In climate change, you always have to go back to the numbers. The scientific consensus, as far as you can pin it down, urges something in the order of a 60% cut in global greenhouse gas emissions - it would like them today, but 2050 makes a more feasible target.
Bring in considerations of equity, and for richer nations like Britain that means cuts in the order of 90%.
Sir Nicholas Stern, in his new report, broadly endorses these figures, and the overall message is clear: richer countries must cut, and cut now.
Money must be spent not only on low-carbon technologies but on protection, especially for the most vulnerable communities, he says.
And his case to the business and economics communities, which as a former World Bank economist he is well placed to make, is that action now will cost a mere 1% of global GDP by 2050, whereas business as usual could cost up to 20%.
The overall message of the report is not fundamentally new. In its 2001 report the Intergovernmental Panel on Climate Change (IPCC) calculated costs in the same ballpark.
The acid test of Stern is whether his economist's language can bring about the fundamental shift in political and economic direction which other financial analyses - as well as arguments posited on human rights, poverty alleviation, environmental services, health and simple concern for the natural world - have failed to do.
For that, he needs to be heard and understood at all levels of the British government and, more importantly, in every other major government.
Taxing questions
Never let it be said that the current UK administration is inefficient. Its ability to generate several days' headlines from a single report is the stuff of spinmeister legend.
Thanks to the leaks, drips and deluges of Stern-related minutiae over the last few days, one can already gauge how he is perturbing the political landscape within the UK.
Read more here
http://news.bbc.co.uk/2/hi/science/nature/6098124.stm?ls