A change is gonna come: no Arctic sea ice and our planet with a different climate

By Gareth Renowden 24/08/2012


The crunch is coming. Before the end of this month, or very soon after, the Arctic sea ice will set a new record summer minimum for area and extent, by any measure. The only question remaining is by how much 2007′s record will be beaten. For the rest of the world, those of us who aren’t habitually glued to the Arctic Sea Ice Blog (where Neven’s counting the dominoes as they fall — one, two, three, four, five, six so far), or who aren’t checking the wonderful images from space that NASA assembles into an Arctic mosaic, or in the Greenpeace team hanging on to a Russian oil drilling rig, we have a simple lesson to learn. The climate of the northern hemisphere has changed, and with it the climate of the planet. And we have precious little idea of how that change is going to affect all of our futures.

Here’s the University of Bremen’s map of the Arctic sea ice today. You might want to commit it to memory, because in years to come this will look like a bumper year…

Bremen20120823

I’ve discussed what this means for the climate of the northern hemisphere before — in fact, I’ve been banging on about it more or less since 2007′s record loss of ice — but Joe Romm at Climate Progress provides a handy summary of why the weather patterns of the northern hemisphere are going to feel the impact of less ice.

Let’s put it simply. When all that blue ocean in the picture above starts to freeze, it is going to give up heat to the atmosphere. A lot of heat. An enormous amount of heat. A decade ago, that didn’t happen to anything like the same extent. That heat has to go somewhere, and it goes into changing the way the atmosphere moves around the northern hemisphere. Look out for interesting winters in Russia, Europe and north America this year and in years to come.

So where do we go from here? I’m on record as projecting that within a decade — perhaps only five years — we will have an Arctic Ocean effectively ice-free in late summer. A few decades later we may see the Arctic ice free in winter. That’s bad news, but the big changes are already with us, and already locked in. They fall within the “climate commitment” — the thirty years or so it takes the atmosphere and oceans to “catch up” with the heat being trapped by any given level of greenhouse gases. Even if we could wave Harry Potter’s wand and magically hold atmospheric CO2 to today’s levels, the warming will continue and the ice will disappear. There is no way back from where we’re going. It’s inevitable, and it’s scary.

To make matters worse, we have next to no idea what this means for the climate of the northern hemisphere, and therefore for the planet as a whole. Take a look at this graph, from the NSIDC’s August 6th sea ice report. It’s a comparison of what climate models project might happen to the Arctic sea ice, and what has actually happened. I’ve been surprised that very few people seem to have picked up on the real import of this graph.

NSIDCmodelobs

The blue line and shading is what the ensemble of models used in the last IPCC report were suggesting might happen. The red line is the multi-model mean for the projections in the next IPCC report, and the pink shading covers the full range of individual model runs. The black line is what’s actually happened so far — not including this year. It’s one run on the real thing. Reality biting. You may safely assume that this years minimum is going to keep that black line bumping along at or below the lowest individual model runs compiled for the next IPCC assessment, which will therefore be out of date before it’s published.

We’ve known since 2007 that the AR4 modelling wasn’t capturing what was happening in the Arctic. It’s now obvious that the latest modelling isn’t capturing it either. A quick eyeball estimate suggests that this year’s minimum shouldn’t be happening for another 10 or 20 years. Some individual model runs might be capturing some of the dynamics of the ice loss, but on average, they’re underestimating it badly. And if they can’t get the sea ice right, then they can’t — because of all that heat being released to the atmosphere every autumn and winter — get the climate of the northern hemisphere right.

We are, not to put too fine a point on it, up shit creek without a paddle, with mud spattered spectacles and no map. This is not good news. It’s all over bar the shouting, of which you may expect plenty. But nothing’s going to change the direction we’re heading. From here on in, it’s damage control only.

[Otis Redding]