VOTE Blue, Go Green. Vote Brown and, it seems, you'll Go Green, too. Vote Orange, Liberal Democrat that is, and you'll probably go a nice safe shade of magnolia.

But they promise you'll Go Green, too.

Britain's political establishment has signed up to global warming and the urgent need to stop it. David Cameron took the husky trail, hatless, to a Norwegian glacier to demonstrate his commitment to the cause. Gordon Brown used a trip to America to say last weekend that advanced economies have a "moral duty" to tackle climate change, and that everybody has a "personal and social responsibility" to act.

Sir Menzies Campbell hasn't yet taken to a dog sled, or a bicycle for that matter, but he has promised to give up his Jaguar. Cameron and Brown are getting hybrid cars.

Many would say "hear, hear" to this and welcome evidence of so much political commitment to the planet's future. As far as Defra (the environment, food and rural affairs department) is concerned, time is running out -it is the "greatest environmental challenge" the world faces. "Rising global temperatures will bring changes in weather patterns, rising sea levels and increased frequency and intensity of extreme weather events," it said.

Sir David King, the government's chief scientific adviser, is a chemist by training, not a climate scientist, but he was famously bold enough to say climate change was a bigger threat than international terrorism.

Most of us, I suspect, had quietly accepted the three central propositions of global warming, namely:

1. The world is getting hotter, and will do so at an increasing rate.

2. This global warming is due to an increase in greenhouse gases -mainly carbon dioxide but also others -in the atmosphere. 3. This increase in greenhouse gases is man-made, so we must reverse it, even if this means sacrificing growth.

I had certainly accepted most of that and rather scoffed at the global-warming sceptics. So, it seemed, had most scientists. The closer you look at it, however, the thinner the evidence is.

Richard Lindzen, professor of atmospheric sciences at Massachusetts Institute of Technology, will this week receive in Sweden the Leo prize for independent thinking. He stands out against what he describes as "climate change alarmism".

Every freak weather event is blamed on climate change, he pointed out in a recent paper, Understanding Common Climate Claims. Some even blamed the Indian Ocean tsunami, a geological event, on global warming. He describes a "triangle of alarmism", in which scientists make meaningless or ambiguous statements, advocates translate them into alarmist declarations and politicians respond to the alarm by feeding more money to the scientists.

On the central facts of the global-warming case, Lindzen notes the mean global surface temperature has increased by only 0.6 degrees (centigrade) in a century, during a time in which greenhouse-gas emissions in the industrial countries increased sharply. The sensitivity of the climate to greenhouse gases, he suggests, is a lot less than the alarmists suggest. As a rough rule of thumb, he argues, a doubling of greenhouse-gas concentrations in the atmosphere might result in a rise of 0.5C in average temperatures, while a quadrupling produces a 1C increase.

This is a long way from the projections of the hugely influential Intergovernmental Panel on Climate Change (IPCC), which saw temperatures going up by as much as 5.8C by 2100, with sea levels rising sharply as the polar icecaps melt.

Lindzen is not the only sceptic. The excellent House of Lords economic affairs committee, including former chancellors Lawson and Lamont, examined climate change economics. "The scientific context was one of uncertainty," it said, urging the government to encourage "a dispassionate evidence-based approach". While acknowledging most scientists had signed up, it said "majorities do not necessarily embody the truth". It was particularly critical of the IPCC's lack of rigour.

Among the uncertainties the Lords committee had to grapple with was why global temperatures cooled from the 1940s to the 1970s, much of it a "golden age" for the world economy. The climate-change lobby says this was because of the cooling effect of sulphur in the atmosphere. So-called "hockey-stick" projections, where the recent uptick in temperatures is extrapolated, also raise doubts.

Defra's own charts are similar to those used by the Lords committee. But it also appears to have uncovered a big, mysterious, temperature rise in central England.

Nor are doubts confined to temperature. America may still be a culprit when it comes to carbon-dioxide but the Pacific Research Institute's index of leading environmental indicators, published last week, showed stunning falls in US emissions of carbon monoxide, down 56% between 1970 and 2004, nitrogen oxides, down 30%, particulates, down 79%, and sulphur dioxide, down 51%.

This should not be taken to mean there is no such thing as global warming. It does mean we should be sceptical about more alarmist statements, and seriously challenge the lack of precision in officially endorsed projections. It matters hugely if global temperatures rise by 6C over the next 100 years. It doesn't matter much if they rise by between 0.5C and 1C. I don't expect London and New York to be under water by 2100, or the Lake District turned into a tropical rainforest.

The climate-change lobby, and the politicians who have signed up to it, argue on the basis of the precautionary principle. Things might not be as bad as they say, but to get people to act, you have to stoke it up a bit. And just in case it is as bad, you have to act anyway.

But what should that action be? A chancellor determined to show he means business on climate change would look gleefully on the rise in international energy prices and add further tax hikes on top of them to cut consumption. A determined opposition leader would criticise him for not doing so. The price mechanism works rather well. Claiming to be green while only tinkering is just posturing.

Perhaps it is all posturing, but we should still question the naive economics of global warming. The best way to limit China and India's impact on the planet is to encourage them to become more prosperous (richer people demand a better environment) -not limit their growth.

There's also a lack of joined-up thinking. The Society of Motor Manufacturers and Traders, under pressure to reduce carbon emissions from new cars -even after a big reduction in recent years -points out that EU regulatory pressure to fit heavy safety equipment only makes the task harder.

PS: One quarter doesn't make a trend, but in the first three months of this year retail sales were weak, down 0.7% on a seasonally adjusted basis from the fourth quarter of last year. This was exactly mirrored by a rise in industrial production of 0.7%. Even manufacturing rose, by 0.5%. Will it last? The National Institute of Economic and Social Research sees 2.2% consumer spending growth this year, and a 6.1% rise in exports. But it expects manufacturing to trundle along at only 1%.

Meanwhile, my search for the best-value thing you can buy (I suggested the bicycle) continues. One strong candidate is international phone calls. A reader tells me he pays 1.5p for a three-minute phone call to Australia, compared with £ 5 (equivalent to more than £ 85 now) in the mid-1950s. Another interesting suggestion is petrol. It takes a lot to get a litre of petrol from deep in the ground to our forecourts. Yet the pre-tax cost, about 30p a litre, is lower than bottled water, olive oil, processed fruit juices and most other liquids. Keep them coming.

David Smith can be reached at david.smith@sunday-times.co.uk

Getting far too heated over global warming PRI in the News By: David Smith 4.30.2006