Bombing out: Christopher Monckton goes in to bat for two professors at WUWT

Update - click here for a follow up article demolishing disinformation from Murry Salby.

This is still "utter nutter" week at WUWT.  Today Anthony Watts has posted an article by the potty peer from the UK, Christopher Monckton.  Christopher writes in his usual "schoolboy" fashion, using words such as "schoolboys at the University of Queensland", probably referring to John Cook, who runs the award-winning climate website, SkepticalScience.com.

Christopher is resurrecting a couple of old and utterly silly denier memes arguing that the CO₂ we emit somehow disappears by magic and goes goodness knows where.  It's a very mixed up article altogether.

One of the main difficulties I had with the WUWT article is that Christopher keeps referring to other articles and comments but doesn't provide any links to what he is talking about.  I guess he has the WUWT target audience summed up well.  He'd have assumed that no fake sceptic would ever follow a link - that would be heresy to the fake sceptic creed.  They might be mistaken for a real sceptic.  However - in this case Christopher would have assumed wrongly.  His article generated much discussion and got lots of people doing lots of sums.  (Archived here)

Two wrongs don't make a right

As far as I can tell, Christopher Monckton is trying to make a whole out of two disparate denier memes.  One is propagated by an older retired professor Gösta Pettersson.  The other is some convoluted hypothesis or two or three of a younger retired ex-professor Murry Salby.  The two hypotheses don't make any sense on their own.  Try to put them together and you end up with a helluva mess.  But that's what Christopher Monckton is proposing.

The short version is as follows:

Gösta Pettersson

AFAIK, Gösta tries to claim that all the extra CO₂ will only stay in the air for a very short time.  He bases this on flawed deductions from analysis of  ¹⁴CO₂. (Note: In the comments, Lars Karlsson says that Gösta Pettersson has acknowledged he made an error in his analysis.)

Following the bomb testing of the 1950s and 60s, analysis has been done to work out how quickly CO₂ circulates between the atmosphere and the surface.  You can think of it as how long it takes for individual molecules of atmospheric carbon dioxide to disperse through the atmosphere and surface.  This time is quite short.  A matter of a few years.  By contrast, if we stopped adding any CO₂ to the air altogether, it would take around 300 years to remove something like 65% to 80% of the extra we've added in the last 150 years or so, and hundreds of thousands of years to completely remove all the carbon we've added to the air.

Murry Salby

I think, based on what Christopher Monckton has written, that Murry has things completely back to front.  I believe he tries to claim that rising temperature has caused CO₂ to outgas from the ocean and that's why atmospheric CO₂ is rising.  He reckons it's not from burning fossil fuels.

I gather that Murry doesn't have any answer to what happens to all the waste CO₂ we've been tossing into the air.  Nor does he seem to understand that the oceans are getting more acidic - because they are absorbing more CO2 than they are outgassing.

If carbon dioxide is not going into the ocean (it is), in fact if as Murry apparently maintains, CO₂ was coming out of the ocean (it's not), and since biomass on earth hasn't increased that much, then where is all that fossil fuel CO₂  ending up?

That's it in a nutshell.  Murry Salby and Gösta Pettersson both have it wrong.  Christopher Monckton is trying to argue that "two wrongs make a right".

There's more - if you're game :)

Researching this article I found myself delving into all sorts of interesting areas and learnt a heap of new stuff.  This article evolved into a longer post reflecting my meandering travels.  It's probably the longest article I've written and I won't blame anyone for not reading it.  If you've landed on the home page and you're not deterred by my sloppiness in not cutting back to bare bones, you can click here to read more.

