Evidence for Hemispheric-Scale Bicentennial Periodicity in Northern Hemisphere Temperature

Eight reconstructions of temperature in the Northern Hemisphere covering 1192-2015 years were analyzed using both Fourier, wavelet and principal component approaches. A hemispheric-scale cyclicity with a period of 170-250 years was found present in Northern Hemisphere temperature for more than the last millennium. It is shown that this variation may have a certain contribution to warming in the first half of the 20th century. However, the last 4-5 decades are most likely a period of decline of this cycle. Possible origins of the revealed bicentennial periodicity are discussed.