Fascinating paper out this week in GRL on the “leap year bias” in temperature records:

The addition of one extra day in February normally every fourth year produces a significant seasonal drift in the monthly values of that year in four major temperature datasets used in climate change analysis. The addition of a ‘leap year day’ for the Northern Hemisphere creates statistically significantly colder months of July to December and, to a lesser degree warmer months of February to June than correspondingly common (non-leap year) months.

This seems to be of no great import in discussions of long term trends, but it’s a clever bit of work.