By: John Gibbons

The generally accepted starting point for climate measurement is the average global temperatures in the mid 19th Century. At this time, while the Industrial Revolution was in full swing, its impact had not yet been felt in planetary temperatures. The global temperature at this time translates to roughly 280 parts CO2 per million in the atmosphere, and this level of carbon has remained fairly constant for the last 1,000 years or so. (For the uninitiated, CO2 is a potent greenhouse gas. The more of it in our atmosphere, the warmer the planet gets. Our neighbouring planet, Venus, for example has an atmosphere thick in CO2 and its average surface temperature is a scorching 400C)

Climate systems are extremely complex but quite robust, absorbing and generally cancelling out short-term aberrations in order to maintain the climate within a stable zone, ie. a temperature range within which life on Earth flourishes.

However, our climate system has been under sustained, ever-increasing assault for at least 150 years from a panoply of human activity, some direct, much unintended. When you stretch an elastic band, it will return to its original shape once the tension is removed. If stretched for too long, it begins to lose its elasticity before finally – and permanently – snapping.

The Earth’s climate is clearly losing its battle to maintain cool, life-friendly average temperatures. The real losers are the millions of species of flora and fauna – humans included – who are ill adopted to coping with a rapidly warming world.

+0.8C

This is where global temperatures stand in 2007. The extra heat is primarily a result of an additional 105 parts per million (ppm) of CO2 which has been injected into the atmosphere over the last 100 years, and more particularly, since the end of World War 2 and the huge global consumer boom that kicked off in the US in the early 1950s and continues to gather pace today.

You have to go back 650,000 years to find a world with today’s CO2 level of around 385ppm. The bad news is that at that time, global sea levels were much higher. Right now, sea level are again on the rise, glaciers are in full retreat and the edges of some of the world’s great ice fields in Greenland and western Antartica are beginning to destabilise and are showing signs of severe stress. The record heat across Europe in the summer of 2003 left tens of thousands dead, and two years later, hurricane Katrina almost wiped out New Orleans. This, remember, is at just 0.8 degrees of warming, which is where we are right now.

+1.5C

Nobody can say for sure when global temperatures will have increased by an average of 1.5 degrees centigrade, but what is now certain is that this process is irreversible and carries some very unpleasant consequences. For starters, scorching summers such as Europe in 2003 become the norm, not the exception. High summer temperatures lead to drought and massive forest fires. Burning forests are an ecological double whammy; instead of absorbing carbon and cooling the planet, blazing forests instead spew out millions of additional tons of CO2, thus pushing the needle further into the red. Massive sea level rises become unstoppable at 1.5 degrees of extra heat. Greenland is already warming much faster than this global average, and is predicted to go into irreversible melt beyond 1.5C. At this new higher temperature, the death of the world’s remaining mountain glaciers is certain.

This will trigger massive and destructive flooding in the short term, as the glaciers collapse and disgorge vast amounts of water into the valleys below. However, once this phase is over, the might mountain storehouses of fresh drinking water upon which billions of people now depend will be more or less finished. Drought, crop failure, famine and ‘water wars’, especially in India and across Asia into China are seen as inevitable at 1.5C.

+2C

Planet-wide, the system is beginning to come under great strain. As the seas begin to warm, their ability to absorb CO2 declines. Those same rising sea temperatures also spell doom for the world’s great coral reefs, and with them much of the amazing biodiversity of the sea. A warmer sea also provides the fuel for ‘super hurricanes’ of a level of ferocity that hasn’t been seen in at least the last 10,000 years, and probably over a million.

Species extinction today is estimated to be running at a mind-boggling 53,000 species a year, or more than 1,000 species disappearing forever every week. Add a further 2C into the system and extinctions rocket. Virtually all species are finely adapted to the local conditions, and if these get too hot, species that can move migrate north or south to cooler zones. However, this normally takes hundreds or thousands of years, as entire species can only migrate very slowly. Plus of course, humans get in the way. Our roads, cities, fences and agriculture make it impossible for most species to actually escape even if they could move fast enough.

Africa, already today bearing the brunt of the early effects of climate change, is likely to be largely desert with 2C, as will Australia and much of the American mid-west. The old ‘Dust Bowl’ of the 1930s will have returned with a vengeance.

+3C

At this level, the scale of disruption begins to overwhelm most societies, leading to chaos, civil wars and anarchy in many regions. Drought and famine sees hundreds of millions of people abandon their own countries in a desperate attempt to survive. This mass movement of refugees leads to widespread violence. Coastal flooding and storms see many of the world’s great cities, from London to New York, virtually abandoned, adding further to the refugee crisis. On this island, Dublin, Cork, Galway and Belfast would suffer a similar fate.

Agricultural yields in all but the most temperate zones will have plummeted, and severe summer droughts will further reduce food supplies. At 3C the Amazon finally succumbs, and the mighty 7m square kilometre rainforest burns. In the short term, this injects a massive pall of smoke and CO2 into the already overheated atmosphere. Even more seriously, the world’s ‘lungs’ have been lost forever, and the cooling effect of the Amazon on the world’s climate disappears.

At 3C the great permafrost regions of tundra in Alaska and across Siberia will be in full-scale collapse. This in turn adds hugely to the problem, as the vast stores of methane trapped in the icy ground begins to be released. Methane is a far more potent greenhouse gas than CO2. this extra source of warming pushes the system further into catastrophe.

+4C

The planet is now a very different place. All major forests have long since burned, the glaciers have vanished and both ice caps have melted. Sea levels are rising by the month, and an estimated 500 billion tons of methane has been released from thawed permafrost, shunting global temperatures even higher.

One of the most worrying aspects of global warming is that every piece of warming can in turn trigger another piece – and so on. This sets off a climatic domino effect, in which disastrous so-called positive feedbacks make what initially seems like a manageable situation rapidly run totally out of control.

In Europe, the entire Mediterranean area is expected to have been abandoned. Flooding, drought and extreme temperatures have seen the Sahara advance northwards into the heart of Europe, possibly even as far north as Paris. Severe weather in Ireland will have reduced the availability of food. The seas are virtually barren, with almost all fish life killed off by the high temperatures.

In a 4C world, starvation will be on a scale never before seen in human history. By 2047, just two centuries after our own Great Famine, the spectre of corpses piled by the sides of Irish roads and abandoned fields and villages will, in a 4C world, have returned, but this time there will be no way out, no ship in the harbour waiting to take the ragged survivors to the New World.

Beyond +4C

Think of Venus. A very long time ago, its atmosphere was similar to Earth, but a cycle of runaway heating and ‘positive feedback’ turned it into a boiling, lifeless cauldron. Runaway heating would most likely push temperatures on Earth into an unstoppable cycle, causing the atmospheric CO2 levels to shoot up to over 1,000ppm – three times today’s levels and four times the ‘safe’ level for life on this planet. From there, the greenhouse effect is self-perpetuating and utterly unstoppable.

At this point, the Sixth Extinction would be complete. The last one wiped out some 95% of life forms on the planet. The Sixth Extinction, the experts predict, is likely to render the planet as lifeless as our planetary neighbours. For more on a degree-by-degree guide to climate collapse, read the book ‘Six Degrees’ by Mark Lynas or visit his website, www.marklynas.org