Climate, wrote Oscar Wilde, "is what you expect. Weather is what you get." And weather is a chaotic beast. In the past 12 months alone, Ireland has endured some of the worst flooding in a century, followed by the hardest freeze in four decades, and, in recent months, near-drought conditions.
With both environmental activists and climate-change deniers attempting to use one extreme weather event or the other to 'prove' their completely contradictory positions, small wonder that the public and large sections of the media do not know who or what to believe.
Amid all this apparent confusion, the underlying trends are crystal clear. The planet is running a dangerous fever. The first six months of 2010 (which includes the prolonged cold snap in Europe and parts of the US) is now officially the hottest half-year since records began. In fact, the 11 hottest years since accurate global recording began in 1880 have all been in the last 13 years.
Last month's 'State of the Climate' report from the US National Oceanographic and Atmospheric Administration states that global warming is, quite simply "undeniable".
If at this stage you find yourself still doubting climate science, you may also want to re-think whether evolution, plate tectonics and atomic theory may also be elaborate hoaxes, since these too are scientific theories developed, tested, challenged and reappraised by thousands of professionals in the field over decades.
Still, what harm could a couple of degrees centigrade possibly do? To answer this question, think of your own body. No matter what the weather is like, your average internal temperature is maintained at a steady 37?C. Were that temperature to rise by just 10% – to around 41?C – you would fall dangerously ill, and unless that fever were controlled, you would suffer organ failure and worse within hours.
The earth's average surface temperature is around 14.5?C, and, despite wide variations from the poles to the tropics, this average temperature has remained virtually unchanged since the end of the last Ice Age 12,000 years or so ago. This is our planet's 'body temperature', and it is held in constant balance by a highly sophisticated climate system, a system whose complexity – and sensitivity – we are only now beginning to fully grasp. This is why scientists have warned repeatedly about the 2?C "red line" that we must at all costs avoid crossing.
So where are we headed? The Intergovernmental Panel on Climate Change (IPCC) projected a range of temperature-rise scenarios for the 21st century. These run from 1.8?C to 6.4?C. The lower figures are only possible if drastic, urgent steps are taken to cut emissions worldwide by at least 80%, while the higher end reflects the business-as-usual path. The latter is the path humanity, in its wisdom, has decided to follow.
Given that we now are bang on target for at least a 6?C global average temperature increase this century, we ought to know what that actually means. Here's a degree-by-degree guide to the decades ahead, based on a summary of the best available peer-reviewed scientific guidance. Brace yourself for a bumpy ride:
1° - There is little or no wiggle room here, as greenhouse-gas emissions have already pushed the dial up by an average of 0.8?C since the pre-industrial era, with more already 'in the pipeline' due to what's known as climate inertia. As the world reaches the first full degree centigrade (the equivalent of pushing up global average temperatures by around 6.5%), the effects are being felt most acutely at the poles. The Arctic ice pack is already under full-scale assault, and virtually every glacier on the planet is in headlong retreat. Even the mighty Greenland shelf is already feeling the heat. That one degree is destabilising natural systems in a million different ways, some obvious, many subtle, but almost none helpful. The reduction in the number of winter frost days in Canada has led to an explosive increase in pine beetle attacks. In British Colombia alone, an area larger than England is under attack from these beetles, and many of these great forests are now starting to emit, instead of absorb, carbon as a consequence.
2° - According to the EU, this is the line we must, at all costs, avoid crossing. Warming is now accelerating much more quickly, especially in the high latitudes. At this temperature, the world's great glaciers are committed to destruction and the fracturing of the edges of the Greenland ice shelf is underway in earnest. The Arctic ice pack has disappeared and the region is now open ocean for much of the year, leading to a huge increase in solar energy absorption and a further quickening of the warming trend. Globally, extreme weather events roll in with ever-increasing regularity. In a warmer world, precipitation increases, leading to more flooding. However, shifts in rainfall patterns lead to a dramatic increase in desertification, especially in sub-Saharan Africa and Australia. The outlook for the world's oceans at 2° is ominous. Huge increases in absorbed CO2 are leading to ocean acidification, while coral bleaching and die-off from warmer water temperatures becomes widespread. Global food production is down by a quarter as a result of severe weather events and the effects of prolonged high temperatures.
