Past Climate Science Speakers

11/16/2015 - 4:00pm | Climate History: Understanding drivers of conflict and violence in Medieval Ireland, Francis Ludlow, History
Francis Ludlow

Francis Ludlow’s study of 1200 years of monastic chronicles from medieval Ireland reveals a strong relationship between violence and conflict and episodes of abrupt climate change.  A paper he recently co-authored with Michael Sigl in Nature, produced a new chronology of volcanic eruptions dating back 2,500 years, some of which appear synchronous with cooling periods and drought that impacted Ireland and other civilizations around the world.  J.G. Manning speaks Tuesday on his collaboration with Francis that is helping him re-write the history of ancient Egypt

At Yale, Francis works with Prof. Benedict Kiernan of the Department of History and Prof. Michael R Dove of the School of Forestry & Environmental Studies, on a project entitled Climate as Catalyst in 1,224 Years of Violence and Conflict in Ireland, 425-1649 CE. This aims to exploit Ireland’s rich record of medieval chronicles to reconstruct the incidence of a wide array of violence and conflict, including battles, slave and cattle raids, burning of crops and settlements, and the killings of secular and ecclesiastical elites. Such events are recorded systematically in the chronicles on an annual basis, and thereby provide an opportunity to examine the influence of extreme weather, natural hazards and abrupt climatic changes (as registered in natural climate proxies such as the Irish oak tree-ring record) on violence and conflict in a complex agrarian society across a twelve-century period.

Before coming to Yale, Francis held the position of Carson Fellow at the Rachel Carson Center for Environment and Society of the Ludwig-Maximilians-Universität (LMU Munich, 2013-2014). From 2011 to 2013 he was a Ziff Environmental Fellow with the Harvard University Center for the Environment where he worked with Prof. Michael McCormick of the Department of History and the Initiative for the Science of the Human Past at Harvard on a project entitled Unifying High-Resolution Records of Environmental and Societal Stresses for Ireland, 425-1650 CE, combining Irish annalistic and tree-ring records with ice-core records. From 2012 to 2013 he was a Research Affiliate of the Harvard University Center for Geographic Analysis, and from 2011 to 2013 held the position of Research Associate with the Trinity Long Room Hub. From 2009 to 2011 Francis was a pre and postdoctoral Research Fellow with the Trinity Long Room Hub, and from 2007 to 2011 lectured in the Department of Geography, School of Natural Sciences, Trinity College Dublin. He has also lectured in Dublin City University and St. Patrick’s College, Drumcondra, Dublin, and guest lectured in the National University of Ireland, Maynooth. From 2009 to 2011 he was Treasurer of the Irish Quaternary Association. In 2006, he was a Visiting Scholar with the School of Geography, Archaeology and Palaeoecology, Queen’s University, Belfast. There he worked with Prof. Mike Baillie and Mr. David Brown on a comparison of historic weather extremes and the Irish oak dendrochronological record. Francis has also worked in University College Cork (2008-2009) with Dr. Paul Leahy and Prof. Ger Kiely as part of the Extreme Weather, Climate and Natural Disasters in Ireland project, funded by the Environmental Protection Agency, Ireland. Francis obtained a B.A. in Geography and Economics from Trinity College Dublin in 2003, a Postgraduate Diploma in Statistics from Trinity College Dublin in 2005, and a PhD in Geography from Trinity College Dublin in 2011. His PhD thesis is entitled The Utility of the Irish Annals as a Source for the Reconstruction of Climate.

Kline Geology Laboratory, Room 123 See map
210 Whitney Avenue
New Haven, CT 06511
12/01/2014 - 2:00pm | Geo-engineering Impacts on the Hydrological Cycle, Jon Egill Kristjansson, University of Oslo


As global anthropogenic emissions of greenhouse gases continue to rise, there is an increasing risk of serious disruptions in ecosystems due to global warming. As a consequence, research on climate engineering (CE) is receiving growing attention, also among climate scientists. But, even basic CE research using Earth System Models (ESMs) raises a series of ethical questions that need to be considered. Also, CE carries a risk of serious side effects, e.g., concerning the hydrological cycle.

Climate engineering can be divided into Greenhouse Gas Removal and Radiation Management (RM) techniques. RM here refers to the deliberate modification of either incoming solar radiation or outgoing terrestrial radiation. We will review the basic principles of four proposed RM techniques – stratospheric sulfur injections, marine sky brightening, cirrus cloud thinning and desert brightening. We then present recent robust results concerning changes to the hydrological cycle from multi-model ESM experiments within the Geoengineering Model Intercomparison Project (GeoMIP).

