The climate of ten thousand years ago: a numerical simulation

Abstract

A thermodynamic model that includes the annual cycle, an ocean mixed !ayer and a variable cryosphere is applied to simulate the climate of 10 000 years ago.It is shown that in lower latitudes the insolation anomalies dueto the orbital variations were the main factor that produced the departures from the present climate. However, besides the insolation anomalies, the permanent ice sheets also affected the climate of 10 kyr BP in middle and higher latitudes. The average computed land surface temperature in the Northern Hemisphere is l.9ºC warmer than present summer and colder during the other seasons, with an anomaly as large as -2.1 °c in winter. The annual average anomaly being -0. 1°c.The computed surface ocean temperature remains below the present values during the entire year with an average value of -0.8 in winter, -0.2 in summer and -0.SºC for the whole year. It is shown that when present values of surface ocean temperature are prescribed, a warmer climate is obtained, with average land surface temperature anomalies equal to 2.2, -1.6 and -0.3° for summer, winter and annual values respectively. A study on the importance of the inclusion in the model of the annual cycle, the ocean mixed !ayer and the variable cryosphere is carried out.