The difference between speed limits and speed cameras is that speed cameras work. They arouse fear and frustration, but they are in the end obeyed. Speed limits, on the other hand, are generally treated as moralistic exhortations which no one ought to take literally. The distinction between exhortation and enforcement is fundamental to understanding what governments intend when they announce a policy; and the latest report to parliament of the government’s Committee on Climate Change makes it clear that the government’s commitment to mitigating the effects of the climate emergency is still very much at the stage of announcing speed limits: targets and exhortations without any enforcement or real effects on behaviour. As a result, there is a smashup coming. A global rise of 4C in mean temperature is equivalent to the entire rise in temperature since the last ice age, and whereas the preceding rise was spread out over 10,000 years, this one will be a compressed into a century.

The committee’s language is remarkably blunt: “Targets do not themselves reduce emissions”, the report says – any more than speed limit signs make drivers slow down – but even the targets are badly placed; “There are no areas where the government is planning properly”; and, from the former chairman of the Conservative party, Lord Deben, “the whole thing is run by the government like Dad’s Army … this ramshackle system … doesn’t begin to face the issues. It is a real threat to the population.”

Of the 25 targets announced last year, one has been met; work on 10 has not even started. The number of civil servants working directly on policy has been slashed since 2013, and central funding for services to help businesses and regions adapt to the coming changes has disappeared. At the same time the problem has grown larger and more urgent. Few people now believe that we can restrict the global rise in temperature to two degrees; virtually no one believes that the Paris target of 1.5 degrees is realistic; but 4 degrees, which the latest report urges we should be planning for, promises to be catastrophic.

The sea level might rise over time by 10 metres; even the much lower mid-range of predictions would see Scunthorpe, Doncaster and Lincoln in the UK become coastal cities; most of Cardiff would vanish, along with the South Bank in London. Amsterdam and Rotterdam will be inundated along with large parts of the Netherlands. The Danube, the Mississippi, and the Murray-Darling rivers in Australia, on which millions of people depend, will shrink by up to 40%. At least 300 million people will become climate refugees; China and the USA will lose coastal cities. Resource wars are a possibility; famine and epidemic disease are a certainty. There is no simple technological fix: in fact, technological progress can make societies more vulnerable, because they become more complicated.

All this is a realistic prospect by the end of the century and possibly 40 years earlier. These are not crank predictions. They are official estimates, derived from the best scientists the government has available. The inaction and frivolity of the state’s response is breathtaking. It is now 11 years since the then chief scientific adviser to Defra, Professor Bob Watson, warned about the prospect of a four degree rise, which in those relatively optimistic days looked like a worst case scenario. It is past time to plan seriously and to act on these plans. Dad’s Army won’t muddle through this global emergency. However painful real change may be politically and economically, waiting for the inevitable will be worse.