TY JOUR TI Analysis of a piecewise linear trend of average surface temperature in the mathematical model of multifractal dynamics KW temperature KW Northern Hemisphere of the Earth KW multi-fractal dynamics KW trend KW millennium JO Russian Journal of Earth Sciences AU Tsvetkov, V.P. AU Tsvetkov, I.V. PY 2015 IS 15 PB Geophysical Center of the Russian Academy of Sciences