Determining the driving forces behind climate change, as well as the sensitivity of Earth's climate system to these forces, is a central question in paleoclimate research. This study will provide the first explicit evaluation of changes in stochastic versus deterministic climate processes associated with the evolution of the Late Paleogene to Neogene climate system (36 Ma to the present). This timeframe was chosen because high quality, high resolution, continuous data are available for analysis, and because the interval spans the transition from a high pCO2 "Greenhouse" climate to a low pCO2 "Icehouse" world. The investigators focus on the analysis of published foraminiferal oxygen and carbon isotope records and use a number of techniques rooted in Thomson's multi-taper spectral method (MTM), as well as a suite of non-linear time series analysis methods. The project will generate several products: 1) a new high resolution benthic d18O composite record spanning 36 Ma to the present, 2) an analysis of the evolution of orbital signals over the same timeframe, and 3) a quantification of changes in stochastic climate variability during the Late Paleogene to Neogene, and an assessment of the relative dominance of deterministic orbital versus stochastic climate energy through the Greenhouse-Icehouse climate transition. Funding supports collaboration between a young PI and a senior female scientist, as well as graduate student training. The algorithms produced in the course of the research will be made publicly available as a resource for the broader climate science community.
Earth’s Climate Noise: A Key to Reconstructing Past Global Climate Change The rhythm of the seasons has a familiar "deterministic" beat, while random "stochastic" variability hinders accurate long-term weather forecasts. Similarly, both deterministic and stochastic processes influence climate change on much longer time frames. One of the most useful deterministic frameworks for understanding past climate - a phenomenon known as "astronomical forcing" - is due to periodic changes in sunlight distribution across Earth’s surface. These changes in sunlight are caused by changes in Earth’s orbit and rotation, and they result in periodic climate cycles ranging from ~20,000 years to 2.4 million years in duration. Astronomical forcing exerts an important control on climate, including the decay of the large glacial ice sheets that covered much of North America 20,000 years ago. But the stochastic component of climate, which also preserves critical information about the physics of climate change, has been largely ignored in paleoclimate investigations. This study conducts a comprehensive analysis of stochastic climate variability over the past 34 million years by applying advanced computational approaches to evaluate paleoclimate data from the world’s oceans. The evolution of global climate during this time interval is characterized by a transition from warmer conditions with incipient unipolar continental glaciation (Antarctica), to the generally colder world of the present, with large bipolar ice sheets. Results from this study provide new evidence for the history of growth and decay of these glaciers near the north and south poles, helping to resolve previously ambiguous aspects of ice sheet development and climate history, while also demonstrating clear linkages between the stochastic processes and deterministic astronomical forcing. The project also evaluates evidence for linear and non-linear climate response to astronomical forcing, and provides new climate "fingerprints" for climate models, which can be used to test competing hypotheses for observed paleoclimate change.
