This is a guest post by Liz Logan, Postdoc at UTIG/ICES:

 

These days I just tell people I am a climate scientist. That is -- in the broadest brush strokes -- true. It’s more accurate to say that I am a computational glaciologist, a numerical modeler of ice sheets. I use computers to see how Greenland or Antarctica might react to being poked: in the form of warmer air or warmer ocean or just a sea-level-induced jolt of bending.

So that is ultimately why I found myself in Japan, Land of the Rising Sun. It’s true that my work in computational glaciology brought me there, but a nicer way to describe it is that I’m searching for a history. I want to help tell the story of the Greenland Ice Sheet. At least, the Greenland Ice Sheet from ten thousand years ago until now. What did this massive beast do over that time? Lots of interesting things happened between then and now. To be sure, lots of interesting things are happening at this very moment.

No doubt you have seen images or videos of icebergs calving. Large crashes of ice, plummeting into chilly Arctic waters. Cracks in the surface opening like a shotgun, pieces of ice the size of eighteen-wheelers hitting the water’s surface: sounding from a distance (or sometimes, under water) like a bag of popcorn heating up in the microwave. Or perhaps you watched -- mouth agape like me? -- as an iceberg the size of Manhattan slowly detached from Jakobshavn Glacier in Greenland, grinding its death against the glacier behind it, for several minutes, tipping over and beginning its long and slow funeral procession down the fjord and out to sea?

I was in Japan on a decidedly less sexy mission. I was not there to place a camera on a gloomy and windswept rock, trained on the mouth of a glacier, hoping to catch a moment like this. Nope; I was there to merge code. For one and a half years prior I had been tinkering with a colleague’s ice sheet model and was ready (or so I thought) to take my tinkered version and ‘merge’ it with his original, pristine version.

What I had been doing -- I like to envision -- is what mechanics do to old cars: chop out a piece here, replace it with a new part. Turn on the engine, see if it goes. Chop out another, and so on. Only in this analogy I was effectively taking an old pick-up truck, chopping off the flat bed, and stapling on (in reverse direction!) another engine on the back end, that would drive the truck in reverse.

Imagining myself the Marty McFly of ice sheet modeling, I wanted to take my colleague Ralf Greve’s ice sheet ‘forecasting’ model and go ‘back to the future’ with it: in addition to it being able to tell us in some way what the ice might do in the future, I wanted to make this model be able to tell us what the ice did in the past. To do this I needed the model to tell me about how the ice sheet was sensitive to things: how pulses of melting on its tenuous glaciers or more snowfall than usual speeds up or slows down the glaciers that drain out to the ocean. When I knew how (numerically, in a computer simulation) the ice in Greenland is sensitive to things like this I would be able to use that information to, effectively, produce a ‘best fit’ approximation to how the ice sheet behaved in the past.

Why did I care? It turns out we can learn a lot about how the ice sheet is currently moving and changing if we know better what it did in the past. In other words, our forecasts will get a lot better if we can make them ‘pick up’ from where history left off. And we all want better forecasts, right?

As it turned out, the back-facing truck that I was trying to staple onto the original, front-facing truck needed a bit more tinkering, and so no merging of the code happened in Hokkaido, Japan. But I did spend time with Ralf, a professor at the Institute for Low Temperature Science at Hokkaido University in Sapporo, learning more about his model, telling him about mine, and how we could better fit them together. I came back to the University of Texas, Institute for Computational Engineering and Sciences, and have been driving in reverse ever since. (And now, we’re merging!)

Comment