One point that intrigued me about the Muscheler vs Solanki dispute was to see what the underlying data looked like. Here’s a graph and some comments. I don’t purport to know a lot about this; I just wanted to get a feel for the data.
The main source for dC14 readings is Intcal04 here. The top panel shows a plot of the dC14 data (I’ve shown the R-script to show how easy the download is in R. You can parameterize the URLs which is really nice for this sort of quick look). Intcal04 describe fitting a smooth as follows:
IntCal04 age-corrected àÅ½”¬?14C (“°) with a 2-standard deviation envelope showing the 1000- and 2000-yr moving averages (red and blue lines, respectively). For the old end of the data set, the moving average truncates the first 500 or 1000 yr. For the recent end, the moving average window was allowed to shrink to the number of remaining points in the data set to avoid this type of truncation.
This is a pretty weird smooth. I fitted it with lowess using f=1/3, a more usual smooth, just to see what it looked like (top panel). I picked 1/3 to try to match some of the main features to the Intcal04 smooth. (an alternate version not inverted with f=2/3 is here.) Then they take the difference between the curve and the smooth, which I’ve shown in the bottom panel – black: versus lowess smooth; red – Intcal04 version. I’ve reversed the vertical to match with conventional ideas of warm periods and cold periods (i.e. LGM is cold).
For comparison, here is the corresponding figure clipped from IntCalo4 (vertically transposed from bottom panel above).
Figure: red- versus 2000 year smooth; blue – versus 1000 year smooth.
What does it all mean? It doesn’t seem very desirable that results should be so sensitive to fairly arbitrary differences in smooth. With a little difference in smooth, the LGM is more pronounced as is the LIA. Does it matter? I have no idea.
Here’s the R script:
v< lowess(g[,1],g[,4],f=2/3) url<-"http://www.radiocarbon.org/IntCal04%20files/resid04_2000.14c"
h<-read.table(url,skip=11,sep=",") h<-h[1:(nrow(h)-1),] nf <
axis(side=2); axis(side=1,labels=FALSE); box()
abline(h=0); axis(side=2) ;axis(side=1) ;box()