Modulation of Indian monsoon by water vapor and cloud feedback over the past 22,000 years.

To predict how monsoons will evolve in the 21st century, we need to understand how they have changed in the past. In paleoclimate literature, the major focus has been on the role of solar forcing on monsoons but not on the amplification by feedbacks internal to the climate system. Here we have used the results from a transient climate simulation to show that feedbacks amplify the effect of change in insolation on the Indian summer monsoon. We show that during the deglacial (22 ka to 10 ka) monsoons were predominantly influenced by rising water vapor due to increasing sea surface temperature, whereas in the Holocene (10 ka to 0 ka) cloud feedback was more important. These results are consistent with another transient simulation, thus increasing confidence despite potential model biases. We have demonstrated that insolation drives monsoon through different pathways during cold and warm periods, thereby highlighting the changing role of internal factors. Past Indian summer monsoon (ISM) changes are not well understood. The application of an energetic framework to a transient model simulation shows that ISM influences have changed in the past, with rising water vapor more important during deglaciation, whereas cloud feedbacks dominated during the Holocene. [ABSTRACT FROM AUTHOR]