3° - Our fate is sealed. Global starvation from the near-collapse in agricultural production has led to widespread political instability, with many regimes collapsing as starvation and panic spreads. Globalised trade has been sharply reduced, with many of the countries we in the 'first world' currently import our produce from either unwilling or unable to supply us. In a 3° world, the seven million square kilometre Amazon rain forest is in flames, emitting many billions of tonnes of greenhouse gases into the atmosphere. The whole Amazon region becomes a smouldering desert, with far-reaching consequences for the global climate system. Meanwhile, sea levels have begun to rise much more quickly, as a consequence both of thermal expansion (water expands as it warms) and the melting of land-based ice. Greenland is now in full collapse. It will, over time, add seven metres to global sea levels, but already the world's great cities, almost all of which are located on the coastlines, have been abandoned. At 3°, the vast permafrost zones in northern Canada and Siberia are breaking down, and the methane trapped for millennia in this once-frozen landscape is now pouring into the atmosphere. Methane is, molecule for molecule, over 20 times more potent as a greenhouse gas than CO2, so the effect of billions of tonnes of methane seeping into the atmosphere is to ratchet up the cycle of runaway heating still further.
4° - The last time earth was 4?C warmer than today was 40 million years ago, and at that time, the planet was ice-free from pole to pole. While Antarctica is so vast that it will take time for its complete destruction, in a 4? world, western Antarctica has followed Greenland into collapse, adding another five to seven metres to global sea levels over time. Coastal inundation and more severe storms fuelled by hotter ocean temperatures are forcing hundreds of millions of people to flee inland. Vast amount of infrastructure is abandoned. Food production has been severely hit, and famine conditions are spreading from the poorer countries right into the heart of Europe and the US. The good news, such as it is, for Ireland, is that our maritime location and latitude will shield us from the most severe effects for longer than many other countries. However, just how Ireland will be able to prevent millions of desperate climate refugees from mainland Europe seeking sanctuary in 'Lifeboat Ireland' is another matter. At 4?, the global economy has essentially ceased to function; every country, perhaps every family, is now fending for themselves. In this new world, the IPCC projects "worldwide agricultural drought". It's 1845 again, but this time, there is no New World to escape to.
5° - The world is by now a place barely recognisable to today's denizens. There are no rainforests; inland temperatures have risen by perhaps 10?C, leaving vast continental areas uninhabitable and much of what used to be the coastlines under several metres of water. The effect on the natural world has been apocalyptic, with species disappearing in their tens of thousands. The web of complex life on earth is rapidly unravelling. Humanity, from its apex in the early 21st century of just over seven billion, has plummeted, due to starvation and warfare, into just millions. Desperate governments are trying to relocate survivors to the far north. Countries with military wherewithal grab their neighbours' territory; expect the US to invade Canada while China annexes much of Siberia. However, much of the potentially productive land is lost to forest fires, which rage in a hotter, CO2-heavy climate. "A drastic reduction in human populations is unambiguously the most likely outcome of a rise of global temperatures towards five degrees," is how author Mark Lynas expressed it. The above scenario is bad, but unfortunately, it can get worse, much worse.
6° - Hell has been unleashed. The world's oceans are lifeless and toxic, as super storms and tsunamis batter the survivors on land. Deep-sea heating, most likely in the shallower Arctic ocean, destabilises billions of tonnes of once-frozen methane clathrate deposits, which rush to the surface and explode on impact with the atmosphere, triggering the equivalent of a global nuclear holocaust. This happened at least once before, around a quarter of billion years ago, when a 6?C temperature spike led to the kill-off of well over 90% of all life on the planet. An average temperature rise of this magnitude would be akin to your own body temperature hitting 50?C – of course that could never happen, as you would be long since dead. "So far as we know, this is the only planet in the entire universe which has summoned forth life in all its brilliance and variety", wrote Mark Lynas. "To knowingly cut this flowering short is undoubtedly a crime, one more unspeakable even than the cruellest genocide or most destructive war. If each person is uniquely valuable, each species is surely more so… and ignorance is no defence".