Christopher J. Poulsen - US grants

ABSTRACT

COLLABORATIVE RESEARCH: UNDERSTANDING CLIMATE CHANGE DURING THE FINAL STAGES OF LATE
PALEOZOIC GONDWANAN GLACIATION - AN INTEGRATED DATA-MODEL STUDY
Isabel Montanez, University of California, Davis
Vladimir Davydov & Mark Schmitz, Boise State University
Chris Poulsen, University of Michigan
Neil Tabor, Southern Methodist University
Recently developed paleoclimate archives reveal a much more dynamic transition from the late
Paleozoic Gondwanan ice age to a greenhouse world than previously considered - one characterized by
considerable co-variability in climate and pCO2. Recently documented short-lived (1 to 4 m.y.) episodes
of glaciation appear to coincide with large magnitude shifts in atmospheric pCO2, marine and continental
temperatures and relative sea-level suggesting a CO2-climate-glaciation link. This link, however, remains
untested. We propose an interdisciplinary study focused on significantly improving our understanding of
the evolution of the late Paleozoic climate system, and the mechanisms that triggered climate change
during the Earth's last period of transition from icehouse to greenhouse states. The research is designed to
test two hypotheses: (1) that atmospheric CO2 variability was the primary driver for repeated growth and
retreat of continental ice sheets, and, in turn, (2) that late Paleozoic ice sheets strongly influenced global
climate, particularly in the tropics. Specific basins in central and eastern Europe and western Argentina
have been targeted given their stratigraphic and paleogeographic coverage, presence of marine, paralic
and paleosol-bearing terrestrial deposits, and their existing biostratigraphy and potential for further
radiometric dating (i.e., multiple intercalated volcanic tuffs) and biostratigraphic analysis. This research
has three major objectives:
* To establish a radiometrically calibrated, chronostratigraphic framework (Gzhelian to early Middle
Permian) through the integration of new and existing bio-, cyclo-, and chemo-stratigraphic (87Sr/86Sr)
data with U/Pb dating of volcanic tuffs, and the application of these integrated data to multiple
quantitative tools (CONOP, RASC, CASP, GraphCor).
* To further develop and calibrate high-resolution, quantitative proxy records of paleo-atmospheric
pCO2, paleo-precipitation, and marine and terrestrial paleo-temperatures. This includes critical
evaluation and further development of new quantitative proxies as well as direct comparison of proxy
records to sedimentologic evidence for glaciations and 'warmings' in southern Gondwanan
successions.
* Development of a theoretical climate framework for the late Paleozoic glacial-interglacial oscillations
using three-dimensional climate models to quantify the sensitivity of ice sheets on Gondwana to
pCO2, determine the role of ice sheets in driving global climate change, and make climate predictions
that can be tested through comparison with the proxy records.
Broader Impacts: The proposed research will offer four major contributions to the broader scientific
community: (1) a reconstruction of the late Paleozoic climate system at an unprecedented level of
resolution and accuracy, (2) an important test of the pCO2-climate paradigm for climate evolution through
Earth history, (3) documentation of marine-terrestrial climate linkages at unprecedented temporal
resolution for the Paleozoic, and (4) the first test of proposed correlations of cyclothemic successions in
eastern Euramerican and North American basins, and of linkages to the Gondwanan glaciosedimentary
record. In addition, to the planned cross-disciplinary training of undergraduate and graduate students, the
PIs will integrate their research efforts into three educational outreach programs designed to enhance the
research and teaching opportunities of underrepresented undergraduate students and high school science
teachers. We will make our data and model simulations available to the greater scientific community by
importing them into the CHRONOS System (and its partner website, PaleoStrat), a web-based interactive
resource with which PI Davydov is directly involved.

