapter (31, The last thing we should talk about) on geo-engineering. He notes:

“If fossil-fuel burning were reduced to zero in the 2050s, the 2Gt[/yr] flow from atmosphere to ocean would also reduce significantly. (I used to imagine that this flow into the ocean would persist for decades, but that would be true only if the surface waters were out of equilibrium with the atmosphere; but, as I mentioned earlier, the surface waters and the atmosphere reach equilibrium within just a few years.) Much of the 500Gt we put into the atmosphere would only gradually drift into the oceans over the next few thousand years, as the surface waters roll down and are replaced by new water from the deep.”

Now, the model I have in my head of CO2 uptake by the oceans is one of flows of CO2, rather than a chemical equilibrium. David MacKay’s comment caused some self-doubt on my part. The Professor is clearly not what we chess-players might refer to as a “rabbit”. Strong grand-master would be nearer the mark.

As regular readers will be aware, I’d reached a somewhat different conclusion to that of Professor MacKay. I concluded that the ocean will continue to helpfully take up 2GtC/yr from the atmosphere, on the basis that this may be the capacity of the processes to remove CO2 from the atmosphere.

I specifically doubted, though, that the oceans will continue to absorb a fixed proportion of our emissions, on the grounds that “the ocean ‘knows’ nothing about emissions – all it can possibly be affected by is the level of CO2 in the atmosphere.”

But this idea of “equilibrium” between the surface waters and the atmosphere suggests instead that the ocean can be considered as an extension of the atmosphere, so that if the total increase in CO2 in a year from fossil-fuel burning and terrestrial biosphere changes was (say) 6GtC, 4GtC would stay in the atmosphere and 2GtC would end up in the ocean; if it were 12GtC, 4GtC would end up in the ocean.

Now, undoubtedly there is an equilibrium between the waters at the very surface of the ocean and the atmosphere: that’s how these things work. Horrifically, I’m suddenly reminded of questioning on a very similar topic during a mock interview for university conducted by my school headmaster, who had himself written chemistry textbooks…

Anyway, undoubtedly, too, there are flows of carbon in various forms to and from the deep ocean.

The question is how we combine these idea of equilibrium and flows into a single model that will help us at least put a sign to flows of CO2 from atmosphere to ocean in various scenarios.

The consequences of a pure equilibrium would be that:

1. The ocean will continue to absorb a fixed proportion of net emissions, i.e. it will proportionally reduce the impact on atmospheric CO2 levels of future increases in atmospheric CO2.

2. As soon as atmospheric CO2 levels peak, the ocean will start to release a fixed proportion of any net reduction. i.e. it will be more difficult to get the atmospheric CO2 level back down, say to 350ppm.

On the other hand, if the true explanation is that in a (hypothetical) steady-state there is a balance between flows of CO2 from the ocean to the atmosphere and vice versa, then we need a different sort of explanation. We would have to conclude that processes that remove CO2 from the atmosphere are sensitive to a higher concentration of CO2 and are therefore proceeding more rapidly because CO2 is at around 390ppm compared to a historic level of 200-280ppm.

It’s likely that the processes controlling the interchange of CO2 between the air and the sea are sensitive to other factors, such as temperature and acidity (affected by the cumulative total of CO2 absorbed). But so far, these parameters have changed relatively little. When they do, all the evidence is that they will slow the rate of CO2 uptake by the oceans.

But the crucial point is that in a flow model, the oceans will continue to remove CO2 from the atmosphere as long as the atmospheric level is above the stable long-term level which prior to industrialisation was 200-280ppm.

To jump ahead a little, the question as to whether an equilibrium is dominant is likely to reduce to what we mean by the “surface waters”, since, at the limit, the surface of the ocean must be in equilibrium with the atmosphere next to it. In other words, how quickly does CO2 disperse away from the surface of the ocean?; and from power-station chimneys through the atmosphere to the surface of the ocean?

Looking at the rest of Professor MacKay’s chapter on geo-engineering, I couldn’t help reflect that there is a contradiction. If an equilibrium between the surface waters and the atmosphere is the dominant mechanism, then one would have thought there was little to be achieved by geo-engineering approaches to increase the absorption in a limited area of ocean (sprinkling them with calcium carbonate to absorb CO2 directly or with iron filings to encourage algal growth).

So, for the umpteenth time, I found myself referring to “the doorstop” – the AR4 IPCC Scientific report. And I can report that parts of the relevant sections of this document are virtually content-free. Now, I’ve been in situations when a lack of content has been highly desirable. The objective of some business communications, for example, is to say precisely nothing of any significance. I suggest, though, that the IPCC should not be playing this game.

Let’s turn first to section 6.4.1.4 on p.452. Here we learn that:

“There is evidence that terrestrial carbon storage was reduced during the LGM [last glacial maximum] compared to today. Mass balance calculations based on C13 [isotope] measurements on shells of benthic foraminifera yield a reduction in the terrestrial biosphere carbon inventory (soil and living vegetation) of about 300 to 700GtC…”

This doesn’t really tell us much about the mechanism of CO2 exchange between the oceans and the atmosphere, but is a rather scary fact. Warming leads to carbon leaving the oceans and being taken up by land flora. Ah, I hear you think, the trees take up carbon and the oceans release it to restore equilibrium. Sorry, Grasshopper. The trouble is that as the planet warms the level in the atmosphere goes up as well. This suggests to me that the oceans do indeed release carbon as the planet warms. It’s not pull by the “trees”, but push by the “seas”.

