FAQ

Surface Temperature Frequently Asked Questions

What globally gridded surface temperature anomaly products are available?

The three most commonly cited are:

NASA GISS GISTEMP
http://data.giss.nasa.gov/gistemp/

CRU/MET HadCRU
http://www.cru.uea.ac.uk/cru/data/temperature/

NOAA/NCDC
http://www.ncdc.noaa.gov/cmb-faq/anomalies.html

In addition,

Japan Meteorological Agency (JMA) Global Average Surface Temperature Anomalies
http://ds.data.jma.go.jp/tcc/tcc/products/gwp/temp/ann_wld.html

Where is the code?

NASA GISTEMP is freely available:
http://data.giss.nasa.gov/gistemp/sources/

CRU/MET released some anomalization and gridding code for use with their released data.
http://www.metoffice.gov.uk/climatechange/science/monitoring/subsets.html

Why isn’t more code available?

Climate scientists have typically published descriptions of their methods for data processing rather than releasing their code directly. This allows interested third parties to independently reconstruct their methods which is a more robust form of confirmation than simply recompiling and rerunning the original code.

What independent confirmations of the globally gridded anomaly methods have been made?

In addition to the cross-checks available by comparing and contrasting GISS, CRU, NCDC, and JMA, several technical bloggers have created their own globally gridded temperature anomaly records.

Jeff Id and Roman M
Joseph at Residual Analysis
Zeke Hausfather
Nick Stokes
Chad Herman
Steven Mosher

The “Clear Climate Code” project, which includes Nick Barnes and Dave Jones, refactored the GISTEMP code into python, uncovering some minor bugs, which were then corrected in the official GISTEMP code.

Steve McIntyre, analyzing the GISTEMP product data sets, uncovered a discontinuity around the year 2000 which was subsequently corrected.

What about satellite records?

Two satellite records are often cited as ‘surface temperature records’. These actual measure Lower Tropospheric Temperature. They both use information from Advanced Microwave Sounding Units (AMSU). The most recent AMSU platform is the AQUA satellite.

UAH
http://vortex.nsstc.uah.edu/data

RSS
http://www.ssmi.com/msu/msu_data_description.html

Are the AMSU readings calibrated against surface records?

No. The MSU instruments are calibrated against open space measurements and integrated metal plates heated to a known temperature (blackbody measurements).

What surface data is used in globally gridded temperature anomalies?

GISS GISTEMP mostly uses GHCN unadjusted data. In addition, it swaps in USHCN data for the United States. It also adds SCAR Antarctic data and data for Hohenpeissenburg.

NOAA NCDC uses GHCN data with adjustments.

Hadley CRU gathers data from National Meteorological Centers, which largely mirrors the GHCN data set, and combines that with data from other sources.

So the major surface temperature anomaly constructions use mostly the same data?

Yes. GHCN unadjusted (raw) data (or data from common sources) is used as the primary input for most globally gridded temperature anomalies records.

Where is the surface data?

CRU/MET
http://www.metoffice.gov.uk/climatechange/science/monitoring/subsets.html

GHCN v2
ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/v2

GISS add-on data
_SCAR
_Hohenpeissenburg

USHCN v2 monthly
ftp://ftp.ncdc.noaa.gov/pub/data/ushcn/v2/monthly

Is GHCN losing stations over time?

Yes. The number of stations with current records falls over time. The initial GHCN data set was manually compiled from numerous (~30) sources. After the initial definition of the data set, GHCN relies on National Weather Services (NWS) to submit current records and over time fewer stations have been reported resulting in a drop of available stations.

In addition to the attrition problem described above, there _appears_ to be some deliberate (but undocumented?) culling of stations from countries overrepresented in the data set.

Is the loss of stations biasing the GHCN data set?

Not that anyone has been able to identify.

