August 5, 2011
In an article published August 5 in Science, UW-Madison professor of atmospheric and oceanic sciences and environmental studies Zhengyu Liu offers his perspective on a new analysis of ancient lakebed sediments that challenges established views of Indian monsoon dynamics.
Zhengyu Liu
An important annual climate cycle, the Indian summer monsoon has major implications for human well-being, in part because it influences seasonal rainfall in South Asia. Climate researchers have long sought to understand the factors that cause the monsoon's intensity to vary and how climate change may affect it.
Researchers have come to believe that during the Pleistocene (about 2.6 million years before the present), the Indian summer monsoon weakened during cooler periods as glaciers in the northern hemisphere expanded, and that the monsoon strengthened during warmer periods as the ice sheets melted.
This paradigm now faces a serious challenge, Liu writes. New research -- also published in the August 5 issue of Science -- suggests that the Indian summer monsoon often reached its weakest point, and even began to strengthen, before global volumes of glacial ice reached a maximum. The authors also propose that during glacial periods, the development of the monsoon was driven by cooling in the southern hemisphere, highlighting the role of interaction between the atmosphere in the northern and southern hemispheres.
"Independent observations and climate modeling are needed to confirm and under¬stand this new paradigm, but it may help reduce the uncertainty surrounding the response of the [Indian summer monsoon] to global warming," Liu concludes.
Liu is a faculty affiliate and past director of the Nelson Institute Center for Climatic Research and co-leader of a team of scientists at UW-Madison modeling the Earth's climate. Their computer model intertwines the forces and energy at play in the atmosphere, in the oceans and in great swaths of glacier ice.