Tropical Connections in a Warming World: Pacific Equatorial Dynamics to Atlantic Hurricane Risk

Kristopher Karnauskas

University of Colorado Boulder

Friday, Sep 05, 2025, 2:00 pm MT
DSRC Room 1D403

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Abstract

Tropical cyclogenesis in the Atlantic is influenced by environmental parameters including wind shear, which is sensitive to forcing from the tropical Pacific. Reliable projections of the response of such parameters to radiative forcing are key to understanding the future of hurricanes and coastal risk. One of the least certain aspects of future climate is the warming of the eastern tropical Pacific Ocean. In this lecture, I will give an update on the state of the field aimed at understanding the response of the tropical Pacific to climate change, followed by a brief presentation of two recent studies. First, we will explore the question of how fast the upwelling is in the equatorial Pacific—the engine behind one of the seminal theories for how the tropical Pacific responds to radiative forcing. By synthesizing ~20 historical observational studies attempting to estimate the mean upwelling velocity going back to Wyrtki (1981), I will show that the sampling strategies of these campaigns very nicely explain their spread. Then, a deep dive into modern data suggests the mean upwelling in the equatorial Pacific is an order of magnitude faster than we thought, and similarly faster than simulated by global coupled models. Next, motivated by this uncertainty and systematic model bias, we use a global atmospheric model to investigate how the formation regions of Atlantic hurricanes may change in the future, specifically as a function of eastern equatorial Pacific warming. We find that this feature of the warming pattern strongly influences predictions of future changes in Atlantic hurricanes, including how El Niño affects them. Specifically, a strong eastern Pacific warming causes a change in the vertical structure of zonal winds over the tropical Atlantic, which shifts where hurricanes will tend to form in the future and increases the effect of El Niño. I will close by discussing the broader implications for uncertainties in projections of climate change impacts and risk.

Bio: Kris Karnauskas is a Fellow of the Cooperative Institute for Research in Environmental Sciences (CIRES) and an Associate Professor in the Department of Atmospheric and Oceanic Sciences (ATOC) at the University of Colorado Boulder, with secondary faculty appointments in the CU School of Medicine and the Colorado School of Public Health. Prior to joining the CU Boulder faculty in 2015, Kris spent six years on the faculty of the Woods Hole Oceanographic Institution (WHOI) and the MIT-WHOI Joint Program in Oceanography (also teaching at Boston College, followed by sabbatical at the Institut Pierre Simon Laplace (IPSL) in Paris, France, through a Research Fellowship from the Alfred P. Sloan Foundation. During the spring of 2022, Kris was on sabbatical at Harvard University's Center for the Environment.

Kris completed his B.S. at the University of Wisconsin-Madison and Ph.D. at the University of Maryland-College Park, both in Atmospheric and Oceanic Sciences, followed by a postdoctoral fellowship in Ocean and Climate Physics at the Lamont-Doherty Earth Observatory of Columbia University. Kris currently serves as Editor-in-Chief of Geophysical Research Letters and co-chairs the Joint US CLIVAR/NIH Working Group on Climate & Health, and recently served on the Scientific Steering Committee (SSC) of the U.S. Climate Variability and Predictability Program (US CLIVAR). Kris was the recipient of the 2017 AGU Ocean Sciences Early Career Award and the 2024 AGU Atmospheric Sciences Turco Lectureship.