Climate Variability: Physical Mechanisms and Relationship with Future Warming

February 18, 2019

Nicholas Lutsko, Visiting from MIT

Hosted by Dave Thompson

Abstract

Variability of the climate system, especially of surface temperature and precipitation, strongly affects human society and natural ecosystems, and changes in variability are likely among the most impactful aspects of future climate change. In this talk I will discuss recent work on the physical mechanisms that control variability in today's climate and on the relation between the climate system's internal variability and its response to CO2 forcing. First, I will consider the impact of large-scale orography in the Northern Hemisphere on winter synoptic temperature variance. I will explain why the presence of the Rockies on the western edge of North America increases North American temperature variance, while the presence of the Tibetan Plateau and the Himalayas on the eastern edge of the Eurasian continent damps temperature variance over most of Eurasia. Second, I will present results which suggest that internal variability on ENSO timescales could yield a potential "emergent constraint" for Earth's Equilibrium Climate Sensitivity. This constraint is based on frequency-dependent regressions of top-of-atmosphere energy fluxes and global-mean surface temperature from CMIP5 simulations, which allow the relationship between outgoing energy fluxes and global-mean surface temperature to be characterized on different frequencies. Finally, I will discuss some still unaddressed questions about variability in the climate system, and how a combination of physical modeling and observations could allow us to tackle these questions in the future.