From the IPCC - we have messed with the carbon cycle

Before I go into the detail of Monckton's silly ideas, here is the relevant section from page TS-58 of the latest IPCC report (my bold italics):

The natural carbon cycle has been perturbed since the beginning of the Industrial Revolution (circa 1750) by the anthropogenic release of CO2 to the atmosphere, virtually all from fossil fuel combustion and land use change, with a small contribution from cement production. Fossil fuel burning is a process related to energy production. Fossil fuel carbon comes from geological deposits of coal, oil and gas that were buried in the Earth crust for millions of years. Land use change CO2 emissions are related to the conversion of natural ecosystems into managed ecosystems for food, feed and timber production with CO2 being emitted from the burning of plant material or from the decomposition of dead plants and soil organic carbon. For instance when a forest is cleared, the plant material may be released to the atmosphere quickly through burning or over many years as the dead biomass and soil carbon decay on their own. {6.1, 6.3; Table 6.1}

The human caused excess of CO2 in the atmosphere is partly removed from the atmosphere by carbon sinks in land ecosystems and in the ocean, currently leaving about 45% of the CO2 emissions in the atmosphere.

Natural carbon sinks are due to physical, biological and chemical processes acting on different time scales.

An excess of atmospheric CO2 supports photosynthetic CO2 fixation by plants that is stored as plant biomass or in the soil. The residence times of stored carbon on land depends on the compartments (plant / soil) and composition of the organic carbon, with time horizons varying from days to centuries. The increased storage in terrestrial ecosystems not affected by land use change is likely to be caused by enhanced photosynthesis at higher CO2 levels and N deposition, and changes in climate favoring carbon sinks such as longer growing seasons in mid-to-high latitudes. {6.3, 6.3.1}

The uptake of anthropogenic CO2 by the ocean is primarily a response to increasing CO2 in the atmosphere. Excess atmospheric CO2 absorbed by the surface ocean or transported to the ocean through aquatic systems (e.g., rivers, ground waters) gets buried in coastal sediments or transported to deep waters where it is stored for decades to centuries. The deep ocean carbon can dissolve ocean carbonate sediments to store excess CO2 on time scales of centuries to millennia. Within a thousand years, the remaining atmospheric fraction of the CO2 emissions will be between 15 and 40%, depending on the amount of carbon released (TFE.7, Figure 1).

On geological time scales of 10,000 years or longer, additional CO2 is removed very slowly from the atmosphere by rock weathering, pulling the remaining atmospheric CO2 fraction down to 10 to 25% after 10,000 years.

TFE.7, Figure 1: Percentage of initial atmospheric CO2 perturbation remaining in the atmosphere in response to an idealized instantaneous CO2 emission pulse in year 0 as calculated by a range of coupled climate-carbon cycle models. Multi-model mean (blue line) and the uncertainty interval (±2 standard deviations, shading) simulated during 100 years (left panel) and 1,000 years (right panel) following the instantaneous emission pulse of 100 PgC.
Source: IPCC AR5 WG1 page TS-117. 

The IPCC report states on page TS-16 that up to 2011, we'd released about 560 PgC to the atmosphere, of which about 240 PgC has accumulated in the air - with the rest making the oceans more acidic as well as going into plants.  And in the first decade of this century, atmospheric carbon has grown by about 4 PgC a year.  That means any "pulse" (see chart above) falls a fair bit short of 5000 PgC.  However I don't think that's the whole story.  There are feedbacks that may well factor in over time (carbon from permafrost etc).

From what I've read, the bottom line is that if we were to stop emitting carbon dioxide altogether (which is unlikely), there would be a fairly rapid drop in atmospheric CO₂ in the first three centuries.  However a proportion of what we had already thrown into the air would stay there affecting the climate of earth for tens of thousands of years.  For all intents and purposes what we've done already can be considered irreversible, though the future is not unavoidable.  We can control what we do in the future.

Christopher is trying to argue that if we stop polluting the air with CO2, almost the entire amount of added CO₂ would disappear in just a few decades.  Although he later denies it, Christopher seems to be confusing the time it takes for individual molecules of carbon dioxide to move between the air and the surface, with the time it would take to reduce the total amount of carbon dioxide in the air and get it back to pre-industrial levels. Assuming of course that we stopped adding it to the air - which won't happen.

Christopher has put numbers on his claims.  As you'll see below he is claiming that almost all (98.5%) of the additional carbon dioxide would be removed from the surface within a century if we were to stop adding carbon dioxide to the air.  I think he believes the oceans and plants will just swallow it all up in a geological instant.  But they can't.  It's a physical impossibility.

