Calculate a global wavelet power spectrum & rectify bias WaveletScalogram?

How to calculate (and plot) a global wavelet power spectrum ?
How to rectify the bias in WaveletScalogram according to
Liu, Y., San Liang, X., & Weisberg, R. H. (2007)
Rectification of the bias in the wavelet power spectrum
Journal of Atmospheric and Oceanic Technology, 24(12), 2093-2102.