American Meteorological Society (AMS) Seminar  - “Hurricanes and Climate Change,” Friday, Sept. 21,2007, 12pm, Dirksen Senate Office Bldg Rm G-50, The Capitol, Washington DC.
From:    Anthony Socci <socci@ametsoc.org>

Hurricanes and Climate Change: What’s Resolved and What Remains To Be Resolved?

Is there a scientific basis for anticipating that human-induced climate warming
does and/or will affect hurricanes in some way, over and above natural climate
variability? Do observations and model simulations support that expectation, or
are there issues with data and observations that make the task of sorting out
linkages more difficult? If the latter, what are the observational and data
issues that continue to make this a challenging scientific problem? What do we
know now that we did not know two years ago? What role do model simulations play
in helping to sort out linkages, if any, between global warming and hurricanes,
in the absence of data/observation or the presence of unreliable
data/observations? How can we best develop a coordinated national effort to
provide urgently required information for planning, community response and
infrastructure development.

Public Invited*

Friday, Sept. 21, 2007
12:00 Noon - 2:00 pm
Dirksen Senate Office Building, Room G-50
Washington, DC

Buffet Reception Following

Moderator:
Dr. Anthony Socci, Senior Science Fellow, American Meteorological Society

Speakers:

Dr. Kerry Emanuel, Professor of Atmospheric Science, Massachusetts Institute of
Technology, Cambridge, MA

Dr. William K. M. Lau, Chief, Laboratory for Atmospheres, NASA/Goddard Space
Flight Center, Greenbelt, MD

Dr. Greg Holland, Director, Mesoscale and Microscale Meteorology Division, Earth
and Sun Systems Laboratory, National Center for Atmospheric Research, Boulder,
CO

Dr. Gabriel Vecchi, Research Oceanographer, Climate Diagnostics Group,
Geophysical Fluid Dynamics Lab/NOAA, Princeton, NJ.

Thomas R. Knutson, Research Meteorologist, Climate Dynamics and Prediction
Group, Geophysical Fluid Dynamics Lab/NOAA, Princeton, NJ.

Program Summary: Overview of Hurricanes and Climate Change (a.k.a. global warming)

The understanding of climate change, including its effects on hurricanes, rests
on three essential scientific techniques: theory, observation, and computational
modeling. Each of these three approaches has unique strengths and limitations.
In this talk, I will discuss the application of each of these to understanding
the effect of climate change on hurricane activity and demonstrate that while
each approach is compromised by uncertainties, taken together they present a
persuasive picture of increasing hurricane risk as the climate warms.

Rainfall Extremes, Saharan Dust, Tropical Cyclones and Climate Change

Trends in tropical rainfall are more readily detectable in the form of changes
in rainfall characteristics, rather than in rainfall total.  >From satellite
data, we find that in the tropics there is a strong positive trend in extreme
heavy and very light rains, coupled to a negative trend in moderate rain.
Climatologically over tropical oceans, a large portion (over 60%) of most
extreme heavy rainfall (top 5%) can be identified with those coming from
tropical cyclones.  Over the Atlantic, the contribution of tropical cyclones to
heavy rain events has almost doubled in the last quarter century.  Over the
Pacific basin, the increase is lesser at about 10%. The differences in the basin
may be related to the percentage change in the warm pool (SST> 28 ºC) areas in
both oceans.  Overall, tropical cyclones appear to be feeding more extreme
rainfall events in the tropics in recent decades.

Saharan dust can affect tropical cyclones development, and may be a factor
contributing to long-term hurricane statistics and possibly in seasonal
hurricane forecasts.   The Saharan Air Layer (SAL) can suppress tropical
cyclogenesis through entrainment of hot, dry air into a developing cyclone,
increasing stability and denying the developing system of its moisture supply.
Saharan dust may also pre-condition the Atlantic, cooling the ocean surface
through attenuation of solar radiation, during the early hurricane season.
Additionally, differential radiative heating of the atmosphere by Saharan dust
may induce changes in the large-scale circulation over the West Africa and
Atlantic region.   All these effects may provide a feedback on the coupled
ocean-atmosphere system over the Atlantic, modulating the seasonal statistics of
hurricanes.  Analyses of satellite data and historical records show a more
(less) active hurricane season is generally associated with less (more) Saharan
dust over the Atlantic.

