Episode 26: Rob DeConto

I think I first learned of Rob DeConto when I saw his paper entitled Thresholds for Cenozoic bipolar glaciation, published soon after my arrival at Nature.  Specific and testable thresholds for the initiation of large scale glaciation in Antarctica and the Northern Hemisphere? Interesting!

Soon after, I handle Rob’s next two papers at Nature: Modelling West Antarctic ice sheet growth and collapse through the past five million years (led by David Pollard) and Obliquity-paced Pliocene West Antarctic ice sheet oscillations (led by Tim Naish). Published in the same issue, the two papers showed — from the ANDRILL observations and a simple “hybrid” ice sheet model — that the West Antarctic Ice Sheet waxed and waned over a few thousand years, sometimes retreating to almost nothing. Interesting!

Then my colleague Juliane Mossinger handled Rob’s provocative paper Past extreme warming events linked to massive carbon release from thawing permafrost, suggesting that the Paleocene-Eocene Thermal Maximum could have been caused by terrestrial carbon cycle processes on an ice-free continent. Rob was essentially new to the field, but dove in anyway:

I think sometimes when you’re so close to something, it’s easier for somebody to come in from the outside, with a fresh perspective, because they don’t know any better.

Interesting, interesting stuff (and that’s not even delving into Rob’s other publications in Science and Nature Geoscience). Where did all these disparate ideas, skills, models and insights come from?

As it turns out, they come from one of the most seemingly straightforward careers I’ve yet come across: childhood interests in geoscience and outdoor recreation > Earth Science degree at UC Boulder > graduate work at UC and NCAR with people like Bill Hay, Starley Thompson and Warren Washington > faculty position at the University of Massachusetts-Amherst > long-term involvement in the awesome Urbino Summer School for Paleoclimatology > Tinker Muse Prize > geoscience superstardom. It was, as Rob says:

Just the right combination of everything.

Yes, but … that doesn’t mean it’s easy. A huge chunk of our conversation centers around Rob’s long-running collaborations with David Pollard, which surely has to be one of the great partnerships of modern geoscience. It was just luck that they were both in Starley Thompson’s group at NCAR, and luck that they ended up being quasi-neighbors on the East Coast.

Rob had long realized that — even with the deglaciation of Greenland, West Antarctica and peripheral glaciers and ice sheets — modelers still could not produce the ~ 20 m sea level rise in the Pliocene warm period. For a while, Rob was convinced that surface melt must be the answer, which could in turn lead to hydrofracturing. Nope! Increased basal lubrication?* Still not enough!

Sitting in the audience at Rob’s EGU talk, David Pollard wondered if Richard Alley’s ideas on ice cliffs might be important. But how, exactly, would cliffs come into play? David and Rob turned to an elegant theoretical model from Jeremy Bassis describing the maximum height an ice cliff could attain, from structural properties: about 100 m, it turned out. All of which, when put together, leads to the marine ice cliff instability (MICI) mechanism.

Rob and David looked to the Pliocene and last interglacial to better constrain the model parameterization. As was the case for Rob’s early work on latitudinal temperature gradients, the geological record is the key to understanding modern processes:

We were looking at these ancient climates, but it was really to understand the dynamical processes that could create a world like that … I’m looking to the geological record for some guidance in really trying to understand the system, not trying to use an understanding of the system to try to say something about these past times.

With the mechanisms in place and the model able — finally! — to simulate the range of past sea levels, Rob could turn to the future, and a 0 to ~ 15 m range of possible sea level contributions from Antarctica, published in Nature just a few months ago:

deconto nature17145-f5
Figure 5 from “Contribution of Antarctica to past and future sea-level rise” doi:10.1038/nature17145

As is so often the case, an advance that seemed to leap out of nowhere arose, instead, out of long collaborations, hitting dead ends, being open to external input, experimenting, doggedness, and, sometimes, having the right person in the audience at the right time.

*In the interview, Rob says that he first explored the idea of surface melt leading to basal lubrication. In follow-up discussions, he clarified that he first examined the melt > hydrofracturing idea, and then added basal lubrication, which still produced insufficient Antarctic melt.

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