Former diplomat and now a leading authority on climate change: Sir Crispin cut an authoritative figure upon first sight of him at the Peterhouse Politics Society. After his talk “Thinking Differently: Out of the Box and into the Future”, we sit down to talk.

Having been one of Britain’s top diplomats for many years, his career changed direction significantly in the mid-1970s, something he describes as “a product of chance, because I had a sabbatical year off at Harvard in the mid-1970s and contrary to the advice I was given at the time, I focused on the relationship between climate change and politics. I was able to read all the literature in something like 3 months whereas now it would take me 30 years.”

His 1977 book Climate Change and World Affairs was incredibly influential, and led to him advising successive British governments, including Thatcher’s.

He muses “I think my biggest achievement has been to help people understand the problems of climate change”, despite a spell as Britain’s representative on the UN Security council.

He boasts that during his time there “I never once used my veto”- no mean feat, considering that he was present during the breakup of the Soviet Union and the first Gulf War. The secret, he explains, was that he used to have all five members at his house for meetings; he believes it certainly helped having a friendly relationship with his opposite numbers.

Throughout, Sir Crispin stresses the need for academics from different disciplines to work together in order to combat the multiple crises we currently face, both economic and environmental.

“In an ideal world, you’d make an arrangement whereby people very rapidly change their energy policies. But that means thinking again about economics and measuring things differently and putting your priorities in different places. If you did that you may be able to stay or delay some of these things happening and get it under control. There are one or two things where we are past the tipping point though; such as sea level rise.”

He does accept that multilateral treaties, such as Kyoto or Copenhagen, do not necessarily provide the best way of achieving these changes, stressing that “Governments have to somehow understand these changes are not only for the good of the planet but for the good of themselves.” The attitude of “Why should Britain damage itself for the sake of the world?”, as shown in a recent speech by George Osborne, is labelled deplorable and Sir Crispin calls for one of the larger countries to take leadership of the issue.

Sir Crispin also emphasises the need for a New Economics: “I welcome the demonstrations against market capitalism at present; I’ve walked amongst those people at St Paul’s and I don’t think they know what they want but much of the resentment about bankers giving themselves huge bonuses is part of the unease about the system as a whole.”

He expands on this topic: “Out of date economics should be recognised as a dangerous mental condition which is driving the world in an alarmingly wrong direction”. He points out that there is no such thing as a true free market, that we need to determine the character of regulation and somehow take these externalities into account. Illustrating these points he asked “how do we value uncut rainforest?” He envisages a future where instead of focusing purely on GDP, we measure health, wealth and happiness.

As we draw to a close, I ask him what he feels about the prospects of the changes he outlines actually being implemented in order to stop what he describes as climate destabilisation. “Optimism of the intellect and pessimism of the will”, he replies, but he carries on with cautious hope, stressing that not only British political parties are aware of the issue, but also those in France and Germany. the question is now when, not if; hopefully before a tipping point.