The developing world\'s rapid growth has sharply cut extreme poverty, created a new middle class and put the economies of Brazil, China and India on a path to overtake the globe\'s wealthiest nations, the UN says. Although developing nations are now driving economic growth, a lack of action on climate change and persistent inequalities could threaten those gains, the United Nations Development Programme said in a study. The report sees a \"dramatic rebalancing of global economic power\" and forecasts that the combined economic output of Brazil, China and India will surpass that of the United States, Canada, Britain, France, Germany and Italy by 2020. The most striking changes had occurred in the southern hemisphere, a region which had seen \"unprecedented\" rises in living standards, said the study, titled \"The Rise of the South: Human Progress in a Diverse World.\" \"Never in history have the living conditions and prospects of so many people changed so dramatically and so fast,\" said the report presented in Mexico City. China and India doubled their per capita economic output in less than 20 years, a rate twice as fast as Europe and North America experienced during the Industrial Revolution. The proportion of people living in extreme poverty worldwide fell from 43 percent in 1990 to 22 percent in 2008, with more than 500,000 million people rising above the poverty line in China alone.The share of people living on less than $1.25 per day has been cut in half, meeting one of the main targets of the Millennium Development Goals. The southern hemisphere\'s share of the global middle class grew from 26 percent to 58 percent between 1990 and 2010. By 2030, more than 80 percent of the world\'s middle class will live south of the Equator, the report said. \"The Industrial Revolution was a story of perhaps a hundred million people, but this is a story about billions of people,\" said Khalid Malik, the report\'s lead author. But the developing world faces similar long-term challenges as the leading industrialized nations, from an aging population to environmental pressures and social inequalities. Lack of action against climate change could even halt or reverse human development progress in the world\'s poorest countries, pushing up to three billion people into extreme poverty by 2050 unless environmental disasters are prevented, the report said. \"The challenge now is to carry that progress forward, share the experiences, and enlist the growing influence of the South to move our world onto a sustainable and inclusive development path for all,\" said UNDP chief Helen Clark, who released the report alongside Mexican President Enrique Pena Nieto. \"The balance of influence in our world is visibly changing,\" said Clark, a former prime minister of New Zealand. \"The contribution of the South -- intellectual, economic, social, environmental, and political -- will play a significant part in building a better future for us all.\"