Guardian: What’s the bottom line? To have a chance of keeping warming under the dangerous 2C mark, a global 50% emissions cut is needed by 2050, compared with 1990 levels. Copenhagen must put the world on a clear course towards this, with firm 2020 targets. Who should make the cuts? Industrialised countries such as the US and UK have emitted by far the most carbon and still emit vast amounts per person, so they have a responsibility to make deep cuts. Emissions from China and …