No abstract

Previous studies have shown that there are several indices of global-scale temperature variations, in addition to global-mean surface air temperature, that are useful for distinguishing natural internal climate variations from anthropogenic climate change.Appropriately defined, such indices have the ability to capture spatio-temporal information in a similar manner to optimal fingerprints of climate change. These indices include the contrast between the average temperatures over land and over oceans, the meridional temperature gradient, the temperature contrast between the Northern and Southern Hemisphere and the magnitude of the annual cycle of average temperatures over land. They contain information independent of the global-mean temperature for internal climate variations at decadal time scales and represent different aspects of the climate system, yet they show common responses to anthropogenic climate change. In addition, the ratio of average temperature changes over land to those over the oceans should be nearly constant for transient climate change. Hence, supplementing analysis of global-mean surface temperature with analyses of these indices can strengthen results of attribution studies of causes of observed climate variations.In this study, we extend the previous work by including the last ten years of observational data and the CMIP3 climate model simulations analysed for the IPCC AR4. We show that observed changes in these indices over the last ten years provide increased evidence of an anthropogenic influence on climate. We also show the usefulness of these indices for evaluating the performance of climate models in simulating large-scale variability of surface temperature.

Abstract:A regional climate model (RCM) for New Zealand has been developed. The RCM is embedded within a GCM and both models are run under pre-industrial conditions. Seasonal mean output of the RCM is compared against NCEP data and the New Zealand national climate database. Regional and seasonal aspects of modelled surface temperature and precipitation are to a large extent simulated correctly. The main anomalies are related to the difficulty of incorporating New Zealand's orography appropriately and to the initial and lateral boundary conditions, which were supplied by the GCM. The largest anomalies occur over the Southern Alps, where the modelled temperatures are too low and where the amount of precipitation is too high. Many parts of the east coasts in both the North and South Island are too warm and too dry. Correlation patterns of temperature and precipitation with mean sea-level pressure differ considerably from the equivalent patterns constructed from NCEP data, but do show in general the dominant relationships between wind direction and temperature and precipitation.