Incorporating SST and Land/Ocean models

The part of Gistemp that most people who look into it shy away from is where the gridded ocean data is included to make a global land/sea index. With some reason, because it's awkward, but not particularly challenging - the HadSST data is already gridded, and what remains is the messy stuff of keeping the grid methods consistent.

Other recent reconstructions have concentrated on land stations too, perhaps because, as Zeke says, the context was the examination of claims that drift in selection of stations creates biases.

The least squares method used here makes the incorporation of ocean data easier, because there is no intermediate gridding step. So I tried it, I downloaded HadSST2 data, and added a set of 2592 (36x72) synthetic stations - one at the centre of each grid cell. HAD uses the same 5x5 grid as I use for weighting for station density. So where the station sits in an ocean-only cell, it is fully weighted as the sole representative of that cell, and where ocean overlaps land, the new station is weighted according to the number of land stations in the same cell. If the cell is land only, there is no new data, so that cell does not add to the analysis.

New code

This all required some new coding. That's tied up with some other changes, so I'll post ver 1.3 shortly. The change was mostly in the preprocessor, which rearranges the Had data to the GHCN format and creates the new station file.

A summary of this series of posts is here.

Trends

Here is the table of trends from my analysis:

Trend	LandSea	SST	NHLandSea	SHLandSea
Number	9872	2592	7281	2591
1901-2005	0.06616	0.06654	0.06428	0.0684
Trend se	0.004501	0.003879	0.005979	0.00381
1979-2005	0.182	0.151	0.2445	0.1094
Trend se	0.0224	0.0178	0.03169	0.0171

Update: I hope to be routinely quoting standard errors for trends. At present these are based on OLS - no correction for correlation of residuals. So they are smaller than the AR4 values below.

 
I chose the time intervals for comparison with Table 3.3 from the AR4:

	Temperature Trend (oC per decade)
Dataset	1850-2005	1901-2005	1979-2005
Northern Hemisphere
CRU/UKMO (Brohan et al., 2006)	0.047 ± 0.013	0.075 ± 0.023	0.234 ± 0.070
NCDC (Smith and Reynolds, 2005)		0.063 ± 0.022	0.245 ± 0.062
Southern Hemisphere
CRU/UKMO (Brohan et al., 2006)	0.038 ± 0.014	0.068 ± 0.017	0.092 ± 0.038
NCDC (Smith and Reynolds, 2005)		0.066 ± 0.009	0.096 ± 0.038
Globe
CRU/UKMO (Brohan et al., 2006)	0.042 ± 0.012	0.071 ± 0.017	0.163 ± 0.046
NCDC (Smith and Reynolds, 2005)		0.064 ± 0.016	0.174 ± 0.051
GISS (Hansen et al., 2001)		0.060 ± 0.014	0.170 ± 0.047

Plots

Here my plots are compared with the published gridded data, taken from WFT. The smoothing uses the 13-point filter from AR4 Chap 3

The anomaly base periods have been adjusted to match in each case to the published data.