Right, the same old song that only makes sense to those who need a straw to grasp. The differential analysis of those US sites which were claimed to be badly sited compared to those confirmed to be well sited showed the well sited set had a higher increase than the others.
1 I disagree, the good ones showed less warming.
2 Nope, this is in addittion to that potential contamination of the data.
so... recent data is LESS accurate now? something smells fishy with your arguments (fishy as in flopping around when caught)
Recent data is more accurate but it is also more detailed which will make changes look more dramatic when compaire to the same changes in the past because the data for the past temperatures has been smoothed out by less fidelity in the way it has been measured.
If you measure the temperature with the best million dollar equipment today to get superb results you must be extreemly careful about how you compair these results with the historic data which was collected by a college professor in his spair time. The old data may be from the same actual temperature conditions but has lower figure just because the professor was in class when the temperature hit maximum.
For the record, I think it has got a bit warmer recently. If this is unusual is a different question.