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As a preamble and reprise, I think that it is reasonable for Cowtan and Way to take exception with HadCRU’s failure to estimate temperature in Arctic gridcells and to propose methods for estimating this temperature. At a time when the climate community argued that differences between the major indices and accessibility to CRU data didn’t “matter”, I thought that both mattered. One of the reasons for transparency in CRU data and methods was so that interested parties could carry out their own assessments, as Cowtan and Way have done.

There has been some discussion of Cowtan and Way 2013 take on HadCRUT4 at Lucia’s, Judy Curry’s, Nick Stokes and elsewhere. HadCRUt4 has run cooler than other datasets (including UAH satellite) in recent years. Cowtan and Way observe that HadCRU does not estimate temperature in many Arctic gridcells. Because Arctic temperatures have risen more than low-latitude temperatures, they state that recent HadCRU temperatures are biased low. (Since GISS extrapolates into the Arctic, it is less affected by this bias.)