Big, cold and slow? Ice speeds up as climate talks slow down

Antarctic ice sheets are formed when glaciers meet the sea.

Things are changing down in the Antarctic. Up until recently, you could pretty much describe the ice sheets there as big, cold and slow. But now, as climate change has an effect on the bottom of the planet, we're seeing news stories about changes in the ice occurring much faster than has been expected, revealing new insights into how the ice sheets of our planet behave.

Most dramatically, the Wilkins ice shelf is breaking up. An ice shelf is a thick, floating sheet of ice that forms when glaciers or land-based ice sheets meet the sea. Just like a shelf sticks out from the wall of your house, so ice shelves stick out from the Antarctic continent, floating on the Antarctic ocean, but attached to the land.

The seaward edges of these ice shelves are where icebergs 'calve' - breaking off from the shelf to float off into the southern oceans. Most ice shelves have been around for thousands of years, and some of the Antarctic ice shelves are huge - the massive Ross shelf is bigger than Japan. Big, cold and slow.

But that's changing, and fast. Last year saw the Larsen B shelf on the eastern side of the Antarctic peninsula disintegrating. The ice shelf had been stable for millennia. This year it's the turn of the Wilkins ice shelf, which is 13,680km2 of compacted sea ice on the west of the Antarctic peninsula - 100 miles long and 70 wide, about half the size of Scotland.

The Wilkins ice shelf is on the West of the Antarctic peninsula. From Wikicommons

Here's the ice shelf in more detail, as of the start of this year. The shelf is sandwiched between two islands (to the left) and the Antarctic peninsula (to the right, off the picture.)

The Wilkins Ice Shelf © NASA

Last year, a large chunk of the shelf disintegrated, (where it's labelled ‘melange' in the photo), leaving only a narrow ‘ice bridge' pinning the ice shelf in place against the Antarctic peninsula. In places, that bridge is as thin as 500 metres, and over only the past few days, it's begun to look like the bridge may be collapsing.

Why is this happening? Well, temperatures in the region have risen 2.5 degrees since the 1950s. Ice shelves are more sensitive to warmer temperatures than land-based ice because they're warmed both from above by warmer air, and from below by a warming ocean. This means that when we see ice shelves collapsing, we're actually seeing early warning signs that the ice on the Antarctic landmass is itself warming up.

With the thin strip of ice holding the shelf to the land and keeping it stable breaking up, the ice shelf has become a neat symbol of many of our fears over climate change.

But beyond serving up another newspaper story, why is an ice shelf breaking up important? As mentioned, although they are attached to the land, ice shelves float on the surface of the ocean. Although they're massive, they already displace sea water - so when they melt, they don't cause sea level to rise. It's like chucking a load of ice into your bathtub - it raises the water level when you put it in, but the bath doesn't get any fuller when it melts. Ice shelves melting, or collapsing, isn't going to directly raise sea levels.

But it's slightly more complicated than that. Ice shelves stay stable because they are ‘fed' by glaciers, which balance the ice lost through the breaking-off of icebergs with new ice from the land. This is what has kept the shelves stable for so long, but the shelves also play an important role in controlling the speed at which glaciers discharge ice into the sea. If an ice shelf collapses, the glaciers feeding it will dump ice directly into the sea instead of feeding it onto a shelf, and that means that they speed up. And that's bad news.

Take the Larsen B ice shelf, on the other side of the Antarctic peninsula to the Wilkins shelf, which in 2002 suffered a complete collapse. As you can see from the map below, between 2001 and 2002 (yellow and red lines), a huge section of the shelf disintegrated, meaning that the glaciers which were feeding the shelf are now discharging directly into the ocean - faster. A study published last year showed that over the decade between 1996 and 2006, ice loss in Antarctica increased by 75 per cent because of glaciers speeding up.

The Larsen B ice shelf - fed by glaciers shown by red dots. From Wikicommons

When we think of ice sheets, glaciers, and ice shelves, all of the associations in our minds are to do with slowness - it's not an accident that ‘glacial' also means incredibly slow. But ice dynamics - the study of how ice sheets melt, break up, refreeze and disappear entirely - is a complicated science and one which we're only just getting our heads around. As temperatures rise in both the Arctic and the Antarctic, there have been plenty of indications that rather than thinking of ice as slow-moving, slow to change and pretty stable, it may actually be the case that things can change surprisingly quickly.

That might be a good lesson for the negotiators who are tasked with agreeing a global deal on reducing emissions at Copenhagen. Ed Miliband and his counterparts need to bring some energy and urgency to the Copenhagen talks, as well as a desire to actually make some tough decisions, because as the ice is speeding up, the talks are slowing down.

While the government is taking its time to make a decision over a new coal plant at Kingsnorth, the climate is busy reminding us that it makes no allowances for political timidity - the death of the Wilkins ice shelf is just the latest example that reminds us the clock is ticking.