In a week since Arctic sea ice extent broke its all-time record low, it has declined another 8 percent. More decline, at least one more week, is inevitable before things level off for the transition from summer to fall. The ultimate low extent record may be about 14 percent below the previous record low set in 2007.
After reading the news reports of the record low in Arctic sea ice, I realize that many people don’t see what a big deal this change is. Weather records get set all the time, and if you believe the news reports, this is just another record. There are four answers I have to give for this.
First, 14 percent is a bigger change than it might sound. We complain about record temperatures that are just a fraction of one percent beyond previous records. A sudden 14 percent change in temperature is unimaginable, except perhaps in a Hollywood apocalypse movie. To make the comparison more personal, imagine if your height suddenly changed by 14 percent. That would be a shocking change that would require all sorts of adjustments on your part.
Second, although extent is the most reliable measurement of Arctic sea ice and the one we focus on the most, other measures are also hitting records. The concentration of ice was at a record low in August, with ice breaking up and spreading out in a pattern never seen before. At the same time, the thickness of the ice has been, for the last three years, lower than ever before seen. Combine these three effects, and the total amount of ice, the ice volume, is only half of what it ought to be.
Third, this summer’s record-setting ice melt happened in spite of unremarkable weather. It has not been particularly warm (looking at surface air temperatures) or sunny on the Arctic Ocean. There was an unusual Arctic cyclone a month ago, but it barely produced a blip on the ice extent graph. Based on the graph, the storm appears to have provided the equivalent of an extra two days of melt — significant, but hardly an explanation for a record-setting melt that lasted all summer. If this kind of melt can happen in ordinary weather, then we can expect a record-setting melt almost every year — and if that’s the case, then it won’t take more than a couple more years to hit zero. Some observers are already extrapolating this year’s melt and predicting a complete melt-out in 2013 or 2014. And those projections are based on the assumption of ordinary weather. If unfavorable weather comes along one summer, the ice will melt that much faster. Either way, there is nothing to suggest that the ponderous Arctic ice of years past can ever come back.
Fourth, it is not just the sea ice. Northern Hemisphere snow cover is also the lowest ever recorded. Water temperatures in the far northern Atlantic and Pacific oceans are higher than usual. At the moment, there is no possible source for a cold wind to cool things off — and there is not much ice left to do that either.