If the engineers can show that a Western-style livelihood is possible with half the CO2 emissions per person per day, then where is the sociology of persuasion to change lifestyles because profligate consumption is widely deemed to be antisocial? If we were to drive less, fly less, source food and goods from more local sources, we could have a real impact on CO2 emissions. Instead, all we have is misplaced technological optimism. There is no free lunch, however, as the implied reduction in transport and economic activity would produce its own downsides. I was relieved that the Pope in his recent encyclical focused on profligacy and waste and urged the development of the poor ahead of halting climate change if the two should conflict.

Those building the biblical Tower of Babel, intending to reach heaven, did not know where heaven was and hence when the project would be finished, or at what cost. Those setting out to solve the climate change problem now are in the same position. If we were to spend 10 or even 100 trillion dollars mitigating carbon dioxide emissions, what would happen to the climate? If we can’t evaluate whether reversing climate change would be value for money, why should we bother, when we can clearly identify many and better investments for such huge resources? The forthcoming Paris meeting on climate change will be setting out to build a modern Tower of Babel.

Lord Stern answers his own question — why are we waiting? — most eloquently in chapter five, “The Ethics of Intertemporal Values and Valuation”, which is a positively theological discussion with other economists asking by how much we should discount future values. If the response now to the perceived challenge of climate change has any relation to discount rates, we should wait until this debate is settled. The empirical data shows that investments in first-generation renewables are wasted if the justification is solving the climate change problem, as only 1 per cent of global energy comes from these since R&D started in the 1970s after the first oil shocks, and we are over halfway to 2050 when they are supposed to have reduced our carbon emissions by 80 per cent from 1990 values.

Past pessimists such as Thomas Malthus, William Stanley Jevons and Paul Ehrlich have been proven comprehensively wrong in their predictions of gloom, and I am confident that Nicolas Stern will join them. As Patrick Allitt observed in A Climate Of Crisis: America In The Age Of Environmentalism (Penguin, 2014): “Few people have paused to ask: How would we benefit now if our grandparents and great-grandparents had exercised more self-restraint and self-denial? Would we live better if they had exercised greater prudence and self-control?” The wise response now and for the foreseeable future is to continue to develop the world using mainly fossil fuels, to pursue R&D towards alternative low-cost energy sources,  and to adapt as and when future changes in climate actually emerge.