Climate change scenario
Burning fossil fuels and using the atmosphere as an open sewer has turned out to be a recipe for disaster. The Earth is warming and the pace is quickening. Where will it end? Tune in to the late 21st century to find out...
Hello and welcome to On the Agenda.
My guest today is Angela Eiss, science historian and author. Those of you who have been living under a rock for the past few months might not have noticed that this year is the 100th anniversary of the Earth Summit. Dr Eiss's new book, What have we done? charts global climate changes over the past century. Angela, back in 2001 scientists were hopeful that with a concerted effort we could crack this problem, what went wrong?
Well, what those researchers didn't quite appreciate is that once warming took hold it would spiral out of control. But they did know that things were bad, even back then. Reports in 2001 from the Intergovernmental Panel on Climate Change, the forerunner of CCOOL, said unequivocally that human-induced climate change was happening and that it was likely to get a whole lot worse. The reports claimed that the carbon dioxide produced from burning fossil fuels was already warming up the world, and that if nothing was done it would have all sorts of disastrous consequences.
But there was one hopeful sign. At that stage, the climate wasn't heating up nearly as much as anyone thought it should. There had been a slight increase in temperature on the ground. But satellite measurements showed that higher up in the so-called "free troposphere", things didn't seem to be getting much warmer. Incidentally, this led to a whole movement of mainstream sceptics who for quite a while tried to insist that no climate change was happening at all.
Anyhow, the status of the free troposphere became a very big deal, and here's why. By itself CO2 wasn't enough to cause serious climate change. Most of the warming predicted in the models came from a feedback involving water vapour. Crucially, for the models to be right and the feedback to happen, the free troposphere had to warm up. The feedback only works because a warmer atmosphere can hold more water vapour from the oceans. Because water is a very potent greenhouse gas in its own right, that would multiply the effect of CO2 several fold and the overall effect would just snowball. But if the free troposphere didn't warm up, it wouldn't hold more water and the feedback wouldn't be triggered. And according to the models, it made a big difference. With the feedback, models predicted that temperatures would increase by up to 6 degrees C over the century. Without it, there wouldn't be much of a change at all, even if the amount of CO2 in the atmosphere doubled.
Well, we've seen more than a 6 degrees C rise in the past century. What happened?
The guys from CCOOL still argue about what masked tropospheric warming in those early days. Whatever it was, it didn't last. By the mid-30s balloon experiments started to show more water vapour in the free troposphere and the disastrous feedback mechanism that researchers had predicted began to kick in. What's more, within a few years researchers were recording increases in the proportion of high clouds relative to lower ones.
It's not much of a surprise that with more water vapour in the atmosphere you'd get more clouds. The problem lies in the kind of clouds. If they form quite low in the atmosphere, they tend to reflect sunlight well and help to counteract the effects of warming. High clouds, on the other hand, make everything worse by trapping more heat. And guess what we got - the high ones. That's one of the reasons warming really took off. At the turn of the century nobody had predicted this, because no one could find an effective way of including clouds in the climate models.
So was this why we suddenly had the Big Thaw in the Arctic?
It was certainly a trigger. Researchers had long suspected that the first real signs of global warming would show up at the poles. The Arctic's particularly sensitive even to small warming, because when white sea ice melts it exposes dark ocean. That absorbs more sunlight and things start to heat up much more rapidly. Of course, the Arctic Ocean passage across the North Pole has become a crucial shipping route between Europe and Asia since the Middle East Water Wars disrupted movement through the Suez Canal. But it hasn't been quite such good news for Arctic wildlife. Polar bears, for example, used to rely on sea ice to reach their prey. When it melted they started dying in droves. And though it seems brutal to us now that the last remaining wild bears were shot, it was no joke for the people of Churchill who were terrorised by half-crazed starving animals. Back in those days, of course, megafauna weren't nearly as rare as they are today.
Only yesterday there was a report predicting caribou extinction by 2110...
Yes, it's all connected. The dramatic fall in caribou is a direct result of the thaw, which has spread to lower latitudes and is affecting the northern permafrost. I was in Siberia last year and the tundra is rapidly turning into a quagmire. And the smell of rotting mammoths!
But it's not just the caribou that are in danger from melting permafrost. Vast quantities of methane and CO2 are escaping as the vegetation thaws and rots. As you know, methane is a potent greenhouse gas so, like the polar thaw, this is another vicious circle. The planet's repaying us with interest for our polluting past. There are huge amounts of carbon locked up in the tundra and now it's being released back into the atmosphere. That can only make the warming even worse.
What other effects will this accelerated warming have?
Well, we've seen many of the effects already and those are likely to get worse. Flooding for instance. Sea level has risen by nearly a metre over the past hundred years and that's a direct effect of global warming. Of course, melting sea ice didn't make any difference to sea level, but many glaciers have disappeared and they certainly contributed, as did the thermal expansion of the water itself.
And although not much land has been directly inundated, rising sea level makes periodic flooding much worse. When you start from a higher base level, it's that much easier for storm surges to tear inland. With more warming on the way, we're bound to see more of the sort of floods that have devastated low-lying areas such as Bangladesh and the Nile Delta in the past decade. Two-thirds of Bangladesh is now regularly under water. And environmental refugees will continue to flee places like Mozambique because it's so susceptible to tropical cyclones.
