The recent paper by Cowtan and Way (2013) Coverage bias in the HadCRUT4 temperature series and its impact on recent temperature trends made the rounds in the climate change blogosphere. Posts at RealClimate (here) and at SkepticalScience (here) looked on the paper as the second coming of…errr…Hansen’s GISTEMP maybe, saying Cowtan and Way (2013) proved the UKMO HADCRUT4 data underreports by half the warming of global surface temperatures since 1997. The posts at WattsUpWithThat (here) and at Judith Curry’s blog (here) weren’t so flattering, to put it mildly. Lucia at her blog TheBlackboard had three posts (here, here and here.) Lucia spoke favorably about Cowtan and Way (2013), but offered in a comment (here):
That said: We do need to put the changes in context of testing models, and they don’t make a big difference. Models still look pretty bad, though maybe a tiny bit less bad. If the models are bad we can be pretty confident the divergence will increase over time — though it might take longer. OTOH: if the models are ok, the divergence will correct itself. Observing this puts us exactly where we were before C&W was published!
And Steve McIntyre’s post (here) illustrated the apparent 2005 breakpoint in his Figure 2. I’ll discuss in this post why that’s odd, among other things.