[note: This post was first written around a year ago, pre-Copenhagen, when the mechanics of climate change weren’t quite so generally well-known as they are now and when a 2 degree rise didn’t seem quite so inevitable.  I spent some time thinking about how best to tinker with it, but decided in the end, especially in the light of the East Anglian hysteria, to keep it as it is for the time being.  Apologies, therefore, if it appears to be stating the obvious. ]

…Planet is the usual word.  It’s a pity it’s so misleading.  Whatever we are likely to destroy with our oil-glugging lifestyle, it isn’t the chunk of rock rotating around the sun.  Earth sounds a bit cuddlier, but isn’t much more helpful, while the environment sounds like something only a geography teacher would get excited about.  The trouble with all these words is that they sound like slightly geeky minority interests.  You know; Charlotte collects stamps, Oliver plays chess and Duncan saves the planet. Yawn.

 What we really mean is us, the earth’s inhabitants; we humans together with the other creatures, animal and plants, with whom we share this little space, everything that provides us with food and shelter and most of everything that gives us inspiration and comfort.   Not the human race in centuries to come but our fellow men and women in the world now, certainly our children, and probably ourselves, unless we’re planning to pop our clogs within the next few months. 

 Yes, it’s all the things you’ve been feeling a bit awkward about as long as you can remember, the rainforests and pandas, but now it’s oak trees and polar bears as well, in fact most plants and animals except for cacti and mosquitoes, and most people who aren’t  billionaire survivalists (and even they are likely to have a pretty dull time, with no one else but cacti, mosquitoes and other billionaire survivalists to talk to). 

 So this is about global warming, right?  I know about that, it’s er….

 …  Um.  It’s a bit like girls and the offside rule, we know we’ve had it explained a few times, but the actual mechanics of the thing still seem to slide around to the dark bit at the back of our brains.  Briefly, global warming is the rise in the earth’s temperature which happens as a result of increased concentrations of greenhouse gases in the air.  These gases, most importantly carbon dioxide and methane, are called ‘greenhouse’ because they let the short-wave heat from the sun through to the earth, but trap the long-wave heat rays that are reflected back again. So, just like the little glass hut  your Grandad grew his prize tomatoes in, the earth gets hotter and hotter. 

  Of course, we need some greenhouse gases, otherwise too much of the heat that reached the earth would bounce off again and the global temperature would be around -18 degrees.  Not exactly bikini weather.  The problem now is that, since the beginning of the Industrial Revolution, the concentrations of these gases, which were just right to sustain life as we knew it, have gone up dramatically.  Carbon dioxide concentrations have increased by around a third and  those of methane have doubled.  So far we haven’t seen too much impact on temperatures, as most of the heat has been absorbed by the sea, but we’ve already seen global increases of 0.8 degrees, and are set for far more to come.

 A short digression for those who, like me, weren’t paying attention during geography lessons at school.  When we read about global temperature rises of a few degrees and wonder what all the fuss is about, we are probably confusing weather and climate.  As the NASA website puts it, “climate is what you expect, like a very hot summer, and weather is what you get, like a hot day with pop-up thunderstorms”. 

 It’s a bit like taking a pack of shuffled cards and turning them over one by one.  You might get an ace first time, but then have to turn over another twenty or thirty cards until you find another one.  That’s like weather, and the wide variation between one day and the next.  But if you were to keep drawing cards from the deck and reshuffling it for long enough, you’d find that an ace turned up on average once in every thirteen cards.  That’s more like climate; the long-term trend. If you found, over thousands of deals, that you were getting aces more or less often than that, you’d know that there was something dodgy about that pack of cards.  In the same way, increases in the average global temperature, though they may sound small, represent real and important changes in our lives. 

 For example, the terribly hot European summer of 2003, when up to 35,000 may have died from the heat, forest fires raged, crops failed and there were widespread water shortages, was only 2.3 degrees  higher than the average.  And in the other direction, during the deepest freeze of the last Ice Age, when New York was under a mile of solid ice, average global temperatures were around six degrees lower than they are now.

 But so far it’s less than a degree hotter than…?

 Than before the Industrial Revolution, yes.  But there’s enough greenhouse gases already in the system to make another half or degree of warming inevitable.  There’s nothing we can do about that; it’s already there, just hasn’t shown through in the actual temperatures  yet. So we’re talking about a 1.4 degree rise, even if everyone immediately stops doing everything.  What really matters is how much hotter than that it’s going to get.  As I write this the IPCC (the Intergovernmental Panel on Climate Change) are estimating a rise of between the minimum of 1.4 and 5.8 degrees.

 That’s nearly six degrees.  

 It is, yes. The earth was six degrees hotter once before, 251 million years ago, during an episode called the Permian Crisis.  It sounds like something your granny might have at the hairdressers, but it led to the extinction of at least 90% of all plant and animal species.  If we got anywhere near that level of global warming then the prospects for any sort of life would be pretty slim. Actually, as we’ll see soon, the rise could be even more than six degrees.

 There seems to be a lot of uncertainty about these figures.  Can’t these scientists be any more exact than that?

 Not until we are.  There is a lot of uncertainty, but it’s mainly about what the actual greenhouse gas emissions are going to be over the next few years.  And that, of course, depends on what we do.  If we continue as we are, ‘business as usual’ then we will definitely be looking at the upper end of the range and at widespread disaster.  If we act immediately to cut our emissions and to help others to do the same then hopefully we can keep the rise to a manageable level.  

 Which would be?

 Probably under two degrees.  That’s because of the direct effects of a higher rise but also because of something called ‘positive feedbacks’.  (No, not the kind you get for buying stuff on eBay.)  These are effects of global warming which themselves also speed up the warming process.  In the European heatwave of 2003, one of the scariest things that happened was that plants, severely stressed by the heat and drought, shut down their photosynthesis mechanisms.  Now instead of absorbing carbon dioxide they were producing it.  The same kind of thing is already happening in the soil, which normally stores carbon but at higher temperatures, where bacteria work faster, releases it as carbon dioxide.  Meanwhile layers of permafrost are melting in the Arctic, Alaska and Siberia, exposing ancient peat bogs which give out carbon dioxide and methane.  As one ecologist put it,

‘We are unplugging the refrigerator in the far north.  Everything that is preserved there is going to rot.’

Another type of feedback happens at the poles, where traditionally white snow and ice have reflected back a large part of the sun’s rays.  Now that they are melting, more heat is absorbed, and more snow and ice melt, in a vicious warming spiral.  

Two degrees of warming is generally considered to be the point at which these kinds of feedback would become unstoppable, pulling us into faster and fiercer temperature rises.  And these feedback effects aren’t included in the IPCC estimates, which is why, once they really take hold, a rise of over six degrees could easily happen.  We have been warned….