A systematic wavelet-based exploratory analysis of climatic variables

Nonstationarity and time scale dependence are essential features of the climate system that may be simultaneously dealt with using wavelet analysis. In this study, we present a systematic analysis of a set of climate system variables, which include both natural and anthropogenic contributions, using wavelet-based exploratory methods. The tools of the continuous wavelet transform, the wavelet spectrum, coherence, and phase offer a comprehensive assessment of the characteristic modes of variability of climate system forcings and of the scale-based relationships of anthropogenic and natural climate variables with global surface temperature. Shorter term variations in global surface temperature are associated with internally generated natural climate variability and external climate forcings, while longer term variations are strongly related to human induced changes only. In this respect, a long term component of the net radiative forcing of human activities longer than 30 years displays a statistically significant relationship with global warming and cooling periods identified in the climate change literature