Episode 3: Kim Cobb

Obsessed by El Niño

Corals and speleothems are some of our most useful recorders of past climate variability. The spectacular speleothem records from eastern China, for example, have been instrumental in building our understanding of past variations in the East Asian Monsoon. But as is the case for most any paleoclimate proxy, corals and speleothems do not record a direct record of … well, anything.

The usual metric is δ18O, a measure of the amount of 18O relative to 16O. In principle, δ18O sounds simple enough. In a speleothem, more negative δ18O might reflect more precipitation or a stronger monsoon, as the heavier isotope is progressively “rained out”. But recent work has shown that δ18O is influenced by numerous other processes, like precipitation seasonality, atmospheric transport, atmospheric conditions in the location where the air mass was formed, etc. The relative influences differ by location and, almost certainly, over time.

Kim Cobb works to figure all of this out, especially for El Nino. In this episode of Forecast, Kim and I talk about what corals and speleothems are telling us and what we know about past variations in El Nino. Kim and her students work with their many collaborators to bring together geochemical, computational, and dynamical understanding in a way that I think is really moving the field forward. Isotope enabled GCMs emerge as an especially promising tool. We also touch on some of the unavoidable problems in this sort of work – like diagenesis. But as Kim says, it’s good to have scientific obsessions, big questions, and if you can push through the problems, there’s a real pot of gold waiting at the other side.

Kim is also a keen advocate for women in science, and we discuss some of the many issues facing young female scientists, and what can be done to increase opportunity and fairness. NB: prospective job seekers, Georgia Tech comes off awfully well in terms of supporting women scientists who are in the midst of a tenure run and raising a family.

In episode 2 we heard Mat Collins’ take on El Nino from a modeling perspective. I hope you enjoy Kim’s take, from a more geochemical perspective.

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