'We're doomed; we're all doomed,'' as Private Frazer of Dad's Army fame would have it. Another report on climate change this week suggests the Arctic permafrost is melting more quickly and will release much more carbon into the atmosphere than previously thought as the plant material held stably below freezing turns to decomposing mush.

It will cause a vicious cycle of more warming therefore more melting and even more warming, the report from the United Nations Environment Program suggests.

It is a bit like the vicious cycle of the melting ice caps and glaciers. As the ice melts there is less reflective white stuff to send heat back into space and more dark sea to absorb it. So the Earth heats faster than would be the case with just the extra carbon from industrialisation going into the atmosphere.

Well, we have heard all these doomsayers before haven't we? And we are still here. Surely, the Earth is robust enough not to worry too much about some human-made gas. And the UN and climate scientists are in a green-communist conspiracy to destroy capitalism, freedom and liberty.

Well, that is what self-interested industries would have you think. And so would some self-interested politicians. A few maverick scientists and commentators have seen their chance to be noted as brave and healthily sceptical people willing to buck the conventional view. They say that there is not enough evidence of warming, or enough evidence that humans have caused it. Or that the Earth has natural warming and cooling cycles and this is nothing to worry about.

Unfortunately, the theory of human-made climate change is fast becoming a minority opinion among the general population. And how nice it would be to not worry about the potential for catastrophic change or the possibility that our generation will leave the world a much worse place for our grandchildren than we inherited.

The change in public opinion is evidence that the world's scientists are failing us - badly. They are being far too cautious in their evidentiary requirements. They are being negligent in their duty to explain things to the public. They are being too inactive in advocating suggestions about what should be done about their scientific findings.

Yes, of course people should be sceptical, but not sceptical forever or sceptical in the face of ever-mounting convincing evidence - a bit like the tobacco-cancer link.

But one thing the climate-change sceptics are right about is that we have heard all this before - indeed several times.

Two occasions were especially instructive: in 1962 when the doomsayers, in particular Rachel Carson in Silent Spring, said the insecticide DDT would destroy not only insects but the birds and the rest of the food chain, and in 1974 when University of California chemists Frank Rowland and Mario Molina said chlorofluorocarbons (CFCs) would result in the destruction of the ozone layer which protects the Earth from deadly ultra-violet radiation.

Industry went on the attack. For example, biochemist and former chemical industry spokesman Robert White-Stevens stated, ''If man were to follow the teachings of Miss Carson, we would return to the Dark Ages, and the insects and diseases and vermin would once again inherit the Earth.''

And the industrial company DuPont denounced the ozone-depletion theory as ''a science-fiction tale … utter nonsense''.

Both theories were initially rejected by scientists as well: not enough evidence; need to be cautious; bans on DDT or CFCs would destroy the economy; action should be delayed until we know more; it is not the job of the scientist to advocate policy; it is for politicians to act on the science etc.

The authors of the theories were not quintessential scientists - cautious plodders slowly gathering evidence and publishing bit by bit in peer-reviewed journals. But they committed two cardinal sins in the scientific community. They took their science directly to the public and they became advocates for a policy response to their findings.

They urged a ban on DDT before spring became silent and devoid of birdsong, and a ban on CFCs before the ozone got so depleted the rise in the number of skin cancers would make outdoor life impossible and disrupt the plant-animal food chain.

Nonetheless, in those days governments were more courageous and science was more respected. Moreover, the two theories were more testable and explicable to the masses than climate change. After all, the weather is always variable.

But the hole in the ozone lawyer over the Antarctic was measurable. And the simple chemistry was explicable and frightening. CFC molecules rising to the upper atmosphere could latch on to ozone molecules (molecules with three oxygen atoms) and combine with one of those atoms leaving the other two as ordinary oxygen. Moreover, the reaction would result in yet another loose chlorine atom, which would be available to react with yet another ozone molecule causing a catalytic chain reaction lasting up to two years for each rising CFC molecule before the chlorine sank.

CFCs were banned throughout the world when the Montreal Protocol came into force in 1989. Fifteen years were wasted by the sceptics and deniers and the ozone layer will not be restored until 2050 - but doom was averted because two scientists were gutsy enough to stand up to industry and to science-funding sources and go public - so there were no excuses for inaction.

It was similar with silent spring. DDT was banned, or at least heavily restricted and doom was averted.

Human ingenuity can deal with climate change but only if we act in the way we did when warned about DDT and CFCs. We acted and acted vigorously. That's how you deal with climate-change doomsayers.

Science has got more spineless since the 1960s and '70s. And politicians love it because they do not have to make uncomfortable decisions.

Science is too dependent on research grants and beholden to industry to rock the boat. Scientific institutions are too scared their scientists might make them look foolish if breakthroughs are proved wrong. And the peer review system for scientific papers is defective. Why hand your work to anonymous competitors who have a vested interest in bagging it?

Carson, Rowland and Molina did not conform to the scientific community's norms. They went out on a limb and helped save the world.

Rowland and Molina were awarded the Nobel prize in 1995 - 21 years after the event.

With CFCs, the science was accepted and humankind was saved from millions of extra cases of skin cancers and other radiation effects on plants and animals. But we were only just in time. And the ban on DDT has spared us much environmental destruction.

With climate change there is not much time left for serious action before it is too late. This week's permafrost report is yet another warning for us to ignore at our peril.

I am indebted to Michael Brooks for his excellent book The Secret Anarchy of Science that was published earlier this year.