Tuesday, January 16th: The Physics of the El Nino Response to Climate Change: What Can We Learn from Climate Model Simulations?

Event Date: 

Tuesday, January 16, 2018 - 4:00pm

Event Date Details: 

Refreshments served at 3:40pm.

Event Location: 

  • Webb Hall 1100
  • Physics Colloquium

El Nino events have devastating impacts throughout the world, and their development and evolution is affected by many atmosphere and ocean processes which are expected to change in the future. Projections using climate models are the primary tool for assessing how such events may respond to 21st century climate change, but differing models disagree completely on the future magnitude of El Nino. Interpreting the causes for these disagreements can be quite difficult due to the number of differences in relevant physical processes across models, as well as the large degree of randomly generated 'internal' climate variability present on decadal timescales.

Recently, modeling centers have begun to address these issues by creating 'ensemble' suites of simulations with identical configurations but differing in their initial conditions; in this way, internal variability may be robustly sampled and the effects of inter-model physical differences assessed more robustly. I will present results from two such ensemble suites, run with two different climate models: the Community Earth System Model (CESM) maintained at the National Center for Atmospheric Research, and the Earth System Model 2M (ESM2M) maintained at the NOAA Geophysical Fluid Dynamics Laboratory. These two models show divergent responses of El Nino strength to climate change, with CESM projecting stronger and ESM2M weaker El Nino events in the future. These changes are attributed to differences in the mean climate response: depending on the vertical and horizontal gradients in sea surface temperature (SST), feedbacks which amplify or damp El Nino development are altered as a result of climate change. The atmospheric impacts of El Nino events are also investigated, and the sensitivity of precipitation to SST anomalies is shown to fundamentally alter the rainfall response to future strong El Nino events. I will also discuss the implications of these results for the reliability of climate model projections of extreme events.


Samantha Stevenson, UCSB