As I said, this is a rather scary fact. Given that the planet is warming rather rapidly. And that the exchange of carbon between atmosphere and oceans takes place at the surface. Where it’s warming. The fact that the deep ocean takes millennia to cool is not really relevant. Hmm, maybe I’ve jumped ahead again.

But back to the story.

Turn now to p.446 of the IPCC report, where we find Box 6.2: What Caused the Low Atmospheric CO2 Concentrations During Glacial Times? (Seems an odd way to phrase it, as glacial times are the norm, but let’s go on!). The answer is no-one really knows. (Actually, the answer to the IPCC’s question is easy: in glacial times the atmospheric CO2 level is so low it limits photosynthesis, so we should really be asking: What causes higher CO2 levels in interglacials?). Still, no-one really knows. Or as the IPCC put it:

“In conclusion, the explanation of glacial-interglacial CO2 variations remains a difficult attribution problem.”

There’s one proviso. There’s a speculative theory (no more than a hypothesis, really) that increased amounts of dust containing iron cause increased phytoplankton growth which causes the ocean to take up carbon from the atmosphere. I mention this because the complete line of reasoning is that colder conditions cause less plant growth, that is more deserts from where dust can blow… This would restore the idea of a “push” by the land – more trees, less dust leads to more carbon in the atmosphere. The trouble is that there’s no evidence that this mechanism could explain more than a small proportion (if any) of the observed changes in CO2.

So much for the top-down approach.

Is our understanding of the physical processes any better?

Let’s see how far we can get. The IPCC Science report notes in section 7.3.1.1 (p.514) that there are 2 “pumps”, i.e. processes that remove CO2 from the atmosphere:

1. The solubility pump – dissolving CO2, giving carbonic acid:
CO2 + H20 <—> HCO3+ + H+ (1)
buffered by carbonates (e.g. CaCO3, calcium carbonate):
CaCO3 <—> Ca++ + CO3– + HCO3+ + H+ <—> Ca++ + 2HCO3+ (2)
(see a previous post for how this might be helped along by dumping some more chalk in the sea).

2. The biological pump whereby phytoplankton (algae) takes up carbon as it grows.

The IPCC note that:

“Together the solubility and biological pumps maintain a vertical gradient in CO2… between the surface ocean (low) and the deeper oceans (high)…”

[my emphasis]

This is where this whole topic starts to do my head in. How can it be that there is less CO2 at the surface, yet the oceans are taking up the CO2 we’re emitting through burning fossil fuels and forests?

Obviously there is a circulation in the oceans. The IPCC note (we’re still on p.512) that:

“In winter, cold waters at high latitudes, heavy and enriched with CO2… because of their high solubility [sic, I don't know what they're trying to say either], sink from the surface layer to the depths of the ocean. This localised sinking, associated with the Meridional Overturning Circulation (MOC)… is roughly balanced by a distributed diffuse upward transport of [CO2] primarily into warm surface waters.”

This exchange of dissolved CO2 – lots coming up, rather less going down – constitutes the “solubility pump”, but the biological pump, which, remember, involves organisms taking up CO2 near the ocean surface – effectively from the atmosphere – only operates downwards.

So here’s what I think is happening: there is still a net release of CO2 from the solubility pump, but less CO2 is released now that atmospheric CO2 is around 390ppm compared to when it was lower (280ppm say), because of simple equilibrium chemistry. This assumes there is plenty of carbonate about to stop, through equilibrium (2), the oceans becoming more acidic, reducing CO2 uptake by pushing equilibrium (1) to the left.

So whereas previously with CO2 at 280ppm, the solubility pump would have released (say – these are hypothetical figures) 4 GtC/yr and the biological pump taken 4GtC/yr back to the ocean depths, now, with CO2 at 390ppm, the solubility pump might be releasing only 2GtC/yr but the biological pump is still taking up 4GtC/yr. Hence the net 2GtC/yr uptake by the oceans which is in large part saving us from ourselves.

Digression: I have to say that I can’t help making the observation that the solubility pump depends on the MOC, and that there are those who think the MOC might eventually fail, driven as it is by the cooling of surface waters flowing from low to high latitudes (the IPCC discusses this in Box 5.1, p.397). This would, according to my reasoning, lead to a decrease in the release of CO2 via the solubility pump, increasing the net uptake of CO2 by the oceans, though this may be offset if the biological pump is also weakened (by a reduction in nutrient upwelling, say). I am therefore hypothesising a mechanism (a negative feedback) helping to cause interglacial warming periods to be self-limiting. I should point out, though, that this is completely the opposite of what the IPCC say (e.g. sections 7.3.4.1 and 3 to 5, p.530 and 532-3 and 7.3.5.4 on p.536). Digression over.

Let’s summarise where we are: I am suggesting that the equilibrium between CO2 in the atmosphere and in the oceans is potentially important. Even though the oceans release CO2 through this mechanism, the equilibrium chemistry means they release less as atmospheric CO2 rises.

But how much less?

I mentioned at the outset that it is not in dispute that CO2 is in equilibrium between the air and the water at the surface of the ocean. But how deep is the surface? What is the gradient in CO2 concentration away from the surface of the ocean? How much extra CO2 can be taken up (or as we have seen how much less released) in a year? Is the mechanism saturated at 2GtC/year as I assumed when I reported on my home-made carbon-cycle model?