Wrong Number One: Bombing out

Christopher Monckton starts by posing a question:

Is the ~10-year airborne half-life of ¹⁴CO₂ demonstrated by the bomb-test curve (Fig. 1, and see Professor Gösta Pettersson’s post) the same variable as the IPCC’s residence time of 50-200 years? If so, does its value make any difference over time to the atmospheric concentration of CO₂  and hence to any consequent global warming?

Christopher didn't give any other clue as to what post by Professor Gösta Pettersson he was talking about.  No link. Nothing.  I figured out that he is probably referring to a WUWT article from a few months ago at WUWT - archived here, which I wrote about at the time.  Basically Gösta was resurrecting the old confusion surrounding the time it takes for an individual molecule of CO2 to be exchanged between the air and the surface, compared with the time it takes for the surface and air to come into equilibrium with regard to CO2.  The latter takes thousands of years when you factor in the entire carbon cycle.

Christopher posted a chart he attributed to Gösta Pettersson, which purported to show the fraction of ¹⁴CO₂ in the atmosphere over time, before and after nuclear bombs were exploded around the world.

I found a better chart from Guilderson (2012) showing the amount of ¹⁴C in the surface and the atmosphere expressed as a percentage of total carbon.  Correction: it shows the change in ¹⁴C:¹²C ratio - thanks, Lars.) The chart below shows more detail than Monckton's chart.  It includes changes in the northern and southern hemisphere as well as changes in ocean surfaces from a variety of sources. (Click the chart to enlarge it.)

Figure 1. Atmospheric and surface ocean post-1950 history of radiocarbon as measured in atmospheric CO2, tree-rings, and reconstructed from reef-building hermatypic corals. The decrease in atmospheric Δ14C is a consequence of the net isotope and carbon exchange between the atmosphere, ocean, and terrestrial biosphere. The large seasonal amplitude in the early 1960s is a reflection of stratosphere (where much of the initial ‘bomb’ 14C was deposited) – troposphere exchange. The early asymmetry between the northern and southern hemispheres is due to the convolution of hemispheric atmospheric mixing and the preponderance of atmospheric weapons tests occurring north of the equator.
Source: Guilderson (2012)

As the chart above shows, ¹⁴CO₂ increased sharply coinciding with bomb testing, reduced again fairly quickly before tapering off.  It can't go back to pre-bomb levels for a long time because ¹⁴C decays with a half-life of 5730 years.  The reason it reduced in the troposphere is because it exchanged with terrestrial and oceanic reservoirs.  What happens is just what one would expect to happen.  It doesn't take very long before ¹⁴C mixes with all the other C in the air and in the oceans and in the biosphere and in the soil.

As an aside, you can see from the above chart that it takes about a year for carbon dioxide (a well-mixed greenhouse gas) to get mixed up all around the world.

What has all this got to do with the increasing level of CO₂ in the atmosphere you ask?  Precious little at the macro level.  Each year humans continue to add billions of tonnes of CO₂ to the air.  It's a waste product from burning fossil fuels - oil and coal in particular.  About 55% of those emissions are getting absorbed by the oceans (~30%) and biosphere (~25%) and about 45% is staying in the air, slowing the rate at which long wave radiation goes out to space, and therefore heating up the earth.

Although the turnover time of atmospheric doesn't tell you anything much about the overall shift of carbon between the atmosphere and the surface, this information is extremely helpful for a number of things.

The thing is, up until all the bomb testing took place, ¹⁴C was pretty much in a state of equilibrium.  ¹⁴C gets formed naturally in the stratosphere by cosmic-derived neutrons when they collide with ¹⁴N, adding a proton and spinning off a neutron.   Very soon afterwards, ¹⁴C is oxidised to form ¹⁴CO₂.

One of the unplanned effects of the bomb tests was to provide a means of analysing the movement of carbon through the earth system by tracking ¹⁴C.   It can also be used to help confirm CO2 emissions from burning fossil fuels (fossil fuel-derived CO₂  doesn't have ¹⁴C - because fossil fuels are so old virtually all the ¹⁴C they might once have, has decayed).  (An adverse outcome of bomb testing was that it messed up carbon dating.)

