Washington ( CNN ) -- The symbolic `` Doomsday Clock '' scientists use to portray what they feel is the risk from nuclear holocaust has moved a minute closer to midnight . The Bulletin of Atomic Scientists made the adjustment in reaction to an increased risk of weapons proliferation , the failure of a nuclear power plant in Japan , and terrorist threats to use `` dirty bombs '' with stolen atomic material . The clock was moved to five minutes before midnight after a symposium where experts presented their reasoning and risk assessment . It had been at six minutes before midnight since January 2010 , when scientists moved the hand back , reflecting a decreased risk of nuclear proliferation . `` Two years ago , it appeared that world leaders might address the truly global threats we face , '' said Allison Macfarlane , who chairs the group 's science and security board . `` In many cases , this trend has not continued or has been reversed . For that reason , the Bulletin of Atomic Scientists is moving the clock one minute closer to midnight , back to it 's time in 2007 . '' The group , in announcing the decision Tuesday at a news conference , said in a news release that one factor was the question of nuclear weapons management `` in a world of increasing economic , political and environmental volatility . '' Nuclear weapons are one of several issues that determine the setting of the Doomsday Clock . Atomic energy also contributed to the higher risk represented by moving the clock ahead one minute . But the group declined to take a position on the future viability of nuclear energy , just its existing threat to human survival , including the diversion of atomic material for weapons production . Kennette Benedict , the group 's executive director , told reporters that even after more than 60 years of the scientists assessing nuclear risk , `` it remains to be seen whether the safety and the proliferation risks can be addressed in a way that really is acceptable to people . '' `` Management issues , rather than technical issues , seemed to have been the problem in Fukushima , '' said Lawrence Krauss , who co-chairs an executive board with the Bulletin of Atomic Scientists . He said the disaster in Japan represented a broader political lack of will to ensure safe global energy . `` The need to act is urgent , '' he said , saying action also is needed against the factors scientists believe cause global warming . `` Climate change is happening , '' Krauss said , listing it among the risk factors in the Doomsday Clock announcement . `` It 's happening now , it 's measurable , and it 's clearly related to human activity , and the need to react becomes more urgent . '' The Doomsday Clock was established in 1947 by scientists who helped develop the first atomic weapons in the Manhattan Project . The countdown to catastrophe has grown to reflect the risk to humanity and the planet not just from nuclear weapons , but also from a broad range of possible sources .
NEW : ` ` The need to act is urgent '' in a range of problem areas , one scientist says . The Doomsday Clock moves ahead a year . A third of scientists cites a fresh risk from atomic weapons and a lack of arms talks .