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Online Seminar
Climate sensitivity, non-consgtand feedbacks, and irreducible uncertainty in surface temperature patterns
Mar. 17, 2020, 14:00 - 15:00
University of Leeds

For decades scientists have used equilibrium climate sensitivity — the equilibrium surface warming associated with doubling the atmospheric CO2 concentration — 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 recent debates about its usefulness.

The methods to quantify equilibrium climate sensitivity are still debated. Computational costs have lead 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 higher than those obtained using extrapolation methods from shorter simulations. Specifically, 27 simulations with 15 climate models forced with a range of CO2 concentrations show a median 17% larger equilibrium warming than estimated from the first 150 years of the 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. 

Further, I will discuss to which degree climate models are expected to reproduce observed changes in sea surface temperature patterns. With several 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.

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

MPI Hamburg
University of Leeds
University of Leeds
Mail:M VanDerGuchtLsu9∂leeds ac uk
Employees, Scientific Staff, Young Scientists
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