The grandeur of mountain topography has for millennia captured the attention of poets, artists, and scientists. How plate tectonic processes of mountain building and mountain erosion by surface processes interact to produce topography over millions of years is now at the forefront of Earth science research. A fundamental question that arises when studying the evolution of mountains is: what did the past topography of mountain ranges look like? This question has proven very difficult to answer. Recent developments in both computer modeling of mountain building and erosional processes, and developments in geochemistry have made progress in reconstructing paleotopography. Advances in new geochemical techniques and mathematics (inverse problem theory) now allow a means of testing computer model predictions with geochemical (thermochronometer) data from rocks exposed at the Earth's surface today. These data record the cooling history of rocks as they are exhumed to the surface by erosion and faulting. This interdisciplinary project is addressing questions and hypotheses that are fundamental to quantifying the evolution of mountain topography including: (1) How can geologically meaningful interpretations of tectonic and geomorphic processes influencing mountain topography be improved from an integration of thermochronometer data, computer modeling, and mathematics? (2) How sensitive are thermochronometer data to different mountain building and erosional processes and how can sampling strategies be optimized to improve interpretations? and (3) What is the magnitude and rate of topographic change that can be resolved from mathematical inversion of thermochronometer data?

To address these questions, this project investigates the forward and inverse problems of mountain topographic evolution with a comprehensive model. Coupled 3D thermal, hydrologic, and kinematic computer models are under development in addition to a surface process model accounting for glacial, fluvial, and hillslope erosional processes. The coupled model is used to explore the sensitivity of thermochronometer data to different processes and mathematically invert a dense network of new and existing thermochronometer samples from the southern Coast Mountains, B.C., for the regional paleotopography. Field work is in progress for the collection of additional data. Several novel mathematical techniques are also under development. In particular, a low pass filter technique and a regularized iterative method are being used to solve the notoriously ill-posed backward parabolic equation and large scale, nonlinear inverse heat transport equation. These problems are by nature interdisciplinary and in the forefront of predicting and interpreting thermochronometer data and mountain topography.

The formation of the Andean Plateau is not well understood partly because the timing and rates of plateau uplift are poorly constrained. Estimates based on paleoclimate and thermochronometer data are consistent with formation of a plateau of modern width by about 13 million years ago. In contrast estimates based on stable isotope paleoaltimetry, a relatively new technique that employs the oxygen isotope concentration (delta-18O) of ancient soil carbonates to infer past elevation change, suggest a rapid uplift about 10 to 7 million years ago. Isotope paleoaltimetry is a promising new tool for quantifying elevation change, but several outstanding issues may complicate its interpretation. In particular, changes over the last 40 million years in surface temperature, atmospheric circulation, precipitation rate, and vapor source may affect the oxygen isotopic concentration of ancient soil carbonates. If substantial, these effects could compromise paleoelevation inferences based on the isotopes The objective of this project is to evaluate the processes that control delta-18O of precipitation in the Andes and to test the hypothesis that Andean Plateau uplift was in fact steady over the last 20 million years. The apparent rapid rise of the plateau in the late Miocene may be an artifact of changes in Cenozoic climate and atmospheric circulation that caused depletion of Andean precipitation 18O. Global and regional climate models with the capability to predict oxygen and deuterium isotope transport and fractionation provide a tool for quantifying these effects over the Andean Plateau. However, before these models can be used with any confidence, they must be validated against modern observations of oxygen isotopes in precipitation, which are currently sparsely available in the Andes. In this project, a multi-year sampling campaign across central Peru and southern Bolivia measures monthly variations in the oxygen isotope composition of precipitation. These data, when integrated with existing measurements, meteorological data, and backtracking analyses will provide critical data for assessing climate model predictions of precipitation oxygen isotopic composition and evaluate whether a Rayleigh law adequately predicts isotope fractionation on the Andes. The validated regional and global climate models are used to predict past changes in Andean delta-18O composition and to assess the influence of past climate changes on precipitation delta-18O used in soil carbonates for paleoaltimetry studies.

