More than 100 heads of states and tens of thousands of people are gathered in Brazil for the Rio+20 Earth Summit, the largest United Nations conference ever. The gathering comes 20 years after the 1992 U.N. Earth Summit in Rio de Janeiro, when leaders pledged to protect the planet by endorsing treaties on biodiversity and climate change. Since then, few of the development goals have been reached in areas like food security, water, global warming and energy.