EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Milankovitch Theory and Global Monsoon

Hai Cheng
Hai Cheng
  • Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an, China (

  The Milankovitch Theory of orbital climate change postulates that changes in the caloric summer half-year insolation (or Northern Hemisphere summer insolation (NHSI) at ~65°N latitude) drive changes in the ice-sheets extent (i.e., global ice-volume) at Earth’s orbital periods (i.e., the sensu-stricto theory). These insolation-driven changes in turn, incite ancillary changes in other parts of the global climate systems via various forcing and feedback mechanisms (the sensu-lato hypothesis). In this theoretical framework the high-latitude glaciation processes took the center stage while the low-latitude global monsoon was essentially excluded. In the last two decades, large numbers of cave d18O records with precise radiometric chronologies have propelled speleothems to the forefront of paleoclimatology. Of particular interest are the speleothem records from North America that reveal a persistent orbital pacing of the North American climate at the precession band, which is nearly in phase with changes in the global ice-volume and atmospheric CO2 but lags June insolation at 65°N by ~5000 years, in accordance with the sensu-stricto Milankovitch theory. Contrastingly, the low-latitude tropical speleothem records manifest an orbital-scale pattern of global monsoon, which is dominated by precession cycles with a nearly anti-phased relation between the two hemispheres. Importantly, the monsoon variations track summer (July/January) insolation without significant lags at the precession band. We thus suggest that precession-induced changes in summer insolation produce distinct climate variability in the ice-sheet proximal and tropical regions predominantly via the (delayed) ice-volume/CO2 forcing/feedbacks and nearly-in-phase monsoon/CH4 responses/feedbacks.

  As for global-scale millennial events that were superimposed on orbital-scale climate variations, the essence of these events—i.e., conventional ice age terminations and other smaller events (the so-called ‘low-amplitude versions of terminations’), is virtually similar. The time-series of millennial-scale variations after removing orbital insolation signals from the speleothem monsoon record and long-term trend in the Antarctic ice core temperature (δD) record characterize the millennial climate variances of both ice age termination and low-amplitude versions of termination events. Remarkably, the millennial-scale variations show significant obliquity and precession cycles that are in-phase with North Hemisphere June insolation, implying a critical role of changes in orbital insolation in triggering the ice age terminations. These observations, in turn, provide new insights into the classic ‘100 ka problem’.

  Indeed, a more comprehensive picture of orbital theory of climate is steadily emerging with the growth of new geological proxy data, particularly the low-latitude speleothem data from the vast global monsoon regime, providing critical complements to marine and ice-core data.

How to cite: Cheng, H.: Milankovitch Theory and Global Monsoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1422,, 2022.