Professor Lord Nicholas Stern, world renowned economist and leading authority on climate change, presented his lecture on "Blueprint for a Safer Planet" at Oxford's Sheldonian Theatre on Thursday 7 May.  Lord Stern made headlines in 2006 with the publication of the influential Stern Review on the Economics of Climate Change.  The lecture is part of the 21st Century School's Distinguished Public Lecture series.

The Stern Report received public and critical acclaim when it was published in 2006. It was the first time that climate change had been analysed as an economic challenge rather than an issue exclusively for science and technology. What Stern came up with in that ground breaking document was the, perhaps surprising, conclusion that the cost of reversing climate change was infinitely less than doing nothing.

In Lord Stern’s lecture his only expressed revision to the 2006 report was that, maybe, he had underplayed the degree of urgency at the time. He now concedes that urgent action is paramount.

But what action and how? Stern insists that the twin issues of climate change and world poverty are inseparable. They are inseparable because climate change can only be resolved through international collaboration, and collaboration demands a rebalance of the world’s wealth. Without help to the developing nations to raise their GDP per head of population, there will be no global agreement to a course of action. Climate change does not recognise borders. We are all in this together from the Wall Street banker to the subsistence farmer in the Indian sub-continent.

So what do we need to do and what will it cost? Stern believes that we must stabilise the level of CO2 in the atmosphere to 450 parts per million. Currently the level is 435 but at present

growth rates, in 100 years it will be 750, which would give rise to a global temperature increase of 5 degrees, enough to destroy civilisation. (Homo-sapiens have been around on the planet

 for 200,000 years but the last time that the planet was 5 degrees hotter than now was 30 million years ago and was an age of equatorial swamps. Such a temperature rise would totally change the physical geography of the world.) Can we hold CO2 levels at 450? Stern believes we

 can and if it does rise to 500 parts per million we would see a temperature rise of 2 to 3 degrees from which it would be essential to ensure a gradual reduction back to 450 again.

What will it cost? Globally, Stern estimates the cost to be $1.95 trillion. Sounds a lot of money, but the world’s GDP is currently $50 trillion and by 2050 is expected to rise to $100 trillion. So, for at most 4% and perhaps just 2% of our international wealth we can save the planet. Not a bad insurance premium I’d say. And there are spin-offs. Better energy security, less air pollution and the development of new technologies are all positive expectations from challenging climate change and will enhance economic growth world-wide.

How do we get there? The developed nations of Europe and the US will need to achieve an 80% reduction in CO2 by 2050 (actually 90% in the US, but 80% is Obama’s current target). Stern is a supporter of the principle of carbon trading. He sees the concept as a means to allow under-developed nations to trade their carbon "rations" for cash to invest in their infrastructure and development. Most of these countries already have Climate Change Action Plans expressly for this purpose. Stern also wants to see greater sharing of technology since collaborative solutions will not emerge from a restrictive approach to technological innovation. He sees a need for a clear internationally recognised "price" for carbon, the rapid transfer of energy generation to zero carbon technologies and the replacement of deforestation (which accounts for 20% of the increase in carbon emissions) with comprehensive and globally supported alternative agricultural strategies.

In the subsequent question and answer session, Stern acknowledged the hysteresis effect of climate change i.e. global temperatures rise and melts the permafrost which releases massive volumes of methane which in turn increases the rate of global temperature rises. He was encouraging about the political climate, despite some scepticism from the audience.  He believes that China, the US under Obama, and the UK government are all serious about the issues.  And he was clear that the best way to ensure that world leaders are left in no doubt as to the importance of the issue when they meet at the December Copenhagen conference was by engaging in clear rational debate now.

Which, after all, is what Sustainable Woodstock is all about!