Trends in record-breaking temperatures for the conterminous United States

In an unchanging climate, record-breaking temperatures are expected to decrease in frequency over time, as established records become increasingly more difficult to surpass. This inherent trend in the number of record-breaking events confounds the interpretation of actual trends in the presence of any underlying climate change. Here, a simple technique to remove the inherent trend is introduced so that any remaining trend can be examined separately for evidence of a climate change. As this technique does not use the standard definition of a broken record, our records^* are differentiated by an asterisk. Results for the period 1961-2010 indicate that the number of record^* low daily minimum temperatures has been significantly and steadily decreasing nearly everywhere across the United States while the number of record^* high daily minimum temperatures has been predominantly increasing. Trends in record^* low and record ^* high daily maximum temperatures are generally weaker and more spatially mixed in sign. These results are consistent with other studies examining changes expected in a warming climate.