Why was there a Little Ice Age?
Quantifying climate forcings and feedbacks in coupled climate simulations of the last millennium
The Bolin Centre for Climate Research, Stockholm University,
invites you to attend a science seminar by David S. Battisti, University of Washington.
Historical and proxy data of climate show that the period 1600–1850 CE was unusually cold compared to the climate of the past millennium. This period is called the Little Ice Age. In this talk, I will briefly review the evidence for this cold period and then examine the results from PMIP3 program to simulate the climate of the last millennium, including the Little Ice Age, using the CMIP5 climate models. I will then present an analysis to illuminate the cause of the cooling during the Little Ice Age.
Radiative forcings and climate feedbacks are quantified for each climate model using the Approximate Partial Radiative Perturbation method and radiative kernels. Analysis shows that the Little Ice Age cooling is largely driven by volcanic forcing (comprising an average of 77% of the total forcing among models), while contributions due to changes in insolation (10%) and greenhouse gas concentrations (13%) are substantially lower. The combination of these forcings directly contributes to 40% of the global cooling during the LIA, while the remainder of the cooling arises due to the Planck response and the sum of the climate feedbacks. The dominant positive feedbacks is the water vapor feedback, which contributes 29% of the global cooling.