We show that the changes in the hydrological cycle depend strongly on which RM technique is applied. For instance, cirrus cloud thinning influences the hydrological cycle in a distinctly different way than techniques that reduce incoming solar radiation. We will demonstrate how that finding can be explained from atmospheric energy budget considerations.

11/03/2014 - 2:00pm | Deep Ocean Circulation in the North Atlantic and Rapid Climate Change During the Last Ice Age
Jerry McManus, Lamont-Doherty Earth Observatory

Rapid climate changes characterized the last ice age and deglaciation, with dramatic warming following the coldest intervals in the northern hemisphere. The repeated pattern of alternating temperature swings revealed in ice cores from Greenland and Antactica suggest a bipolar see-saw of heat redistribution by a dynamical component of the Earth system such as the large scale Atlantic Meridional Overturning Circulation (AMOC). Computer model simulations support this possibility, yet direct evidence for these changes in deep ocean circulation has been difficult to obtain. We have examined multiple geochemical and isotopic tracers of the deep circulation throughout the last ice age from rapidly accumulating sediments in the North Atlantic Ocean.  They document the systematic association of variations in AMOC and abrupt climate change through the glaciation and deglaciation.  Diminished AMOC accompanied the millennial northern coolings, including the cold, stadial, portions of so-called “Dansgaard-Oeschger (DO) events” as well as the extreme stadial “Heinrich events” associated with catastrophic iceberg discharges. Perhaps most notably, rapid increases in AMOC, in the form of surges in the depth and export of North Atlantic Deep Water from the North Atlantic Basin, accompanied the dramatic northern warmings that punctuated the ice age, underscoring the important potential role of internal Earth systems in climate change.


10/27/2014 - 2:00pm | South Pacific Convergence Zone (SPCZ) Variability and Biases in Models. Ben Lintner
Ben Lintner, Rutgers


The South Pacific Convergence Zone (SPCZ), an area of intense deep convection and low-level convergence extending southeastward from the western Pacific warm pool into Southern Hemisphere mid-latitudes, is a dominant feature of the tropical Pacific.  Despite its significance to the climate of the South Pacific, many fundamental aspects of the SPCZ, including its orientation and intensity, remain poorly understood.   One theorized control on the position of the SPCZ is the amount of low-level inflow from the relatively dry southeastern Pacific basin. Building on the analysis of observed SPCZ-region synoptic scale variability by Lintner and Neelin (2008), composite analysis is performed here on two reanalysis products as well as output from 17 models in phase five of the Coupled Model Inter-comparison Project (CMIP5). Using low-level zonal wind as a compositing index, it is shown that the CMIP5 ensemble mean, as well as many of the individual models, captures patterns of wind, specific humidity, and precipitation anomalies resembling those obtained for reanalysis fields between strong- and weak-inflow phases. Lead-lag analysis of both the re-analyses and models is used to develop a conceptual model for the formation of each composite phase. This analysis indicates that an equator ward displaced Southern Hemisphere storm track and an eastward displaced equatorial eastern Pacific westerly duct are features of the weak-inflow phase, though as indicated by additional composite analyses based on these features, each appears to account weakly for the details of the low-level inflow composite anomalies. Despite the presence of well-known biases in the CMIP5 simulations of SPCZ region climatologies, the models appear to have some fidelity in simulating synoptic scale relationships among low-level winds, moisture, and precipitation, consistent with observations and simple theoretical understanding of interactions of dry air inflow with deep convection.


I earned a BS in Physics at Texas A&M in 1997.  From 1997-2003, I pursued my graduate studies at UC Berkeley under the direction of Inez Fung, with my dissertation research focusing on the role of atmospheric transport in determining the spatial and temporal variability of trace gases.  After completing my PhD, I moved up two floors for a postdoc with John Chiang, during which I studied the teleconnection between the El Niño/Southern Oscillation and tropical climate.  In 2005, I joined David Neelin’s research group, working on various topics in tropical climate dynamics.  In 2009, I joined the faculty of the Department of Environmental Sciences Rutgers as an Assistant Professor.  I currently serve as the atmospheric sciences graduate program director at Rutgers as well as an associate editor of Journal of Climate.