It’s when we try to answer these questions that the IPCC Science report becomes – how shall I put it? – a little disappointing.

We turn now to Chapter 7: Couplings Between Changes in the Climate System and Biogeochemistry. In section 7.3.4.1 (p.528) we “learn” that: “Equilibration of surface ocean and atmosphere occurs on a time scale of roughly one year.” My school headmaster would have a fit! This sentence is indeed content-free. There is no definition of what is meant by “surface ocean”. Is it 1mm, 1m or 100m? Until we can answer this question we are unable to quantify the effect of the “solubility pump”.

Back to chapter 5. Section 5.4: Ocean Biogeochemical Changes includes some interesting diagrams (p.405) showing how “anthropogenic carbon” is dispersed in the oceans. These show that carbon levels are most elevated, compared to pre-industrial levels, in the top 200m or so of the oceans – “more than half of the anthropogenic carbon can be found in the upper 400m” (p.404) – and in the North Atlantic.

The trouble is, we’re no nearer answering the question as to how long we can consider it takes to renew the active layer of the oceans that exchanges CO2 with the atmosphere.

Let’s try another tack. Let’s say (generously) that the layer is 100m, on average, based on inspection of CO2 diffusion diagrams in the IPCC report. Let’s say it takes 1000 years for the oceans to completely turn over – a figure noted a few times by the IPCC. If the oceans are 5000m deep (on average) as shown in the IPCC figures, then the 100m “surface layer” is renewed every 50th (100/5000) of 1000 years, that is every 20 years.

Now we can try to answer the question posed at the start:

“If we reduce the level of CO2 in the atmosphere from its present 390ppm or an even higher level in future, will the oceans release CO2 they are currently absorbing (about 2GtC/year)? And, if so, over what timescale?”

The answer depends on the timescale we are looking at:

1. If we reduced the level of CO2 in the atmosphere overnight (more realistically by say 1ppm from one year to the next), then the surface layers of the ocean will release some carbon as it re-equilibrates with the atmosphere.

2. But if, more realistically, we reduce the level of atmospheric CO2 from one 20 year period to the next, we can consider the outcome as follows:
- in both 20 year periods the ocean will outgas the same amount of CO2 from the deep;
- in the first period the ocean will carry away more carbon (or release a little less) than in the second period.
There is no correlation between what happens in the second period and in the first.

3. After a millennium or so, the ocean might release more carbon because of the extra carbon it is absorbing now. On the other hand, more carbon may simply end up in sediments.

Conclusion: The oceans will not release a significant proportion of the anthropogenic carbon they have absorbed since industrialisation if we reduce the level in the atmosphere back to 280ppm over a century or two.

“Equilibrium” and “flow” models of oceanic carbon uptake are relevant over different timescales. The flow model is applicable to decades and centuries, the equilibrium model to years and (possibly) millennia.

I believe it is inaccurate to say, as David MacKay does, that:

“If fossil-fuel burning were reduced to zero in the 2050s, the 2Gt[/yr] flow from atmosphere to ocean would also reduce significantly.”

The increase in annual oceanic CO2 uptake due to the difference between CO2 levels in the atmosphere and the ocean is partly due to the difference between CO2 levels now and when the current surface waters were last exposed to the atmosphere, that is, the difference between 390ppm and 280ppm approx. and partly due to the difference between the CO2 level compared to the previous year – about 2ppm. If (as I’ve assumed) 1/20th of the surface waters are renewed each year, we should allow 1/20th of (390-280)ppm, that is 5.5ppm as the comparable CO2 concentration difference. 5.5 is several times 2, so the dominant cause of net oceanic CO2 uptake at present is the renewal of oceanic surface waters, not annual increases in atmospheric levels of CO2.

In other words, when Professor MacKay goes on to say:

“Much of the 500Gt we put into the atmosphere would only gradually drift into the oceans over the next few thousand years, as the surface waters roll down and are replaced by new water from the deep.”

he is correct – this process is going on. But, I suggest, it accounts for at least 75% of the 2GtC/yr of our CO2 pollution that the oceans are helpfully soaking up for us.

And if we were to reduce atmospheric CO2 levels by say 1ppm/year (e.g. by ceasing fossil-fuel burning and enacting a programme of worldwide reforestation), oceanic surface re-equilibration would reduce the annual decrease by only about 10%, and with atmospheric CO2 at its current level, and all else being equal (unfortunately it probably won’t be), the solubility pump performance attributable to oceanic surface water turnover will continue to remove around 1.5GtC/year (about another 0.75ppm).

To go on, reducing atmospheric CO2 concentrations at a rate of 1.65ppm (based on the above figures), reducing to 1ppm as we approach the pre-industrial equilibrium, would allow us to return from 450ppm to 280ppm in around 170/1.325 [(1.65+1)/2] or around 130 years.

[Though, as I said, all else is not equal and positive feedbacks due to warming of the oceans and decreased albedo because of loss of ice-cover, etc. will most likely increase this timescale significantly.  On the other hand, if we do it before the deep ocean has warmed, we might just save the planet!].

Save the forests, save the world, part 2

There must be something in the air in the spring, because it seems to be the time of year when I gain the energy to review a bit of GW science. It is almost exactly a year ago that I wrote briefly about how difficult it is going to be to prevent dangerous climate change (CO2 > 450ppm) if we don’t increase the amount of carbon stored in the terrestrial biosphere (shorthand: “forests”).

