Climate change is one of the unfolding calamities of our times. It is our moral responsibility as a country, and as individuals, to address the global threat that may engulf our children. We are compelled to make difficult choices and change our lifestyles. It is essential that we make changes based on reason, but not group-think. There is a danger that the green herd, in pursuit of a good cause, stumbles into misguided campaigns.

Analysis without facts is guesswork. Sloppy analysis of bad science is worse. Poor interpretation of good science wastes time and impedes the fight against obnoxious behaviour. There is no place for bad science, or weak analysis, in the search for credible answers to difficult questions.

The most troubling recent example of bad science is Andrew Wakefield's allegation, subsequently comprehensively quashed, of a link between the MMR vaccine and autism. History is sadly overpopulated with other examples. In 1995 environmental lobbyists obliged Shell, the oil giant, to abandon plans to scupper its Brent Spar platform in the Atlantic and instead tow it to a Norwegian fjord to be dismantled. Break-up came at a high energy cost. and was subsequently shown to be a greater risk to marine pollution.

Airliners are accused of speeding climate change by fouling the upper atmosphere. But cold analysis of hard facts shows that the damage done is more perceived than real. Imports of cut flowers from Africa were subject to a vociferous consumer campaign because it was assumed that the air freight cost was scandalous. A 2007 report published by Cranfield University showed that imported flowers created just 17 per cent of the carbon emissions of Dutch growers using heated greenhouses. Hilary Benn, as Secretary of State for International Development, said British shoppers should buy African flowers because it helped to sustain African livelihoods. The environmental benefits of biofuels have been exaggerated. By using land that might otherwise be used to grow edible crops, biofuels have created shortages of food and price rises. Brazilian rainforest is also endangered, as additional land is cleared for food production. Development of genetically modified (GM) disease-resistant crops was needlessly impeded by fears that mutant weeds would cause lasting damage. Almost no scientific evidence exists to support the scaremongering.

Wilful ignorance of good science is as depressing as the misinterpretation of bad science. Rising demand for low-carbon energy will be best met from nuclear science. Unfounded fears about the size of nuclear risks, however, threatens the pursuit of this commonsense answer.

Many of those who have demonised plastic bags have enlisted scientific study to their cause. By exaggerating a grain of truth into a larger falsehood they spread misinformation, and abuse the trust of their unwitting audiences. Gordon Brown's Government may be about to fall for a spurious argument, while simultaneously pandering to wrong-headed populism.

In this case an apparently fair piece of scientific research has been dragooned into the attack. In 1997 David Laist, an American, published a paper suggesting that every year 100,000 sea animals, and one million birds, meet an untimely end thanks to plastic pollution. Dr Laist never suggested this was an incontrovertible fact. But the assertion was, and is, respected as a reasonable estimate. Upon this unassuming foundation, however, is built an edifice of mistaken assumptions. Plastic nets entrap animals and off-cuts from the manufacture of everything from credit cards to watering cans poison or choke. Another piece of work, analysing 243 dead albatrosses, suggests that 90 per cent had come into contact with plastic but only one had died because of a plastic bag.

Plastic bags are objectionable because they make litter, but containers, such as water bottles, are a greater evil because they degrade more slowly. Plastic bags create some emissions but on this really large concern they are marginal. Carbon emissions will only come under control with fundamental shifts in domestic, corporate industrial and agricultural practice. Little good will come from fiddling with the small things while burning issues are ignored.