What on Earth? The concerned citizen's guide to global warming

Worried, but maybe just a little confused? Never fear. David Randall cuts through the conflicting claims with his concerned citizen's guide to global warming

Few of us are environment specialists, least of all me. I'm what most of us probably are on the eve of Copenhagen: a concerned citizen with only passing lay knowledge, who's getting more confused by the day.

After all, the past few weeks have brought the inevitable pre-climate-conference rash of reports, dismal forecasts and counter-claims from the warming sceptics, not to mention the leaking of worrying emails from this country's leading climate experts.

My position is probably that of many readers: the world has warmed considerably during the last century, and with a speed that suggests, at the very least, some non-naturally occurring factors at work. And, given the 10-fold rise in human population since the eve of industrialisation in 1750, plus our massive consumption of carbon-based fuels and materials and the expansion of livestock agriculture, it would be extraordinary if human activity had not played a role – probably a crucial one – in this warming.

But while, for most of us, climate is a matter of science, there are those at either extreme who have fanaticised it to the point where evidence is irrelevant. Faith, and point-scoring, are all. (If you doubt that, look at any newspaper's message board on the subject.) There are hucksters who have given even parts of the recycling and carbon-reduction business a questionable name; and there's the trainee Jeremy Clarksons who take any cool summer and use it as ammunition for their saloon-bar scoffing. So, head down to dodge the crossfire of opposing polemicists, salesmen and mission-statement writers, I set out to discover what exactly we now know, and don't know, about global warming.

What is the truth about global temperatures?

Global temperatures have risen 0.74C (1.3F) since 1906 (Intergovernmental Panel on Climate Change). The warmest year in recorded history was 2005, according to Nasa (or 1998 according to the Met Office's Hadley Centre), and the 10 warmest years have all occurred since 1997. But, although temperatures have been historically among the very highest in the past 10 years, they have not risen steadily. Sceptics have asked why, if global warming is true, this is so. Natural variation (mostly due to the influence of El Niño and La Niña, the two Pacific systems) is the answer, and it will take a second round of these mechanisms (which starts next year) to know if temperatures are rising in the medium term. In the long term, there seems no doubt at all: the world is warming. It may stop, but it's hard to see why it should.

What impact is warming having on the world now?

In 2007, the Arctic had an ice cover that was 39.2 per cent below the 1979-2001 average, and in summer the North-west Passage is now unfrozen and open for shipping. The loss of ice in the Antarctic is proportionately less dramatic, but still happening. Worldwide, in 12 years we've lost ice sheets the size of Alaska. Global sea levels have risen 17cm (over 6ins) during the 20th century, according to the European Environment Agency, and 3.8cm since Kyoto in 1997. The seas are becoming more acidic, glaciers are melting (now shrinking three times faster than in the 1970s) and the northern permafrost is thawing (if only 10 per cent goes, that alone could cause as much warming as we've had in the previous 100 years). As for whether extreme weather events are more frequent, there is not a long enough run of historical data to tell. But warmer winters, especially, are having unthought-of consequences. More than 37 million acres of Canadian and US pine forest have, for instance, been damaged by beetles surviving milder winters.

Can we be sure evidence is not being cooked up – on either side?

Not definitively – none of us has the training or data empirically to test what we are told. We have to rely on what seems likely, and my hunch is that to be a climate sceptic you'd have to believe that the overwhelming majority of scientists in the world have – in order to prise research grants from our grasp – conspired to hoodwink us all. Devout sceptics think the University of East Anglia emails prove exactly this, and an examination of them proves a worrying willingness to consider excluding, to coin a phrase, some inconvenient truths. Thankfully, theirs is not the only dataset. But while the case for global warming remains good, periodic over-statements of it give aid to the sceptics, especially when they are doomsday-awful and based on questionable assumptions (see below).

What is forecast to happen to climate this century?

Until recently, the IPCC's forecasts for temperature rise by 2100 ranged from 1.8C-4C. The higher figure assumed that no measures, other than those in place by 2000, were taken – a highly unlikely eventuality. Three weeks ago a report by the Global Carbon Project warned that carbon dioxide (CO2) emissions are rising far faster than previously thought, and temperatures by 2100 could be as much as 6C warmer. This, observers said, would render large parts of the planet – including southern Europe – virtually uninhabitable by humans. Earlier IPCC reports predicted a sea-level rise of just over half a metre. Such forecasts are based on modelling, albeit of the most sophisticated kind, and their key assumptions are the unlikely ones of a lack of effective action or of the advent of any new technologies. Long-term forecasts need further tyre-kicking.

How certain are we that warming is not a natural phenomenon?

Certainty is not a word that climate scientists use. The world's climate is governed by such complex mechanisms that, although broad patterns are understood, variations (and therefore modelling the future) are a still-developing science. Solar activity also plays a part, perhaps a significant one, as do the regular variations in the Earth's orbit pattern. And, say the sceptics, there have always been naturally occurring oscillations such as ice ages and inter-glacials. Yet the IPCC has said the evidence for warming is "unequivocal", and that human activity influencing it is a more than 90 per cent probability. A significant indicator is that night-time temperatures are warming more than day-time ones – a sure sign, says the European Environment Agency, that the warming is non-natural. And, tellingly, CO2 has increased 6.5 per cent in the 12 years since Kyoto, an eventuality that would be difficult to portray as in any way natural.

What are the main causes of the greenhouse effect?

