Searching for tipping points in Pleistocene climate: Are they real? Are they portents for the future?

Abstract:

Paleoscientists seek fundamental knowledge of Earth systems, and have unique views of system dynamics on the timescales longer than recent observations. This is important, because some processes that may control the trajectory of change in the not-so-distant future are not well illustrated or constrained in the short history of instrumental observations; paleo data offer our only observational window on these longer scales. But paleo vision is also a bit blurry, and sometimes biased. It matters how we approach the records to focus on the right things, and it matters how we communicate our insights so that we can teach models to approximate real Earth system behaviors. In the six decades since Cesare Emiliani set us on the path of quantitative observational paleoscience, we’ve observed more and more. Each year brings more “proxies,” more sites, more resolution, and the more we look the more we find interpretable signals. This data complexity makes the paleo literature daunting to outsiders; it is hard to get past the stories. Most of our narratives are grounded in linear systems, focusing on forcing and response, and we data generators struggle to infer even modest nonlinearity. But the concept of massive nonlinearity, tipping points, has recently entered the public consciousness, and the search is on anew for such events in paleo data. The reality of tipping points as well as the processes that may drive such events are not yet fully clear, but the search is essential because if humanity does indeed push the Earth system across an irreversible tipping point into a new state, we need to know how this might play out and over what time frames. Can we really learn about such occurrences, and the processes that control them, in paleo records? Do we need to think about the past differently? Will this change how we think about the future? Will it inform what we do about the future? Emiliani thought it should. This lecture will explore how.