TRAINING SESSION ON HOMOGENISATION METHODS

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TRAINING SESSION ON HOMOGENISATION METHODS
Nature of the problem
Bologna, 17th-18th May 2005
Maurizio Maugeri, University of Milan
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Nature of the problem
The whole current debate on climate change is
deeply connected with data quality and
homogeneity. Data quality is a very capital
factor in any climate-change-related issue. It is
at the moment one of the most widely debated and
controversial topic in the field of climatology.
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A good example of the problems related to
observational data is presented by Redder et al.,
2004.Radiosonde data, which are generally
assumed to be unbiased, are often used to
determine and remove biases in satellite
observations.
Nature of the problem
Radiosonde temperature data over the United
States are shown to have significant and
unexplained inhomogeneities in the
mid-troposphere.
Redder et al., 2004 Unexplained discontinuity
in the U.S. radiosonde temperature data, J. Atm.
Oc. Tech., vol. 21, 1133-1144.
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Nature of the problem
It is necessary to highlight how, in climate
analyses, data quality must be continuously
brought into question, in order to draw
conclusions as more solidly as possible. Fu et
al., 2004 address the inconsistencies between
temperatures observed globally by the
mid-tropospheric channel of satellites (channel
two) Microwave Sounding Unit (MSU) showing a
warming trend of less than 0.1 K per decade and
surface temperatures based on the in situ
observations (showing a larger trend, of more
than 0.17 K per decade). This trend difference
-they conclude- is mainly due to differences in
data adjustments related to instrument
calibration and diurnal drift correction. The
problem probably depends on the fact that
although the original purpose of MSU
measurements was to improve weather forecasts
the data are often used to satisfy climate
research requirements. So, even if a continuing
data analysis effort has been made to assure
homogeneity, there are probably a lot of open
questions concerning this topic.
Fu et al., 2004 Contribution of stratospheric
cooling to satellite-inferred tropospheric
temperature trends, Nature, vol. 429, 55-58.
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Nature of the problem
The scientific community is well aware that any
reconstruction of past climate variability and
change must rely on the most solid, reliable
and homogeneous data-sets
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The problems beyond the data

• Problems are not always connected with the data
  themselves, but they can also be related to the
  meaning we attribute to the data problems of
  misinterpretation.
• Soon et al., 2004 We conclude that published
  results suggesting that the Northern Hemisphere
  surface air temperature has increased by the
  extremely rapid rate of about 1 to 2.5C per
  decade during the last one year (2002-2003) are
  most likely artefacts of methodology and
  procedure of trend smoothing.
• ? Accurate communication of methods and
  avoidance of data-padding procedures for
  smoothing and/or filtering of climatic time
  series should be incorporated in reporting data
  trends.

Soon et al., 2004 Estimation and representation
of long-term (gt40 year) trends of
Nothern-Hemisphere-gridded surface temperature A
note of caution, Geophys. Res. Lett.., vol. 31,
L03209, doi10.129/2003GL019141.
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The problems beyond the data

• In some cases the problems depend both on the
  data and on the analytical techniques. A good
  example is related to the work performed by Mann
  et al. (2003 and previous papers) on a large
  amount of proxy records.
• Stephen McIntyre and Ross McKitrick claimed
  various errors in Mann's research, but McIntyre
  and McKitrick offered no explanation as to why
  their analysis also differs from other
  reconstructions. McKitrick has been accused of
  making errors in his own analyses. In turn, Mann
  (supported by Tim Osborn, Keith Briffa and Phil
  Jones of the Climatic Research Unit) has disputed
  the claims made by McIntyre and McKitrick ,
  saying they have made critical errors in their
  analysis that have the effect of grossly
  distorting the reconstruction of Mann et al.,
  2003.

Mann et al., 2003 Global surface temperatures
over the past two millennia , Geophys. Res.
Lett., vol. 30, 1820, doi10.129/2003GL017814. McI
ntyre, and McKitrick, 2003 Corrections to the
Mann et al 1998 proxy data base and Northern
hemispheric average temperature series Energy
Environment 146, 751-771.
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The problems beyond the data

• In 2004 Mann, Bradley, and Hughes published a
  corrigendum to their article, correcting a number
  of mistakes in the online supplementary
  information that accompanied their article but
  leaving the actual results unchanged. MM have
  published another Geophysical Research Letters
  article on February 12th, 2005, claiming that the
  "Hockey Stick" shape was a result of a
  programming error, and that using the same steps
  like Mann et al., they were able to obtain the
  Hockey Stick graph in 99 percent of cases even if
  red noise was used as input. Mann and his
  collaborators have responded to articles by
  Stephen McIntyre and Ross McKitrick via various
  means, including the blog Real Climate
• It is also to be noticed that Moberg et al. have
  recently generated reconstructions with
  significantly more variability than the
  reconstructions of Mann et al., 2003.

Mann et al. Corrigendum Global-scale
temperature patterns and climate forcing over the
past six centuries, Nature, 430, 105,
2004. McIntyre and McKitrick Hockey sticks,
principal components, and spurious significance.
Geophys. Res. Lett., vol. 32, L03710,
doi10.1029/2004GL021750, 2005.
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Focus on the data
First Postulate of Any Researcher involved in
studying past climate variability and change It
is not possible to consider any record of
climatic data as entirely reliable and
homogeneous It is quite likely that the
situation will stay as such for some time in the
future.