  We present a mathematical analysis of records drawn from independent random
variables with a drifting mean. To leading order the change in the record rate
is proportional to the ratio of the drift velocity to the standard deviation of
the underlying distribution. We apply the theory to time series of daily
temperatures for given calendar days, obtained from historical climate
recordings of European and American weather stations as well as re-analysis
data. We conclude that the change in the mean temperature has increased the
rate of record breaking events in a moderate but significant way: For the
European station data covering the time period 1976-2005, we find that about 5
of the 17 high temperature records observed on average in 2005 can be
attributed to the warming climate.
