Model-proxy comparison is a cornerstone of climate change science. This project introduces a new, quantitative approach to model-proxy comparison for application to the new and rapidly developing field of transient climate modeling. The approach expands applicability of model-proxy comparisons to a broader research community and the range of proxy records that can be used in comparison with model results.
Specifically, the work involves a collaborative effort between investigators at Brown University, the University of Wisconsin, and the Institute of Earth's Environment, Chinese Academy of Sciences (CAS), Xian. A fully-coupled climate model (Community Climate System Model-version 3; CCSM3) will be run in time-dependent mode using accelerated insolation forcing in order to simulate the evolution of climate during two key intervals in Earth history, the past 300,000 years (a time of high-amplitude climate variability related to changing greenhouse gases, polar ice sheets and sea level) and 3.142 to 2.842 million years ago (an interval of time with the same insolation forcing but much smaller amplitude changes in greenhouse gases, ice sheets, and sea level). These two model experiments and their component forcings will be compared to one another to study the sensitivity of the model-produced climate to changing ice volume and greenhouse gases with an emphasis on tropical surface temperatures and monsoonal circulation. The model results will also be compared to previously published records of surface temperature and monsoonal circulation from marine and terrestrial geological archives. This comparison will focus specifically on the timing (phase) of changes in surface temperature and monsoonal circulation relative to changes in insolation (orbital), ice volume and greenhouse gases. This focus on comparing the phase of the climate response in the model and proxy records leverages the fact that phase is a robust metric that can be quantified from a wide range of proxies. Successful model-proxy comparisons serve to validate model reliability and promote confidence in the use of models for identifying the underlying physics of climate change.
Model results will be widely available and archived at the NOAA/NCDC World Data Center. Funding supports a full time graduate student at Brown University, who will work closely with a full time post-doctoral researcher at CAS (no cost to this project). This interaction will ensure an in-depth experience in climate modeling for the student and experience in geological proxy generation and analysis for the post-doctoral researcher. Fostering this close collaborative approach, including oversight and scientific leadership by the senior researchers, is crucial to furthering the synergistic integration of researchers from these two fields.