The Andean Plateau is one of the most dramatic topographic features on Earth. Despite its impressive nature, the mechanisms and rates of its formation remain poorly understood. A range of competing geodynamic models have been proposed to explain the formation of plateaus. To distinguish between these models it is necessary to understand the deformation and erosion history associated with the plateau and its marginal thrust belts, the present day crustal and lithospheric structure, and the paleoelevation history of the plateau. Of these, current understanding of Andean paleoelevation is arguably the most uncertain, and yet offers great insights into the formation of the plateau. The paleoelevation history can be used to make inferences about the rate and timing of mountain building, and ultimately the geodynamic processes that govern mountain building. The results of this project will provide an important evaluation of the isotope paleoaltimetry technique and provide improved calculations of the surface uplift history of the Andean Plateau.

This is an ambitious project that has the potential to fill in important gaps in the overall picture of orogenesis in the central Andes, and of convergent-margin tectonism in general. The project is constructed around a well defined basic-science question, did the Andes rise in a rapid pulse, or did they rise gradually? Producing elevations and crustal thicknesses of the magnitude found in this study area remains a key problem in continental tectonics.

This question provides a foundation from which the PIs develop a variety of linked projects, including: 3-D structural analysis of fold-thrust belt shortening in the Andes, testing of new methods of paleo-elevation analysis, use of seismic studies to characterize the roots of the range (both in the deep crust and in the underlying mantle), creative use of petrologic and isotopic data to constrain thickened crust at times in the past. The project has the potential to address 3-D mass balance issues during orogeny, as well as the impact of a rising mountain belt on continent-scale weather systems. Of note, to put the analysis of orographic weather studies in context, the PIs will also undertake a broader paleo-climate study. All of the questions to be studied are current and important, and are of interest across traditional disciplinary boundaries and, the research strategy as outlined has a high potential to answer the questions that it poses.

Changes in Earth's orbit through time are one of the main drivers of low frequency climate change. Though the influence of Earth's orbit on insolation is known, understanding of the orbit-climate link is incomplete. The orbital characteristics in many Plio-Pleistocene paleoclimate records are not consistent with local insolation forcing. The objective of this work is to investigate how orbital forcing affects the climate system, and to identify climate processes and feedbacks that modulate this forcing. To do this, the PIs have developed an earth system model that includes atmosphere, ocean, ice sheets, and vegetation responses, and is capable of running long transient simulations over multiple orbital cycles. In addition to generally investigating the orbit-climate link, the PIs will also use their model to address paradoxes raised by Plio-Pleistocene proxy records including (i) the glacial 41-kyr problem, (ii) the tropical 41-kyr problem, (iii) the evolution of climate sensitivity to orbital forcing, and (iv) the glacial 100-kyr problem. The award will support a graduate student and research experiences for undergraduates. A museum display on Ice Ages will be developed in collaboration with the University of Michigan?s Exhibit Museum of Natural History.

Previous studies of stable isotopic paleoclimate proxies found in intermontane basins and adjacent metamorphic core complexes suggest that the topography of western North America developed diachronously, obtaining high elevations first in British Columbia at about 50 million years ago and sweeping into Nevada by about 40 million years ago. The stable isotopic studies show that there are rapid and large isotopic shifts that cannot be due to surface uplift alone and call for climatic controls. This research aims to test the hypothesis that relief development and possibly regional scale surface elevation (driven by tectonics) attained threshold values that caused rapid climate and precipitation shifts by actively interfering with atmospheric vapor transport and/or stability. To test this hypothesis, the research team is using a multi-disciplinary approach that involves: (1) collection of stable isotopic data from intermontane basins over discreet time intervals and over a wide geographic area so as to compare with isotope results from climate models; (2) measurement of cooling ages of detrital minerals in an effort to constrain relief and mountain building development within the basin catchments; (3) detailed sedimetological and high-resolution geochronologic studies in basins in order to place the detrital thermochronology and stable isotopic analyses in proper geologic context; and (4) simulation of climate conditions and isotopes of precipitation under different topographic/elevational scenarios using global and regional climate models as a way to interpret the observed stable isotope signals. The goal is to discriminate between two markedly contrasting tectonic models both of which are consistent with current data sets. One calls for the construction of dynamic topography from a moderate elevation low-relief landscape to a north-to-south swell of a high elevation landscape in the Eocene to Oligocene. The other is the north-to-south collapse of a low-relief, high elevation so-called Nevadaplano into region of similar to lower mean elevation but with significantly higher-relief.

