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Cycles in Earth’s Climate – Part 1: The Trend Setters

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rangerrebew:
Cycles in Earth’s Climate – Part 1: The Trend Setters
22 hours ago 

Richard Willoughby

Introduction

The emergence of the Isthmus of Panama, starting around 5Ma, due to uplift of the Caribbean plate was a major event in Earth’s recent climate history.  It altered the depth of cyclic glaciation, which resulted in oceans being 138m deeper than the present level 23,000 years ago.  This article looks at the cycles that drive the climate trends that create glaciation and interglacials.  Chart 1 provides the reconstructed temperature history based on EPICA Dome C and the Spratt 800kyr sea level reconstruction over the past 800kyr.


Chart 1 also shows the top of the atmosphere (ToA) solar electro-magnetic radiation (EMR) for July at 15N (left hand scale).  The basic frequency of the solar EMR is 23kyr corresponding to what is termed Earth’s axial precession cycle, which is modulated by eccentricity of the orbit around the sun and axial obliquity,  Over the last 1Myr, eccentricity has exhibited  a period of 89kyr and obliquity  a period of 39kyr.

Fourier Transform of Temperature and Sea level Histories

Fourier transformation of time based data transforms the data from the time domain to the corresponding frequency domain to tease out the significant cyclic components in the data.  Chart 2 displays the frequency components inherent in the change in sea level for the sea level shown in Chart 1.


There are three period peaks in the frequency domain.  The two shorter periods, 23.3kyr and 39.4kyr align reasonably well with precession and obliquity cycles.  The peak at 102.3kyr is a little longer than the period of eccentricity in the present era.  It is noted here that the time interval for the sea level data is 1kyr with 512 data points so the resolution for longer periods is quite poor.

https://wattsupwiththat.com/2024/05/16/cycles-in-earths-climate-part-1-the-trend-setters/

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