[1] Lintner, B.R., and J.D. Neelin, 2008: Eastern margin variability of the South Pacific Convergence Zone. Geophys. Res. Lett., 35, L16701, doi:10.1029/2008GL034298.

[2] Niznik, M.J., and B.R. Lintner, 2013:  Circulation, moisture, and precipitation relationships along the South Pacific Convergence Zone in reanalyses and CMIP5 models.  J. Clim., 26, 10174—10192, doi:10.1175/JCLI-D-13-00263.1.

see also:

Kline Geology Laboratory Auditorium, Rm 123 See map
210 Whitney Ave
New Haven, CT 06511
10/20/2014 - 2:00pm | Elements of Sea Level in a Changing Climate. Stephen Griffies, NOAA
Stephen Griffies, NOAA


In this talk, we survey the physics of global and regional sea level, with a focus on how sea level has changed in the past century and may change in the future.  We start by exploring global mean sea level changes arising from ocean heating (thermosteric sea level rise) and from changes to the ocean mass.  Regional sea level variations can be large relative to the global mean, meaning they are a primary concern for sea level impacts.  Examples of such regional variations include fluctuations due to natural modes of climate variability (e.g., Pacific Decadal Variability, North Atlantic Oscillation, Atlantic Meridional Overturning Circulation), and from mass redistributions that alter the earth’s gravity field.  Scenarios for future global mean sea level changes typically include an upward trend due to ocean warming.  Less certain is our ability to project changes involving ice sheets. We conclude the talk by describing a mechanism for potentially large ice sheet melt arising from projected changes in Southern Ocean winds and the associated shallowing of relatively warm coastal currents circling Antarctica.


Stephen Griffies is a senior research scientist at NOAA’s Geophysical Fluid Dynamics Laboratory (GFDL) in Princeton, NJ.  His education includes a PhD in physics, masters in applied math, and bachelors in chemical engineering.  After a three-year post-doc at Princeton University’s Geosciences Program, he joined the GFDL staff in 1996. His research centers on aspects of the ocean’s role in the global climate system, both from a fundamental process perspective and large-scale climate perspective.  A recent focus of his work involves the study of global and regional sea level fluctuations/trends, which forms the topic of his talk.

Klein Geology, Room 123 See map
210 Whitney
New Haven, CT 06520
04/22/2014 - 4:00pm | A Changing Biosphere and the Future of Planet Earth
G. Warfield "Skip" Hobbs

Since its creation 4.5 billion years ago, Earth has experienced constant change. Whereas geologic change usually requires tens of thousands—if not hundreds of thousands or millions—of years, human civilization has made and continues to make profound changes to the planet in a much shorter time. These changes have altered the chemistry and physical state of the atmosphere and oceans at rates that have not previously occurred in geologic history, except possibly during a few cataclysmic events. This talk will discuss the human factor in geologic change, its effect on the biosphere, and the importance of sustainability in all future natural resource extraction.

G. Warfield “Skip” Hobbs is Managing Partner of Ammonite Resources Company, an international petroleum geotechnical and business consulting firm located in New Canaan, Connecticut. Hobbs was 2011 President of the American Geological Institute, a nonprofit federation of 47 geoscientific and professional associations that was founded in 1948 and represents more than 120,000 geologists, geophysicists and other earth scientists. He has also served as President of the American Association of Petroleum Geologists (AAPG) Division of Professional Affairs, President of the Eastern Section of AAPG, and is a trustee of the New Canaan Nature Center. Hobbs is a graduate of Yale University Department of Geology & Geophysics.

Kline Geology Laboratory Auditorium (KGL 123) See map
210 Whitney Avenue
New Haven, CT 06511
04/14/2014 - 2:00pm | Impacts of Aerosols on Arctic Mixed-Phase Boundary Clouds During M-PACE and ISDAC Field Campaigns: Implications for Modelling Studies
Greg McFarquhar, University of Illinois, Department of Atmospheric Sciences

Comprehensive data on arctic boundary layer aerosol and cloud microphysical and radiative properties were collected during the 2004 Mixed-Phase Arctic Cloud Experiment (M-PACE) and the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC). During M-PACE, the University of North Dakota Citation executed spiral ascents and descents through 27 mixed-phase clouds on 7 separate days over ground-based remote sensing sites at Barrow and Oliktok Point, Alaska. Data from in-situ microphysical sensors have been used to characterize how cloud particle shape, size, phase and bulk properties vary with height. These data have been used extensively to evaluate models that have contributed to our fundamental understanding of microphysical processes in mixed-phase clouds and produced potential explanations about the role of aerosols on observed ice nuclei concentrations.