This proposal addresses a fundamental problem in paleoclimate analysis ? the cause for rapid climatic shifts. It has been proposed that with increased global warming the Earth may undergo rapid reorganization of climate regimes once critical thresholds are reached. Identifying these rapid climate changes during times when the Earth was significantly warmer and had higher concentrations of carbon dioxide is essential for our understanding of how the Earth?s climate behaves during warming episodes. The research team has identified areas in the American West through stable isotope analysis that record rapid climatic shifts when the Earth was significantly warmer (50 to 40 million years ago). What causes these climatic shifts is unknown, however. By combining global climate models with isotope paleo-precipitation measurements it is possible to assess what may have caused these rapid climate shifts. Specifically, the project will test whether they represent regional responses to the rise of mountains or large-scale reorganization of climate.

This project is investigating the potential that the combination of mobile devices and cloud computing offers to engage middle school children in scientific exploration using the same simulations and other tools that scientists employ to decompose, visualize, and understand complex systems, e.g. the spread of infectious disease or the sourcing, production, and use of energy across the globe. Drawing on Learner-centered Design (LCD) guidelines and research on motivation and learning, the project team is developing the Participatory Simulations Software Factory (PSimSF) which would produce Participatory Simulations (PSims) for various science processes that run on a broad range of mobile devices. The investigators posit that personal participation in the simulation, where a broad range of visualizations are employed, increases student engagement - with greater time on task and real-time conversation amongst the students, which in turn increases student achievement. The intellectual merit of the project rests in its team's combination of expertise and experience in working with emergent technologies, cutting-edge science methodology, and inquiry-based learning. Moreover, in creating and testing a number of prototype PSims, the project is helping the larger educational community to understand better what is the potential for these new technologies to support active, project-based learning. Finally, the mobile learning environment with its multi-player, game-like interactions builds on the characteristics of today's digital natives. The broader impacts of the project lie in the freely distributed PSims that the project is creating along with grade-level appropriate curriculum materials. The project is also aiming to make the work scalable and sustainable, with a specific focus on potential commercialization.

Topography in mountainous regions is a product of the erosion and export of material across the landscape. The frequency and magnitude of erosion events occurring in these regions is controlled by the local climate. The topography of the mountain ranges, in turn, influences the climate. This suggests a coupling between atmospheric and geomorphic processes in regions of active mountain building. Observational studies of climate-topography-erosion relationships, however, have been equivocal. One potential reason for this disparity in observational results is that the modern climate, for which most studies depend on, is a poor representation of the integrated climate history over landscape. Over the timescale of mountain building, climate can vary due to orbital variations, greenhouse gas concentrations, and the development of topography. This work will develop a coupled climate-landscape evolution model framework to quantitatively investigate interactions between climate, topography, and erosion on geologic timescales. The co-evolution of climate and landscapes will be modeled at different latitudes (e.g. tropical, sub-tropical, and mid-latitude) and for different orbital configurations in order to increase our understanding of the spatial and temporal variability inherent in the coupled climate and landscape systems. This work will complement previous and ongoing empirical studies exploring the interaction of climate and topography.

