The Nature of the Macroweather-Climate Scaling Break in Holocene Climate

Wednesday, 17 December 2014: 4:30 PM
Kristoffer Rypdal, Tine Nilsen and Hege Fredriksen, University of Tromsø, Tromsø, Norway
There exists a large body of literature which demonstrates the existence of long-range memory scaling in climate time series, but there are very few papers that attempt to explain its origin. Huybers and Curry (2006) claim an apparent higher scaling exponent β>1 on time scales greater than a century, corresponding to a non-stationary time series. Lovejoy et al. (2013) also claim a break in the scaling, and denotes the stationary regime with β~0.1 on the time scales 10 days <τ<102 yr the macroweather regime and the non-stationary time-series on the scales τ>102 yr the climate regime.

By closer scrutiny, however, the break in scaling for ice-core records from Greenland and Antarctica seems to be a result of indiscriminate use of paleoclimatic records over periods that include both glacial and interglacial climate. By analysis of these time series for glacial and Holocene climate separately, the scale break in the Holocene is shifted to τ~103 yr, while it remains at τ~102 yr during the last glacial maximum, and is associated with the DO events. Moreover, the scaling for 103 < τ<104 yr is still stationary with β ~0.8. The scale break observed in some multiproxy data at τ~102  yr for global or hemispheric mean temperatures for the last two millennia is associated with an oscillation of period approximately 103 yr, involving the MWP and LIA. This oscillation can be attributed to a combination of volcanic and solar forcing. If we correct for this forced oscillation we obtain a consistent scaling with β~0.8 up to τ~103 yr, which match perfectly onto Holocene ice-core scaling for τ>103 yr. The low β ~0.1 observed for ice-cores at scales τ<103 yr is typical for local, continental temperature records, while the multiproxy scaling with β ~0.8 is typical for global temperature scaling in the Holocene. Thus, with exception of the millennium-period oscillation observed in global-scale multiproxy records there is consistent macroweather scaling in global temperature records with β~0.8 on all scales above the weather regime throughout the entire preindustrial Holocene.

In the industrial period an apparent scale break at τ~10yr is due to the anthropogenic trend. After removal of this trend there remains an effect of a global oscillation of period ~60 yr associated with the AMO, but not really a break in scaling.