You may have read in the newspapers last summer that the ice coverage on the Arctic Ocean was at an all-time low in recorded history. The newspaper reports may have had an intellectual impact, but it can be difficult for us as individuals to fully register the magnitude of the event.

On the web site of Professor Ignatius Rigor, of the Department of Atmospheric Physics, University of Washington, one finds a most amazing visual depiction of the fate of Arctic sea ice over nearly the last thirty years. It is an MPEG animation file where each frame of the animation represents the state of ice coverage for one month from 1979 to November 2007.

Follow this link to the animation. It may take a little effort to get the animation to work, but it is worth it. Old, "permanent" sea ice is shown in white. Younger ice is represented in increasingly dark shades of blue.

Then go here to visit Dr Rigor's home page containing a detailed, if rather technical, explanation of the animation and the scientific interpretation around it.

There are two things I wish to observe here: first, the ice did not melt where it stood in the freezing confines of the Arctic. It was flushed into the Atlantic ocean. Second, this was not as simple as saying "it got warm then the ice melted". The real mechanism at work here was a radical shift in wind-driven ice drift that allowed for the ice to be flushed out into the Atlantic, evading the ring of land that nearly completely surrounds the Arctic Ocean. Therefore the interpretation that global warming is behind the disappearance of the Arctic ice, while perhaps true, defies simplistic explanations. Which to me, in a way, is deeply worrisome. Once more the Earth shows itself to be a marvelously complex system that keeps springing surprises at us.

Now let's be clear: I am not saying all this in order to set up a statement of denial of anthropogenic global warming, and neither is Dr Rigor. My personal view, in a nutshell, is that the life's work of a generation of climatologists strongly supports the reality of anthropogenic global warming. The details of the mechanisms at work are complex and need much further research, but there has been sufficient evidence to warrant action for many years now.

No matter. Believe what you will, the fact remains that what happened in the Arctic is momentous. The lost "permanent" ice won't be back any time soon, for better or for worse, now that summer sunlight can penetrate into the Arctic waters and warm them, even a little. And that will have consequences that we are now only beginning to grapple with.