401 Hinds
Dept. of the Geophysical Sciences
5734 S. Ellis Ave.
The Univ. of Chicago
Chicago, IL 60637
Office: (773) 702-0440
Home: (773) 955-4058
Email: geshel@uchicago.edu
My research seeks to understand geophysical phenomena with
great human relevance, mostly employing methods and ideas of classical
physics and statistics. My thematic focus is dynamics-based
ocean-atmosphere diagnostics, with a geographic focus on the arid
subtropics, especially the Red Sea-Mediterranean region. Compared to
the deep tropics or midlatitudes, the subtropics are not dynamically
and climatically well characterized, nor are they so intensely
studied. Yet, they are home to a large portion of the global human
population, and are the locus of intense water scarcity-related
strife. The physical and dynamical mechanisms that govern subtropical
precipitation processes vary on a broad spectrum of spatial and
temporal scales, and touch on most aspects of atmospheric science:
dynamics; dry and moist thermodynamics; turbulent surface fluxes of
momentum, water vapor and heat; cloud physics. My research straddles
many of those topics as I strive to better understand the mechanisms
of modern and paleo subtropical climate variability, especially
subtropical precipitation processes, with the goal of improved
prediction. Most of my research projects involve interactions of the
atmosphere with the underlying ocean and land. Methodologically, all
combine modeling - most often using simple, home-brewed models - with
advanced and novel statistical data analysis methods designed to take
advantage of large modern geophysical datasets. A subset of my recent,
current, and planned research endeavors is described below.
Outer-Tropical Climate Mechanisms and Predictability.
Climate research is currently in a position similar to that of weather
research just after World War II. While society urgently needs
reliable climate predictions to mitigate some of the human costs of
extreme events such as droughts or heat waves, the scientific basis
for such predictions is nascent. Given that climate is the long-term
average of weather, it is natural that the principal tool used for
climate prediction has been that used for weather forecasting:
numerical models expressing the physical laws that govern
climate. While a powerful tool, numerical climate models have obvious
limitations. To be tractable, models neglect or crudely parameterize
significant aspects of the relevant physics. In addition, climate can
sometimes exhibit chaotic behavior, and estimates of its state are
under-resolved, resulting in contamination of long model runs by
exponentially growing error. While modern ensemble methods ameliorate
some of those difficulties, their full, statistically robust,
implementation is still prohibitively expensive in most cases. Because
numerical long-lead forecasts are currently uncertain, the
spatio-temporal statistical approach to interannual climate
forecasting provides a useful interim approach until numerical models,
and the hardware on which they run, mature further.
Following several papers which collectively demonstrated the
relationship of Middle-Eastern droughts to earlier North Atlantic (NA)
climate anomalies (Eshel 2002; Eshel and Farrell 2001; Eshel, Cane and
Farrell 2000; Eshel and Farrell 2000), I devised a statistical
interannual climate prediction model of those droughts. The model is
data-driven, choosing predictors from several three- and
four-dimensional geophysical datasets based on optimized space
reduction. Later adopted by the Israeli Meteorological Service, the
model has led to substantial and verifiable improvement of their
seasonal forecasts. In Eshel (2003a,b), I applied similar ideas to the
principal mode of climate variability outside the tropics, the
so-called NA Oscillation (NAO). My paper on NAO interannual prediction
is the first NAO forecasting attempt, and its skill is still
comparable to that of numerical model-based forecasts. My interest in
atmospheric predictability has also led to investigating more
fundamental questions of rates of information loss (in the Information
Theoretic sense) in the ocean and atmosphere, as reported in Eshel
(2003; JGR. 108(C2)) and Eshel (2006; JAS
63(2)), respectively. The former of these papers identified a
location in the NA that is singularly revealing of the state of the NA
ocean as a whole. The detailed examination of deep-sea cores from this
location is the centerpiece of a collaborative paleoclimate project
(with K. Billups, Delaware, and P. Martin, Chicago) currently
underway.
In the near future I plan to extend my statistical NAO predictability
study to the underlying physics. I will be guided by the mechanism I
view as most viable, in which snow cover variability over mountainous
western North America plays the pivotal role in the Pacific-NA
teleconnection. The basic idea is to present a model atmosphere with
patterns of Pacific surface anomalies that were shown to be powerful
predictors of future states of the NA, and to diagnose the dynamical
response. These spatial patterns are not derived in the usual way,
which is to maximize spanned variance. Rather, the choice of these
patterns is based on their being linear optimal excitations, affecting
future phase space trajectories most strongly for a given anomaly
magnitude.
Coastal Upwelling and the African Humid Period.
North Africa, currently extremely arid, is believed to have been much
more hospitable ~8-6 kyBP (thousand years before present). The
mild, moist climate of the region during this African Humid Period has
been invoked as a central element in the ecological success of
humans (e.g., deMenocal et al., 2000: Quat. Sci. Rev.,
19, 347-361). Much of what is considered known about the climate
of that period has been derived from subtropical Atlantic deep-sea
cores. Complicating the interpretation of these cores is the fact that
they record both continental airborne material of African origin and
biogenic material produced in the intensely productive upwelling zone
off northwestern Africa. Better understanding of the interplay between
North African meteorology and coastal upwelling off northwestern
Africa is needed to improve interpretations of the evidence for the
African Humid Period climate. Jess Adkins (CalTech), Peter deMenocal
(Columbia) and I have recently launched a collaborative effort
striving to understand this interplay. In the first paper resulting
from our work (Adkins, Eshel and deMenocal 2006), we analyze paleo
information along with some modern ocean-atmosphere data. The
followup study (Eshel, Adkins and deMenocal, in preparation for
Paleoceanography), presents a thorough analysis of the various
components of the modern state: vegetation cover, precipitation,
coastal upwelling and the low-level atmospheric state. This
multi-dataset analysis employs a generalization of two-field joint
analysis using singular value decomposition, heavily used in climate
research, to N>2 three- or four-dimensional datasets. This
generalization is described in my forthcoming book (Eshel 2007,
solicited for publication, based on my web-available notes, by
Princeton University Press). A central element of our results is the
importance of NAO variability to modulations of productivity off
northwestern Africa. In the near future, we will use this dynamical
framework to re-interpret the existing records of North African
climate during the period 8-6 kyBP.
