Atmosphere Ocean Science Colloquium

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Investigating the Role of External Radiative Forcing in Driving the Atlantic Multidecal Oscillation

Speaker: Katinka Bellomo, Columbia University

Location: Warren Weaver Hall 1302

Date: Wednesday, February 22, 2017, 3:30 p.m.

Synopsis:

In this talk, I will investigate mechanisms driving the Atlanitc Multidecadal Oscillation (AMO) in climate model and observations. Previous studies suggested that internal variability, in particular the Atlantic Meridional Overturning Circulation (AMOC), drives the Atlantic Multidecadal Oscillation (AMO) while external radiative forcing only creates a steady increase in SST. More recently, this view has been challenged and new evidence has emerged that aerosols and greenhouse gasses could play a role in driving the AMO. Here I examine the drivers of the AMO using the CESM Large Ensemble and Last Millennium Ensemble. The radiatively forced component of the AMO is isolated by computing the ensemble mean, while the role of internal variability is estimated using the ensemble spread. The result is that phase changes of the AMO cannot be explained in the absence of historical forcings. Further, 68-78% of the AMO variance is driven by radiative forcing only. Single forcing experiments show that greenhouse gases and aerosols are the main drivers of the AMO in the latter part of the 20th century.