Joshua K. Willis of NASA’s Jet Propulsion Laboratory is deeply involved in efforts to clarify oceanic ups and downs using space-based and deep-diving instruments. I frequently reach out to him when people tussle over the data and analysis pointing to rising seas in a human-heated world.
This arena remains dogged by durable uncertainty on time scales relevant to policy debates even as the long-term picture of centuries of rising seas is clear. One persistent issue is the dynamics of ice sheets. Another is persistent questions about how much heat the seas absorb. Not long ago I caught Willis for a brief Skype interview that explores some important recent studies and assertions:
I hope you will excuse the low resolution. I think the content makes it worth dealing with fuzziness and lag. Among other things, he speaks about the recent study that, using patterns in layered salt marsh sediment, found a sharp recent uptick in the rate of sea-level rise after 2,000 years of fairly stable conditions — a pattern Willis refers to as a “sea-level hockey stick” — an allusion to the suite of studies finding a similar pattern for global surface temperatures (albeit a hockey stick with a warped shaft).
He also talks about the limits of knowledge gleaned from research on past changes:
They’re just outside the accuracy in terms of time and height changes that we need to say something about the 100-year timescale. It’s still really a few thousand years it goes up by a few meters, a few thousand years it goes down by a few meters.
I noted how the overall rate in some studies, even on the scale of meters per millennium, “is not one of these uber-catastropes,” but that how much variation can occur within a century remains saddled with uncertainty, producing an “ugly mix of long-term certainty and short term murkiness.”
His response:
Right. Is it a step or a gentle easing into a world of new sea level? That’s the million–dollar question right now, or I guess trillion-dollar question.