I’m in the process of preparing a presentation provisionally titled “Save the Forests: Fixing Global Warming for Dummies”. So I suppose it is serendipitous that my New Scientist magazine (dated 4th April 2009) fell open a couple of hours ago at a Fred Pearce article titled “Keeping the planet’s heart pumping“. I say I “suppose” it is serendipitous, because the article presages some of the ideas I was going to include in my presentation. I guess the reinforcement of my point by the publication of this article outweighs the reduction in its originality.

I’ve started to get a little ratty when anyone suggests that reforestation may be an ineffective policy. The problem is that many people realise that carbon offsetting is a sham. But the principle that we should preserve and increase the area of natural forest and preserve its integrity is absolutely correct. Right policy, wrong financial instrument (and in the case of monoculture plantations, poor execution). I intend to go into this point in more detail, and even have a title for the blog post (I’m telling you now in case I never get round to this one): “Don’t throw the forest out with the trees!”. Play on words is for children. Real men play on idioms. And eat quips!

Fred reports on the research of Victor Gorshkov and Anastassia Makarieva of the St Petersburg Nuclear Physics Institute. See here for a precis.

Gorshkov and Makarieva point out that forests generate rising air (low pressure) not just because they are dark (absorbing heat, expanding air, making it less dense and causing it to rise) but also because of what they call the “biotic pump”. That is, the trees pump moisture into the air (cooling themselves) which condenses at higher altitude. When the resulting water drops fall through the air column (my interpretation) – even to the ground as rain – the airmass becomes less dense and rises. Condensation not only reduces volume, but also releases heat, again causing airmasses to expand and rise. Rising air draws up air below it and other air rushes in from the sides and even from above. This process happens on (within reason) all scales of airmass. The effect can be clearly seen in billowing cumulus clouds. The early part of “A Cloudspotter’s Guide” describes the experience of a parachutist in a storm cloud, alternately falling and being carried up in rising pockets of air within the cloud. I don’t see how this could be explained without something like the “biotic pump”.

What really strikes me about the article, though, is that NS reports that Makarieva claims that:

“Nobody has looked at the pressure drop caused by water vapour turning to water.”

And the article – written, remember, by Fred Pearce, who has been reporting environmental issues and GW in particular for decades – goes on to note that:

“…because forest models do not include the biotic pump, it is impossible to say what wiping the Amazon off the map would mean for rainfall worldwide.”

I’ve recently been wondering whether our understanding of the climate is quantitatively strong, but qualitatively weak. Too much reliance on those computer models – remember, it’s garbage in, garbage out.

Now, the climate and weather models should be foolproof because they are held to rely on the laws of physics. But if they fail to capture accurately the process of lowering of air pressure due to the condensation of water vapour they could, I suppose, be systematically in error.

Even if this mechanism is implicit in the models, and it’s just the humans who fail to recognise it (quite feasible if the models correctly implement the laws of physics), they definitely fail (because they don’t implement feedbacks from climate to vegetation) to capture the positive feedback that causes forests to spread across continents. That is:
1. Moist forests create low pressure air masses (the rising air may directly result in rainfall over the forest and surrounding areas, in particular inland);
2. Drawing in moist air from the ocean (hence the importance of coastal forests emphasised by Gorshkov and Makarieva);
3. Creating airflow (at least seasonally) from the coast;
4. Providing rainfall to maintain and increase the area of the forest.

So, once established, a rainforest is self-sustaining, and indeed will tend to grow until it fills the continent at least over a latitudinal band or some other process or natural obstacle (e.g. mountain range) keeps it in check. Deforestation creates the reverse feedback. Once a tipping point is reached, the drying-out of a forest may become unstoppable.

I find it hard to believe that Gorshkov and Makarieva’s idea is new. Indeed, some commenters on the NS article note antecedents, notably something called the Permaculture movement, a 1970s idea of Bill Mollison and David Holmgren, though the “biotic pump” doesn’t seem at first glance to be central to the Permaculture philosophy. But NS also reports “that current theory doesn’t explain clearly how the lowlands in continental interiors maintain wet climates.”

I’m rather puzzled, since I’d always assumed that this mechanism explained cloud formation, storms, hurricanes, monsoons and why there is no forest in North Africa and air pressure there is predominantly high. I thought the problem was communication, or rather the lack of it, by the scientists. If Fred Pearce’s article can be taken at face value, it seems that the problem may instead be one of understanding, or rather the lack of it.

Global Warming and the Nature of Science, or, The Ofcom has Spoken!

Yes, finally the Ofcom has spoken. Not very loudly, it seems. It’s really just a rap on the knuckles for “The Great Global Warming Swindle”, largely because:

“…whilst Ofcom is required by the 2003 Act to set standards to ensure that news programmes are reported with ‘due accuracy’ there is no such requirement for other types of programming, including factual programmes of this type.”

Unbelievable. What planet are they (or rather the legislators responsible for this insanity) on? One that is going to get a hell of a lot warmer, it seems, if we can’t work out how to make rational, science-based decisions. How can the category “factual programmes” even exist without “standards [of] due accuracy”? Has anyone thought about what the word “factual” actually means??

Remind me if I don’t return to this argument later on, but to state the thesis briefly, in complex domains, problems – whether big ones (like GW itself), or small ones, like “Swindle” – almost always have many causes. Dealing just with the immediate cause may be futile. In the case of “Swindle” it may be most effective putting effort into changing the rules of the media game, rather than engaging in trench warfare. Because, if the ultimate arbiter of truth is not factual accuracy then we just end up with a popularity contest. Hey, why not incorporate audience votes in science programmes? Phone-in to vote for your favourite theory of gravity!

