The world currently generates 2 billion tons of solid waste every year, according to the World Bank. By 2050, that figure will rise to 3.4 billion, with most of the increase coming from low- and middle-income countries in Africa and Asia, where greater urbanization and prosperity will generate more consumption, and more trash. That's a huge political challenge for urban governments around the world. Here's a look at who generates the most trash today — and in the future.