Wrong Number Two: Reversing cause and effect

Christopher writes a lot of seemingly irrelevant gunk and then moves onto Murry Salby's idiotic claims:

Annual fluctuations of anthropogenic CO2 emissions are small, but those of atmospheric CO2 concentration are very much larger, from which Professor Salby infers that their major cause is not Man but Nature, via changes in temperature. For instance, Henry’s Law holds that a cooler ocean can take up more CO2....

The above doesn't make a lot of sense on first reading.  Christopher writes about "their major cause" but I don't know what he means by "their".  Is he talking about annual fluctuations of anthropogenic emissions?  Or is he talking about annual fluctuations of atmospheric CO₂ concentrations.

Let's presume it's the latter.  Annual fluctuations of CO₂ are "very much larger" than annual fluctuations of anthropogenic CO₂ emissions? I don't think they are "very much larger".  In any case, what is important is not the seasonal or interannual fluctuations of atmospheric CO2, it's the overall amount of CO2 and more particularly the rapid growth in atmospheric CO₂.  The more CO₂ increases in the air the longer it takes for energy to escape relative to the energy coming in.  Energy builds up on earth.  That's why earth is heating up.

SkepticalScience has an article pointing out the major flaws in Murry Salby's claim.  As far as I can make out, Murry's claims can be boiled down to:

• the increase in atmospheric CO2 is caused by the increase in global temperature
• the increase in global temperature is caused by ???
• CO2 emissions from burning fossil fuel aren't being added to the atmosphere
• the billions of tonnes of CO2 we're pouring into the air are disappearing - by magic???

(Salby's hypotheses seems to be dumb on the face of it and even dumber when you look into it.)

CO₂ is plant food!

Christopher states somewhere in his WUWT article that:

... Increase the CO2 concentration and the biosphere responds with an observed global increase in net plant productivity. The planet gets greener as trees and plants gobble up the plant food we emit for them.

Oh my! Back to CO₂ is plant food.

If "trees and plants" (does Christopher think that trees aren't plants?) gobbled up all the CO₂ we emitted then atmospheric CO₂ wouldn't be increasing.  The very fact that CO₂ is rising so rapidly shows that we are adding a helluva lot more CO₂ than can be absorbed by plants and the ocean.  In the short term (decades to centuries), after we stop adding more carbon dioxide to the air than can be absorbed, things will settle down some but the long term processes will take, well, much longer. Plants and soils and the oceans together will eventually outgass as much as they are absorbing for example.  For now, the surface is actually absorbing more CO2 than it is giving up to the air - and yet there is a whole heap more CO2 accumulating in the air each year.  Eventually, tens of thousands of years after we stop shovelling billions of tonnes of CO2 into the air each year, the slow part of the carbon cycle will settle to a new equilibrium. (That is, as much as the earth system is ever in equilibrium - there will always be something changing whether it's incoming radiation or whatever).

CO₂ sinking into the ocean

More from Christopher:

Similarly, if the weather gets a great deal warmer, as it briefly did during the Great el Niño of 1997/8, outgassing from the ocean will briefly double the annual net CO2 emission. But if it gets a great deal cooler, as it did in 1991/2 following the eruption of Pinatubo, net annual accumulation of CO2 in the atmosphere falls to little more than zero notwithstanding our emissions. It is possible, then, that as the world cools in response to the continuing decline in solar activity the ocean sink may take up more CO2 than we emit, even if we do not reduce our emissions.

Is it possible that earth would cool enough for the oceans to absorb more CO₂ than we emit?  The time frame for oceans in the carbon cycle is hundreds of years.  The thermohaline current takes a thousand years for a single cycle.  Christopher thinks it can happen virtually overnight!

You will also recall, no doubt, that CO2 sinking into the ocean is what is causing ocean acidification, which is a big threat to marine life.

Fact check: wild claims collide with observations and lose

How about Christopher's claim about "outgassing from the ocean" briefly doubling the net CO₂  emission in 1997-98? Or the net annual accumulation of CO₂  falling to "little more than zero" in 1991-92? Below is a chart of CO₂  as measured at Cape Grim in Tasmania.