Luckily, in the case of “The Great Global Warming Swindle”, the programme:

“…broke rules on impartiality and misrepresented the views of the government’s former chief scientist…” even though it “was ‘on balance’ cleared of ‘materially misleading the audience so as to cause harm or offence’”. (Quotes from the Guardian’s news story on the findings).

But what if they hadn’t broken any rules?

And at least in this case George Monbiot got his retaliation in first, with a comment (and CiF) piece in today’s Guardian, as well as an essay in G2. [Illustrated with the usual photographs, incidentally: someone should devise a market instrument for investors in pictures of power stations, melting ice and - my personal tip - pictures of solar panels and photogenic children in Africa. Oh, sorry, it slipped my mind for the minute that markets are in the dog-house right now.]

George does an excellent job, as usual, in his forensic G2 piece (though there’s a touch of conspiracy theory in his analysis of Channel 4) but in the very last column it all falls to pieces. [See yesterday's post for my views on conspiracy theories and the need to read the detail - in this case right to the end - to avoid Taleb's randomness illusion]. Even so, I urge you to read George’s dissection of “Swindle”: you may be surprised. I recollect that I had moreorless bought into the idea (which Monbiot debunks) that Thatcher’s espousal of GW science was partly due to her search for weapons to use against the UK’s coal-mining industry.

Remember, though, that, as well as the particular pathology – in this case the way “Swindle” was given a platform – we also need to look at the underlying causes.

This is where a major problem lies in George’s piece:

“[Channel 4] says [its scheduling of "Swindle" and other programmes] ‘is against the background of the IPCC [Intergovernmental Panel on Climate Change] stating that there is a 90% certainty that the causes of global warming are man-made, it follows that there is a 10% uncertainty. Yet this 10% uncertainty receives a disproportionately small amount of airtime.’ I [George continues] find this argument extraordinary. A 90% level of confidence does not mean that 10% of the evidence suggests that an effect is not occurring — in fact, there is no reliable evidence showing that man-made global warming is not taking place. It is expressed in this way because there is no absolute certainty in science. The ‘very high confidence’ the IPCC expresses in the global warming thesis is the strongest statement any reputable scientist would make about his area of study. It is legitimate and right to stress that there can be no absolute certainty about global warming.” [my italics stress].

90% is not in fact a very high probability when we are discussing scientific findings. In my opinion, it would be more than justified to say that we’re “virtually certain” that “man-made global warming is [...] taking place”, and by virtually certain I mean at least 99%. A 99.9% claim would be perfectly reasonable. So why does the IPCC not say this? Saying 90% gives the green light to people like Martin Durkin (the maker of “Swindle”).

I’ve just done a bit of weight-training and consulted the IPCC’s latest massive report (The Fourth Assessment Report, or “AR4″). If we look at Table 1 on pages 120-1 of the Scientific Basis (there are 3 parts to the overall report) we see that, although the IPCC is happy to use the words “virtually certain”, it only does this when a result “can be estimated probabilistically”. For example, a particular set of data may have a definable probability of indicating a trend.

[Note that our ability to calculate such statistics requires us to make assumptions about randomness - i.e. a bell-shaped curve or Gaussian distribution. This implies that we have a theory about the causes of variation in the data in the first place! For example, if we say we're 99% certain that the glaciers are melting this finding must have been calculated against a null hypothesis that changes in glacier volume are subject to random fluctuations. This may not be true. There could be reasons we are entirely unaware of for all the world's glaciers to either melt or grow at the same time (on top of reasons for correlation between glaciers in the same region which have presumably already been taken into account). Such "unknown unknown" correlation would invalidate the null hypothesis and hence the 99% "virtual certainty". If we're 99% sure what the data tells us, then surely we must be at least 99% sure of our theoretical understanding. I'm sure Taleb would agree with me! It's entirely illogical to have more faith in data-driven findings than in any aspect of the underlying theory explaining them! But this is not my main point today.].

No, what baffles me is why the IPCC restricts itself to a maximum of “very high”, that is, 90%, confidence when it comes to “scientific understanding”.

Politics may have played a part in the IPCC process. Some governments may have lobbied for 90% rather than 99% as the maximum possible confidence. But let’s put that to one side. I want to argue that a critical factor is widespread misunderstanding of the scientific process.

Practising scientists often cite the philosopher Karl Popper. They understand that theories can be “falsified”. Some may even have heard of Thomas Kuhn and appreciate that such “falsification” takes place in “scientific revolutions”.

But what happens in such revolutions? In fact, scientific theories are superseded rather than “falsified”. Let’s consider one or two examples very briefly. When Einstein “overturned” Newton’s theory of gravity he didn’t demonstrate that Newton’s equations were wrong. Rather, he showed the limitations of Newton’s theory. Crucial experiments (where the difference was large enough to be measurable) showed that Einstein’s theory made more accurate predictions than Newton’s. In effect, Einstein incorporated Newton’s findings in his own theory of gravity. Albert never said: “Silly old Isaac’s made a mistake there.”

