If the Cowtan and Way adjustment correcting for a shortage of Arctic Weather Stations is performed on recent data, why is it not required for long term historical correction? [Alan]

This question troubled me for some time – until I realized the following: The trend of global warming is not globally consistent and has not always been globally consistent. In other words, we know that some parts of the planet are warming faster than others, and that this unequal warming phenomenon is somewhat recent.  Especially relevant, we know that the Arctic is now warming much faster than the remainder of the globe (even than the Antarctic). This seems to be largely a function of the fact that Arctic sea ice is melting during summer. As it melts, less incoming radiation is reflected back into space with the consequence that more reaches the ocean surface and is turned into heat.  This, then, warms oceans and radiates back out thus in turn warming the atmosphere.  Since the Arctic ice melt is accelerating, this Arctic warming is also accelerating.  When the Arctic was not warming substantially faster than the rest of the planet, the presence of fewer weather stations in that region was less critical than it is now.