Quantifying the interaction between the climate and topography is relevant to a number of societal issues including the rate of sediment input to reservoirs, the terrestrial carbon cycle, and the intensity of erosion processes in agricultural and uplands systems. The role of climate in controlling erosion rates also has broader geological implications due its potential influence on tectonic processes in regions of active mountain building. Moreover, fully understanding the Earth as a system, including surface and lithospheric components, requires a quantitative framework for linking climate, erosion, and tectonics. This research will contribute towards this goal. Additionally, the proposed project will develop a deployable middle-school curriculum and interactive museum display in collaboration with the University of Michigan Museum of Natural History.

The late Cretaceous period (83-66 Ma) saw an important climatic transition from the extreme warmth of the early Late Cretaceous to the cooler conditions of the Early Paleocene. Evidence from multiple ocean basins indicates that this transition was accompanied by major changes in ocean circulation. However, the nature of these oceanographic changes and their role in global cooling are the subject of debate. Some interpretations call for expansion of southern component water (SCW) through the global ocean, possibly causing widespread cooling through low-latitude upwelling of cold deep waters. Others suggest shifts in the dominance of regional sources of deep-water formation, including initiation of North Atlantic sources, leading to changes in intra-basinal heat transport and climate.

This collaborative research, involving scientists from the University of Missouri-Columbia, the University of Florida, and the University of Michigan, seeks to resolve these controversies. Building on their earlier findings, the researchers will generate new geochemical proxy data from locations that will, in combination with existing data, constrain possible intermediate- and deep ocean sources and circulation modes. They will also evaluate the plausibility of paleoceanographic interpretations through climate model simulations, testing hypotheses regarding the effect of gateways and greenhouse gas concentrations on circulation patterns and deep convection and their links with global climate change.

The results of this work will add to our knowledge about the relationship between ocean circulation and global climate change and, in this way, contribute to efforts to predict future climate change. In addition, the researchers will conduct specific activities that contribute to general education and the dissemination of scientific understanding, and the training and mentoring of young scientists including the following: (i) developing short videos to communicate the excitement and novelty of paleoceanographic research to the public, to be featured in displays at natural history museums at the researchers? home institutions, and posted on popular websites, (ii) training graduate students at each of the participating institutions, and (iii) disseminating results through publications, presentations at professional meetings, and by integrating research into lecture material, discussions, and classroom exercises for graduate and undergraduate students.

COLLABORATIVE RESEARCH :Integrated Data-Model Analysis of CO2-Climate-Vegetation Feedbacks in a Dynamic Paleo-Icehouse

by

Isabel Montanez, Univ. California, Davis EAR-1338281
Christopher Poulsen, Univ. Michigan, EAR-1338200
Joseph White, Baylor University, EAR-1338247
Michael Hren, Univ. Conneticutt, EAR-1338256