A case closer to the topic in question is the oft-cited theory of the 1970s that we were about to enter a new ice age. Now this theory hasn’t gone away. The Earth would be cooling (though there is debate as to when the next ice age would occur), if it weren’t for global warming. The current theory of global warming includes the ice age cycle as well as all other prior theories for the variation in the Earth’s climate, such as the effect of volcanic eruptions. Quantitative statements about man-made global warming take into account numerous other causes of climate variation.

Now, it’s possible to imagine reasons why the Earth might not warm as much as projected. For example, the solar system could enter some as yet undetected dust cloud. But any quantitative estimates of the effect of such a dust cloud would have to include the effects of man-made GW. And if the planet cooled dramatically as we entered the dust cloud we’d still have to worry about its temperature rising beyond today’s level because of our greenhouse gas emissions when we came out again. Just the same as, if we solve the problem of global warming and get the climate back to something resembling its pre-industrial state, we will – over the longer timescale of millennia rather than decades – need to take account of the Earth’s ice age cycle which was apparently of such concern in the 1970s.

There are examples in science of theories that are (or could be) flat wrong. But these are theories for which there is no evidence or for which the evidence has been misinterpreted due to problems inherent in the data-gathering process. This is most likely when observations are difficult, such as at the frontiers of physics. For example, the infamous string theory could be wrong because it makes no new predictions.

Any replacement for a theory with lots of firm data, such as global warming, would have to provide explanations for all that data. Clearly this is easiest if the new theory explains the old theory as a special case, rather than by invalidating it entirely.  In the history of science theories are almost always shown to be incomplete rather than “wrong”.  In my opinion, Imre Lakatos understands this process most clearly, even though this aspect of his ideas is rarely stressed.

The probability of the theory of global warming actually being wrong is therefore vanishingly small.  Our level of certainty is, in fact, far more than 99%.

So one of the underlying causes of programmes like “Swindle” is that even the scientific establishment is unclear as to the nature of its theory. Even if there are unknown unknowns and the planet does not end up warming over the 21st century and beyond this would not in itself invalidate the theory of global warming.

Ocean CO2 uptake update

The IPCC AR4 Scientific Basis report is a real goldmine of information, even if it isn’t perfect, as I recently pointed out.

As I discussed in a previous post, an idea I later developed a little, policies to address global warming must rely on an understanding of how natural systems will respond to the increase in atmospheric CO2.  Will the oceans keep absorbing a couple of GtC worth of CO2 each year (as estimated since 1990 – AR4, p.26, as referenced previously) or more (as implicitly assumed by many) or less?  And will land ecosystems manage to take up more or less carbon than in the past?  Especially if we continue to reduce the area of ecosystems able to do this – since agricultural land clearly does not progressively store carbon.

I’ve been looking at a critical section in AR4 on ocean uptake of CO2.  This is 5.4.2.2 on p.403-5 (though the main section on the carbon cycle is 7.3, p.511 ff).  I quote:

“The fraction of net CO2 emissions taken up by the ocean (…) was possibly lower during 1980 to 2005 (37% +/- 7% [that is, 118 +/- 19 of 283 +/- 19GtC of emissions]) compared to 1750 to 1994 (42% +/- 7% [that is, 53 +/- 9 of 143 +/- 10 GtC of emissions)...  The decrease in oceanic uptake fraction would be consistent with the understanding that the ocean CO2 sink is limited by the transport rate of anthropogenic carbon from the surface to the deep ocean, and also with the nonlinearity in carbon chemistry that reduces the CO2 uptake capacity of water as its CO2 concentration increases".  (my inserts in [ ]’s – based on Table 5.1, p.404).

And we also have to worry about “a decrease in CO2 uptake capacity” as the ocean warms.

On the other hand section 7.3.2.2.5 (p.521) notes that:

“The ocean uptake has increased by 22% between the 1980s and 1990s, but the fraction of emssions (fossil plus land use) taken up by the ocean has remained constant.”

though of course the ocean “knows” nothing about emissions – all it can possibly be affected by is the level of CO2 in the atmosphere.

We really need to get a handle on what the oceans are going to do in the future since it makes such a huge difference to the level of carbon emissions we can get away with.  It’ll be the first section I turn to in AR5.  As AR5 is due around 2012 (I suppose), maybe we should have a think about where we focus scientific resources now…

Some thoughts on sorts of science sources

OK, it’s not quite up there in the tongue-twister stakes as my best creation: “We’re wearing weird red wellies”. Try saying that quickly after a few pints!

About 10 days ago my Sunday morning was spoilt by the sight of the really rather scary, formerly reassuringly plump (maybe he’s become a vegan) ex-Chancellor of the UK Exchequer Nigel Lawson on Andrew Marr’s weekly political couch-fest. Why had he crawled out of his coffin? Well, to plug his book, of course. It is indeed one of the world’s great mysteries why the BBC is so careful not to mention products by name (to utter “Coca-Cola” without permission would be blasphemous in Beebland), yet so shamelessly allows so many people to promote their products. The occasion of Ryanair’s financial results, for example, seem to provide a free 1 minute advertising slot for Michael O’Leary. I’m surprised he doesn’t move to quarterly reporting.

Presumably, if you have good PR help, a public profile or the right connections, you can get as much time to plug a book on the BBC as you want, because, blow me down if I didn’t hear Count Lawson again on the radio a few days ago, on some type of pick of the week show on Radio 4. At least he was being grilled this time – listen and learn, Andrew Marr. But surely there should be some criteria for whether a book is worthy of BBC airtime? E.g. positive reviews by experts in the field?? Tricky, but how could anything be worse than the apparent old school tie basis of selection we have today?

