Rectification and precession signals in the climate system

P Huybers,C Wunsch

doi:10.1029/2003gl017875

Abstract

Precession of the equinoxes has no effect on the mean annual insolation, but does modulate the amplitude of the seasonal cycle. In a linear climate system, there would be no energy near the 21,000 year precession period. It is only when a non‐linear mechanism rectifies the seasonal modulation that precession‐period variability appears. Such rectification can arise from physical processes within the climate system, for example a dependence of ice cover only on summer maximum insolation. The possibility exists, however, that the seasonality inherent in many climate proxies will produce precession‐period variability in the records independent of any precession‐period variability in the climate. One must distinguish this instrumental effect from true climate responses. Careful examination of regions without seasonal cycles, for example the abyssal ocean, and the use of proxies with different seasonal responses, might permit separation of physical from instrumental effects.

Highlights

[2] One of the most important elements in the discussion of climate change concerns the appearance in, and possible dominance by, Milankovitch cycles in paleoclimate records
In a linear climate system, there would be no energy near the 21,000 year precession period
We raise the question of whether these signals are due to subannual climate variability or, at least in part, are an artifact of the way in which climate signals are recorded

Summary

Wunsch

Received 2 June 2003; revised 14 August 2003; accepted 28 August 2003; published 14 October 2003. In a linear climate system, there would be no energy near the 21,000 year precession period It is only when a non-linear mechanism rectifies the seasonal modulation that precession-period variability appears. Such rectification can arise from physical processes within the climate system, for example a dependence of ice cover only on summer maximum insolation. The possibility exists, that the seasonality inherent in many climate proxies will produce precession-period variability in the records independent of any precessionperiod variability in the climate. One must distinguish this instrumental effect from true climate responses.

Introduction

A More Complete Discussion

Conclusion