Lord Stern at the DFID Conference.

I was lucky enough to be at this talk.

"....The management of climate change requires the reduction of emissions of GHGs. The G8 nations at recent summits have endorsed the goal of reducing global emissions by at least 50% by 2050 (which should be relative to 1990). Such cuts are broadly in line with a path could hold greenhouse gas levels below 500ppm CO2e and then start to reduce them. According to the Hadley Centre climate model, this would reduce the probability of a 5ºC increase in global temperature from around 50% to 3% or less. Such insurance could be bought for a worldwide cost of 1 or 2% of GDP over the coming decades and may well be lower than that if technical progress continues with its current acceleration. That action is very sound economics as well as a moral imperative.

We know from the long-term target where countries will need to be in 2050 and we can infer current actions from this. The target 50% reduction means halving global emissions from 40 gigatonnes a year to 20, or around 2 tonnes per capita, given that there are likely to be around 9 billion people in 2050.

For the global target to be achieved, few countries can be much above the annual emissions level of 2 tonnes per capita, since there are likely to be few that are far below. This provides a benchmark against which countries can assess how the sectoral pattern of their emissions may need to change for them to reach this level cost-effectively.

These simple headline numbers mean that, even if developed countries reduced their emissions to zero, the forecast 8 billion people living in developing countries in 2050 would still be able to emit only 2.5 tonnes per capita. With the majority (by population) of countries not covered in Annex 1 of the UN Framework Convention on Climate Change, broadly the non-Annex 1 are the developing countries, already above this level, it is clear that emissions in these countries will have to fall in the long term. Aggregate emissions by developing countries will probably need to peak in the next 20 years if the global 2050 targets are to be achieved. Emissions in rich countries must decline, and decline strongly, from now and be at least 80% lower in 2050 than 1990 if they are to get their emissions in the region of 2 tonnes per capita by then. ..."

Lord Stern at the DFID conference, March 09.

That's the best bit, but here's the full transcript and the video.