Holocene Climatic Optimum - Milankovitch Cycles

Milankovitch Cycles

This climatic event was probably a result of predictable changes in the Earth's orbit (Milankovitch cycles) and a continuation of changes that caused the end of the last glacial period.

The effect would have had maximum Northern Hemisphere heating 9,000 years ago when axial tilt was 24° and nearest approach to the Sun (perihelion) was during boreal summer. The calculated Milankovitch Forcing would have provided 8% more solar radiation (+40 W/m2) to the Northern Hemisphere in summer, tending to cause greater heating at that time. There does seem to have been the predicted southward shift in the global band of thunderstorms called the Intertropical convergence zone.

However, orbital forcing would predict maximum climate response several thousand years earlier than those observed in the Northern Hemisphere. This delay may be a result of the continuing changes in climate as the Earth emerged from the last glacial period and related to ice-albedo feedback. It should also be noted that different sites often show climate changes at somewhat different times and lasting for different durations. At some locations, climate changes associated with this event may have begun as early as 11,000 years ago, or persisted until 4,000 years before present. As noted above, the warmest interval in the far south significantly preceded warming in the North.