Obvious question is whether similar adjustments were made to other regions' data. There are reports of such to South American and Icelandic data, but I can't confirm them. It would be worth finding out though. In fact, as so much money hinges on climate measures, there should be an independent team put onto this.
Difficulty is in the word 'independent' though, it's such a politically charged area of science that any team, no matter who, is going to be accused of being in one camp or the other and thus having confirmation bias.