Data Source: CSIRO

And below is a chart of the year to year change in CO₂ over the period from 1986 to now.  That is, the CO₂ in ppm in one year, minus the CO₂ in ppm in the previous year.

Data Source: CSIRO

As you can see, there was no "doubling" of net atmospheric CO₂ in 1998, the year of the super El Niño.  CO₂ did rise by 2.5 ppm in 1998, which is more than it did any other year except for this year (2013) from the look of it. But it wasn't double that of other years. (Note that this year's data only goes to September.  However looking at prior years, September is generally not too different to December.  And it gets worse - there is no super El Niño this year!)

As for Christopher's claim that Pinatubo caused a rise of "little more than zero" - he's wrong.  In no year did the net accumulation fall to near zero.  The closest it got was from 1992 to 1993.  This is thought to be affected by Pinatubo, but it still grew by 0.74 ppm.

It wasn't just Pinatobo though.  You may recall there was a global recession in the early 1990s, which resulted in a drop in CO₂ emissions.  Below is a chart of emissions from all sources through to 2009 from CO2now.org based on data from Friedlingstein et al.

Source: CO2Now.org

The heart of the matter

With all his to-ing and fro-ing it wasn't always easy to figure out what Christopher was driving at.  His article made little sense.  I came across these few lines which seemed to be getting close to the crux of his argument.

It is trivially true that we are adding newly-liberated CO2 to the atmosphere every year, in contrast to the 14C pulse that ended in 1963 with the bomb tests. However, the bomb-test curve does show that just about all CO2 molecules conveniently marked with one or two extra neutrons in their nuclei will nearly all have come out of the atmosphere within 50 years.

To look at it another way, if we stopped adding CO2 to the atmosphere today, the excess remaining in the atmosphere after 100 years would be 1.5% of whatever we have added, and that is all. 

Can you spot the fallacy?  Christopher is arguing that because ¹⁴CO₂ in the atmosphere is exchanged with carbon on the surface then all the CO₂ must be falling out of the sky and not getting replaced.  But if that were the case then CO₂ would not be accumulating.  But it is.  Christopher has taken the mechanism whereby one isotope of carbon gets mixed with all the other isotopes of carbon_, and confused it with the net transfer of the total amount of carbon from the atmosphere to the surface.

It would defy the laws of physics for all the extra CO₂ to simply drop out of the sky into the land and oceans in just 100 years.  There is no way that plants can "gobble up" all the extra CO₂ in the air in just 100 years, no matter how hungry they got.  Perhaps he is thinking that dead plants will turn into coal and oil in only 100 years.

All that his "bomb test" showed is how long it takes for carbon atoms to circulate between the atmosphere and the surface and back into the air again.  It doesn't say much about net shifts of carbon from the atmosphere to the surface and back again.  If we stopped adding CO₂ to the air, it wouldn't all suddenly disappear back into the ground.  Where does he think it would go I wonder.  It can't all go into plants.  The ocean can only absorb so much at a time - and that's governed by the partial pressure of CO₂ as well as by the slow movement of ocean currents.  The latter is a very long process.

Christopher makes another error when he writes:

Atmospheric CO2 concentration is already accumulating in the atmosphere at less than half the rate at which we emit it. Half of all the CO2 we emit does indeed appear to vanish instantly from the atmosphere. This still-unexplained discrepancy, which the IPCC in its less dishonest days used to call the “missing sink”, is more or less exactly accounted for where, as Professor Pettersson suggests, CO2’s atmospheric residence time is indeed as short as the bomb-test curve suggests it is and not as long as the 50-200 years imagined by the IPCC.

He's wrong about that - all of it.  He's confusing the turnover time of carbon atoms between the air and the surface with the total time for the extra atmospheric CO₂ to drop and come into equilibrium with the surface carbon - which is dictated by the various processes in the different parts of the carbon cycle.

