AIUI, Hadley is the origin of much of the baseline data that everyone else uses. And that data itself isn't just raw numbers, but is massaged to factor out the heat island effect, for example.

The snippets of emails that I saw suggest (but don't prove, contrary to their opposition) that the methodology for building that baseline data was tainted.

So if that underlying data must now be considered corrupt, then it also calls into question any other research that used the baseline data.