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Past Climates

CCR researchers are examining the impacts of variations in the Earth’s orbit, greenhouse gases, volcanic activity, and solar fluctuations on the Earth system over periods of centuries to millennia. Areas of investigation include the response of plant species, ecotones, ice sheets, megafauna, and fire regimes to both gradual and abrupt climate change over extended time durations, along with the impact on climate and the global carbon budget of early-human agricultural practices.

Principal Investigators

Sara Hotchkiss, John Kutzbach, Zhengyu Liu, Michael Notaro, Patricia Sanford, Steve Vavrus, Jack Williams

Ongoing Projects

Project: Response of lakes to long-term drought – A paleoecological test of the landscape position hypothesis
PI: Patricia Sanford
We are providing cladoceran (Crustacea: Branchiopoda) zooplankton fossil evidence in the assessment of the frequency of droughts over the last 1000 years and then over the last 5000 years by close interval analysis of lake sediment cores from several lakes chosen from a 61 lake data base of Vilas Co. WI lakes.

Project: Reconstruction of dissolved reactive silica in northern Wisconsin lakes using sponge spicule width: Assessing limnological response to drought, fire, and/or Euro-American settlement activity
PI: Patricia Sanford
Using short lake sediment cores from 10 Vilas Co. WI lakes, undergraduate students measured smooth sponge spicule widths to obtain an estimate of dissolved reactive silica in lake waters at 6 time points covering pre- and post- Euro-American settlement times to document limnological responses to landscape and climate changes.

Project: Exploring the early anthropogenic hypothesis
PI: Steve Vavrus, John Kutzbach, Bill Ruddiman
We are investigating whether anthropogenic global climate change began thousands of years ago upon the advent of agriculture, as opposed to the traditional perspective that humans began large-scale modification of climate only with the start of industrialization.

Project: Simulating and understanding abrupt climate-ecosystem changes during Holocene with NCAR-CCSM3
PI: Zhengyu Liu
With funding from the Department of Energy, we are using NCAR CCSM3 to examine two major abrupt environmental changes: the collapse of North African monsoon-ecosystem in mid-Holocene and sudden cooling event in Pan-Atlantic ocean-atmosphere system around 8,200 years ago.

Project: Transient climate evolution of the last 21,000 years – Understanding climate sensitivity and abrupt climate change using CCSM
PI: Zhengyu Liu
With a grant from P2C2 with the National Science Foundation, we are performing the first set of synchronously coupled climate model simulations of the transient climate evolution of the last 21,000 years using NCAR CCSM3, while exploring a new paradigm of model-data comparison.

Project: PHASEMAP, a new paradigm for paleoclimate model-proxy comparisons: Stage I, Pleistocene surface climate and global monsoons
PI: Zhengyu Liu

Project: Development of an isotope-enabled CESM for testing abrupt climate changes
PI: Zhengyu Liu, Bette Otto-Bliesner

Project: A pilot study of simultaneous parameter and state estimation in coupled ocean-atmosphere general circulation models using the ensemble Kalman filter
PI: Zhengyu Liu
With funding from the National Science Foundation, we are developing a novel strategy for systematic parameter optimization in an ocean-atmosphere global climate model using an ensemble-based data assimilation strategy, with a focus on reducing tropical biases in the model.

Project: Deglacial Laurentide mass balance
PI: Anders Carlson
We are testing the response of the Laurentide Ice Sheet to climate warming during the last deglaciation.

Project: Extent of the southern Greenland Ice Sheet during past interglacial periods
PI: Anders Carlson
We are determining how much smaller than present was the Greenland Ice Sheet during earlier interglacial periods that were naturally warmer than present.

Project: Holocene sources of sea-level rise
PI: Anders Carlson
We are dating the Holocene retreat of the Laurentide and Scandinavian Ice Sheets to constrain sources of sea-level rise and how fast an ice sheet can melt in a warmer than present climate.

Project: Onset of the last deglaciation in Wisconsin
PI: Anders Carlson
We are dating when the Laurentide Ice Sheet began to retreat in Wisconsin to measure how sensitive an ice margin is to small changes in radiative forcing

Project: Deglaciation of southwest Greenland
PI: Anders Carlson
We are dating southwest Greenland Ice Sheet retreat to investigate its natural rates of retreat in a warming climate.

Project: Drought as a trigger for rapid state shifts in kettlehole ecosystems
PI: Sara Hotchkiss
This project studies the relationships among hydrological variability, floating peat mat establishment and expansion, and lake-ecosystem dynamics within kettle basins along a landscape gradient in Wisconsin to test the hypotheses that 1) floating mat development is episodic and triggered by hydroclimate variability, 2) basin morphology and landscape position determine kettle ecosystem susceptibility and response to floating peatland development, and 3) rapid development of floating peat mats triggers an abrupt ecosystem state-shift in remnant lake systems and increases in whole-system rates of carbon accumulation.