Secondly, AFAIK there is no unexplained discrepancy in uptake of CO₂ on the land and in the oceans.  As described by NASA, the oceans are absorbing about 30% of the extra CO₂ from human emissions and plants are absorbing about 25%.  It's not all that straightforward to predict what will happen when we're changing the whole earth system more rapidly than ever.  For example, this is from NOAA's PMEL website:

Evidence suggests that the past and current ocean uptake of human-derived (anthropogenic) CO₂ is primarily a physical response to rising atmospheric CO₂ concentrations. Whenever the partial pressure of a gas is increased in the atmosphere over a body of water, the gas will diffuse into that water until the partial pressures across the air-water interface are equilibrated.

However, because the global carbon cycle is intimately embedded in the physical climate system there exist several feedback loops between the two systems. For example, increasing CO₂ modifies the climate which in turn impacts ocean circulation and therefore ocean CO₂ uptake. Changes in marine ecosystems resulting from rising CO2 and/or changing climate can also result in changes in air-sea CO₂ exchange. These feedbacks can change the role of the oceans in taking up atmospheric CO₂ making it very difficult to predict how the ocean carbon cycle will operate in the future.

One of the many mistakes I think Christopher makes is confusing the short carbon cycle with the ocean cycle.  It takes thousands of years for the ocean to equilibrate with the atmosphere.  Not only that, but we are shifting carbon from what NASA describes as the slow carbon cycle (fossil fuels) into the atmosphere, so we've upset the status quo in a big way.

NASA has the best description of the carbon cycles that I've come across.  I wonder if Christopher Monckton or the people at WUWT have ever read it?  Or do they take the view that real science is crap and pseudo science reigns supreme.

Thinking of all this in the broader context of climate change, I've posted the diagram below a few times.  It puts time elements on various climate feedbacks.  The longest time frame is over thousands of years.

Source: RealClimate.Org

Change in CO₂ = what's added less what's removed

This section is for people who aren't averse to equations.  Christopher wrote:

Since there is no anthropogenic uptake to speak of, they contrived the following rinky-dink equationette:

ΔCO₂=e_a+e_n-u_n

The kiddiwinks say CO2 concentration change is equal to the sum of anthropogenic and natural emissions less the natural uptake. 

Christopher doesn't explain the terms so I will.  First "kiddiwinks".  This term originated in the 1950s according to the Oxford Dictionary.  It was 1952 when Christopher Monckton first appeared in the world, so maybe as a child he was referred to as "kiddiwinks".  In this case, Christopher is using it to refer to the scientists and other contributors at skepticalscience.com, some of whom would be younger and all of whom are much more informed about science than the ageing peer.  Does Christopher envy youth?

As for the other terms, here they are:

• ΔCO₂ is the change in atmospheric carbon dioxide.
• e_a is the CO2 added from anthropogenic sources such as emissions from burning fossil fuels
• e_n is the CO2 added from natural sources such as by plant respiration or from volcanoes
• _un is the CO2 absorbed from the atmosphere, such as the absorption by the oceans or by plants in photosynthesis.

Forget the equations and symbols.  All this means is:

Change in CO2 = what's added less what's removed

With his "rinky-dink equationette", does that mean Christopher think that a change in atmospheric CO2 is something other than what's added less what is taken out?  Perhaps he thinks there is another source of CO2, that isn't from human activities or the ongoing carbon cycle.  Aliens maybe?

It's net flux not residence time that determines atmospheric CO2 level

Here is the skepticalscience.com article to which Christopher was probably referring.  It's about a paper by Gavin Cawley, and shows why the claims by Christopher Monckton, Murry Salby and other science deniers are wrong.  The abstract is very clear.  The nub of the issue is that the surface is absorbing more carbon while atmospheric carbon dioxide is increasing.  In other words, carbon is increasing everywhere -(ie in the short to medium term components of the carbon cycle.  I don't mean that new carbon is being created.).  We're busy shovelling out carbon that had been safely buried for millions of years and tossing it into the air and the oceans.

...it is straightforward to show, with considerable certainty, that the natural environment has acted as a net carbon sink throughout the industrial era, taking in significantly more carbon than it has emitted, and therefore, the observed rise in atmospheric CO2 cannot be a natural phenomenon. 

