Little Ice Age wetting of interior Asian deserts and the rise of the Mongol Empire Aaron E. Putnam a, b, * , David E. Putnam c , Laia Andreu-Hayles b , Edward R. Cook b , Jonathan G. Palmer d , Elizabeth H. Clark b , Chunzeng Wang c , Feng Chen e , George H. Denton a , Douglas P. Boyle f , Scott D. Bassett f , Sean D. Birkel a , Javier Martin-Fernandez b , Irka Hajdas g , John Southon h , Christopher B. Garner f , Hai Cheng i , Wallace S. Broecker b a School of Earth and Climate Sciences and Climate Change Institute, University of Maine, Orono, ME 04469, USA b Lamont-Doherty Earth Observatory, 61 Rt. 9w, Palisades, NY 10964, USA c College of Arts and Sciences, University of Maine at Presque Isle, Presque Isle, ME 04769, USA d Climate Change Research Centre, School of Biological, Earth and Environmental Sciences, The University of New South Wales, Sydney, 2052 NSW, Australia e Institute of Desert Meteorology, China Meteorological Administration, Ürümqi, China f Department of Geography, University of Nevada, Reno, Reno, NV 89557-0154, USA g Ion Beam Physics, ETH, Zürich, Switzerland h School of Physical Sciences, University of California, Irvine, Irvine, CA 92697, USA i Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an 710049, China article info Article history: Received 29 April 2015 Received in revised form 12 October 2015 Accepted 21 October 2015 Available online xxx Keywords: Asian hydroclimate 14 C Dendrochronology Paleohydrology Mountain glacier Snowpack Westerlies Asian monsoon Tarim Basin Taklamakan Desert Lop Nor abstract The degree to which warming of the planet will alter Asia's water resources is an important question for food, energy, and economic security. Here we present geological evidence, underpinned by radiometric dating and dendrochronology, and bolstered by hydrological modeling, indicating that wetter-than- present conditions characterized the core of the inner Asian desert belt during the Little Ice Age, the last major Northern Hemispheric cold spell of the Holocene. These wetter conditions accompanied northern mid-latitude cooling, glacier expansion, a strengthened/southward-shifted boreal jet, and weakened south Asian monsoons. We suggest that southward migration of grasslands in response to these wetter conditions aided the spread of Mongol Empire steppe pastoralists across Asian drylands. Conversely, net drying over the 20th century has led to drought that is unprecedented for the past ~830 years, and that could intensify with further heating of the Asian continent. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Sub-millennial climate fluctuations and associated changes in moisture availability can have important effects on human civili- zations (Zhang et al., 2008; Buckley et al., 2010; Cook et al., 2010; Pederson et al., 2014; Davi et al., 2015). Water-climate in- teractions are particularly important in Asia, Earth's largest and most populous continent, where hydroclimatic changes may have attended cultural shifts over the past two millennia (Zhang et al., 2008; Pederson et al., 2014). Although atmospheric temperatures over the center of the Asian continent are highly sensitive to radi- ative heating of the land surface (Solomon et al., 2007; McKinnon et al., 2013; McKinnon and Huybers, 2014), it is uncertain how the hydrological system will respond to future warming (Chiang * Corresponding author. School of Earth and Climate Sciences and Climate Change Institute, University of Maine, Orono, ME 04469, USA. E-mail address: aaron.putnam@maine.edu (A.E. Putnam). Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev http://dx.doi.org/10.1016/j.quascirev.2015.10.033 0277-3791/© 2015 Elsevier Ltd. All rights reserved. Quaternary Science Reviews 131 (2016) 33e50