What We Don’t Know About Climate Change and Why it Matters

Bjorn Stevens

Managing Director, Max-Plank Institute for Meteorology

Professor, University of Hamburg

Lecture: Thursday, May 5 2022 6:00 pm

Reception: Thursday, May 5 2022 5:00 pm

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The outline of climate change is well understood. Theory, modelling and observations place useful bounds on how much warming can be expected for a given increase in greenhouse gases, and why this warming is expected to be amplified at higher latitudes (most immediately in the north) and over land. We also have a basic understanding of what warming implies for the hydrological cycle and extremes, at least in a general sense. Our understanding makes a compelling case for reducing greenhouse gas emissions. What remains unclear is what happens when it warms. In fact, it is difficult, and in many places impossible, to scientifically advise societal efforts to adapt in the face of unavoidable warming. Our knowledge gaps are frightful because they make it impossible to assess the extent to which a given degree of warming poses existential threats. In this talk, I will outline what we don’t know about climate change, why it matters, and the challenge this poses scientifically. In particular, I will outline how a new generation of Earth system models- those specifically designed to incorporate processes that Michio Yanai spent his career researching- can help open new scientific frontiers that will allow us to better understand the implications of warming.