U.N. meet on global warming witnesses dire predictions War, hunger, poverty and sickness will stalk humanity if the world fails to tackle climate change, a 12-day UN conference on global warming heard on Monday. A volley of grim warnings sounded out at the start of the marathon talks, a step to a new worldwide treaty to reduce greenhouse gases and help countries exposed to the wrath of an altered climate. "Humankind in its activity just reached the limits of the closed system of our planet Earth," said Polish Environment Minister Maciej Nowicki, elected to chair the December 1-12 meeting in the city of Poznan. "Further expansion in the same style will generate global threats of really great intensity -- huge droughts and floods, cyclones with increasingly more destructive power, pandemics of tropical disease, dramatic decline of biodiversity, increasing ocean levels," said Nowicki. "All these can cause social and even armed conflict and migration of people at an unprecedented scale." The forum of the 192-member UN Framework Convention on Climate Change (UNFCCC) comes halfway in a two-year process, launched in Bali, Indonesia, that aims at crafting a new pact in Copenhagen in December 2009. Nowicki's warning was underscored by Rajendra Pachauri, head of the Nobel-winning Intergovernmental Panel on Climate Change (IPCC), which provides neutral scientific opinion on global warming and its impacts. "The impacts of climate change, if there is inaction, can be extremely serious," he said, delivering some sobering statistics to sharpen minds among the almost 11,000 conference participants in Poznan. The number of people living in severely stressed river basins is projected to rise from 1.4 to 1.6 billion in 1995 to 4.3-6.9 billion in 2050, Pachauri said. "That's almost the majority of humanity," he said. Between 20 and 30 percent of species assessed will be at increasingly high risk of extinction as global temperatures exceed two to three degrees centigrade (3.6-5.4 degrees Fahrenheit) above pre-industrial levels, he said. Progress under the so-called Bali Roadmap has been bogged down over demands for concessions and the sheer complexity of a deal. Rich countries are historically to blame for most of today's warming. They are lobbying for emerging giant countries, led by China and India, which will be the big polluters of tomorrow, to do more to tackle their surging emissions.