Zeke Hausfather, ‘Extraordinary Claims’ in KUSI Broadcast On NOAA, NASA … but ‘Extraordinary Evidence’? , Yale Forum on Climate Change and the Media, January 21, 2010

Dave Jones, The 1990s station dropout does not have a warming effect, Clear Climate Code, Feb 26, 2010

Nick Stokes, Just 60 stations?, Moyhu, May 1, 2010

Dave Jones, Just 440 stations,Clear Climate Code, Aug 3, 2010

Has the GHCN data set trended more towards urban stations and away from rural stations?

Yes

Is urbanization biasing the GHCN data set?

Possibly. But UHI bias estimates vary greatly and are confounded by complex environmental factors.

Ron Broberg, GHCN: High Alt, High Lat, Rural, The Whiteboard, 2010 February 1

Dr Roy Spencer, The Global Average Urban Heat Island Effect in 2000 Estimated from Station Temperatures and Population Density Data, Global Warming, March 3rd, 2010

Ron Broberg, GISTEMP: High Alt, High Lat, Rural, The Whiteboard, 2010 March 8

Zeke Hausfather, In search of the UHI signal, The Blackboard, 9 March, 2010

Joseph, US Rural -v- Urban Temperature Changes,Residual Analysis, March 30, 2010

Nick Stokes, Just 60 stations?, Moyhu, May 1, 2010

Dave Jones, Just 440 stations,Clear Climate Code, Aug 3, 2010

Has the GHCN data set trended more towards lower latitude stations and away from higher latitudes?

Yes.

Is the trend to lower latitude stations biasing the GHCN data set?

Not that anyone has been able to identify.

Ron Broberg, GHCN: High Alt, High Lat, Rural, The Whiteboard, 2010 February 1

Ron Broberg, GISTEMP: High Alt, High Lat, Rural, The Whiteboard, 2010 March 8

Has the GHCN data set trended more towards lower altitude stations and away from higher altitudes?

Yes. But the trend is very slight, about 15 meters over 50 years.

Is the loss of high altitude stations biasing the GHCN data set??

Not that anyone has been able to identify.

Ron Broberg, GHCN: High Alt, High Lat, Rural, The Whiteboard, 2010 February 1

Ron Broberg, GISTEMP: High Alt, High Lat, Rural, The Whiteboard, 2010 March 8

Has the GHCN data set trended towards using more airports?

Yes.

Is trend towards airports biasing the GHCN data set??

Not that anyone has been able to identify.

Dave Jones, Airport Warming, Clear Climate Code, May 14, 2010

Zeke Hausfather: Airports and the land temperature record, The Blackboard, 27 May, 2010

Aren’t there issues with many stations being poorly sited? Micro-siting issues?

Yes. Anthony Watts’ “Surface Station” project has documented many instances of poor siting in the USHCN network. There is no reason to believe that GHCN is immune from similar siting issues.
http://surfacestations.org

Does the poor siting of station introduce bias in the USHCN data set?

Not that anyone has been able to identify.

Menne, Williams, and Palecki, On the reliability of the U.S. surface temperature record, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, D11108, doi:10.1029/2009JD013094, 2010

I am still not comfortable with the changes happening in GHCN. Isn’t there another data set that can be used?

Yes. The Integrated Surface Hourly (ISH) and its daily summary, Global Surface Observations Daily (GSOD), also provide world-wide coverage. The data set does not extend back in time as far, but it has many more stations than GHCN after 1973. No appreciable difference from GHCN is demonstrated when this larger data set is used.

Dr Roy Spencer, New Work on the Recent Warming of Northern Hemispheric Land Areas, Global Warming, February 20th, 2010

Ron Broberg, GISTEMP with GSOD: Round 2, The Whiteboard, 2010 June 29

Why are there multiple records and duplicate flags for the WMO station IDs in GHCN?

Are the methods for combining the station records biasing the surface trends

Yes. Jeff Id, using methods developed by Roman M, demonstrated that the CRU method of station combination introduces a slight cooling bias.

GISTEMP’s method of taking the means of latitudinal weighted zones leads to cooler record than CRU’s method of using weighted cells within hemispheres.

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