News You Can’t Use About Arctic Ice Climate Change
Every month the National Snow and Ice Data Center (NSIDC) issues a report on how much of the Arctic Ocean and surrounding waterways are covered in ice, and whenever that happens — most notably in summer, when the ice melts back to reveal open water — people like me feel the urge to write a news story about it. That's especially true when the ice coverage seems ominously low. So when the NSIDC put out its June report yesterday, announcing the second-lowest ice coverage in the 32-year satellite record, many of us gave in to our primal journalistic urges. The climate blogger Joe Romm, for example, using one of his patented apocalyptic metaphors, wrote about the Arctic Death Spiral.
Stripped of it's horror-movie title, the post (and other recent commentaries, including one by my colleague Andrew Freedman at The Washington Post) make a number of valid and important points. First, a progressive decline in summer ice cover has long been predicted as a consequence of overall global warming, due to a process called "Arctic amplification." The idea is simple: in a warming world, ice melts back in summer, replacing white, light-reflecting ice with darker, light-absorbing sea water. The water warms up, so that refreezing in winter comes a bit later, and produces ice that's a bit thinner. The next summer, this thinner ice, along with rising air temperatures, creates more melting, which exposes more ocean, and so on.
Other factors influence year-to-year melting, including ocean currents, cloud cover and wind patterns, so the "death spiral" might well take a pause, or even reverse a tiny bit, in a given year. But over decades, the ice should steadily decline, until at some point, decades from now, the Arctic Ocean should be mostly ice-free in late summer.
In the real world, this is exactly what satellite observations have shown.
As you can see in the chart above, the biggest meltback happened in 2007 — the only month where June ice was lower than this year (it rebounded slightly after that year, but not much, which nicely illustrates the "other factors" point above). So it well might be that 2011 will be a new record year for open water in the Arctic, or that it may be a second-worst year.
Or maybe it won't. Once again I invoke other factors. If the weather up north does something unexpected, we could end up with more ice this coming September than everyone expects. Or we could end up with less. At this point, nobody really knows for certain. It's kind of like hurricane-season forecasts, or presidential-race handicapping. Who the front-runner is for the 2012 Republican nomination (this is about the presidential race, just to be clear) is absolutely meaningless at this point — yet politicial pundits can't help filling newspaper columns and hours of airtime talking about it. What this summer's hurricane season would look like from the perspective of last winter, when the first forecasts came out, was not quite as meaningless. But it was hardly anything to rely on.
Seen in that context, last months' ice extent isn't a hugely meaningful fact. It won't be hugely meaningful either, if the ice situation is worse in September than it was in 2007, or worse than last year, or slightly better. On the one hand, reporters like me try to explain to our readers that climate change is an overall trend, played out over many decades, and that a single year that's warmer than the year before, or cooler, doesn't mean a blessed thing.
And on the other hand, we sometimes make a huge deal when a given year is warmer or less icy than the year before — while deriding climate skeptics if they should trumpet a cooler than average year, or make a fuss about the fact that Arctic ice hasn't yet reached the lows of 2007.
It's all a bunch of noise, in both the statistical sense and the more conventional sense as well.
What matters (yes, I'm repeating itself) is the trend over years — and the trend has been toward an increasingly warmer Arctic, at least since 1979, just as climate modelers predicted. There's absolutely no reason, based on theory or models or the experience of the last three decades, to expect this trend to change.
And that, rather than the ice report from last month or next month or the entire summer season, is the important thing to focus on.