ABSTRACT
Overview: Vegetation-CO¬2-climate feedbacks have been shown to be an important component of the climate system, capable of perturbing atmospheric circulation, continental surface temperatures, and hydrological cycling on regional- to global-scales. Recent work indicates that vegetation-climate feedbacks likely had the potential to push the late Paleozoic climate system between glacial and interglacial states and to strongly modify the climate regime within these states. The details of the nature, time-scales, and potential impact of these feedbacks remain elusive. This multi-disciplinary project, driven by three interlinked hypotheses, addresses these shortcomings and analyzes the roles of CO2- and orbital-forcing and vegetation-climate feedbacks in promoting glacial-interglacial transitions on eccentricity- to multi-million year time-scales:
- The response of vegetation to primarily CO2-driven glacial-interglacial transitions depended on the timing, magnitude and duration of CO2 forcing and whether critical ecological thresholds were reached.
- Tropical vegetation, by way of physiological forcing, impacted low-latitude climate and water & C cycling
- Vegetation-climate feedbacks - on a global-scale - amplified radiatively forced glacial-interglacial transitions through changes in direct surface forcing and terrestrial C & N cycling.
These hypotheses are being tested through integrated empirical, experimental and multi-scale modeling approaches across a spectrum of time- (10 to 1,000,000 yr) and spatial-scales (leaf-to-canopy-to-global climate system). Climate-CO2-vegetation feedbacks, including the role of plant physiological forcing of climate will be assessed through a two-stage modeling effort that will first reformulate a terrestrial biosphere model (BIOME-BGC) using the empirical and experimental results coupled with modeling sensitivity experiments to define plant functional traits for late Paleozoic PFTs. In the second stage, we will incorporate these PFT traits into NCAR's fully coupled Community Earth System Model and use this version to investigate glacial-interglacial dynamics.
Intellectual Merit: This research will generate the first high-resolution, high-precision reconstruction of atmospheric CO2 during the LPIA, which when incorporated into the climate modeling will provide insight into the evolution of earth system processes, including the terrestrial biosphere, in an icehouse under changing CO2 levels relevant to our long-term future. This study will be the first modification of terrestrial biosphere models to account for paleo-PFT traits and investigation of paleovegetation-climate feedbacks thus providing an improved understanding of the potential of non-angiosperm plants to influence hydrologic and C cycling through physiological forcing.
Broader Impacts: Cross-disciplinary training and mentoring will occur through in-residence internships for the Ph.D. students. Underrepresented students to Earth and environmental sciences will be integrated through a range of summer and academic year internships and programs at the collaborating institutions. This study will contribute directly to a Carboniferous exhibit planned for the Paleontological Halls of the National Museum of Natural History, Smithsonian Institution. All data generated by this study will be archived and shared via publications, and web-accessible tools.

Although plate tectonics provides a first-order explanation of the origin of mountain belts, the tectonic processes that drive surface the uplift and exhumation of mountain belts are not well understood. Even less well understood are the interactions of between uplift, erosional processes, and climate that shape the mountain landscape. This project uses state-of-the art to examine the interaction of tectonics, erosion, and climate in the Peruvian Andes to test new and controversial ideas concerning the uplift of the Andes. The project advances desired societal outcomes through: (1) full participation of women and underrepresented minorities in STEM through support of an female researchers and students plus outreach programs to high school and undergraduate students from underrepresented minorities; (2) increased public scientific literacy and public engagement with STEM through participation of outreach programs that provide research experiences for high school and undergraduate students from underrepresented minorities ; (3) development of a diverse, globally competitive STEM workforce through undergraduate and graduate student training and support of several early career researchers; and (4) increased partnerships through international collaboration. The Division of Earth Sciences Tectonics and Geomorphology & Land Use Dynamics Programs and the NSF Office of International Science and Engineering supported this project.

Earth's surface topography responds directly to mantle processes and plate tectonics, controls surface drainage and sediment transport patterns, and influences atmospheric circulation and climate. As the type example of ocean-continent subduction-generated high topography, the Central Andes are critical to evaluating geodynamic models of orogenesis. Although previous studies of the structural history, past elevations, and incision record have provided important insights on surface uplift, these studies also suggest a disparate range of uplift histories and associated tectonic drivers. Current geodynamic models for Andean orogenesis include: (1) continuous late Cenozoic crustal thickening and shortening, resulting in gradual surface uplift and canyon incision; (2) late Cenozoic delamination of South American lithosphere, resulting in rapid surface uplift and a late Miocene pulse of incision; and (3) early Cenozoic contraction-driven crustal thickening, resulting in near modern elevations in the west by late Eocene and propagating deformation eastward through the Cenozoic. To distinguish between models, this project uses: (1) stable isotope analyses of volcanic glasses and soil carbonates to provide quantitative estimates of paleoelevations over time, coupled with geochronology to constrain timing; (2) isotope-enabled general circulation modeling to determine how changing elevations affected climate and to quantitatively interpret stable isotope data, constrained by modern elevation-isotope and climate-isotope relationships; (3) data-validated fluvial erosion modeling to predict the erosional response to different models; and (4) fluvial and lacustrine sedimentology and sediment provenance to identify changes in drainage system extent and basin development. By synthesizing these data, the research team will quantify surface topography and erosion during orogenic evolution and distinguish between proposed tectonic and climatic controls.

