Events

 
Online Seminar

Climate sensitivity, non-constant feedbacks, and irreducible uncertainty in surface temperature patterns

Tuesday, 17 November 2020, 14:00-15:00
University of Leeds

Abstract: For decades scientists have used equilibrium climate sensitivity to project future climate change, to test our understanding of climate feedbacks and paleo proxies, and as a benchmark in model intercomparisons. I will discuss the strengths and weaknesses of the concept of climate sensitivity and radiative feedbacks and recent debates about their usefulness. The methods to quantify equilibrium climate sensitivity are still debated and computational costs have led to the widespread practice of extrapolating equilibrium conditions from transient simulations. This is shown to be problematic, because the assumption that radiative feedbacks are constant is invalid on many time scales. We collect millennial-length simulations of coupled climate models and show that the global mean equilibrium warming is substantially higher than those obtained using extrapolation methods from shorter simulations. The spatial patterns of radiative feedbacks change continuously, in most regions reducing their tendency to stabilize the climate. In the equatorial Pacific, however, feedbacks become more stabilizing with time. The global feedback evolution is initially dominated by the tropics and later by the mid-latitudes. I will further discuss to which degree climate models are expected to reproduce observed changes in sea surface temperature patterns. With several climate model large ensembles we find that the internal variability on the local scale is too large to differentiate between systematic model biases and a forced response yet. This implies that predicting the future evolution of surface temperature patterns and global mean temperature is currently limited by understanding the causes of local internal variability in decadal timescale trends and the relative influence of warming in different regions on global radiative feedbacks.

About the speaker: Prof. Rugenstein is an Assistant Professor at the Department of Atmospheric Science at Colorado State University. She has been a PostDoc on a Humboldt fellowship at the Max-Planck-Institute for Meteorology in Hamburg. Prior to that she conducted her Ph.D. research in Reto Knutti’s groups at ETH in Zürich (2017) and her Master’s research at Princeton University/GFDL. Prof. Rugenstein is interested in how the ocean influences atmospheric feedbacks on large scales, and stores and redistributes heat. She likes thinking about first-order controls on Earth’s climate, deep time paleo climate, internal variability, and the theory and sociology of science. She is coordinating a model intercomparison of millennia long simulations of global coupled Atmosphere-Ocean Models. 

This event is part of the eventgroup ICAS External Seminar
Speaker
Assistant Professor Maria Rugenstein

Colorado State University
Organizer
School of Earth & Environment
University of Leeds
Leeds
Mail: M VanDerGucht does-not-exist.leeds ac uk
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