It has been a strange week for weather.
A massive rainstorm has flooded historic Harper’s Ferry, West Virginia, not an unprecedented event, but still dramatic. At the same time, drought-struck California has begun what may be its worst wildfire season in recorded history. Perhaps even more disturbing, widespread flooding in the Balkans has caused multiple landslides, inundated whole villages, and the still-rising water now threatens Serbia’s most important power plant. At one point, a third of Bosnia was under water. The most frightening detail is that some of the flooded and destabilized areas were active mine fields left over from the Bosnian war, and now nobody knows for sure where those mines are.
Whether these floods and droughts would have happened without global warming is debatable; the Balkan floods especially are unusual, the worst in 120 years, since record-keeping in the region began, but unusual whether has always happened occasionally. As a general rule, of course, larger and more frequent flood events, with correspondingly drier periods in other places or between floods, are par for our course now in many parts of the world.
What is unambiguously a result of climate change is the recent bad news about the Antarctic.
There has been a lot of confusion about ice in Antarctica, in part because some of the ice there has actually been growing in recent years. But the part of the ice that really matters has been shrinking and the bad news is it’s shrinking twice as fast now as it was only a few years ago.
To clear up the confusion, the big distinction for Antarctic ice is between sea ice and glacial ice. Glaciers begin their existence as snow that falls on land. If more snow falls in the winter than can melt, the snow builds up and eventually is crushed into ice by its own weight. Because of that weight, glaciers flow gradually towards the sea, like giant frozen rivers. Glaciers store the snow of thousands of years. That is a lot of water. If a glacier melts or flows into the sea faster than new snow can replenish it, that water comes out of storage and the sea level rises.
In contrast, sea ice forms when the sea freezes. The extent of sea ice matters for all sorts of reasons, but sea level rise isn’t one of them. That is because floating ice takes up exactly the same amount of room in the water as the meltwater from the ice would. That is why you can make your drink overflow by dropping ice into it, but when you let the ice sit and melt the level of your drink does not change at all. Try it sometime. What matters for sea level is not whether water is liquid or solid but whether it is in the sea already or not.
Antarctica’s expanding sea ice does not negate global warming because, unlike the arctic sea ice, it mostly melts during the summer already. When we talk about the northern ice cap shrinking, we’re talking about its size over the summer. Summers are getting warm enough now, even in the arctic, to melt a lot of it. But most of Antarctica’s sea ice already melts away during the summer, so when we talk about its changing size we are talking about it in the winter, and Antarctica’s winters are nowhere near warm enough to melt ice. Its increasing sea ice probably has more to do with changing wind patterns and a less salty ocean (from all the glacial meltwater) than temperature per se.
Another possible source of confusion is that Antarctica has multiple distinct regions of glacial ice and one of its regions actually was growing more ice until recently. The most recent measurements show that region as stable, neither gaining nor shrinking. But most of Antarctica’s glaciers have been shrinking for a while now.
But the bottom line is that recent satellite data shows that the melting of some of Antarctica’s glaciers has sped up dramatically in recent years; the satellite can see the surface of the ice dropping in elevation. This is not a prediction or a model, it is observed data. Researchers are sure now that some of the glaciers of Western Antarctica are going to completely melt. The only major question is how long will they take to do it?
There is enough water in those glaciers to raise global sea level by four feet. All that melting could take two hundred years, but that’s hardly reason to ignore the threat, and of course there are a lot of other glaciers that could melt also, speeding up sea level rise.
The headlines from all of this are mostly that the melting is now “unstoppable,” which obviously implies quite a bit of doom and gloom. But the researchers themselves don’t say that now is the time to throw in the towel; now is the time to get busy. “Unstoppable” doesn’t mean exactly what it seems. I’ll get into more details on that later this week.
For now, the take home message is that there is no time to wait. The water is coming.