Archive for December, 2010

BOM vs GISS- Who’s Right?

December 6, 2010

Ken Stewart,  December 2010

Thanks to Chris Gillham who first noticed this oddity and has posted at

http://www.waclimate.net/bomhq-giss.html

The Goddard Institute of Space Studies (GISS) produce global temperature records with raw data sourced from raw GHCN data with USHCN corrections, which in turn comes from meteorological agencies all over the world. In Australia, the Bureau of Meteorology (BOM) supplies the data from selected sites. As it is important that the data is as accurate as possible, good quality sites are preferred. In Australia, there are two sets of preferred sites for climate analysis: the High Quality (HQ) series and the Reference Climate Station (RCS) sites. These two sets overlap – there are many sites in both.

As BOM explain: “Operational monitoring of Australia’s changing climate is based on (the) high-quality data series.”

http://www.bom.gov.au/climate/change/hqsites/about-hq-site-data.shtml

 

… and …

“The Australian Reference Climate Station (RCS) network has been established for high quality, long-term climate monitoring, particularly with regard to climate change analysis. The establishment of the network followed a request by the World Meteorological Organisation to all of its member nations in 1990.”        See

http://www.bom.gov.au/climate/change/reference.shtml

 

The HQ sites are used to produce BOM’s trend maps and time series graphs, and the CSIRO uses RCS data to produce the State of the Climate reports. The primary purpose of RCS is to provide a set of timeseries from which data can be interpolated/ extrapolated to check and/or fill in missing data when gridding. Therefore data from these sites are critical.

Chris Gillham has analysed the records from the HQ sites which are still being used by GISS in 2010. A large number of sites, mainly rural, were dropped after 1992. Most of these have very long temperature records. It seems that all of the sites he has looked at except Launceston Airport, Perth Airport and Brisbane Airport are RCS sites. It appears that GISS get their data from a selection of RCS sites, major airports, and one other site- Eucla.

In this post I will look at the remaining RCS sites.

I have found exactly the same phenomenon as Chris found in his analysis. The GISS annual data matches the raw BOM data almost exactly in most years before 1995, and monthly data is exactly the same in 2010 (there are slight differences as GISS calculates annual data from December to November, not calendar years). Therefore we can say with confidence that the GHCN raw data which GISS uses is drawn from BOM raw data.

When I examined the data, I found that between 1995 and 2009 for the majority of sites the GISS raw data, which should be the same as the BOM data, is significantly less (29 sites significantly less than BOM,  2 higher and 14 similar). It is up to 1 degree Celsius lower, but typically about 0.3 to 0.6 lower.

This is very odd. The result is that trends calculated from BOM’s raw data for the CSIRO climate analyses are much greater than those from GISS. However, for many sites, the RCS data is far too short to be of any use!

It’s an embarrassment. They can’t both be right.

There must be a logical explanation for this. Perhaps there has been a system wide problem with download/ upload of data, or with interpretation of site information (latitude/ longitude).

Whatever the reason, the 1990s / 2000s divergence between BOM and GISS means must be investigated and corrected.

In summary:

Sites with 1993- 2006 data missing:

Cape Nelson Lighthouse, Nowra RAN, Winton, Maree, Forrest (92- 2000), Christmas Island, Oodnadatta, Cape Bruny Lighthouse, Tarcoola, Robe, Wilsons Promontory, Cape Otway Lighthouse, Yamba Pilot Station, Richmond RAAF, Moruya Heads Pilot Station, Richmond PO, Amberley RAAF, Cape Leeuwin, Melbourne Air (1993-99).

Following are plots of the RCS sites. For the remainder, see http://www.waclimate.net/bomhq-giss.html

First, the only site in all of Australia recently used by GISS that is neither HQ nor RCS: Eucla in Western Australia.

It seems likely that Eucla was once considered as a possible HQ/RCS site but was subsequently not included. However, its feed to GISS continued from 1997, albeit with gaps in the yearly record.

Note: two sites with GISS data above BOM:

Oodnadatta:

Lord Howe Island:

Note that Antarctic sites do not show this pattern – only mainland and offshore islands.

Macquarie Island:

Casey:

Davis:

Mawson:

Concerning Antarctica: there are certainly few indicators of global warming (rising temperatures, mainly minima, mainly in winter and greater in polar regions) at Australia’s Antarctic bases.

• Rising temperatures? While the temperatures at Davis and Casey are rising at about 1.2C and 1.0C respectively per 100 years, this is no worse than many Australian sites; Macquarie Island’s trend is about 0.85C, peaking in the 1980s and falling since, and Mawson is cooling at -0.2C.

• Mainly minima, mainly in winter? The fastest warming site, Davis, is warming less in winter (0.3C) than the rest of the year and minima trend (0.5C) is less than maxima trend.

Davis minima:

Davis winter:

• Greater temperature rise in polar regions? The average trend at these sites is 0.71C compared with 1 degree Celsius for the Australian mainland (according to BOM).

Offshore islands-

Willis Island:

Cocos Island:

Norfolk Island:

Christmas Island:

Mainland:

Learmonth Air:

Forrest:

Gove Air:

Maree:

Mt Isa Air:

Townsville Air:

Winton:

Coffs Harbour:

Williamtown RAAF (1998 above!):

Nowra RAN:

Canberra Air:

Cape Nelson Lighthouse:

Eddystone Point:

Hobart Air:

Sydney Air:

Melbourne Air:

Adelaide Air:

References:


http://data.giss.nasa.gov/gistemp/station_data/

 

http://www.bom.gov.au/climate/data/

 

 

 

Advertisements