12th July 2012
Response to John Quiggin re: longevity of “man-made” CO2 in the atmosphere
Here's my response to the first part of the two issues on which I've agreed to provide you with more information (being the question of how long CO2 remains in the atmosphere). I'll talk about the peer review issue separately.
Let me note at the outset that I fully understand how you feel about IPCC's work. Not long ago, when I didn't have time to investigate the issues in detail (I have even now barely scratched the surface, but I believe I've gained enough knowledge to become somewhat intelligently engaged in the debates), I too "believed" that IPCC findings should be taken seriously.
After devoting much time to understanding the science, however, I've been left with more questions than answers, and a poor impression of IPCC's analytical skills. First, it is evident to me that climate science is not settled, with gaping holes in our knowledge. The day all my questions are adequately addressed by IPCC, I'll promote IPCC's findings just like you do. Second, while we should act to prevent catastrophe if there is any reasonable chance of runaway global warming, there is not the slightest shred of evidence that such a risk exists.
On a subject as important as this, on which the fate of the planet itself presumably depends, let me suggest that we can't afford to take anyone's word as sacrosant. We must open our eyes and find out the truth ourselves. We must raise questions and we must be given the satisfactorily answers.
1: We don't know the precise level of CO2 in the atmosphere
Let me begin with the most fundamental and basic area of uncertainty. Before we can say with some confidence that CO2 emissions will last for centuries in the atmosphere, we need to be sure that our instruments are accurately measuring CO2. Unfortunately, CO2 measurement problems appear to be too many to mention. The measured level of CO2 in the atmosphere seems to vary with (a) the method used, (b) the height of the measuring instrument above sea level [CO2 dramatically varies across different heights], (c) time of day, (d) time of year, and (e) the nature of nearby activity.
In particular, CO2 level data prior to 1959 are problematic, being based on different methodologies to those used today. Even today's methodologies are being refined as the complexity of measurement is better understood. Nevertheless, post-1959 data are robust enough, and so I will ASSUME IPCC's reported data regarding CO2 levels since 1959 are valid (given we don't have anything better). But we must be prepared to interrogate even this basic data over the coming years.
2: Scientific debate about carbon cycle and how long CO2 stays in the atmosphere
The carbon cycle is very poorly understood. There are debates not just about "missing sinks" but about the very sources of carbon in the air (given that an overwhelming proportion of carbon is not found in the atmosphere but in the oceans). A plausible theory even suggests that since global warming commenced before 1860 (due to natural causes), it is that warming which is driving the release (degassing) of CO2 from the oceans. This implies that observed increases in CO2 could be due to warming, not warming due to CO2. The matter is stupendously complex.
Even The Guardian's FAQ on climate change notes that: "The lifetime in the air of CO2, the most significant man-made greenhouse gas, is probably the most difficult to determine. Between 65% and 80% of CO2 released into the air dissolves into the ocean over a period of 20–200 years." [Source]
I want to repeat this for effect, that longevity estimates are between 20 and 200 years (a 10 times difference!). Imagine what you would say of a demographer reported that an average Australian lived between 20 and 200 years. In fact the range of estimates in the case of CO2 is probably even wider than this.
Note a key point, that should the smaller figure be valid, most manmade CO2 would be absorbed rapidly – and will not accumulate.
The IPCC itself is constantly changing its mind on this issue. The first assessment report defined the lifetime of CO2 as 50-200 years while the second and third assessment reports lowered the lower limit to 5 years. The most fourth and most recent assessment report changed the language entirely to say (quoted from the paper): "Carbon dioxide cycles between atmosphere, oceans, and land biosphere. Its removal from the atmosphere involves a range of processes with different time scales. … The remaining 20% may stay in the atmosphere for many thousands of years."" This kind of vagueness is amazing for something known as "science"!
A massive chunk of CO2 emitted in the last two centuries (mostly in the last fifty years) has DISAPPEARED from the atmosphere.
Where did it go? That's been a source of great mystery.
"Today's current level of atmospheric carbon dioxide is only around half of what scientists have predicted atmospheric levels should be, based on estimates that humans have contributed 244 billion metric tons of carbon dioxide to Earth's atmosphere. Oceans have taken up 48 percent of all carbon dioxide emitted from fossil fuel burning and cement manufacture (a major source of the gas) between 1800 and 1994." [National Geographic, reporting a peer reviewed study: Source]
But if the view that CO2 is emitted from oceans upon warming is confirmed (a view that sounds plausible to me), then we can expect new estimates which may indicate MUCH greater absorption of man-made emissions, being the only way to account for the modestly increasing total atmospheric CO2.
