Guest post by David Middleton
NOAA temperature record updates and the ‘hiatus’
In a new paper in Science Express, Karl et al. describe the impacts of two significant updates to the NOAA NCEI (née NCDC) global temperature series. The two updates are: 1) the adoption of ERSST v4 for the ocean temperatures (incorporating a number of corrections for biases for different methods), and 2) the use of the larger International Surface Temperature Initiative (ISTI) weather station database, instead of GHCN. This kind of update happens all the time as datasets expand through data-recovery efforts and increasing digitization, and as biases in the raw measurements are better understood. However, this update is going to be bigger news than normal because of the claim that the ‘hiatus’ is no more. To understand why this is perhaps less dramatic than it might seem, it’s worth stepping back to see a little context…
Global temperature anomaly estimates are a product, not a measurement
The first thing to remember is that an estimate of how much warmer one year is than another in the global mean is just that, an estimate. We do not have direct measurements of the global mean anomaly, rather we have a large database of raw measurements at individual locations over a long period of time, but with an uneven spatial distribution, many missing data points, and a large number of non-climatic biases varying in time and space. To convert that into a useful time-varying global mean needs a statistical model, good understanding of the data problems and enough redundancy to characterise the uncertainties. Fortunately, there have been multiple approaches to this in recent years (GISTEMP, HadCRUT4, Cowtan & Way, Berkeley Earth, and NOAA NCEI), all of which basically give the same picture.
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The ‘hiatus’ is so fragile that even those small changes make it disappear
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– See more at: http://www.realclimate.org/index.php/archives/2015/06/noaa-temperature-record-updates-and-the-hiatus/#sthash.B1t4pbWO.dpuf
If “the ‘hiatus’ is so fragile that even those small changes make it disappear,” the underlying trend must also be so fragile that small data fudges are the difference between hiatus and the road to AGW calamity.
In the meantime…