The carbon cycle includes exchange fluxes that constantly redistribute vast quantities of CO2 each year between the atmospheric, oceanic, and terrestrial reservoirs. As a result, the residence time, which depends upon the total volume of these fluxes, is short. However, the rate at which atmospheric concentrations rise or fall depends upon the net difference between fluxes into and out of the atmosphere, rather than their total volume, and therefore, the long-term rise is essentially independent of the residence time.

Not only has atmospheric CO2 risen by a huge amount (a further 40% has been added since industrialisation), surface reservoirs (oceans and plants) are acting as a net carbon sink.  Oceans and plants are absorbing about half of all the extra carbon waste that humans are generating.  If not for that extra absorption, atmospheric CO2 would be much greater than it is today.

Mean lifetime from human injection of CO2 is 30,000 to 35,000 years

It's not just skepticalscience.com where this is shown.  For example, Zeke Hausfather explains what is happening on the Yale Climate Forum. As Zeke writes:

Determining the residence time of carbon dioxide in the atmosphere is a rather complex problem. A common misconception arises from simply looking at the annual carbon flux and the atmospheric stock; after all, with 230 gigatons absorbed by the oceans and land every year, and a total atmospheric stock of 720 gigatons, one might expect the average molecule of CO2 to remain in the atmosphere for only three to four years.

Such an approach poorly frames the issue, however. It is not the residence time of an individual molecule that is relevant. What really matters is just how long it will take for the stock of anthropogenic carbon emissions that has accumulated in the atmosphere to be reabsorbed.

The simplest way to approximate the time it will take to reabsorb the anthropogenic flux is to calculate how long it would take for the atmosphere to revert to preindustrial levels of 280 parts per million if humans could cease emissions immediately. If the current net sink of around 4 gigatons of carbon per year remained constant over time, it would take about 50 years for the atmosphere to return to 280 ppm. However, there is no reason to think that these sinks would remain constant as emissions decrease. Indeed, it is more realistic to anticipate that the net sink would shrink in proportion to the decrease in emissions.

Scientists can approach this problem in a number of different ways. They can use models of carbon sink behavior based on their best knowledge of the physics of ocean carbon absorption and the biosphere. They can also use records of changes in atmospheric carbon dioxide during glacial periods in the distant past to estimate the time it takes for perturbations to settle out.

Using a combination of various methods, researchers have estimated that about 50 percent of the net anthropogenic pulse would be absorbed in the first 50 years, and about 70 percent in the first 100 years. Absorption by sinks slows dramatically after that, with an additional 10 percent or so being removed after 300 years and the remaining 20 percent lasting tens if not hundreds of thousands of years before being removed.

As University of Washington scientist David Archer explains, this “long tail” of absorption means that the mean lifetime of the pulse attributable to anthropogenic emissions is around 30,000 to 35,000 years.

CO2 waste: 300 years, plus 25% that will last forever

Here is an image created by Robert Rhode at GlobalWarmingArt which illustrates the above (as always, click to enlarge):

Credit: Robert Rhode, Global Warming Art

The diagrams are based on this paper by David Archer.  From the summary:

The carbon cycle of the biosphere will take a long time to completely neutralize and sequester anthropogenic CO2. We show a wide range of model forecasts of this effect. For the best guess cases, which include air/seawater, CaCO3, and silicate weathering equilibria as affected by an ocean temperature feedback, we expect that 17– 33% of the fossil fuel carbon will still reside in the atmosphere 1 kyr from now, decreasing to 10– 15% at 10 kyr, and 7% at 100 kyr. The mean lifetime of fossil fuel CO2 is about 30– 35 kyr.

[20] A mean atmospheric lifetime of order 104 years is in stark contrast with the ‘‘popular’’ perception of several hundred year lifetime for atmospheric CO2. In fairness, if the fate of anthropogenic carbon must be boiled down into a single number for popular discussion, then 300 years is a sensible number to choose, because it captures the behavior of the majority of the carbon. A single exponential decay of 300 years is arguably a better approximation than a single exponential decay of 30,000 years, if one is forced to choose.

