Centennial-scale trends in the Indian summer monsoon and the Inter-tropical Convergence Zone during the last 2,000 years

There is growing evidence from paleoclimate proxies that over thousands of years, as the northern hemisphere warms, the Inter-tropical Convergence Zone (ITCZ) moves northward and the monsoons strengthen. This observation is highly relevant to future climate change scenarios that reveal the largest warming in the northern hemisphere. On shorter, centennial time-scales less is known. Here we present new paleoclimate records of the Indian summer monsoon winds over the past few thousand years derived from Arabian Sea sediments, and compare them with other records of the monsoon and ITCZ. We find the monsoon winds were stronger, and the ITCZ located northward, during a warm interval sometimes termed the Medieval Warm Period. We find that the monsoon winds were weaker, and the ITCZ located farther south during the Little Ice Age, when the northern latitudes were cooler. Our study reveals a natural oscillation in climate upon which future change might be superimposed, and also indicate a potential relationship between northern warming (induced by greenhouse gas accumulation), the monsoons, and the ITCZ.