June 12, 2012 View all news The GuardianJonathan WattsTwenty years after trying and failing to halt humanity's destruction of our planet, the governments of the world will gather again in Rio this month for a "once-in-a-generation" Earth Summit that will open with great fanfare but low expectations of success.With a new United Nations study warning that the deterioration of the environment is accelerating, more than 130 national leaders will attend the Rio+20 conference from 20-22 June to try to thrash out a new blueprint for a "green economy" and a stronger system of global governance.Despite the urgency of the task, negotiators have been hamstrung even before the event starts by the European financial crisis, US election campaign and longstanding differences between rich and poor countries. David Cameron, the British prime minister, and German chancellor Angela Merkel will send deputies. US President Barack Obama has yet to confirm. In their likely absence, the political weight will be tilted towards the emerging economies of Brazil, Russia, India and China, all of which will be represented by national leaders.Read more Categorised in: Climate Change