Get this, Lawson’s book was turned down, he said on TV, by 7 UK publishers, but he has a “good agent” who managed to get it published overseas. Makes you wonder if it’s really worthy of promotion in the mainstream media, don’t it? I was therefore going to put TV bottom of the list of reliable science sources.

But then I read the Times’ review of Nigel Lawson’s contribution to the debate. Astonishingly, the reviewer, an Alexander Cockburn, chides Lawson for accepting the anthropogenesis of global warming! In fact, Cockburn’s review leaves me with the impression that Lawson may be saying something useful. A view dispelled by a somewhat more comprehensive (family connections?) review in the Spectator. Lawson, it seems (before I rush out to buy his work), doesn’t deny global warming, he merely downplays it, in order to argue against doing anything much at all (I’ll be more specific when I’ve read the book – which I will likely do, because, unfortunately, publicity grants de facto credibility, requiring a response). Insidious.

So, let’s award 0/10 for the informativeness of the mainstream print media (Times) and 1/10 for the broadcasters (BBC), who at least attempt to be impartial. Let’s give general current affairs (Spectator) 2/10. And let’s give published works 3/10. At least the publishers tried to stop Lawson, if to no avail; perhaps his memory of the Spycatcher affair stood him in good stead.

Now, compare this piece by Gwyn Prins from the Guardian’s Commentisfree site. For all I know, Gwyn Prins makes similar points about the ineffectiveness and counterproductivity of existing policy responses to GW as does Nigel Lawson, but at least he does not base his argument on false premises. In fact, I was interested enough to download Prins’ paper “The Wrong Trousers: Radically Rethinking Climate Policy” (written jointly with Steve Rayner). Prins & Rayner argue that GW is serious and urgent, but the Kyoto mechanism ineffective. They therefore advocate “enlightened self-interest” (ouch!). Still, a step forward from the “downplaying” strategy of a failed UK Chancellor (the Lawson Boom was followed by an inflationary bust – anyone else notice a pattern starting to develop? – let’s ignore problems until it’s too late, shall we, Nigel?).

So, let’s say 4/10 for op-ed (as the Yanks call it), and 5/10 for online publications.

But what I want to draw attention to are the exchanges in the comments on Prins’ piece. First, let’s backtrack a little. Lawson (like Nigel Calder) apparently claims the Earth is no longer warming, since annual average global temperatures have not returned to their 1998 record level. Now, as we all know, temperatures are bound to fluctuate from year to year about a long-term warming trend. All the scatter of annual mean temperatures tells us is that the annual variability of transfer of heat from the surface of the oceans exceeds the amount of heat gained by the planet each year. But, if the oceans were to cease gaining heat, without an overt cooling cause (such as a volcano) then GW theory would be in trouble – it would imply (since the oceans are so large and important in this context) that the Earth is no longer cooler than it needs to be for it to be in energy balance. Unfortunately, this is exactly what the IPCC’s 4AR implies. Yes, Fig. 5.1 on page 390 shows the oceans cooling over the last few years. Does the IPCC really explain this anomaly? No. It is “bottom-up” science – based more on observation than theory-driven.

So, say 8/10 to the IPCC. Maybe they need to put a bit more effort into the coherence of the whole package, and resolve or at least discuss these sorts of problems before rushing their 900 pages to CUP.

Anyway, I was mulling over this problemette when I noticed it discussed by PacificGatePost and deconvoluter in the comments on Prins’ Guardian piece. Phew! It turns out there was a problem with the measurements. deconvoluter refers to a Realclimate piece that gives chapter and verse.

So let’s give blogs (Commentisfree) 6/10 and specialist blogs (Realclimate) 9/10. Now we’re getting somewhere.

But there’s more. The Prins piece was in response to an article in Nature, by Roger Pielke et al arguing that the IPCC scenarios (actually I consider these unrealistic and irrelevant, but let’s put that to one side for now) are over-optimistic. The scenarios – shock!, horror! – assume some carbon “savings” will occur without specific policy to reduce emissions (um, anyone seen the price of oil today?). Now, even though the Pielke article and a Nature editorial are accessible on the internet, much of their content is subscriber only, so it does rather perturb me that so much debate (rather than actual science) is being conducted (in Scienglish) in the pages of Science and Nature. Not their fault, but what are the mainstream media doing? I believe as many people as possible need to develop their own understanding of the science and the issues. “Trust me, I’m a scientist” is only going to get us so far.

So, 7/10 in our informativeness competition to science magazines.

I gave the Realclimate site 9/10 – for trying to bridge the gap between the scientific world and normal people – but they’re not the real winner. 10/10, and the top prize goes to – yes, you’ve guessed it! – the internet itself which has made all this possible. Without it, I suggest the GW debate would be years behind even where it is now.

Confused by carbonates

Somebody please help!

I’m having great difficulty reconciling two things that I’ve read:

1. There is a carbonate “saturation horizon” at a specific depth in the oceans. Below this depth carbonates dissolve because of the high pressure. (The “saturation horizon” depth is also less where it is colder).