One-celled plants are like bacteria. Give them food and they multiply. There are almost no limits to their growth. These natural sinks are barely beginning to be understood. Expect the science to change DRAMATICALLY in the coming decades as we start understanding the 100s of factors that operate on the climate, a little bit better.
In any event, your assumption that CO2 remains unchanged for a hundred years is very likely to be incorrect. You can't multiply annual temperature estimates by 100. You must factor in the dissipation of the carbon which would have naturally occurred.
Climate science has almost no linearities, only complex physical non-linearities and organic feedback loops. Simplistic kindergarten arithmetic doesn't work.
Once again, my purpose of writing this is NOT to provide you with a definitive answer on what is correct (I have no time to find that out – even assuming the correct answer exists), but to point out that there is a DEBATE on this issue. You should not take IPCC as bible, for even IPCC (rightly) keeps changing its mind.
Finally, you asked for peer reviewed papers, so here are a couple:
Essenhigh, R.E. 2009: Potential dependence of global warming on the residence time (RT) in the atmosphere of anthropogenically sourced carbon dioxide. Energy & Fuels 23: 2773-2784.
- He finds that the RT for bulk atmospheric CO2, the molecule 12CO2, is ~5 years, in good agreement with other cited sources (Segalstad, 1998), while the RT for the trace molecule 14CO2 is ~16 years. Both of these residence times are much shorter than what is claimed by the IPCC.
- He points out that the annual oscillations in the measured atmospheric CO2 levels not be possible without a short atmospheric residence time for CO2 molecules [This is because you can't expect CO2 to start fading out in a few months, unless it was being rapidly re-absorbed by Earth.]
Moore, B., III, and B. H. Braswell (1994), The lifetime of excess atmospheric carbon dioxide, Global Biogeochem. Cycles, 8(1), 23–38, doi:10.1029/93GB03392.
- This papers notes that "Our best estimate is that the single half-life for excess CO2 lies within the range of 19 to 49 years, with a reasonable average being 31 years".
3. The mere existence of greater CO2 levels doesn't imply runaway global warming
I don't want to extend this discussion, but there is a fundamental problem with this fuss about CO2: Even assuming CO2 remains in the atmosphere for hundreds of years, its [proven, warming] effect on global temperature is dissipated by many self-correcting effects.
The proof is in the pudding. Global temperatures have not risen anywhere close to IPCCs model predictions. There are therefore many dampening effects at work, mostly unknown to science. The challenge for scientists today is to find out more about what might be happening.
They need to understand (a) how to measure CO2 (and temperature) properly, (b) what the sources and sinks of CO2 are, (c) the longevity of man-made CO2 and (d) what's preventing the Earth from over-heating with existing CO2, given its greatest proportion of warming effects are at the lower, not higher densities.
IPCC, in trying to get politicians involved, has significantly reduced its value as a scientific body.
Essenhigh's study has been later refuted. See John Quggin's comment below.
The complete discussion
- I'm sorry Australia has such a disappointing person on its Climate Change Authority
- Strip Al Gore and IPCC of their Nobel Prize and give it to these people
- If Kevin Rudd continues to abuse those who ask questions, then Australia should bid goodbye to science
- It is not Donna Laframboise but Rajendra Pachauri who is a HUGE liar
- Now John Quiggin says that the world's top scientists are stupid! This is getting absurd.
- John Quiggin, IPCC's peer review process is riddled with holes. I now expect a detailed correction on your blog.
- John, thanks for withdrawing your allegation against Donna's integrity. Here's other stuff you and I should know.
- The total mess that is IPCC. This is very serious stuff. Please do read.
- John (Quiggin), Donna's methodology is totally transparent. Please PROVE she is a liar.
- Now John Quiggin says that Donna Laframboise is lying. I'll ask her about it.
- Second point for John Quiggin: to what extent does IPCC use peer reviewed literature?
- Response to John Quiggin re: longevity of "man-made" CO2 in the atmosphere
- Very important new study that rebuts IPCC generated panic
- Inviting input from readers re: climate change facts, to conduct a debate with John Quiggin
- John Quiggin, I suggest you review your estimate of the impact of Australian CO2 reductions