Global Warming and Hurricane Activity

The past century has seen North Atlantic hurricanes occurring in three periods
of relatively stable frequency separated by sharp upward transitions. Each
period has experienced 50% more hurricanes than the previous one and each was
associated with a distinct change in eastern Atlantic sea surface temperatures
(SSTs). After taking account of missing cyclones in earlier periods due to poor
observing systems, we have experienced an 80-100% increase in hurricane
frequency over since the early 1900s. Natural variability has contributed to
some of the observed changes, but the compelling conclusion is that the overall
increase has been substantially influenced by greenhouse warming. Superimposed
on this increasing hurricane frequency is a completely independent oscillation
in the proportions of major and minor hurricanes (compared to all storms). This
oscillation has no distinguishable net trend and may arise largely from internal
oscillations of the climate system. The period of enhanced major hurricane
activity during 1945-1964 arose entirely from this oscillation. Unfortunately,
the period since 1995 has experienced a double-whammy of a sharp increase in
both numbers of hurricanes and the proportion of major hurricanes.

This heightened hurricane activity is unlikely to decrease in the future and we
may see further increases. If so, current planning, building and coastal levee
systems may prove to be inadequate, leading to more New Orleans-type disasters.
The National Hurricane Research Initiative is designed to provide us with the
tools to assess this future threat, to develop improved forecast and community
response approaches, and to establish coastal planning approach to minimize the
potential for future disasters. It is an initiative of critical national
importance, which deserves strong and urgent support.

Long-term changes in Tropical Cyclone Activity: Looking Forward and Looking Back

To understand how human-induced climate change influences global and Atlantic
tropical cyclone activity it is essential to have accurate records of past
tropical cyclone variations and to model future climate conditions.  The ways
that tropical cyclones are measured have evolved over time, thereby influencing
the homogeneity of the record. Statistical techniques can help, however, to
estimate these deficiencies in the century-scale record.  To project future
conditions, global climate models (GCMs) – though not perfect – are our best
tools.  Although current computing power prevents GCMs from explicitly
representing tropical cyclones, GCMs do indicate robust changes in many of the
large-scale environmental conditions that are known to influence tropical
cyclone activity, such as the thermodynamic structure of the atmosphere and
vertical wind shear. Analyses of climate models and reconstructions of past
tropical cyclone records indicate:

Observational evidence for century-scale changes in tropical cyclone activity is
mixed, depending on the metric chosen, on the statistical correction applied to
the data and on the time interval being examined.
Climate model projections of the Atlantic and East Pacific response to global
warming exhibit mixed changes in cyclone-relevant parameters, with both an
increase in thermodynamic potential intensity of tropical cyclones and an
increase in vertical wind shear. More refined methods are needed to understand
the detailed response of tropical cyclones to these environmental changes.

Outside of the Atlantic and East Pacific, projected changes to both the
thermodynamic potential and the wind shear indicate conditions more favorable to
tropical cyclone activity under global warming.

Although questions remain about the detailed response of tropical cyclone
activity to human-induced climate change, we have relatively much greater
confidence in the projected response of other large-scale climate conditions to
increasing greenhouse gases (e.g., global warming, surface temperatures over
land warm faster than over ocean, Arctic sea ice reduction, increase in ocean
heat content, etc.).

Modeling the Response of Atlantic Hurricanes to Climate Variability and Change

A pressing question concerning ongoing global warming is whether human-caused
warming of the planet has had any discernible impact on Atlantic hurricane
activity.  Confidence in any such a link is currently hampered by both data
quality issues for the hurricane observational record and by limited work
specifically targeting this question from a modeling perspective.   Based on
existing studies to date:

Observed data, including consideration of data problems, give conflicting
indications on whether there have been significant increases in Atlantic
tropical storm and hurricane numbers.  U.S. land-falling numbers have not
increased.  Models have not yet reproduced some reported long-term (~100 yr)
increasing trends in basin-wide numbers.
High resolution models consistently project increasing hurricane intensities and
rainfall rates for the late 21st century, but whether there will be more or
fewer hurricanes remains uncertain.
A new modeling approach reproduces many important aspects of Atlantic hurricane
activity observed since 1980, and thus shows promise as a tool for both
understanding past variations and for making more reliable projections of future
hurricane activity.

Biographies:

Dr. Kerry Emanuel is a professor of atmospheric science at the Massachusetts
Institute of Technology, where he has been on the faculty since 1981, after
spending three years as a faculty member at UCLA. Professor Emanuel’s research
interests focus on tropical meteorology and climate, with a specialty in
hurricane physics. His interests also include cumulus convection, and advanced
methods of sampling the atmosphere in aid of numerical weather prediction. He is
the author or co-author of over 100 peer-reviewed scientific papers, and three
books, including Divine Wind: The History and Science of Hurricanes, recently
released by Oxford University Press and aimed at a general audience, and What We
Know about Climate Change, published by the MIT Press.

Dr. William Lau is currently the Chief of the Laboratory for Atmospheres at
NASA, Goddard Space Flight Center, and Adjunct Professor at Department of
Meteorology U. of Maryland.  His research work spans three decades and covers a
wide range of topics including climate dynamics, tropical and monsoon
meteorology, ocean-atmosphere interaction, and climate variability and change.