Greenhouse gases exist in the atmosphere and trap heat, warming the world's temperatures. Without the greenhouse effect, Earth would have a temperature below freezing. But these gases (CO2, methane and nitrous oxide) can be present in such quantities that they cause excessive warming. CO2 emission occurs quite naturally, and at a level far in excess of human-related ones, but this is balanced by plants photosynthesising. About 40 per cent of human-related CO2 – caused by the destruction of carbon-absorbing forests and the burning of fossil fuels – is absorbed naturally; the rest goes into the atmosphere. These emissions have increased 31 per cent since 1997, and those from China, now the world leader in this pollution, have doubled in that time.

And then there's methane. Last month, two World Bank advisers concluded that 51 per cent of all greenhouse gas emissions are caused by livestock rearing and meat production – more than the combined impact of industry and energy. Overall, according to New Scientist, "about 50 per cent of the greenhouse effect is due to water vapour, 25 per cent to clouds, 20 per cent to CO2, and 5 per cent to other gases, including methane." So why aren't we panicking about water? Because it hangs around for only a day or so – carbon can stay in the atmosphere for centuries. Methane, which, although smaller in quantity, is far more potent in its greenhouse effect, lasts for about 10 years.

Is there a "tipping point", and when will it come?

Several junctures have been proposed for when we would be stuck with a strikingly warmed planet for the foreseeable future. These are most commonly (and unhelpfully) given as temperature rises. In September, for instance, the Met Office warned that we could, by 2060, have an average global temperature rise of 4C, causing collapse of some ecosystems, death of rainforests, submerging of cities, and the creation of a new 21st-century breed: climate refugees in search of habitable space. Such predictions assume no technological advance and little effective action, and seem to be less accurate foretellings than well-intentioned, though misguided, attempts to gee up policy makers. More plausible, as indicators of where we might be headed, are totals for carbon in the atmosphere. Mark Lynas, climate adviser to the threatened Maldives, cites a report in Nature that said a carbon "ceiling" of 350 parts per million would hold the temperature rise to C above what we have now. Trouble is, he points out, "we are already at 387". Since the stuff can stay up there for centuries, this gives some idea of how long (given no invention of a method for speedily reducing it) we would have to wait before a point of return. To talk, given our pipsqueak lifespans compared to geological time, of a point of no return may be politically expedient, but is scientifically improbable.

So why don't we, with one great political heave, aim to have the world carbon-neutral within a generation?

To appreciate how difficult this is, it's instructive to consider the few countries that have set out to cut emissions to zero. (What this means, in effect, is that they can use carbon, but only if their emissions are captured, buried or offset by forests or trading.) There were five – New Zealand, Iceland, the Maldives, Costa Rica and Norway. The first two have dropped out because of high cost; and the other three are struggling, despite having immense natural advantages (Norway's hydroelectric power generation, for instance, is not easily imitated in, say, the Netherlands or Bangladesh). Costa Rica also has hydro power, widespread forests (which it hopes Copenhagen will give it credits for) and plans for major railways. But, for all its good intent, carbon emissions are still increasing. The Maldives, which because of its vulnerability to rising sea is the most warming-conscious nation on Earth, aims for carbon-neutrality in 10 years. But the cost will be heavy – $1.1bn (£660m), or $3,548 for each of its 310,000 people. Norway, which aims for neutrality by 2030, has cash (a fund of $444bn – $100,000 per head of population – thanks to its oil industry), and buying its way to cleanliness via carbon trading is, in the words of its environment minister Erik Solheim, "in some ways peanuts for us". But it wants to achieve the target with the help of new technology and so is spending $620m a year on research – almost as much as the estimated annual cost of carbon trading. The results have not yet come, and Mr Solheim says: "It will be very hard to achieve carbon neutrality if we have no big technological change." The result? Norway, of all places, is actually failing to meet its Kyoto targets.

And what about the changes I'm making in my life? Are they having any effect?

Ask most people what action they've taken to combat warming, and they'll point to the odd forsaken car ride or flight, low-energy light bulbs, not leaving devices on standby and some council-enforced recycling. Perhaps the biggest benefit of these is readying us for society-wide changes that are not just a matter of individual choice – such as using the tax system to direct us away from carbon-greedy services and products. Perhaps in the future, meat, flights and fossil fuels – like cigarettes now – will carry a deterrent-level tax. Or we'll all have a personal carbon rating that will increase, or reduce, the level of income tax we pay. But the law of unintended consequences can apply. Some years ago, ethanol (fuel made from vegetable matter rather than petrol) was one of the great hopes of a greener future. But that was before it was realised that cereal producers, especially in the US, were switching en masse to growing corn for fuel, rather than food.

Can we stop global warming?

Carbon dioxide remains in the atmosphere for between 50 and 200 years. And, given the pent-up appetite for industrial and consumer progress in China, India, the rest of Asia and Africa, plus the inevitable rise in population, it's difficult to see existing technologies (and/or voluntary restraint) supplying the necessary carbon reduction.

But there are two grounds for hope. One is that no doomsday scenarios – be they from the Rev Malthus, successive warners of depopulation, coming ice ages, ubiquitous Aids infections or global YK computer breakdowns – have ever been borne out by reality. The second is that predictions about conditions at the end of the century made at the beginning of it are likely to be no more accurate than any Edwardian's prediction for 2000. The idea (and it is found in the small print of the wilder forecasts of the effects of climate change) that technology will remain undeveloped for the next 100 years is obvious nonsense. So while we should mitigate – and reduce if we can – our carbon emissions, salvation lies in developing radical new technologies. We may even come up with a way of diminishing the carbon already in the atmosphere. This may seem fanciful, but then so, to Edwardians, would have been civil aviation, space exploration, penicillin, organ transplants, nuclear power, computers, the internet, nanotechnology and mobile phones. It seems to this concerned but bewildered citizen that what global warming needs is rather more science, and a lot less hot air.