Sack Lunch Seminar (SLS)

From turbulence to icesheets - a travel across time and space


The new generation of GCMs are able to reproduce the current climate quite realistically, but it is not obvious whether they are also good at predicting future climate change. One test is to use them to reproduce past climates, especially climates that involve changes to the heat, water and carbon cycles as large as the ones expected for the next century. We used CCSM4 in its AR5 configuration to reproduce the last glacial inception solely by changing Earth's orbital parameters.

CCSM4 is the first GCM to reproduce the reconstructed pattern and magnitude of reduced snow melt, and therefore provides a major new piece of evidence for the Milankovitch Hypothesis. In the talk we will analyze how CCSM4 transitions from an interglacial into a glacial, and quantify the positive and negative feedbacks. While the CCSM4 heat and water cycle responses to orbital forcing are deemed realistic, the carbon cycle response is not. Additional experiments with CESM1 reveal that glaciation leads to a reduction in ocean mixing that increases the ocean uptake of carbon and reduces the atmospheric CO2 - just as observed.