This new paper by Dr. Ross McKitrick of the University of Guelph is a comprehensive review of the GHCN surface and sea temperature data set. Unlike many papers (such as the phytoplankton paper in Nature, complete code is made available right from the start, and the data is freely available.
There is a lot here that goes hand in hand with what we have been saying on WUWT and other climate science blogs for months, and this is just a preview of the entire paper.This graph below caught my eye, because it tells one part of the GHCN the story well.
1.2.3. Growing bias toward lower latitudes
The decline in sample has not been spatially uniform. GHCN has progressively lost more and more high latitude sites (e.g. towards the poles) in favour of lower-latitude sites. Other things being equal, this implies less and less data are drawn from remote, cold regions and more from inhabited, warmer regions. As shown in Figure 1-7, mean laititude declined as more stations were added during the 20th century.
Here’s another interesting paragraph:
2.4. Conclusion re. dependence on GHCN
All three major gridded global temperature anomaly products rely exclusively or nearly exclusively on the GHCN archive. Several conclusions follow.
- They are not independent as regards their input data.
- Only if their data processing methods are fundamentally independent can the three series be considered to have any independence at all. Section 4 will show that the data processing methods do not appear to change the end results by much, given the input data.
- Problems with GHCN, such as sampling discontinuities and contamination from urbanization and other forms of land use change, will therefore affect CRU, GISS, and NOAA. Decreasing quality of GHCN data over time implies decreasing quality of CRU, GISS and NOAA data products, and increased reliance on estimated adjustments to rectify climate observations.
From the summary: The quality of data over land, namely the raw temperature data in GHCN, depends on the validity of adjustments for known problems due to urbanization and land-use change. The adequacy of these adjustments has been tested in three different ways, with two of the three finding evidence that they do not suffice to remove warming biases.
The overall conclusion of this report is that there are serious quality problems in the surface temperature data sets that call into question whether the global temperature history, especially over land, can be considered both continuous and precise. Users should be aware of these limitations, especially in policy sensitive applications.
Read the entire preview paper here (PDF), it is well worth your time.
h/t to E.M. Smith