What’s going on is that there is a chemical equilibrium:

Ca²⁺ + HCO₃^- <–> CaCO₃ + H⁺

Adding CO₂ to the oceans – a result of adding it to the atmosphere – makes the problem worse. It acidifies the water, driving this equilibrium to the left, in effect dissolving carbonates, such as the shells of marine organisms. (The big danger is that this process will raise the carbonate saturate horizon to the surface in the polar oceans, leading to a sudden increase in acidity in the absence of the carbonate buffer, which will reduce the ability of the ocean to absorb carbon dioxide, as well as prevent organisms from making carbonate exoskeletons).

2. There is a plan afoot to dump carbon dioxide underground, in gas and oil fields and in saline aquifers (“carbon capture and sequestration” or CCS). There was an interesting article on this by Fred Pearce in last week’s New Scientist (subscriber’s only, I’m afraid). Now, said Fred, “… the chemical reactions might gradually convert the CO₂ into carbonate rock…”. But Fred also mentions the Frio project when the CO₂ “…acidified the brine allowing it to dissolve metal-oxide minerals in the rock…” which “…might eventually create tunnels in the cap rock through which CO₂ might escape”.

My question is, why wouldn’t the CO₂ in general form an acid (I assume there’s plenty of water about) and dissolve the rock? In particular, how could it form carbonate rock, when, as we see in the oceans, CO₂ in solution forms an acid which dissolves carbonate rock – more effectively at pressure? Surely this could only happen once all the CO₂ had been converted to some intermediate form? – since otherwise any remaining CO₂ would form acid and dissolve the carbonate. Can we therefore always rely on the sequestered CO₂ staying where it’s put?

Of course, I’ve consulted “Sustainable Fossil Fuels” by Mark Jaccard who notes that: “… the CO₂ may eventually either dissolve into the aquifer water (hydrodynamic trapping) or precipitate as a solid carbonate mineral by reacting with the surrounding rock (mineral trapping).” OK…

When I look at the IPCC Special Report on CCS, I see they go into all this in more detail, of course. I guess I’m happy with the chemistry – on its own – and I’m happy with the mechanics – permeability, cap-rocks etc. – on its own. It’s the interaction between the chemistry and the physics of the rock formations that bothers me. The IPCC notes that:

“Reaction of the dissolved CO₂ with minerals can be rapid (days) in the case of some carbonate minerals…” (section 5.2.2.3, p.209).

and that:

“Reaction of the CO₂ with formation water and rocks may result in reaction products that affect the porosity of the rock and the flow of solution through the pores. This possibility has not, however, been observed experimentally and its possible effects cannot be quantified.” (section 5.2.2, p.210).

Perhaps we’d better quantify it before we get our hopes for CCS up too high. What was the Frio project if it wasn’t an experiment? Puzzlingly, the IPCC report only mentions the Frio project as 1600tCO₂ “pilot” (Table 5.1, p.201) and one of several that:

“…demonstrate that subsurface injection of CO₂ is not for the distant future, but is being implemented now for environmental and/or commercial reasons.” (section 5.1.2, p.204).

What is this? A scientific evaluation or a sales brochure?

In general, is the approach being adopted to evaluating CCS one of identifying all the problems so that we can avoid them when we roll-out the technology, or one of trying to show that there are no problems, so that we can carry on planning to burn fossil-fuels (and building coal-fired power-stations) with as few qualms as possible?

One other annoying fact: liquid CO₂ is less dense than water, so if there is enough pressure and the reservoir is not sealed, it’s the CO₂ that will leak out, not the H₂O.

Any comments that might help allay my fears are more than welcome.

Save the forests, save the world

It’s amazing what you can do with Excel. I thought I’d have another quick look before breakfast at my 450ppm stabilisation scenario (hey, kids, you can play this game at home!).

Here’s what I was referring to yesterday (all numbers approximate):

To some extent I’m being optimistic. The 4AR mostly refers to scenarios that we would not now countenance as we’ve come out of denial over the last few years (I suggest they review their approach for the next report, 5AR). But if we look at the Scientific Basis, page 791 (I kid you not – strictly I should also be using a 3 line reference to the chapter – 10, section 4.1 as it happens), we see some discussion of stabilisation scenarios. The IPCC suggest a higher peak in fossil fuel emissions (about 12GtC/yr compared to the 9GtC I’ve shown), but with a steeper reduction. Their scenario allows 596GtC over the 21st century, whereas I came up with 566GtC. But the key point is that the IPCC also calculate some scenarios with positive carbon cycle feedbacks – that is, when we listen to the science and assume that warming will cause ecosystems to release carbon, or in actual fact merely to take it up more slowly than at present – and in these scenarios taking account of carbon cycle feedbacks we are “allowed” to emit 105 to 300GtC less. That is, even an aggressive scenario to stabilise CO2 at 450ppm relies on a get-out-of-jail-free card.

A more rigorous analysis – I would next separate out land use change (deforestation) from the fertilisation effect altogether – is unlikely to give a different conclusion, because the sanity check (total fossil fuel emissions) succeeds. This simple spreadsheet, adding together the main parts of the the carbon cycle is compatible with the sophisticated models cited by the IPCC. And it shows that, at first approximation (as the scientists say) we have to manage both components we can influence – fossil fuel burning and land uptake of CO2.

The critical point is that, if we want to save the planet, we’ve got to make sure that land carbon uptake over the next century – by natural ecosystems, such as forests, wetland and grassland – increases, not decreases. And if we plough them up and plant even more crops, then they will release carbon for a while and then store a roughly constant amount.

This is the macro reason why promoting biofuels is a really, really bad idea. In fact, it’s difficult to think of a worse policy response to the threat of global warming.