Solar Forcing, Climate Change and the Invention of Agriculture

Joan Feynman [joan.feynman@jpl.nasa.gov] and Alexander Ruzmaikin, Jet Propulsion Laboratory, California Institute of Technology, Pasadena.

    Climate change, driven by orbital variations, affected the major event in human history, the invention of agriculture. Our Homo Sapiens ancestors appeared almost a half million years ago but agricultural societies did not arise until 11,000 years before the present (ybp). After that agriculture was independently developed at least four times, demonstrating that it is not very difficult to invent agriculture if the conditions are right. But what are the right conditions and why did they not occur until 11,000 years ago?

            The anatomically modern species of human being (Homo Sapiens Sapiens) first appeared in East Africa 130,000 ybp and the first migrations from Africa took place 55,000 ybp. These time scales are close to those of the climate records archived in polar ice cores, marine sediments and coral cores. From the archeological data we estimate that the first development of an agricultural society required 2,000 years of climate stability. However, we show the climate proxy data imply continuous strong climate variability on times scales between 450 and 800 yrs throughout the period between 55,000 and 11,000 ybp. These climate changes ended 10,000 ybp allowing the development of agriculture in multiple independent regions of the world.