You see, that's another effect of global warming. Tropical cyclones are also becoming more frequent and more devastating. The cyclone that hit the Bay of Bengal last year killed more than a million people and left tens of millions homeless. It's the same place that was hit way back in 1991. At the time, that was considered a terrible natural disaster, but the death toll was 138,000. It was devastating, but nothing like as bad as we have today. The problem with tropical cyclones is that the higher the overall temperature, the greater the intensity of all cyclones. In the late 20th century, researchers predicted this. They realised that the temperature sets the maximum intensity a storm can reach. They also noticed that any given intensity is equally likely up to this maximum. So if you increase the temperature, you increase the intensities of all tropical storms - just as a rising tide raises all the boats. More recent research from CCOOL shows these researchers were spot on. And then there's El Ni–o.
That's the strange reversal of Pacific currents that bring drought to Australia and the Far East and deluge to the west coast of the Americas. But correct me if I'm wrong Angela, aren't El Ni–os a perfectly natural phenomenon that's been around for aeons?
Yes, they have been around for a long time, but not like they are today. El Ni–os used to happen only once every seven years or so, but now they are almost always here, and they're more severe than ever. That's why the flooding and mudslides have been so devastating in California. It also explains the Australian droughts and the chronic famine the people of the African Sahel have been experiencing for decades. El Ni–os seem to bring changes to the weather in places you'd least expect.
And that's why the Amazon is blazing too. Even though the Brazilian government sited the rainforest remnant parks right in the heart of the Amazon basin where they should have been safe, the fires have still got to them. The El Ni–os, on top of the rest of the warming, have just caused mayhem. It's so hot there now that the trees are starting to lose their leaves, and that lets sunlight break through the canopy, dry out the leaf litter and turn the whole place into a tinderbox. Upshot: it's all burning.
It's not all doom and gloom, though, is it? I read your description of British summers at the turn of last century with horror
There's no doubt that folks living in the states of northern Europe are enjoying a much better climate than their grandparents did, but they shouldn't feel too smug. There could be a strange reversal on the way. There's a place near Greenland where the ocean water becomes very dense and starts to sink, which drags warm surface water up from the tropics. This is why northern Europe is warmer than other places at the same latitude - Canada for instance or Siberia. But listen to this. Because the ocean's getting so much warmer than it used to be, and also because there's more fresh water running into the northern Atlantic, it looks as if the seawater's becoming much less dense. The sinking might stop any day now. If that happens, all the warming could start to reverse in Britain and northern Europe, and they might even plunge into a mini ice age. The early models predicted all this.
So global warming could lead to cooling. Does that mean we'll be able to start skiing in the Alps again?
Possibly, but with lots of other feedback mechanisms turning up the heat, CCOOL scientists still can't predict exactly what might happen. If the past century has taught us anything it's that the climate system is so complicated that messing with one part of it is likely to have big knock-on effects. Take ozone loss: in the early days nobody realised it was connected with global warming. It seems naive now, but they assumed that all they had to do to get the ozone holes to close up was stop using CFCs - the chemicals that did all the damage in the first place.
We know now that it wasn't that simple. Harmless stable chlorine compounds derived from CFCs are transformed into their rapacious ozone-destroying forms out in the stratosphere. But it has to be really cold for this to happen, and that's where global warming comes in. The problem is that greenhouse gases act like a blanket, trapping heat in the lower atmosphere. To balance the books, cooling occurs in the next layer out - the stratosphere.
The effect didn't make that much difference in the Antarctic because there the stratosphere was cold enough in winter to trigger the destructive chain reaction anyway. But we really suffered in the northern hemisphere. As global warming increased, a huge ozone hole opened up here just when the Antarctic hole seemed to be on the mend. Of course, CFCs ran out in the end, but not before we had a massive leap in skin cancer.
Wasn't that partly because in those days so many people spent their holidays just lying on beaches?
Yes, in the early part of the century there were beaches everywhere: the seaside was as popular as EcoParks are today. But it wasn't just about people frying themselves in the Sun. You could dive among coral reefs in the Caribbean and off the eastern coast of Australia. It must have been amazing. The corals contained symbiotic bacteria that helped provide them with food and gave them jewel-like colours. But when the oceans warmed beyond a certain threshold, these microscopic inhabitants couldn't take the heat. All that's left today is the bleached-out husks.
We're bound to feel nostalgic for the days when people could see wildlife in its natural setting - when our experiences of the environment weren't so sanitised. Any chance of turning back the clock?
It's too late to stop many of these effects. There are so many feedback loops and connections between various climate systems, and they seem to be conspiring to make things worse. It's almost as if the planet has taken over. But now that it's illegal to burn fossil fuels anywhere in the world, we can at least try and contain the changes. For the rest of it, we're just going to have to get used to the new world we've made for ourselves.
Dr Angela Eiss, thank you very much
Gabrielle Walker
http://www.newscientist.com/hottopics/climate/climatescenario.jsp