Cowtan and Way trends

A new paper by Kevin Cowtan and Robert Way in QJRoyMetSoc is getting a lot of discussion. See Real Climate here, SkS here and here, Lucia here and here, Cliamte Etc here.

The authors say:
"A new paper published in The Quarterly Journal of the Royal Meteorological Society fills in the gaps in the UK Met Office HadCRUT4 surface temperature data set, and finds that the global surface warming since 1997 has happened more than twice as fast as the HadCRUT4 estimate."

Some eyebrows have been raised at the size of the trend change from improving a relatively small area. I was surprised, too. So I did some calculations to see.

Update: The R code for calc and plotting is here. The data is provided by the authors here.

The need for the change

Met station coverage of the Earth is uneven. When grid averages are taken, and then combined for a hemisphere or global average, quite a lot of cells have no data. What to do?

The default is to leave them out of the average. But that is not a neutral decision. In arithmetical effect, they have been replaced by the average value of the cells with observations. And this may be a poor approximation. It should be improved with whatever information is available.

The particular issue with Hadcrut is data at the poles. In computing trends, missing cells are given the global average trend, but the poles are warming much faster. This is a big bias.

Cowtan and Way used UAH satellite data to get that improvement. I won't go into detail here about how they did it, but I'll just look at the dataset results. They looked in particulat at a period from 1997-2012 (16 years) which is commonly discussed as a pause. They showed trends including their hybrid method, which uses UAH-based infill:

Dataset	HADCRUT 4	UAH	C&W hybrid
Treend C/dec	0.046	0.094	0.119

Actually, I don't think they cited the UAH trend, but I calculated it from the data they used.

So the new trend isn't that much greater than UAH. But to see just how modifying polar trends made the difference, I'll show the latitude averages for the 5° ranges.

Latitude averages

In computing these for the HAD 4 data, I replaced data-free cells with the global average for that month. So they aren't a good guide (for HAD 4) to actual trends, but, as described above, they do correspond to what effectively goes into the global average, so you can see the effect of changes. Here's the plot:


(An earlier version of this plot had the sign of latitude wrong)

As you'll see, the Antarctic and Arctic trends for the hybrid are large, but not so very much larger than UAH. I am still a little surprised that this is so, but it's not unbelievable.

Appendix

Here are the numerical results as plotted:

Latitude	HAD 4	UAH	C&W hybrid
87.5	0.139	0.819	1.509
82.5	0.19	0.987	1.692
77.5	0.373	0.897	1.452
72.5	0.617	0.641	1.196
67.5	0.57	0.495	0.825
62.5	0.236	0.317	0.353
57.5	0.041	0.12	0.088
52.5	-0.083	0.05	-0.035
47.5	-0.056	0.013	-0.034
42.5	0.115	-0.028	0.102
37.5	0.061	0.026	0.066
32.5	0.067	0.131	0.074
27.5	0.085	0.104	0.086
22.5	0.051	0.068	0.091
17.5	0.074	0.009	0.09
12.5	0.085	-0.015	0.093
7.5	0.056	-0.008	0.059
2.5	-0.003	-0.027	-0.011
-2.5	-0.031	-0.017	-0.044
-7.5	-0.039	-0.037	-0.04
-12.5	-0.01	-0.039	-0.004
-17.5	-0.002	-0.028	0.01
-22.5	0.05	0.036	0.063
-27.5	0.088	0.062	0.093
-32.5	0.137	0.066	0.141
-37.5	0.082	0.053	0.094
-42.5	0.046	0.126	0.074
-47.5	-0.079	0.202	-0.048
-52.5	-0.114	0.215	-0.039
-57.5	-0.17	0.154	-0.041
-62.5	0.04	0.102	-0.009
-67.5	0.08	0.152	0.099
-72.5	0.079	0.569	0.566
-77.5	0.122	0.437	0.646
-82.5	0.086	0.299	0.685
-87.5	0.101	0.223	0.901
Global	0.054	0.094	0.119

TempLS global temp very small increase in October

The TempLS monthly global anomaly for October 2013 was 0.502°C, compared with 0.493° in September. TempLS has been very stable for the last five months. UAH showed a modest decrease.

Here is the spherical harmonics plot of the temperature distribution:
Update 18/Nov I see that by mistake I had link graphics for April in place of October. Fixed.




NW USA cold, SW Europe and central Asia warm..
And here is the map of stations reporting:

September GISS Temp up by 0.13°C

GISS LOTI went from 0.61°C in August to 0.74°C in September. because of the US shutdown, the report was exceptionally late, and in fact the surface indices were reported in the reverse of the usual order, with HADCRUt first. GISS showed the highest rise; NOAA 0.03°C, HADCRUT 4 and TempLS less than 0.01°C. But the satellite indices showed rises comparable to GISS.


Here is the GISS map for September 2013:



And here, with the same scale and color scheme, is the earlier TempLS map for September:

And here is the WebGL map of actual station temps during the month.

Previous Months

August
July
June
May
April
March
February
January
December 2012
November
October
September
August
July
June
May
April
March
February
January
December 2011
November
October
September
August 2011

More data and plots

New page - climate blog index

I described here an experiment I tried in July (when Google Reader faded). I selected about a dozen popular climate blogs, for which I regularly looked at the RSS files (every two hours). They aren't all blogs that I agree with, but they are ones at which I sometimes comment.

A database of posts and comments has accumulated, and I've done some organising to make that accessible without a huge initial download. So I've scrubbed it up and promoted it to a page, visible upper right.

It's just a table of blog names, thread titles, dates and authors (comments and posts). The dates are linked to the source. You can order by each column, or you can subset by each of those properties (in combination, if you want). You can, for example, put up a linked list of all your own comments on those sites over a time period.

It starts with just the current and previous month. But you can vary the time range (more data =slower). More details are at the page.

TempLS global temp up 0.01°C in September

GHCN now seems to be OK after the shutdown. There was a tiny increase from August (0.49°C) to September (0.504°C). UAH seems to be the only other index reporting to date - it showed a much larger increase.

Here is the spherical harmonics plot of the temperature distribution:



Warm spots in Canada and Australia; cold in Siberia and E Europe..


And here is the map of stations reporting:

Shutdown - TempLS delayed

GHCN has been updating, as has ERSST. But when I look into GHCN, oddly, there are only US data, no ROW. So no TempLS post yet.

FWIW, the data that is there suggests a slight fall in Sept.

The Shutdown and updating

Just a note on how the US government shutdown affects updated data here. Hopefully all will be fixed when it ends.

• NOAA SST data isn't getting through, so the SST movies and WebGL trackball daily plots have no October data.
  
• The NASA and NOAA websites are down, so there probably won't be a monthly index update for the duration. UAH is out and RSS should be OK.
  
• GHCN data is getting through, so TempLS should be OK - may be the only one until HADCRUT comes out. The monthly updates of surface temp should be OK.
  
• JAXA is unaffected.