Dr. Lau has received numerous awards for his research and his scientific
leadership, including among others,  the AMS Meisinger Award in 1997; the John
Lindsay Award,1998; the NASA Exceptional Science Achievement Award, 1991; the
William Nordberg Award (GSFC highest award in Earth Sciences), 2002.  He is a
Goddard Senior Fellow, a fellow of the American Meteorological Society since
1988, and a fellow of the American Geophysical Union, 2007.   Dr. Lau has
published over 190 refereed papers, book Chapters in refereed journals.  He is
the principal author of a book “Intraseasonal Variability in the Tropical
Ocean-Atmosphere System”, published in 2006.  Dr. Lau received his B. Sc. in
Physics and Mathematics from the University of Hong Kong, and his Ph.D. in
Atmospheric Sciences from the University of Washington, Seattle.

Dr. Greg Holland is currently Director of the Mesoscale and Microscale
Meteorology Division at the National Center for Atmospheric Research in Boulder,
where he is involved scientifically with hurricane landfall, genesis and climate
related work. He is a fellow of the American Meteorological Society as well as
the Australian Meteorological and Oceanographic Society. Dr. Holland has several
areas of research interests which have carried through to applications and
include improved forecasting of tropical cyclone motion, scale interactions
associated with cyclogenesis, establishment of field facilities, establishment
of programs on coastal impacts of tropical cyclones and the development of
Unmanned Aerial Vehicles (UAVs).

Dr. Holland has authored or co-authored more than 120 peer-reviewed scientific
journal articles and book chapters, as well as dozens of planning documents,
scientific prospectuses and workshop papers. He has given several hundred
invited talks worldwide, as well as many contributed presentations at national
and international conferences on hurricanes and related. He has also convened
several national and international workshops, and served on several national and
international committees and science-planning initiatives.

Dr. Gabriel Vecchi is a Research Oceanographer at the Geophysical Fluid Dynamics
Laboratory (GFDL) in Princeton, New Jersey, where he has been working since
2003. GFDL, which is part of the National Oceanic and Atmospheric Administration
(NOAA), is one of the world’s leading climate modeling centers. Dr. Vecchi
received a B.A. in Mathematics from Rutgers University, and an M.S. in
Oceanography, an M.S. in Applied Mathematics and a Ph.D. in Oceanography from
the University of Washington. His scientific research focuses on the
interactions between the atmosphere and oceans on timescales from weeks to
centuries. His recent research has focused on understanding long-term changes to
tropical circulation and variability, including characterizing changes relevant
to the possible impact of climate change on hurricanes.

Dr. Vecchi currently serves on the Climate Variability and Predictability
(CLIVAR) Indian Ocean Panel, and is an Associate Editor of the Journal of the
Atmospheric Sciences. His awards include the Presidential Early Career Award for
Scientists and Engineers (PECASE), the American Geophysical Union’s Editor’s
Citation for Excellence in Refereeing for Geophysical Research Letters, and the
Cook College, Rutgers University Marine Sciences Student of the Year. He has
over 30 publications in peer-reviewed science journals or book chapters.

Thomas R. Knutson has been a Research Meteorologist at the Geophysical Fluid
Dynamics Laboratory (GFDL) in Princeton, New Jersey since 1990. GFDL, which is
part of the National Oceanic and Atmospheric Administration, is one of the
world’s leading climate modeling centers.
Mr. Knutson has authored several modeling studies in major scientific journals
on the potential impact of climate change on hurricanes.  He now leads a project
at GFDL aimed at simulating past and future Atlantic hurricane activity using
regional high-resolution models.

He currently serves on the World Meteorological Organization (WMO) Expert Team
on Climate Impacts on Tropical Cyclones, and was a major contributor to the
December 2006 WMO “Statement on Tropical Cyclones and Climate Change”.  He is a
member of a U.S. Climate Change Science Program (CCSP) committee developing an
assessment report on “Weather and Climate Extremes in a Changing Climate,” the
AMS Climate Variability and Change Committee, and is an Associate Editor of the
Journal of Climate.  Mr. Knutson has over 30 publications in peer-reviewed
science journals or book chapters.

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This seminar series is open to the public and does not require a reservation.

The Next Seminar is tentatively scheduled for the week of October, 22 or 29,
2007. Tentative Topic: Impact of Global Wqarming on Precipitation Trends, and
the Human Signature of Those Trends.

Please see the following web site for seminar summaries, presentations and future events:
 http://www.ametsoc.org/seminar

For more information please contact:
Anthony D. Socci, Ph.D. Tel. (202) 737-9006, ext. 412

Or
Jan Wilkerson Tel. (202) 737-9006, ext. 436