One of the loudest and longest criticisms of U.S. (and other) temperature data is that the raw data are adjusted to compensate for non-climate factors, so we can better identify the changes due to climate factors (which is, after all, what we really want to know).
All the adjustment procedures are well documented, programs, raw and adjusted data are publicly available, but deniers continue to imply either total incompetence or, far too often, outright fraud — that adjustments only exist to exaggerate warming trends. In truth, adjustments exist to make the data better.
Open Mind 