Analysis of winter and summer warming rates in gridded temperature time series

The Intergovernmental Panel on Climate Change (IPCC) stated in its 1995 report that 'the balance of evidence suggests a discernible human influence on global climate'. The observed nearsurface warming which has occurred in the winter season over the mid-to-high latitudes of the Northern Hemispheric continental areas is used as empirical support for numerical model simulations which suggest a similar pattern of temperature change to occur under conditions of increasing atmospheric carbon dioxide levels. In this work, we investigate, in detail, the seasonal pattern of temperature change as derived from the 2 gridded temperature departure datasets-the IPCC land-based data since 1946, and the MSU (microwave sounding units) satellite-based dataset since 1979. We find that the pattern of temperature trend differentials between winter and summer seasons has not remained constant over the last 50 yr, and over the last 2 decades is in less agreement with numerical model simulations. We find a negative correlation between relative winter warming and average winter temperature, which means that winter temperatures are warming the most in colder locations.