However, M-PACE data were insufficient to evaluate all model hypotheses on causes of mixed-phase cloud persistence due to uncertainties in the microphysical data, the lack of information on aerosol composition and radiative properties, and the limited range of aerosol, surface and meteorological conditions over which data were obtained. ISDAC overcame these limitations and allows for an examination of the influence of aerosols on clouds influenced by ice. During ISDAC, the National Research Council of Canada Convair-580 flew 27 sorties, collecting data with an unprecedented 42 cloud and aerosol instruments for more than 100 hours on 12 different days. Data obtained above, below and within single-layer stratus during three separate days are allowing for a process-oriented understanding of how aerosols affect the microphysical and radiative properties of arctic clouds. Ultimately these data will be used to improve the representation of cloud and aerosol process in models covering a variety of spatial and temporal scales, and to determine the extent to which long-term surface-based measurements at a ground site at the North Slope of Alaska can provide retrievals of aerosols, clouds, precipitation and radiative heating in the Arctic. The need for future measurement campaigns in the Arctic to enhance the range of conditions sampled will also be discussed.

02/07/2014 - 2:00pm | Grand Challenges of Clouds: From Ice Crystal Formation to the Influence of Aerosols and Clouds on Climate. Ulrike Lohmann, IAC-ETH
Prof. Ulrike Lohmann

Ulrike Lohmann is Full Professor for Experimental Atmospheric Physics in the Institute for Atmospheric and Climate Science since October 2004.

She was born in 1966 in Berlin (Germany) and studied from 1988 to 1993 Meteorology at the Universities of Mainz and Hamburg. In 1996, she obtained her PhD in climate modelling from the Max Planck Institute for Meteorology. Prior to her current appointment, she was a post-doctoral fellow at the Canadian Centre for Climate Modelling and Analysis in Victoria and an Assistant and Associate Professor at Dalhousie University in Halifax (Canada). She was awarded a Canada Research Chair in 2002 and was elected as a fellow of the American Geophysical Union in 2008.

Her research focuses on the role of aerosol particles and clouds in the climate system. Of specific interest are the formation of cloud droplets and ice crystals and the influence of aerosol particles on the radiation balance and on the hydrological cycle in the present, past and future climate. She combines laboratory work, field measurements, satellite data and different numerical models.

Ulrike Lohmann has published more than 180 peer-reviewed articles. She was a lead author for the Fourth and Fifth Assessment Reports of the Intergovernmental Panel for Climate Change (IPCC). She is the coordinator of the EU FP7 project BACCHUS. At ETH, she is the head of the Institute for Atmospheric and Climate Science since 2006.

Kroon Hall See map
195 Prospect Street
New Haven, CT 06511
05/02/2013 - 4:00pm | Ice Cloud Seeding: A Viable Geoengineering Mechanism?
Professor Trude Storelvmo — Yale University
Kline Geology Laboratory (KGL) See map
210 Whitney Ave
New Haven, CT
04/10/2013 - 10:00am | The Risks and Efficacy of Solar Geoengineering
David Keith — Harvard University

David Keith appointments are at Harvard where he serves as the Gordon McKay Professor of Applied Physics in the School of Engineering and Applied Sciences (SEAS) and Professor of Public Policy at the Harvard Kennedy School.  Professor Keith has worked near the interface between climate science, energy technology and public policy for twenty years. He took first prize in Canada’s national physics prize exam, won MIT’s prize for excellence in experimental physics, and was listed as one of TIME magazine’s Heroes of the Environment 2009. David divides his time between Boston and Calgary where he serves as President of Carbon Engineering a start-up company developing industrial scale technologies for capture of CO2 from ambient air.


Solar geoengineering may enable a significant reduction in climate risks by partially offsetting climate change due to increasing greenhouse gases, however this emerging technology entails novel risks and uncertainties along with serious challenges to global governance. I will attempt a rough summary of the physics of solar geoengineering and present recent findings regarding (a) the climate’s response to radiative forcing by stratospheric aerosols, (b) methods of producing appropriate aerosol distributions, and (c) risks. In closing I will discuss the trade-off between solar geoengineering, emissions reductions and adaptation in climate policy.

Kline Geology Laboratory (KGL) See map
210 Whitney Ave
New Haven, CT