Project: PalEON: A Paleoecological Observatory
PI: Jack Williams
PalEON (the PaleoEcological Observatory Network) is an interdisciplinary team of paleoecologists, ecological statisticians, and ecosystem modelers. Our goal is to reconstruct forest composition, fire regime, and climate in forests across the northeastern US and Alaska over the past 2000 years and then use this to drive and validate terrestrial ecosystem models. We are developing a coherent spatiotemporal inference framework to quantify trends and extreme events in paleoecological and paleoclimatic time series. Variables such as forest composition, fire regime, and moisture balance will be inferred from corresponding paleoecological proxies, with rigorous estimates of uncertainty. This research is supported by NSF awards EF-1065656, EF-1241868. For more information, see or follow @Pal_EON on Twitter.

Project: Incorporating biotic Interactions into models of species assemblages under climate change: A comparison of single-species and community-level approaches
PI: Jack Williams
How biological communities respond to environmental change is determined both by the tolerances of individual species and by interactions among species. However, most efforts to predict climate-driven changes in the geographic distributions of species have largely ignored species interactions. This project will develop and test new methods that consider species interactions by accounting for patterns of species co-occurrence to predict how species and biological communities respond to changes in climate. Observed changes in the distributions of plants and mammals during the last 21,000 years will be combined with independent simulations of past climates to examine how species interactions vary across broad regions and in response to changes in climate. Results will help address the grand challenge of predicting how changes in climate may alter natural systems and their associated ecosystem services. This research is supported by NSF award DEB-1257508.

Project: Timing and Drivers of Woolly Mammoth Extinction on St. Paul Island, AK
PI: Jack Williams
This project will provide new data on the paleoclimates, paleoenviroments and the biodiversity impacts of sea level rise on the southern edge of the Bering Land Bridge (BLB), and use this information to better constrain hypotheses about the timing and causes of the Holocene woolly mammoth population on St. Paul Island, Pribilof Islands, Alaska. Cores from Cagaloq Lake, St. Paul, will be sampled for stable isotopes, chironomids (aquatic invertebrates), pollen, coprophilous fungi spores, plant macrofossils, charcoal, ancient DNA and cryptotephras. Analysis of ancient DNA will provide data on cryptic plant and animal species that have not been detected by traditional methods of analysis, and can also be used to identify taxa to species. Digital elevations, bathymetric data, sea level curves, and Geographic Information System (GIS) technology will be used to reconstruct island size from the time of its isolation until today. A highly constrained chronology of the Cagaloq record will be achieved by using 14 C dates and tephras. An exhibit on the results of the project will be prepared by the EMS Museum at Penn State University with a web component. In addition, a special on-line, interactive exhibit will allow participants to reconstruct the island at various sizes, populate it with differing mammoth populations and define different climate and environmental factors to observe how each of these components affects mammoth extinction. The interactive exhibit will be available on the Neotoma database. Members of the group will make presentations on the project at the Alaska Quaternary Center in Fairbanks, which serves as a hub for promoting Alaska Quaternary research and outreach to the public. This research is supported by NSF award ARC-1203772. For more information, see

Project: Megaherbivore and climatic controls on fire and vegetation dynamics during the last deglaciation
PI: Jack Williams
The last deglaciation (roughly 17,000 to 8,500 years ago) offers an important model system for studying the effects of climate change on species, interactions among species, and fire regimes. During this time, global temperatures rose by 3 to 5°C, atmospheric CO2 rose from 190 to 280 parts per million, and northern North America was uncovered by the melting of the Laurentide Ice Sheet. Biologically, this period was marked by massive change: the extinction of many large vertebrate species, expansion of species distributions by 100s of kilometers, increases in biomass burning, and the reshuffling of plant species into novel communities. Ecologists have long sought to understand the processes that caused the reshuffling of species into novel ecosystems during the last deglaciation. This project will test the hypothesis that megafaunal extinctions contributed to vegetation change by assessing the relative importance of temperature and trophic controls on deglacial vegetation and fire dynamics. To this end, the research team will collect and analyze a series of lake-sediment cores in the eastern US, using lead-lag relationships among independent paleoclimatic and paleoecological proxies within sites and spatiotemporal patterns across sites as the basis for hypothesis testing. Understanding the ecological effects of the late-Pleistocene megafaunal extinctions has direct implications for contemporary debates about ‘rewilding’ (i.e., re-introducing large vertebrate species or their functional analogs to ecosystems) as a management tool for restoring ecosystem function and disturbance regime and for understanding the trophic consequences of the current wave of extinctions. This work is supported by NSF Award #DEB-1353896.