Midlatitude weather and climate change: expectations and uncertainties
James Booth, City College and The Graduate Center, CUNY
With anthropogenic climate change, global-scale features, such as the Earth’s temperature (T) and energy (E) budget, are changing and will continue to change in a physically clear manner: T increases because EIN > EOUT. On the regional-scale, in the midlatitudes, things are a bit more complicated. However, if one separates the response into thermodynamic- and circulation-based behavior, then it is the case that we have a lot more clarity about the thermodynamic response: mean and extreme temperatures are getting warmer; wet regions are getting wetter. For circulation-based changes, there is less certainty. This is due to two main reasons: (1) there are changes to circulation that will offset each other – one related to the equator-to-pole temperature gradient, the other related to forcing of the circulation due to diabatic heating, and (2) the inherent noise in the midlatitude circulation, associated with natural variability, it quite large. In this talk, I will review the theoretical underpinnings that relate to our confidence in the projected thermodynamic changes in the midlatitudes. Then I will discuss the issues in making projections of the changes in the dynamics. This talk will survey both work that I have done and work from others in the climate science community.