Scott St. George on tree rings

Scott St. George
Scott St. George

Tree rings are one of the key tools in paleoclimate research, and might seem like nothing more than big, woody thermometers. But tree-ring science is ever evolving, constantly debated, and — while it has answered some major questions — still grapples with making the connection to broader climate questions.

Paleoclimatologist Scott St. George from the University of Minnesota works on both the guts of tree rings as climate recorders, and their linkage to the wider climate system. Doing so, however, didn’t always seem like a great idea, and Scott experienced some initial horror at having entered the field …

I've just done a graduate degree in tree rings ... oh god ... what have I done to myself

The despair didn’t last long, and Scott was soon making major advances in using tree rings to research past floods. We talk about these early discoveries, the furor over the missing ring debate, and how the field is now trying to explicitly link tree rings to variations in atmospheric circulation.

The tentacles of Scott’s ideas, however, extend far beyond a narrow interest in tree-ring science, and we have a craic about a couple. Scott and I both share the perception that scientific talks could be … improved somewhat. Mine included! I think presentations can be a sort of intellectual defense system. As Scott puts it:

We want to build this wall in front of us, of our data, our slides, all the points we want to make ... and nobody really wants to get all that detail at once

But unlike me, Scott has taken the time to think about scientific presentations, what tends to go wrong, and how we can all craft a more meaningful talk … oftentimes by talking less, and especially by having some empathy for your audience. You don’t have to get it all done at once:

A presentation is like the opening statement to an ongoing conversation

Scott’s website is a great resource for ideas on how to streamline and hone presentations, and he has a veritable treasure-chest of excellent and thought-provoking graphics.

During the course of teaching a monstrously huge undergrad class, Scott grew frustrated with presenting the standard NASA GISS graph of industrial era climate change, and had long thought that there must be a better way. Ultimately, he was able to convince undergrad Dan Crawford to translate the graph into music. The results spawned a pretty incredible level of interest, and show that there’s a real interest in presenting climate science in ways that make sense to and connect with people.

Science and geopolitics have always been intermixed, sometimes to great effect, other times less so. Witness the recent CSIRO debacle. Scott began his career in the Geological Survey of Canada during a time of interest in climate science, but once the Harper administration was in full suppress-scientists mode, Scott new he’d have to look for other options to pursue his long-term interests. For Scott, this meant leaving Canada and moving to Minnesota. A loss for Canada, but I’m glad that Scott’s found his way, now to a tenured academic position at a great university.


Music: Organ Grinder Swing by ChēēZ π CC BY-NC-SA 4.0; Planetary Bands, Warming World by Daniel Crawford CC BY-NC 4.0; Oh! By Jingo! by All-Star Trio Public Domain Mark 1.0.

An update on the 1.5 °C warming threshold

Over the past few months I’ve discussed with a variety of guests the emerging idea of trying to keep global warming below 1.5 °C, and our family of journals has certainly been active on the topic, particularly with regard to feasibility and mitigation pathways.

From Paris Agreement climate proposals need a boost to keep warming well below 2 °C, Nature doi:10.1038/nature18307.
An example of the emissions required to get close to 1.5 (blue), versus unregulated emissions (red). There’s a lot of space in between! From Paris Agreement climate proposals need a boost to keep warming well below 2 °C, Rogelj et al., Nature doi:10.1038/nature18307.

But I thought it would be a good idea to find out what the IPPC is actually doing on the topic, as one of their three special reports. IPCC Working Group I co-chair Valérie Masson-Delmotte kindly agreed to come back on the podcast for a quick catch-up on the recent 1.5 scoping meeting held in Geneva.

At this point, discussions are extremely preliminary, but it is clear that the IPCC is undergoing a fairly huge change in culture, at least for the special reports. Most notably, the entire framing of the debates, questions, and approaches is taking place across the three working groups. Additionally, the author group chose to bring in outside scientific consultants to bolster their expertise, for example in ethics. As Valérie says, the scoping meeting was:

“… an opportunity to challenge, to question, the way AR5 was framed."

It’s still early days for the report, but I think it will provide an unusually broad discussion of the social and ecological issues that are inextricably intertwined with trying to reach any particular mitigation or climate goal. One notable point of discussion was the potential of the human, as well as climate, system to undergo abrupt change.

If you’re keen to read more on the 1.5 threshold, you can check out the across-journal collection from Nature, Nature Climate Change and Nature Geoscience.


Music: Stance Gives You Balance by Hogan Grip, Creative Commons license CC BY-NC-SA 3.0.


Rob DeConto and Antarctica in the climate system

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:

Figure 5 from "Contribution of Antarctica to past and future sea-level rise" doi:10.1038/nature17145
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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