India's pledge clears a significant hurdle towards a climate deal in Paris

India's announcement means all the world's biggest economies are now publicly in favour of a deal, but there are still challenges ahead

With India's plan for curbing carbon emissions now in, most of the major developing economies have responded to the UN's requests for the commitments on climate change that will form the keystone of an agreement to be signed in Paris this December.

Those commitments - to make absolute cuts in future emissions levels, in the case of developed countries; to curb future emissions growth, in the case of less industrialised nations - will not add up to the cuts that scientists say are needed to avoid more than 2C of warming above pre-industrial levels. This is significant, because the 2C threshold is regarded as the limit of safety, beyond which the changes in the climate are likely to become catastrophic and irreversible.