What is the truth about climate change?

His name was Prof Bob Carter, a retired geologist speaking on behalf of the jocularly named “Non-governmental International Panel on Climate Change” (NIPCC), a ragtag band of doubting Thomases partnered with the Heartland Institute, a free-market think-tank in Chicago whose previous campaigns included working with a tobacco company to cast doubt on research linking cancer to second-hand smoke.

Carter argued that climate is always changing naturally (which is true), and that our attempts to alter its course are therefore misguided. Claiming that the NIPCC is independent, he also averred that having “around 47” contributing scientists (against the IPCC’s 800-plus) made its opinions “widely held”.

Reaction to Carter’s performance and the BBC’s decision to use him was negative. John Ashton, a Fellow at Imperial College’s Grantham Institute for Climate Change, cited the 2011 report from to the BBC Trust, in which the academic and science communicator (and Telegraph columnist) had complained of the corporation’s tendency towards “false impartiality” – the “distinguished professor vs Swampy” problem. Jones had urged the BBC not to give undue prominence to individuals who give the appearance of authority but who in fact have none. Carter was such a person because he was a geologist, Ashton implied.

This conclusion, while superficially true, is also misleading. Carter may be wrong when it comes to climate science but that doesn’t mean geologists, the vast majority of whom agree with the IPCC conclusions, do not have a great deal to contribute to the debate. While climatologists deal in models that predict the future – models that are always uncertain – we deal with the hard reality of the past, a past locked up in the rocks. And we have some insights into changing climates that are denied to anyone studying today’s atmosphere.

Insights from the past: fossils from that era (ALAMY)

How? Well – you might think that 800, 000 years – the longest interval mentioned in the IPCC report – is a long time; but it is a short and unrepresentative eye-blink in the history of the Earth (less than one 5, 000th of its history), consisting mostly of glacial-interglacial cycles.

But because climate scientists only know about this tiny window on the past (albeit in incredible detail), they are fond of repeating the familiar trope that we are conducting a massive and uncontrolled experiment on the world’s climate. Unfortunately, this argument implies uncertainty, and is unhelpful. There are plenty of people sowing unreasonable doubt already without climate scientists doing it to themselves.

The experiment may be massive and uncontrolled, but it is wrong to suggest we have no idea what miseries lie ahead. Ask the geologists, and they will tell you what will happen if we increase greenhouse gas concentrations by the amount we are doing now, because this has happened before. And the results then weren’t pretty.

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