However, the 300 year simplification misses the immense longevity of the tail on the CO2 lifetime, and hence its interaction with major ice sheets, ocean methane clathrate deposits, and future glacial/interglacial cycles. One could sensibly argue that public discussion should focus on a time frame within which we live our lives, rather than concern ourselves with climate impacts tens of thousands of years in the future. On the other hand, the 10 kyr lifetime of nuclear waste seems quite relevant to public perception of nuclear energy decisions today. A better approximation of the lifetime of fossil fuel CO2 for public discussion might be ‘‘300 years, plus 25% that lasts forever.’’

It's taken only around fifteen decades for us to affect earth for the next 35,000 years!

The mean lifetime of fossil fuel CO2 is thirty to thirty five thousand years.  That's three times longer than all of human civilisation.  It's three times longer than the Holocene.  In just a few decades we've managed to affect the future of earth for more than thirty thousand years!  It's hard to get one's head around, isn't it.

Now all the above talk of getting rid of excess CO2 in the atmosphere is interesting from an academic perspective.  But as long as we keep adding more and more CO2 each year, that 300 years +25% taking forever, and the 30,000 to 35,000 year tail are all in the future.  We are nowhere near getting to an equilibrium where the waste we generate is equal to the amount absorbed - whether by natural processes or whether we use geoengineering to remove it from the air.

Further reading:

Matthews, H. Damon, and Susan Solomon. "Irreversible Does Not Mean Unavoidable." Science 340.6131 (2013): 438-439. doi: 10.1126/science.1236372

Graven, H. D., T. P. Guilderson, and R. F. Keeling (2012), Observations of radiocarbon in CO2 at La Jolla, California, USA 1992–2007: Analysis of the long-term trend, J. Geophys. Res., 117, D02302, doi:10.1029/2011JD016533

Archer, D. (2005), Fate of fossil fuel CO2 in geologic time, J. Geophys. Res., 110, C09S05, doi:10.1029/2004JC002625 

Currie,K (2006), ¹⁴CO₂ in the Southern Hemisphere Atmosphere — the Rise and the Fall, Chemistry in New Zealand April 2006

Cawley, Gavin C. "On the Atmospheric Residence Time of Anthropogenically Sourced Carbon Dioxide." Energy & Fuels 25.11 (2011): 5503-5513. doi: 10.1021/ef200914u

Friedlingstein et al. (2010) Update on CO2 emissions.Nature Geoscience, doi: 10.1038/ngeo_1022:


Skepticalscience.com articles

• The Independence of Global Warming on Residence Time of CO2
• Murry Salby finds CO2 rise is natural

NASA Earth Observatory on The Carbon Cycle

Zeke Hausfather at the Yale Forum: Common climate misconceptions: Atmospheric Carbon Dioxide

From the WUWT comments

Quite a few people at WUWT are critical of Christopher's article, some but by no means all for the right reasons.  This article is already way too long and the many of the comments at WUWT are impenetrable.  You can have a shot at wading through them if you're game.  There were comments from many more "notables" than is usual - from right across the spectrum.  They are archived here.

There are lots of people having a shot at figuring out how long all the extra carbon dioxide would stay in the air if we suddenly stopped adding any more.  Which is ironic, given that this is WUWT where coal reigns supreme and the motto is burn, baby, burn.  It would be good if WUWT-ers put as much effort into figuring out how to stop adding carbon dioxide as they did figuring out what would happen if we did stop.

There is lots of confusion about terminology, not helped by the fact the Christopher isn't at all clear about just how little time he thinks it would take for all the extra carbon dioxide to drop out of the sky. (Nor is it helped by the somewhat obscure definitions of "turnover time", "global atmospheric lifetime", "lifetime", "mean residence time", "adjustment time", and "response time" in Appendix III of the IPCC report.)

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Note to readers 

I found it quite difficult trying to unravel the stream of consciousness from Christopher Monckton at WUWT.  In doing so it's quite likely I've made a few mistakes of my own.  If anyone manages to wade through the above, feel free to point out any errors.

I prefer to keep any discussion focused on the science and not on the professional or personal (mis)behaviour of the people mentioned (this really only applies to Murry Salby - Christopher Monckton's idiosyncracies are fair game as always).

Sou
23 November 2013