This project generally aims to develop an understanding of seasonal non-monsoon processes in order to quantify their contribution to climate change in northern Africa. Specifically, the research aims to provide insights into the relative contributions of the West African Monsoon (WAM), extratropical cyclones, Mediterranean cold air surges, and tropical plumes to African Humid Period (AHP) rainfall (~14,800 - 5,000 years Before Present.

At millennial timescales, northern Africa experienced dramatic climate and environmental change. During the early to mid-Holocene AHP, the world's largest present-day hot desert, the Sahara, received abundant rainfall and supported widespread lakes, wetlands, and vegetation. Given the critical role of the present-day Sahara in Earth's radiation budget and its influence on Sahel rainfall, global mineral dust concentrations, biogeochemical cycles, and tropical cyclogenesis, climate variability in the Sahara, such as that observed during the Holocene, has profound impacts on the global climate system. By evaluating the contribution of these processes to AHP rainfall, the research will assist in interpreting the sources of moisture recorded in proxy records from the Sahara-Arabian desert belt which are currently ambiguous because they lie near the border of the tropical monsoon and mid-latitude rainfall regimes.

An assessment of the impact of the new dynamic soil albedo scheme within the Community Earth System Model (CESM) will offer tangible insights for climate model development and improved simulation of the AHP. The development of an objective algorithm for the detection of tropical plumes within general circulation models will be made publicly available and could be used to study the processes that influence tropical plume events across the globe in past, present, and future climates.

The Broader Impacts involve the potential for increasing the pipeline of underrepresented minority (URM) students into the earth sciences through our participation in the University of Michigan (U-M) Earth Camp. Earth Camp is a residential camp for early-career, high-school students from the Detroit-area that educates them about the earth sciences and careers in the earth sciences.

The U-M Earth Camp has consisted of a single summer experience, but is expanding to a multi-summer camp in order to increase the odds that students will study earth sciences in college. As part of our participation in Earth Camp, the participants in this project will develop and instruct a one-day atmospheric science and climate component to the first summer experience in Ann Arbor, MI and create a four-day component for the second summer experience at the U-M field station in Wyoming. In addition to broadening URM participation in the earth sciences, this project will also support the training and career-development of a young scientist and at least one undergraduate student.

This project seeks to investigate the causes and magnitude of Earth?s equilibrium climate sensitivity (ECS). The goal of the proposed project is twofold: (1) to use paleoclimate reconstructions of past cold and warm climates, the Last Glacial Maximum (LGM) and Early Eocene, to constrain ECS and its state dependence in the Community Earth System Model (CESM) series including the latest CESM2, and (2) to provide a comprehensive mechanistic understanding of the physics that govern past and future ECS. The proposed work will include development of new LGM and Eocene simulations using CESM2 and comparison of ECS in CESM2 simulations with existing LGM and Eocene simulations performed with earlier versions of the model (CESM1.2. and CCSM4) that have very different physics packages. Each simulation will be judged against a synthesis of proxy data and a new paleoclimate reanalysis product in order to evaluate the performance of the CESM versions and to identify the best estimate of ECS. The researchers will analyze this suite of simulations using climate feedback decomposition and radiative locking techniques to investigate the physical processes that regulate ECS under LGM, present, and Eocene conditions.

The potential Broader Impacts include model simulations of the LGM and Eocene that would be made publicly available for the broad paleoclimate community for further investigation and model-data comparisons. Other Broader Impacts include outreach activities planned in collaboration with the Earth Camp Program (University of Michigan) to develop a hands-on climate learning module at Camp Davies Field station with the aim to broaden participation of underrepresented minority students in the Earth Sciences. In addition, the project will support the training of an early career scientist (Post-doctoral researcher).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.