Physics seminar - Why the warming can’t be natural: the non-linear geophysics of climate closure


Dr. Shaun Lovejoy, 
McGill University   

Tuesday, January 17th 
3:30 p.m. 

4351 HP 


Why the warming can’t be natural: the nonlinear geophysics of climate closure

Claims with extraordinary consequences require extraordinary evidence. It is not sufficient to prove that the warming is "extremely likely" to be anthropogenic: to achieve "climate closure", we must also disprove the converse theory that it is a natural fluctuation. This disproof requires an understanding of the strongly nonlinear atmospheric variability: since the 1980's this understanding is one of the important contributions of nonlinear geophysics to the atmospheric sciences. Atmospheric variability spans twenty orders of magnitude in time and ten in space, but it can be tamed with the help of emergent high-level turbulent laws and their anisotropic and multifractal generalizations.

We take a voyage through scales and with the help of some new fluctuation analysis tools, we review the arguments and evidence for wide scale range space-time scaling: high level turbulent laws. We examine the consequences for the extreme fluctuations ("grey swan", "black swan" events) and we apply this to estimating the probabilities and return times of extreme centennial, global scale temperature fluctuations.  Even with conservative assumptions, the natural, the natural warming hypothesis can be rejected with >99% confidence.