2011-03-31 20:41:01Critique of Guide's 'human fingerprint' of depleted dC13
John Cook

john@skepticalscience...
124.185.238.238

Someone emailed me this blog post. Wondering if I should start a new forum 'Critiques of SkS' just to keep all these grouped in one place:

http://debunkhouse.wordpress.com/2011/02/24/is-d13c-depletion-really-an-anthropogenic-fingerprint/

2011-03-31 23:00:35
nealjking

nealjking@gmail...
84.151.31.101

It sounds like a good idea.

This seems like a good opportunity to engage more knowledgeable skeptics in real discussion. Is someone up on the details of the isotope argument, and able to take this on?

2011-03-31 23:29:11
grypo

gryposaurus@gmail...
173.69.56.151

I don't know the technical details but this just appears to be a combo of "it's happened before so..." and "its ocean volcanoes".  We know by a priori fact what we are releasing into the atmosphere.  What we find in δ13C is exactly what we would expect to find.  In fact, it's almost as if he's arguing semantics of the word "fingerprint".  Does anyone else get that impression?

 

2011-03-31 23:59:04
Ari Jokimäki

arijmaki@yahoo...
91.154.107.62

I didn't read the linked article, but it seems to me that there is a point. δ13C/δ12C ratio alone doesn't prove that the CO2 is from fossil fuels. I'm going with my memory here so correct if I'm wrong but the change in δ13C/δ12C ratio only tells the CO2 is from plants so it can be either from burning fossil fuels or modern wood. I think that more accurate statement would be that there are several isotope/element tracers which all together make the fingerprint.

Decreasing δ14C (original Suess effect) tells that CO2 is really old and this would be excellent tracer but unfortunately nuclear explosions have messed up this tracer. Carbon monoxide is one rather good tracer of fossil fuels, it can even tell how efficient the combustion was that emitted the pollution. There are other tracers too, I think there is an oxygen isotope tracer and I remember hearing that radon can be used as a tracer too somehow.

2011-04-01 00:04:03
Andy S

skucea@telus...
88.139.144.147

The tone of this particular critique was not too bad, as such things go  (but look elsewhere on the site for the usual conspiracy theories and charges of enviro-marxism).

Ultimately, what this comes down to is a semantic arguments about what a "fingerprint" means as a metaphor and what constitutes a unique and sufficient proof in criminal law and science.

The critic has a point in that the isotope evidence by itself provides corroboration rather than proof that human CO2 emississions are the cause of the upward trend of the Keeling curve. Of course, nobody actually argued that it was, but when you put a single, simplified argument in a box and call it "strong evidence" a casual reader might be forgiven for concluding that that is the crucial observation, whereas there are many other lines of evidence (ocean acidification, a drop in atmospheric oxygen concentrations etc) and the biggest evidence of all is the fact that we have been burning carbon and the CO2 had to go somewhere. The isotope argument is most useful to counter the "it's volcanoes" or "it's bubbling out of the oceans" arguments.

I really don't know what caused the Holcoene carbon-isotope-lightening episodes (clathrate releases, sudden terrestrial biomass reductions?) and while that's an interesting question I don't personally feel like researching it solely to rebut an argument framed by a skeptic that merely attempts to cast doubt on one of the least-disputed facts of recent climate change.

Perhaps it's better to admit that the isotope argument is supportive of anthropogenic changes to the atmosphere but is not by itself proof that would stand up in court like a fingerprint. In the end, this is a nit-pick of an informal text and to treat the critique as a scientific argument is to dignify it with respect that it does not deserve.

2011-04-01 00:14:47
nealjking

nealjking@gmail...
84.151.31.101

It seems to me there are two points:

- One is the issue of what is meant by a "fingerprint". I agree that this is a semantic issue that should be explained, but is not very serious. The use of the term is only figurative anyway: there are no whorls.

- But I think if someone brings the argument up a scientific level, we have to respond; either get into it, or demonstrate that that level of depth is not necessary. It's not good for us to get into a pattern of just dismissing scientific argument.

2011-04-01 00:32:50
Andy S

skucea@telus...
88.139.144.147

oops

2011-04-01 03:58:55
Riccardo

riccardoreitano@tiscali...
192.84.150.209

As his very same graphs show (third graph in particular), the carbon isotope ratio changes in the oceans are much smaller and less noisy than on land. The guide first fingerprint graph shows corals.
His criticism looks much more semantic than scientific. He only says that 13C may vary naturally and this is true. But it's also true that the other fingerprints may occur naturally, provided that there's some CO2 induced global warming. In the end, they're all fingerprints of CO2 induced warming and humans are causing it.

2011-04-01 06:24:39
Alex C

coultera@umich...
67.149.101.148

Reasonable critique, but the discussion on what the data means is lacking.  Take for example the first figure he quotes from Enzel et al 1999 in Science.  The 13C data is from sediment data from a single lake, and from what I gather of their explanation, there is no suggestion that atmospheric 13C levels varied - rather, the response was botanical in origin.  To quote:

The values of

2011-04-01 06:24:51
Alex C

coultera@umich...
67.149.101.148

Reasonable critique, but the discussion on what the data means is lacking.  Take for example the first figure he quotes from Enzel et al 1999 in Science.  The 13C data is from sediment data from a single lake, and from what I gather of their explanation, there is no suggestion that atmospheric 13C levels varied - rather, the response was botanical in origin.  To quote:

The values of

2011-04-01 06:25:38
Alex C

coultera@umich...
67.149.101.148

My response is not going through, and I apologize for the multiple posts.  To make it short: that paper does not conclude atmospheric 13C ratios changed; I've had run-ins with David at Yahoo! Answers methinks, and he has not always been this polite in response.  A previous post of his "refutes" De'ath et al 2009, and makes four major false assumptions/statements in doing so:

- accuses De'ath of using too many cores, though it clearly states within the paper that scores were used, more-so than available online to be sure;

- uses data that De'ath did NOT use in the paper to support his (De'ath's) conclusions; there is far more data that actually spans the time frame in question that is not available at NOAA;

- does not correct for latitudinal bias over time (measurements bias toward warmer waters in later centuries)

- makes very dubious "correlation = causality" statements regarding coral growth - and gee, that seems like something he's trying to not do here.  Point is, he is not consistent.

I think that a response may be warranted, as the argument addresses us directly.  Finding out what his sources actually conclude would be a good start.