USING THE PRECESSION METHODOLOGY TO TIME PAST GLACIAL AND INTERGLACIAL CLIMATES

Eccentricity and precession values time interglacial and glacial climate change as indicated by the Devils Hole, Nevada, d¹⁸O climate change chronology. The pattern of eccentricity minima (more circular orbit) and precession maxima in the southern hemisphere marks the timing of change from interglacial toward glacial climate as indicated by changes in Devils Hole d¹⁸O. Further, the pattern of eccentricity minima followed by precession maxima in the northern hemisphere marks the termination of glacial climate as indicated by changes in Devils Hole d¹⁸O. This pattern shows that the last 400 k.y. cycle can be divided into glacial, interglacial, and intermediate (transitions between glacial and interglacial and vice versa) climate states based on the timing of precession values and paced by eccentricity minima. If this relation is valid, then climate is approaching a major change in state out of present-day interglacial climate. Long lacustrine climate records show that interglacial periods often end with a short episode that is likely warmer than the interglacial period. If present climate corresponds to or is changing toward this short, warm episode, then this natural warm episode could be amplified by human-driven warming over the next few centuries. Correspondence between the termination of interglacial events after the short warm period and the timing of maximum precession (increased summer solar radiation) in the southern hemisphere summer with the Devils Hole d¹⁸O record indicates that northern hemisphere climate begins a cooling trend when heat is being added to the southern hemisphere. This relation indicates that a link between glacial and interglacial periods and tropical insolation may exist.