CET Temperature Trends In March
By Paul Homewood
As is the case with most months, trends in maximum temperatures in England took a step up in the late 1980s. (Mean temperatures also show a similar picture).
But does this mean that all days are getting warmer? Or that the warmest days are getting hotter or more frequent?
I have done some analysis on the CET daily series, which goes back to 1878, and its produces some surprising results.
The average March maximum temperature over the series is about 9.3C, and I have calculated the number of days each year that are over 13C and under 5C. These equate approximately to 10th percentiles.
We find that:
1) The number of hot days in recent years has not been high by historical standards, although they seem to be more regular since 1990.
2) There has been, though, a marked absence of really cold days since the 1980s. The only year that stands out in the last decade is 2013, the coldest March on record in England since 1910.
This all implies that average temperatures have not been increasing because all days have become slightly warmer. Instead it is the absence of cold days which is mainly responsible.
Another way to look at it is temperature extremes are narrowing, rather than the opposite which is often claimed.
We can make one further check. The distribution of the hottest March days shows that the warmest was in 1965, and there is no indication that such days are becoming more common – indeed, the opposite seems to be the case.
We find a totally different picture when we look at the coldest days. As before, there has been a marked absence of these for two decades or more. We also find that many much colder days were experienced prior to 1970, even when we compare the really cold month in 2013.
This is all very clear evidence that it is largely the absence of extremely cold days which has pushed up average temperatures in March.
This is only one month, so it will be interesting to see if we find the same pattern repeated in other months.