COPENHAGEN (March 12) - Hundreds of leading scientists warned Thursday that global warming is accelerating beyond the worst predictions and threatening totrigger "irreversible" climate shifts on the planet. Saying there's no excuse for inaction, the nearly 2,000 climate researchers meeting in Copenhagen urged policy-makers to "vigorously" implementthe economic and technological tools available to cut emissions of heat-trapping greenhouse gases. A United Nations panel in 2007 predicted the following future events would occur because of climate changes around the world. 2009: The world population nears 7 billion as more people now live in cities than in rural areas, changing patterns of land use and adding to smog. (Note: Please disable your pop-up blocker) Skip over this content Their stark message came at the end of a three-day conference aimed at updating the findings of a 2007 report by the Intergovernmental Panel on Climate Changebefore U.N. talks in December on a new global climate treaty. "The worst-case IPCC scenario trajectories (or even worse) are being realized," the scientists said in a statement. "There is a significant riskthat many of the trends will accelerate, leading to an increasing risk of abrupt or irreversible climatic shifts." The climate change panel predicted a sea level rise of 7 to 23 inches by the end of the century, which could flood low-lying areas and force millions to flee.But more recent research presented at the conference suggested that melting glaciers and ice sheets could help push the sea level up at least 20 inches, andpossibly as much as 39 inches, or about 1 meter. Northeast: A map created by University of Arizona scientists in 2007, based on data from the U.S. Geological Survey, shows areas in the Northeast that wouldbecome flooded if the the sea were to rise one meter. (Note: Please disable your pop-up blocker) "Recent observations show that societies are highly vulnerable to even modest levels of climate change with poor nations and communities particularly atrisk," the statement said. It noted that policy-makers already have a range of tools to mitigate global warming. "But they must be vigorously and widely implemented to achieve thesocietal transformation required to de-carbonize economies," it said. The conclusions of the congress will be presented to politicians when they meet in Copenhagen in December to discuss a new global agreement on greenhouse gasemissions to replace the Kyoto Protocol, which expires in 2012. "We know from scientific evidence that climate change is a reality and that climate change will have damaging effects on the economy all over theworld," said Danish Prime Minister Anders Fogh Rasmussen, one of the politicians attending the scientific conference. "Therefore we need an agreementand we need an agreement this year." Many of the world's biggest cities are coastal and highly vulnerable to rising sea levels, according to a 2007 study by the Worldwatch Institute. One suchcity is Bangkok, above, which has an area population of 7,221,000. Click through for other huge cities at risk. (Note: Please disable your pop-up blocker) Earlier Thursday, British economist Nicholas Stern, the author of a major British government report detailing the cost of climate change, told the conferencethat the global recession presents an opportunity to build a more energy-efficient economy. "Coming out of this we have got to lay the foundations for a low-carbon growth, which is going to be like the railways, like the electricity, like themotorcars, this is going to be over the next two, three decades the big driver in investment," Stern said. Stern said green investments make sense because energy-efficient economies will be more sustainable in the future. "We know from this crisis that if we postpone looking risk in the face, it will bite us much more deeply," he said. A prominent British economist and author of a major report on the cost global warming said that if climate change isn't dealt with decisively, it couldcause "extended world war." Lord Nicholas Stern said as weather patterns change, it could create mass migrations which would, in turn, set off massconflict.