Rapid climate change due to sea ice dynamics in the North Atlantic and Arctic oceans

Our Team

David Battisti, University of Washington

Cecilia Bitz, University of Washington

Aaron Donohoe, University of Washington

Camille Li, University of Washington

Dan Schrag, Harvard University

Eli Tziperman, Harvard University

Our project is funded by the Office of Polar Programs at NSF.

Overview of the Project

This proposed study is motivated by the Dansgaard-Oeschger (D-O) events recorded in the Greenland ice cores, showing dramatic and rapid (decadal) climate changes, with atmospheric temperature variations of up to 10 deg C, occurring repeatedly during glacial times, 50-10,000 years ago. A recent modeling study has shown that a modest reduction in sea ice can account for the abrupt changes in temperature and snow accumulation that are recorded in the Greenland ice core. Several questions remain: Why did the sea ice extent change suddenly? Why did the new state persist for several centuries before gradually collapsing back to its original glacial state? And how does this explain abrupt climate changes elsewhere? We propose two possible hypotheses to answer these questions:

The leading hypothesis in the literature attributes (D-O) events to an internal oscillation of the ocean thermohaline circulation (THC). We propose that only a modest change in the THC is needed to drive sea ice changes, and it is the sea ice changes that cause the large rapid climate changes recorded in Greenland. The millennial timescale between the abrupt warmings and the long-lived nature of the warmings (e.g., 300-600 years) follow naturally from the adjustment timescale of the THC in the Atlantic Ocean.

Alternatively we propose that D-O events are due to reconfigurations in the coupled tropical climate system that are long-lived and influence the climate outside of the tropics via teleconnections through the atmosphere or ocean circulation. It is hypothesized that regional changes in sea ice extent are attributed to either remotely forced changes in the local atmospheric circulation or to oceanic teleconnections from the tropics to the North Atlantic.

Our hypotheses will be examined using paleoclimate proxy data and a hierarchy of modeling tools including an intermediate climate model and a state-of-the-art, coupled ocean-atmosphere-sea ice GCM.

Scientific Merit: Our project investigates two fundamental mechanisms that could explain the rapid changes recorded in the Greenland ice cores. In addition to conducting a detailed study of the physics of past abrupt climate changes, we aim to identify the most likely explanation for these events by determining which mechanisms can produce sustained abrupt changes in the sea ice while producing the pattern of teleconnections that is consistent with proxy data of rapid climate change.

Broader Impacts: Our collaboration brings together climate dynamicists, paleoclimate data experts, and climate modeling experts to tackle a major puzzle in Earth's past: the causes of abrupt climate change (or should we be specific and say "the causes of D-O events"?). The project personnel will also interact with a larger group that is now forming formally through the Community Climate System Model (CCSM) project management to study abrupt climate change. Our study, which involves integrating climate models subject to large climate perturbations, will ultimately guide us in making future model improvements. Graduate and undergraduate students will play major roles in the project, and the project results will influence courses that we teach on oceanography, climate and climate change, climate modeling, and applied math.