There’s more than a few climate bloggers who have a dirty little secret. We like to excoriate those who can’t tell the difference between weather and climate, or herald every momentary drop in temperature as evidence that global warming has ended, or revel in each new report that suggests not every single square millimeter of the planet’s surface is experiencing dramatic climate shifts. As we should. But many of us take a peek, every morning, at the daily version of a graph from the National Snow and Ice Data Center depicting current sea-ice extent in the Arctic.
We know that what happens from day to day tells us nothing useful about global climate change. We know that the only things that supply meaningful information are measured on the scale of decades and even centuries, not days, weeks or months. And yet we still obsess on that damn graph. Why?
I’ll tell you why. Because what happens with the Arctic ice cover is critical to projecting the future of the whole Earth ecosystem. Because the changes that have been observed up there are so dramatic. And because we’re human. Even the head of the NSIDC, Mark Serreze, admits to getting caught up in the incredible unfolding story of melting ice. After sea-ice extent dropped waaaay below the 30-year norm in 2007, words from the experts like “death spiral” led some
amateurs more excitable types to predict the entire summer ice cap could gone by 2013.
“In retrospect, the reactions to the 2007 melt were overstated. The lesson is that we must be more careful in not reading too much into one event,” Serreze said.
Of course, reading too much into one season’s ice cover trends is a mistake. But so is using language like “flatlining,” to describe the situation at the moment, as one prominent pseudoskeptic writes. The graph at right may or may not lend itself to that interpretation, depending on when you’re reading this. I am linking directly to the URL that provides a new graph every day.
But given the stakes, it really isn’t that surprising that so much attention is paid to every wobble in the trends. A new paper in Geology goes a long way to explaining why. “Signiﬁcantly warmer Arctic surface temperatures during the Pliocene indicated by multiple independent proxies” says the Arctic was a heck of lot warmer than previously thought during a period of time a few million years ago when carbon-dioxide level were comparable to today’s (390 parts per million). We’re talking somewhere around 19 °C, not just 4 or 5 degrees, warmer. That’s 34 Fahrenheit.
While it is true that many things were different 3 or 4 million years ago, during the Pliocene. CO2 levels are just one of them. But CO2 levels are a primary contributor to the global temperature, and the paper’s results cannot be ignored.
The Canadian, Dutch and American authors of the paper used three proxies to determine local temperatures in the high latitudes — “fossil tetraether lipids” in fossil bacteria (the precise makeup molecules of fat that are sensitive to temperature), oxygen isotope rations in trees, and ancient vegetation diversity. They did this because the standard ice-core data only go back a million years. While it is possible the one or two of the chosen proxies could have built-in biases in the same direction, it is extremely unlikely that all three would be similarly problematic. It turns out that the proxies all produced remarkably similar results:
This more robust temperature estimate suggests that Arctic temperatures were remarkably warmer during the Pliocene. In fact, these estimates are 5-10 °C warmer than previous proxy estimates. These temperature estimates are also consider-ably warmer than model simulations at high latitudes. However, climates at high latitude are known to be very sen-sitive to orbital parameters affecting insolation, and thus proxy estimates with uncertain age constraints are not directly comparable to model simulations that typically span hundreds of years. Nonetheless, the agreement among these estimates indicates signiﬁcant Arctic warming during the Pliocene.
What’s really interesting is not just how much warmer the Arctic was back then than other analyses had assumed, but exactly what part of the thermometer is involved. Instead of the Arctic being -25 to -15 °C or so, it was close to 0 °C. Which means we’re now in the zone where melting is much more easy.
And if the Arctic sea ice melts, the resulting loss of albedo (reflectivity) of the north polar region drops by something like 80 or 90%. The Arctic ocean starts warming, and so does the air above it. The entire region gets a lot warmer. The ice on Greenland starts to melt, too. Sea levels rise. The temperature gradient between the equator and the poles — a gradient that is largely responsible for every major weather pattern on the planet — is significantly weakened. In other words, lose the Arctic sea ice, and everything changes.
The paper’s authors wrap up with this note:
Our independent proxy estimates indicate that Arctic temperatures during the Pliocene were considerably warmer than previous estimates derived from empirical proxies and climate model simulations, despite estimates of Pliocene atmospheric CO2 levels that are comparable to today. This indicates that climate models do not incorporate the full array of atmospheric, biospheric, and cryospheric feed-back mechanisms necessary to simulate Arctic climate. Regardless of the feedback mechanism responsible for ampliﬁed Arctic temperatures, our results indicate that a signiﬁcant increase in Arctic temperatures may be imminent in response to current atmospheric CO2 levels.
And that’s the kind of thing that drive climate change bloggers to skip over the to sea ice extent graph. Yes, it’s kind of good to see the blue line stop plummeting and head over toward what passes for normal in the satellite record (which only goes back to 1979). But we’re not going to stop looking. And there’s another reason.Sea-ice extent isn’t nearly as important as sea-ice volume. And after several years of above-average melt, much of what’s left in the Arctic is thinner than it used to be, and could easily disappears. Some would argue we should be obsessing instead over this graph:
The problem with this graph is it’s generated from a computer model, not the satellite observations behind the ice extent graph. After all, it takes a lot more work to measure ice thickness than simply snapping a photo from orbit. But you can read about why the models are trusted here.
Ballantyne, A., Greenwood, D., Sinninghe Damste, J., Csank, A., Eberle, J., & Rybczynski, N. (2010). Significantly warmer Arctic surface temperatures during the Pliocene indicated by multiple independent proxies Geology, 38 (7), 603-606 DOI: 10.1130/G30815.1