PARIS (AFP) - Already straining to host seven billion souls, Earth is set to teem with billions more, and only a revolution in the use of resources can avert an environmental crunch, experts say. As early as 1798, Thomas Malthus gloomily forecast that our ability to reproduce would quickly outstrip our ability to produce food, leading to mass starvation and a culling of the species. But an industrial revolution and its impact on agriculture proved Malthus and later doomsayers wrong, even as our numbers doubled and redoubled with accelerating frequency. Despite alarmist predictions, historical increases in population have not been economically catastrophic, notes David Bloom, a professor in the Department of Global Health and Population at Harvard. Today, though, it seems reasonable to ask if Malthus wasnt simply a couple of centuries ahead of the curve. On October 31, the worlds population is officially scheduled to hit seven billion a rise of two billion in less than a quarter century. Over six decades, the global fertility rate has roughly halved, and amounts to a statistical 2.5 children per woman today. But this varies greatly from country to country. And whether the planets population eventually stabilises at nine, 10 or 15 billion depends on what happens in developing countries, mostly in Africa, with the fastest growth.