Vostok Ice Core / CO2 correlation - an AGW myth demolished
Jonathan Drake has released an interesting paper called A Simple Method to Correct Carbon Dioxide Concentrations in Ice Core Data for Ice / Gas Age Difference Perturbations.
Before you skip to the next item tarry a while because this is interesting. He had a look at the Vostok ice core data / CO2 correlation, one of the great poster children of the AGW movement.
The ice core data as presented goes back 420,000 years. Various parameters can be measured from it, or inferred. It is understood that the age of the gas (air) trapped is generally younger than the ice containing it and therefore this difference needs to be determined. This is done using models of the system and the measured parameters.
As he says:
For the purposes of my paper, I use IGD, for the ice age to gas age difference. What I noticed was that IGD appeared to move with the CO2 measurement (correlation). I looked for a relationship between IGD and CO2 and found it was close to linear, so I calculated the linear trend. Now using this mathematical function, I adjusted the CO2 levels so that they represent the concentrations at an arbitrary IGD = 0 because this corresponds to what the level of CO2 ought to be had it been trapped at the time the snow hit the ground. A secondary effect of this is to correct the time reference. At IGD = 0, the ice and gas are the same age by definition.
So once the compensation I describe is applied, the resultant CO2 levels are very different to the original, both in level and character. It appears that, for some reason, the temperature is modulating the original CO2 data.
In the corrected version, there is virtually no correlation between temperature and carbon dioxide.
I leave you to draw your own conclusions regarding how this relates to the AGW story.
I like to look at it this way: the original data is like a tail wagging the dog, and the corrected version analogous to the dog wagging its tail.