posted 03-07-2002 09:19 PM            

>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. <<>>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