Rio de Janeiro : World leaders, including Prime Minister Manmohan Singh, gathered today to make a fresh bid to chart out a common environmental blueprint amid economic woes and discord, as a crucial summit on sustainable development opened here. The Rio+20 summit was formally thrown open by UN chief Ban Ki-moon, bringing together representatives of 191 UN members, though US President Barack Obama and leaders of Germany and Britain-Angela Merkel and David Cameron are giving it a miss. The two-day summit, officially called the United Nations Conference on Sustainable Development, comes 20 years after the first Earth Summit was held in this Brazilian city. As calls go out to world leaders to commit to reaching an accord that addresses the most pressing environment and social woes, Singh will pitch for the principle of common but differentiated responsibility during the meeting. Secretary of State Hillary Clinton is leading the US delegation. India will be negotiating to make sure that the Rio principles are reaffirmed and all sustainable development will be viewed with the approach of equity and common but differentiated responsibility so that developing countries can have their share of development. India is also expected to voice its opposition to the Green Economy norms as propagated by the European Union. — PTI