Assessments of the relationship of changes of the global surface air temperature with different natural and anthropogenic factors based on observations

Abstract

We obtained estimates of the relationship of changes in the global surface air temperature (GSAT) with different natural and anthropogenic factors based on empirical data beginning from the middle of the 19th century using the Granger causality test estima� tion and application of cross wavelet analysis. Along with the solar and volcanic activity and changes of the carbon dioxide concentration in the atmosphere, we estimated the role of quasicyclic processes in the Earth's climatic system. We analyzed the climatic vari� ations detected by the index of the Atlantic multidec� adal oscillation (AMO) with a characteristic period of approximately 60-70 years and the variations in the angular velocity of the Earth. We made a conclusion on the basis of the empirical regression models based on data beginning from the middle of the 19th century that the changes of the CO2 concentration in the atmosphere have a determining influence on the longterm (secular) GSAT trends. The natural climatic cycles with periods of a few decades influence significantly only on the relatively fast GSAT variations. The influence of natural factors related to solar and volcanic activity on the longterm trends appeared to be much less significant. One of the modern key problems is estimating the role of natural and anthropogenic factors of global cli� mate changes. The natural climatic variability not related to external forcing is characterized by a wide spectrum of temporal and spatial scales and the effects of an anthropogenic character can hardly be distin� guished against the background of the natural variabil� ity. The problem of distinguishing the anthropogenic influence is strongly complicated by the effects of non� linearity and stochasticity in the climatic system under