A few weeks before the Paris climate conference (Cop 21 of 2015), Lord Nicholas Stern told LifeGate that the agreement, which was indeed subsequently reached, could prove "insufficient" to honour the promise of keeping the rise in average global temperature within two degrees centigrade. "Reaching an agreement is positive," he continued, "but the real challenge is putting it into practice." After Paris, therefore, an "acceleration" would be needed.

Today, during the proceedings of the climate conference under way in Marrakech (Cop 22), in Morocco, Stern adds another dimension to his concerns, maintaining that he has "underestimated the risks" and "underestimated the dangers." The reference is to the celebrated Stern Report published in 2006, which subsequently became the defining document on the economic damage caused by climate change, calculated on the basis of a potential international stalemate in curbing the threat of global warming.

Caught on the sidelines of an event organised by the London School of Economics (Lse), Stern, who now leads the Lse's Grantham Research Institute on Climate Change and the Environment, took stock of why we are not doing enough.

Why do you say that the data contained in your report — which were already striking ten years ago — now need to be revised upwards?
Looking at these past ten years since the publication of the Stern Report, and looking above all at how much CO2 emissions have risen — from around 40 billion tonnes a year to the current 50 billion tonnes — it is inevitable to conclude that the dangers have increased and worsened in equal measure. We now find ourselves at a new starting point, even more complex to manage than ten years ago. At the same time, science has shown us that some of the consequences of global warming are occurring faster than expected and with even greater damage. When I predicted that the costs of doing nothing would be greater than the costs of action, I probably underestimated them because I had not factored in the delays. And this gap is even wider, above all because technological innovations have drastically lowered the costs for those who take concrete action against global warming. What was once seen as an alternative form of economic growth is now inevitable. A low-CO2 future is the only possible choice.

During a meeting here at Cop 22 you said that we should not be too afraid of what Donald Trump will do once he enters the White House. And you cited the opposite case of Canada — previously absent under Stephen Harper, and today in the front line thanks to Justin Trudeau's government. What should we expect over the next four years?
I think we have to start by being optimistic. We know that a good part of American states, cities and companies is moving decisively towards a low-CO2 future because it has understood that the future lies there. That is where competitiveness resides. And they can see it clearly. We will see what policy Trump pursues — right now he is focusing on boosting infrastructure, rightly so from my point of view. We can only hope that that infrastructure becomes cutting-edge, clean and smart, capable of making a difference. That is why we must encourage rather than judge.