STOCKHOLM (AP) — The U.N.'s environmental authority has quietly raised its assessment of the level at which global greenhouse gas emissions must peak to avoid dangerous climate change, as governments seek a new accord to fight global warming. In its first four annual emissions reports in 2010-2013, the United Nations Environment Program said emissions must not exceed 44 billion tons in 2020 for the world to limit global warming to 2 degrees C (3.6 degrees F). Two degrees of warming compared with pre-industrial times, is widely seen as a level where climate change becomes unmanageable, with fast-rising sea levels, intensifying droughts and other impacts. Scientists say temperatures have already risen more than 0.8 degrees C (1.4 degrees F) since the industrial revolution, and that the warming is mostly man-made, mainly due to emissions from the burning of fossil fuels.