Seminar talk: Dan LuntSeminar talk: Dan Lunt firstname.lastname@example.org Tue, 11/17/2020 - 13:21 Seminar talk: Dan Lunt
Dan studied Physics at the University of Oxford before doing a PhD in Meteorology at the University of Reading. After a short postdoc at the LSCE in Paris, he moved to Bristol, where he is now Professor of Climate Science. He leads the international DeepMIP (www.deepmip.org) program.
Climate sensitivity is a key metric used to assess the magnitude of global warming given increased CO2 concentrations. The geological past can provide insights into climate sensitivity; however, on timescales of millions of years, factors other than CO2 can drive climate, including paleogeographic forcing and solar luminosity. Here, through an ensemble of climate model simulations covering the period 150–35 million years ago, we show that climate sensitivity to CO2 doubling varies between ∼3.5 and 5.5 ◦C through this time. These variations can be explained as a nonlinear response to solar luminosity, evolving surface albedo due to changes in ocean area, and changes in ocean circulation. The work shows that the modern climate sensitivity is relatively low in the context of the geological record, as a result of relatively weak feedbacks due to a relatively low CO2 baseline, and the presence of ice and relatively small ocean area in the modern continental configuration.
Arranged date for the seminar talk: Nov 27, 2020 at 12:00
Seminar: Thomas HaineSeminar: Thomas Haine email@example.com Fri, 10/02/2020 - 10:46 Seminar: Thomas Haine
Thomas Haine is a Professor at the Department of Earth & Planetary Sciences at Johns Hopkins University. His research interests are in ocean circulation and dynamics, and the ocean’s role in climate. He is involved in improving estimates of the geophysical state of the ocean circulation through analysis of field data and circulation model results. He is particularly interested in the high latitude oceans, including the subpolar North Atlantic, Arctic, and Southern Oceans. He studies watermass ventilation processes (rates, pathways, variability, and mechanisms), three-dimensional circulation, and geophysical fluid dynamics. He also investigates key physical processes that maintain the state of the extra-tropical upper ocean focusing on fluid dynamics and thermodynamics and their role in controlling sea surface temperature variability over years to decades.
The global ocean overturning circulation carries warm, salty water to high latitudes, both in the Arctic and Antarctic. Interaction with the atmosphere transforms this inflow into three distinct products: sea ice, surface Polar Water, and deep Overflow Water. The Polar Water and Overflow Water form estuarine and thermal overturning cells, stratified by salinity and temperature, respectively. A conceptual model specifies the characteristics of these water masses and cells given the inflow and air/sea/land fluxes of heat and freshwater. The model includes budgets of mass, salt, and heat, and parametrizations of Polar Water and Overflow Water formation, which include exchange with continental shelves. Model solutions are mainly controlled by a linear combination of air/sea/ice heat and freshwater fluxes and inflow heat flux. The model shows that for the Arctic, the thermal overturning is likely robust, but the estuarine cell appears vulnerable to collapse via a so-called heat crisis that violates the budget equations. The system is pushed towards this crisis by increasing Atlantic Water inflow heat flux, increasing meteoric freshwater flux, and/or decreasing heat loss to the atmosphere. The Antarctic appears close to a so-called Overflow Water emergency with weak constraints on the strengths of the estuarine and thermal cells, uncertain sensitivity to parameters, and possibility of collapse of the thermal cell.
Arranged date for the seminar talk: Nov 09, 2020 at 14:15