OSLO (Reuters) - Global warming this century could trigger a runaway thaw of Greenland's ice sheet and other abrupt shifts such as a dieback of the Amazon rainforest, scientists said on Monday. They urged governments to be more aware of "tipping points" in nature, tiny shifts that can bring big and almost always damaging changes such as a melt of Arctic summer sea ice or a collapse of the Indian monsoon. "Society may be lulled into a false sense of security by smooth projections of global change," the scientists at British, German and U.S. institutes wrote in a report saying...