A new look at maximum and minimum temperature trends for the globe

Abstract

A number of recent studies have established that differential changes in daily maximum and minimum temperatures are occurring, resulting in changes in the diurnal temperature range (DTR) for many parts of the globe. Large-scale trends in the USA indicate that minimum temperatures are increasing at a faster rate than maximum temperatures, resulting in a narrowing in the DTR. This paper updates and extends the analysis of changes in the DTR in three ways: (1) by increasing the areal coverage to more than half the global landmass, (2) by addressing the issue of homogeneity of the data, and (3) by examining the potential effects of urban stations on the calculated trends. The update includes data for an additional 15% of the global land area and an extension of the analysis period used in a previous study. Homogeneity techniques were used on the data to adjust individual station data for undocumented discontinuities. Annual maximum and minimum temperature and DTR time series for the 1950-1993 period averaged over 54% of the total global land area are presented. The trend for the maximum temperature is 0.88 C/100 years, which is consistent with earlier findings. However, the trend for the minimum temperature is 1.86 C/100more » years; this is less than found in previous analyses and leads to a smaller trend in the DTR. This finding is not surprising since much of the data added in this study are for tropical and sub-tropical regions where temperature trends are not expected to be as large as in higher latitude regions. The effect of urbanization on the global trends is found to be on the order of 0.1 C/100 years or less, which is consistent with previous investigations. 14 refs., 2 figs.« less

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