Confirmation Of The Dependence Of The ERA-40 Reanalysis Data On The Warm Bias In The CRU Data

UPDATE: pm December 12 2009 – I was asked to clarify the importance of this post.

 The reason that it is important to document the link of ERA-40 to the warm bias in CRU (and thus NCDC and GISS data sets) is that the ERA-40 paper is used to make claims about global and regional warming (with the inference that this is an independent assessment from the surface temperature data trends).

However, the e-mails from Phil Jones show that the surface and ERA-40 analyses are intimately linked. An example of a paper that uses the ERA-40, with its warm surface temperature bias, is

Schar et al,2004,The role of increasing temperature variability in European summer heatwaves. Received 15 September; Letter to Nature; accepted 17 December 2003; doi:10.1038/nature02300. Published online 11 January 2004.

The climate science community needs to recognize that the assessment of global warming using the magnitude of the long term trends in surface air temperatures from the CRU, NCDC and GISS analyses, and from ERA-40, overstate the magnitude of this warming.


There is a remarkable admission in the leaked e-mails from Phil Jones of the dependence of the long term surface temperatures trends in the ERA-40 reanalysis on the surface temperature data from CRU.

 This is a very important issue as ERA-40 is used as one metric to assess multi-decadal global surface temperature trends, and has been claimed as an independent assessment tool from the surface temperature data. The report ECMWF Newsletter No. 115 – Spring 2008 overviews the role of ERA-40 in climate change studies.

The paper by Eugenia (Kalnay) that is presumably being referred to in the Phil Jones e-mails, which I have presented later in this post,  is

Kalnay, E., and M. Cai, 2003: Impact of urbanization and land-use on climate change. Nature, 423, 528-531.

There are a number of subsequent papers that have built on the‘observation minus reanalysis’ (OMR) method analysis methodology introduced by Eugenia including

Kalnay, E., M. Cai, H. Li, and J. Tobin, 2006: Estimation of the impact of land-surface forcings on temperature trends in eastern Unites States. J. Geophys. Res., 111, D06106,doi:10.1029/2005JD006555.

Lim, Y.-K., M. Cai, E. Kalnay, and L. Zhou, 2005: Observational
evidence of sensitivity of surface climate changes to land types and urbanization
. Geophys. Res. Lett., 32, L22712, doi:10.1029/2005GL024267.

Nuñez, Mario N., H. H. Ciapessoni, A. Rolla, E. Kalnay, and M. Cai, 2008: Impact of land use and precipitation changes on surface temperature trends in Argentina. J. Geophys. Res. – Atmos., 113, D06111, doi:10.1029/2007JD008638, March 29, 2008

Fall, S., D. Niyogi, A. Gluhovsky, R. A. Pielke Sr., E. Kalnay, and G. Rochon, 2009: Impacts of land use land cover on temperature trends over the continental United States: Assessment using the North American Regional Reanalysis. Int. J. Climatol., DOI: 10.1002/joc.1996.

Following is the July 8 2004 e-mail from Phil Jones. I have made bold font the text that specifically refers to the conenction between the ERA-40 reanalysis and the CRU data. 

From: Phil Jones <>
To: “Michael E. Mann” <>
Date: Thu Jul 8 16:30:16 2004

Only have it in the pdf form. FYI ONLY – don’t pass on. Relevant paras are the last 2 in section 4 on p13. As I said it is worded carefully due to Adrian knowing Eugenia for years. He knows the’re wrong, but he succumbed to her almost pleading with him to tone it down as it might affect her proposals in the future ! I didn’t say any of this, so be careful how you use it – if at all. Keep quiet also that you have the pdf. The attachment is a very good paper – I’ve been pushing Adrian over the last weeks to get it submitted to JGR or J. Climate. The main results are great for CRU and also for ERA-40. The basic message is clear – you have to put enough surface and sonde obs into a model to produce Reanalyses. The jumps when the data input change stand out so clearly. NCEP does many odd things also around sea ice and over snow and ice.

The other paper by MM is just garbage – as you knew. De Freitas again. Pielke is also losing all credibility as well by replying to the mad Finn as well – frequently as I see it.I can’t see either of these papers being in the next IPCC report. Kevin and I will keep them out somehow – even if we have to redefine what the peer-review literature is !

For your interest, there is an ECMWF ERA-40 Report coming out soon, which shows that Kalnay and Cai are wrong. It isn’t that strongly worded as the first author is a personal friend of Eugenia. The result is rather hidden in the middle of the report. It isn’t peer review, but a slimmed down version will go to a journal. KC are wrong because the difference between NCEP and real surface temps (CRU) over eastern N. America doesn’t happen with ERA-40. ERA-40 assimilates surface temps (which NCEP didn’t) and doing this makes the agreement with CRU better. Also ERA-40’s trends in the lower atmosphere are all physically consistent where NCEP’s are not – over eastern US.

I can send if you want, but it won’t be out as a report for a couple of months.

Prof. Phil Jones
Climatic Research Unit Telephone +44 (0) 1603 592090
School of Environmental Sciences Fax +44 (0) 1603 507784
University of East Anglia
Norwich Email

The claim that “ERA-40 assimilates surface temps (which NCEP didn’t) and doing this makes the agreement with CRU better” is a circular argument as the CRU data (or its close proxy) is what ERA-40 assimilates, so of course it is better! 

The claim that “[a]lso ERA-40’s trends in the lower atmosphere are all physically consistent where NCEP’s are not – over eastern US” must just mean that the ERA-40 agrees better with the IPCC model predictions.  To use a model prediction to test a reanalysis trend product is, of course,  a violation of the scientific process.

The e-mails from CRU documents sloppy science. 

Since the ERA-4o data is a major climate assessment tool, the introduction of surface temperature data with a warm bias (e.g. see, see and see) means that ERA-40 necessarily also has a warm bias in the diagnosis of the magnitude of global warming.  

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