RIO DE JANEIRO — As Brazil prepares to welcome leaders from the world’s 20 largest economies for the Group of 20 summit, another event is taking place in Rio de Janeiro, one that brings global civil society to together for pivotal discussions. The Brazil G20 Social Summit, an initiative by the Brazilian government, marks the first event at which citizens from around the world, as well as nonprofits and community organizations, are invited to participate in a series of smaller conferences. One of the most talked-about initiatives is the launch of the Global Alliance Against Hunger — a group proposed