Thursday, August 17, 2017

Temperature averaging and integration - the basics

I write a lot about spatial integration, which is at the heart of global temperature averaging. I'll write more here about the principles involved. But I'm also writing to place in context methods I use in TempLS, which I think are an advance on what is currently usual. I last wrote a comparison of methods in 2015 here, which I plan to update in a sequel. Some issues here arose in a discussion at Climate Audit.

It's a long post, so I'll include a table of contents. I want to start from first principles and make some math connections. I'll use paler colors for the bits that are more mathy or that are just to make the logic connect, but which could be skipped.

Wednesday, August 16, 2017

GISS July up 0.15°C from June.

GISS was up from 0.68°C in June to 0.83°C in July. It was the warmest July in the record, though the GISS report says it "statistically tied" with 2016 (0.82). The increase was similar to the 0.12°C rise in TempLS.

The overall pattern was similar to that in TempLS. Warm almost everywhere, with a big band across mid-latitude Eurasia and N Africa. Cool in parts of the Arctic, which may save some ice.

I'll show the plot of recent months on the same 1981-2010 base, mainly because they are currently unusually unanimous. The group HADCRUT/NOAA/TempLS_grid tend to be less sensitive to the Antarctic variations that have dominated recent months, and I'd expect them to be not much changed in July also, which would leave them also in much the same place.

Recently, August reanalysis has been unusually warm. As usual here, I will compare the GISS and previous TempLS plots below the jump.

Tuesday, August 8, 2017

July global surface temperature up 0.11°C

TempLS mesh anomaly (1961-90 base) was up from 0.568°C in June to 0.679°C in July. This follows the smaller rise of 0.06°C in the NCEP/NCAR index, and a similar rise (0.07) in the UAH LT satellite index. The July value is just a whisker short of July 2016, which was a record warm month. With results for Mexico and Peru still to come, that could change..

Again the dominant change was in Antarctica, from very cold in June to just above average in July. On this basis, I'd expect GISS to also rise; NOAA and HADCRUT not so much. Otherwise as with the reanalysis, Middle East and around Mongolia were warm, also Australia and Western USA. Nowhere very hot or cold. Here is the map:

Thursday, August 3, 2017

July NCEP/NCAR up 0.058°C

In the Moyhu NCEP/NCAR index, the monthly reanalysis average rose from 0.241°C in June to 0.299°C in July, 2017. This is lower than July 2016 but considerably higher than July 2015. The interesting point was a sudden rise on about July 24, which is responsible for all the increase since June. It may be tapering off now.

It was generally warm in temperate Asia and the Middle East, and even Australia. Antarctica was mixed, not as cold as June. The Arctic has been fairly cool.

Saturday, July 22, 2017

NOAA's new ERSST V5 Sea surface temperature and TempLS

The paper describing the new version V5 of ERSST has been published in the Journal of Climate. The data is posted, and there is a NOAA descriptive page here. From the abstract of the (paywalled) paper, by Huang et al:
This update incorporates a new release of ICOADS R3.0, a decade of near-surface data from Argo floats, and a new estimate of centennial sea-ice from HadISST2. A number of choices in aspects of quality control, bias adjustment and interpolation have been substantively revised. The resulting ERSST estimates have more realistic spatio-temporal variations, better representation of high latitude SSTs, and ship SST biases are now calculated relative to more accurate buoy measurements, while the global long-term trend remains about the same.
A lot of people have asked about including ARGO data, but it may be less significant than it seems. ARGO floats only come to the surface once every ten days, while the more numerous drifter buoys are returning data all the time. There was a clamor for the biases to be calculated relative to the more accurate buoys, but as I frequently argued, as a matter of simple arithmetic it makes absolutely no difference to the anomaly result. And sure enough, they report that it just reduces all readings by 0.077°C. That can't affect trends, spatial patterns etc.

The new data was not used for the June NOAA global index, nor for any other indices that I know of. But I'm sure it will be soon. So I have downloaded it and tried it out in TempLS. I have incorporated it in place of the old V3b. So how much difference does it make? The abstract says
Furthermore, high latitude SSTs are decreased by 0.1°–0.2°C by using sea-ice concentration from HadISST2 over HadISST1. Changes arising from remaining innovations are mostly important at small space and time scales, primarily having an impact where and when input observations are sparse. Cross-validations and verifications with independent modern observations show that the updates incorporated in ERSSTv5 have improved the representation of spatial variability over the global oceans, the magnitude of El Niño and La Niña events, and the decadal nature of SST changes over 1930s–40s when observation instruments changed rapidly. Both long (1900–2015) and short (2000–2015) term SST trends in ERSSTv5 remain significant as in ERSSTv4.
The sea ice difference may matter most - this is a long standing problem area in incorporating SST in global measures. On the NOAA page, they show a comparison graph:

There are no obvious systematic trend differences. The most noticeable change is around WWII, which is a bit of a black spot for SST data. A marked and often suspected peak around 1944 has diminished, with a deeper dip around 1942.

TempLS would be expected to reflect this, since most of its data is SST. Here is the corresponding series for TempLS mesh plotted:

Global trends (in °C/century) are barely affected. Reduced slightly in recent decades, increased slightly since 1900:

start yearend yearTempLS with V4TempLS with V5

Almost identical behaviour is seen with TempLS grid.

Thursday, July 20, 2017

NOAA global surface temperature down just 0.01°C

Down from 0.83°C in May to 0.82C in June (report here). I don't normally post separately about NOAA, but here I think the striking difference from GISS/TempLS mesh is significant. GISS went down 0.19°C, and TempLS mesh by 0.12°C. But TempLS grid actually rose, very slightly. I have often noted the close correspondence between NOAA and TempLS grid (and the looser one between TempLS mesh and GISS) and attributed the difference to GISS etc better coverage of the poles.

This month, the cause of that difference is clear, as is the relative coolness of June in GISS. With TempLS reports, I post a breakdown of the regional contributions. These are actual contributions, not just average temperature. So in the following:

you see that the total dropped by about 0.12°C, while Antarctica dropped from conributing 0.07C to -0.07C, a difference that slightly exceeded the global total drop of 0.12C.

That doesn't mean that, but for Antarctica, there would have been no cooling. May had been held up by the relative Antarctic warmth. But it is a further illustration of the difference between the interpolative procedures of GISS and TempLS and the cruder grid-based processes of NOAA and TempLS grid. I would probably have abandoned TempLS grid, or at least replaced it with a more interpolative version (post coming soon), if it were not for the correspondence with NOAA and HADCRUT.

Update: I see that the paper for ERSST V5 has just been published in J Climate. I'll post about that very soon, and also, maybe separately, give an analysis of its effect in TempLS. I see also that NOAA was still using V4 for June; I assume they will use V5 for July, as I expect I will. The NOAA ERSST V5 page is here.

Here is the NOAA map for the month. You can see how the poles are missing.

Saturday, July 15, 2017

GISS June down 0.19°C from May.

GISS was down from 0.88°C in May to 0.69°C in June.The GISS report is here; they say it was the fourth warmest June on record. The drop was somewhat more than the 0.12°C in TempLS. The most recent month that was cooler than that was November 2014.

The overall pattern was similar to that in TempLS. The big feature was cold in Antarctica, to which both GISS and TempLS msh are sensitive, more so than HADCRUT or NOAA. Otherwise, as with TempLS, it was warm in Europe, extending through Africa and the Middle East, and also through the Americas. Apart from Antarctica, the main cold spot was NW Russia.

So far, July is also cold, although with some signs of warming a little from June. As usual, I will compare the GISS and previous TempLS plots below the jump.