The daily maximum temperatures have increased 0.88 K per century between 1950-1993, on average over the continents, and the minima show a trend of +1.86 K/C (1). Thus the daily temperature range has been diminishing by 0.98 K/C, on average. This is attributed partly to more cloud.
The estimate is based on regular weather stations which represent about 54% of the world’s land area. Only in a few parts have the maxima not increased, viz eastern Canada, southern USA, parts of eastern Europe, southern China and southern South America. The minima increased almost everywhere, but not eastern Canada and small areas of the Middle East and eastern Europe.
In Australia the daily temperature range decreased between 1951 - 1992, especially in areas where summer rainfall exceeds winter precipitation, and in the very southwestern corner of the continent (2). The reduction was by as much as 0.5 K, notably in southeast Queensland. However, the range increased in central Western Austalia and in eastern Victoria. During the same period crop harvests increased, notably of wheat.