Using CCSM3 to simulate climate changes caused by the 8.2ka meltwater pulse

During abrupt climate changes, the climate system is forced across some threshold, causing evolution to a new, persistent state. Studies of abrupt climate changes are necessary to understand how these changes are transferred globally and to gain insight on future climate change. In this research, we simulated an abrupt climate change at 8.2ka (8200 years ago) using the Community Climate System Model (CCSM) and focusing specifically on the global response of temperature and precipitation. This abrupt change was believed to have been caused by a massive amount of freshwater entering the Labrador Sea from a glacial lake near Hudson Bay. Previous simulations of this event used climate models of intermediate complexity or present-day boundary conditions for greenhouse gases and insolation. In this research, we used boundary conditions from 8.2 ka and a more comprehensive coupled climate model to improve the accuracy of the simulation. We found significant global changes, annually and seasonally, in temperature and precipitation. The average annual global temperature before the freshwater perturbation was 12.1 ºC and after the hosing was 10.7 ºC, corresponding to a -1.3 ºC change. Globally, the annual precipitation change was -0.08 mm day-1. T-tests indicate that these changes, globally and regionally, were statistically significant at the 95% confidence level. These changes occurred in part due to a slowdown of the Atlantic meridional overturning (thermohaline) circulation and the resulting increase in the amount of sea ice in the North Atlantic. This, in turn, increased the Earth's albedo and the Earth absorbed less incoming solar radiation.