Reconstruction of Red Sea-Mediterranean Climate in
the Last 10,000 Years. Climate fluctuations on decadal-to-millennial
timescales have been suggested as underlying such diverse recorded
near-eastern archaeological and human-development events as the
Akkadian collapse and the development of agriculture during the
Younger Dryas, among others. Some (e.g., Jared Diamond in Guns,
Germs and Steel) suggest that detailed knowledge of climatic
conditions in the Mediterranean basin and the Middle East is central
to further progress in understanding early human history. Recent
theoretical, observational and methodological developments make the
present time ripe for attempting to create a unified, rigorously
computed reconstruction of Mediterranean paleoclimate. I plan to
construct such a dataset.
The work will benefit from tools developed in the course of my
research on the paleoclimate information recorded by Red Sea corals
(Eshel, Schrag and Farrell 2000), my most recent Red Sea work [Eshel
and Heavens (in preparation for Paleoceanography), Eshel 2006
(JAS 63(2))], and also from the strong ties between the
Mediterranean and the North Atlantic (Eshel and Farrell 2000, Eshel
Cane and Farrell 2000, Eshel 2002). Approximating the state of the
Mediterranean at any time benefits discernibly from North Atlantic
information (Eshel and Farrell (2000) and Eshel et al. (2000)), but is
especially useful over the Holocene because paleo-climate proxy data
in the North Atlantic are high-quality and available at relatively
high spatial and temporal resolutions. The resultant Mediterranean
reconstruction will enhance our understanding of past and present
climates of both the Near East and North Atlantic, shedding light on
the role of Middle-Eastern climate in archaeology and human
development, and also contributing significantly toward preliminary
understanding of the expected response of the Mediterranean region to
anthropogenic changes. In addition, the results of this linear
optimization study will identify geographical regions where data
collection efforts will yield the most additional information for a
given effort.
Human Behavior and Greenhouse Gas Emissions. While rigorously
quantitative, this line of work is motivated by subjective personal
views. First, I view global climate change research as clearly
demonstrating the need for immediate, substantive action. Though
significant remaining uncertainties will continue to cloud climate
predictions in the foreseeable future, the physical sciences have
provided answers to policy-related questions. The most pressing future
issues will be in the realm of human behavior and societal structure,
and therefore a major fraction of the burden of climate change
research will fall to the social sciences.
Second, the political structure of western democracies is less and
less amenable to steering societal actions. In examples ranging from,
e.g., Italy, Israel and the US, electorates are deeply and bitterly
divided, and aspiring elected officials must appeal to the ever more
elusive and rare `undecided voter'. As a consequence, little has been
achieved politically on the climate change front, and I gravely doubt
this situation will change for the better. This state of affairs
renders voluntary individual daily-life decisions a central element of
any realistic campaign that strives to achieve discernible reductions
in greenhouse gas emissions. The line of work described in this
section attempts to contribute to bridging the wide gap between the
physical and social sciences in pursuit of climate change mitigation.
Eshel and Martin (2006) quantified the effect of various personal
dietary choices on greenhouse gas footprint. This is clearly just the
beginning. There are a number of followup avenues I am now pursuing,
or plan to in the near future. With Esther Bowen, a gifted
Environmental Studies undergraduate, I am examining the roles corn
subsidies play in the US greenhouse gas footprint, and the
relationship these roles may have with rising obesity incidence. With
Martin, I am making a more complete effort to establish the
total contribution of diet to the national greenhouse gas footprint,
as opposed to the difference between one set of choices and another,
as done in Eshel and Martin (2006). Martin and I have also made
considerable progress toward securing the necessary support and
partnerships for setting up a watershed-scale, geophysics-based,
sustainable development research and teaching Center in a 500-acre
organic farm in Millerton, NY. A related followup to Eshel and Martin
(2006) that will be facilitated by the Center will be to quantify the
energetic and greenhouse gas consequences of organic versus
conventional, as well as small- versus industrial-scale, farming. The
field course I co-led with Martin in December 2005 went a long way
toward realizing this goal, but the research is by no means finished.
I view my most meaningful contributions as: (1) developing a coherent,
self-consistent dynamical framework to explain ocean-atmosphere
motions and variability in the Red Sea-Eastern Mediterranean region;
(2) developing simple methods for geophysical statistical forecasting
and applying them to two climate phenomena with great human impact,
Middle-Eastern droughts and the North Atlantic Oscillation; (3)
writing a geophysical spatio-temporal statistics book which the
Reviewers described as ``sorely needed'' and ``technically solid,
lucidly written and engaging''; (4) contributing to enhanced dynamical
and statistical rigor in paleoclimate work; (5) advancing a rigorous
argument quantifying the effects of human dietary choices on
greenhouse house emissions; and (6) maintaining extensive civic
engagement that is firmly rooted in physical sciences, but which also
recognizes the enormous importance of national and international
politics to such societal challenges as global climate change.