GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 124-1
Presentation Time: 1:35 PM


RUDDIMAN, William F., University of Virginia, Charlottesville, VA 22904,

In the 70’s-80’s CLIMAP and SPECMAP Projects, Andy McIntyre and I found changes in the North Atlantic polar front and SST at orbital rhythms of 100,000 and 41,000 years. Because they were in phase with ice-volume changes, we concluded that ice sheets drove North Atlantic surface-ocean responses via ‘fast’ downwind effects on air masses, followed by a ‘fast’ downwind transfer into maritime Europe. I also mapped a band of abundant ice-rafted debris at latitudes 40-50oN, where icebergs encountered warmer North Atlantic drift waters. But we sampled at orbital-scale intervals and missed the millennial-scale oscillations later explored by Helmut Heinrich and Gerard Bond. We found that the northern subtropical gyre remained warm while ice sheets were growing and we proposed that moisture fluxes from that region amplified ice-sheet growth. But later work has convinced me that ablation is the main control on ice mass balance.

In the 80’s and 90’s, I was the first to suggest that uplift of the Tibetan Plateau played a major role in climate changes during the last 50 million years. GCM simulations with John Kutzbach and Warren Prell showed that Tibetan uplift amplified meanders in the jet stream and strengthened Asian winter and summer monsoons. I suggested that downstream southward jet-stream shifts over North America were causal in starting ice ages. But Maureen Raymo (then my graduate student) proposed that increased chemical weathering of uplift-fragmented rock debris by amplified summer monsoon rains drew down CO2 and was the real key to global cooling. Her explanation prevails.

Since 2000, I have explored the effects of early farming on Holocene greenhouse gas emissions and climate. I proposed that rising CO2 and CH4 trends during the last 7000-5000 years were opposite in direction from decreases in previous interglaciations because of anthropogenic emissions from farming. This proposal has held up well. In addition, archaeological and paleoecological work during the last few years has show that agricultural activities (forest clearing, rice irrigation, and livestock tending) are major factors in the anomalous pre-industrial greenhouse-gas trends. I anticipate that the early anthropogenic view will prevail.