Analysis of trends in the variability of daily and monthly historical temperature measurements

This investigation analyzes trends in the variability of daily and monthly nera-surface air temperatures. We examined the 5° latitude by 5° longitude monthly temperature anomalies available for many grids around the world. Overall, the trend in intra-annual temperature variance is towards reduced variability and is highly significant over the past 50 and 100 yr. We then examined daily maximum and minimum temperatures from the United States, China, and the former Soviet Union for intra-monthly variability in January and July. Most of the trends also indicated declining variability. A final approach examined the occurrence of record-setting daily maximum and minimum temperatures from the same countries. We found no evidence for an increase in record temperatures. The fact that intra-annual and intra-monthly variance is declining suggests that we should see fewer record temperatures in recent years. There is some evidence for this is in the daily data. In general, our results argue against the proposition that temperatures have become more variable as global temperatures have changed in this century.