WASHINGTON — Policymakers who ignore or trivialize global climate change are pushing humanity closer to extinction, according to an organization of scientists and diplomats.

Lamenting the failure of policymakers worldwide to ease nuclear tensions and curb climate change, the Bulletin of Atomic Scientists on Tuesday moved the symbolic Doomsday Clock one minute closer to midnight.

“World leaders are failing to change business as usual,” said Lawrence Krauss, co-chair of the Bulletin in an announcement in New York.

After lowering setting back the clock to 11:54 p.m. five years ago, the board returned its time to 11:55 p.m., a symbolic move signaling the world is closer to the apocalypse.

The board cited global warming in its decision, as well as deepening nuclear tensions. It stressed that climate change is already happening and that the world’s sluggishness in reversing it will prove disastrous if left unchanged.

Climate change means harsher weather, droughts, famine, water scarcity, rising sea levels, loss of island nations and increased ocean acidification, said Allison Macfarlane, chair of the board and associate professor of environmental policy and international security at George Mason University.

Policymakers must commit to plans to reduce emissions now, she said.

“The actions taken in the next few years will set us on a path that will be extremely difficult to redirect,” she said, explaining that the fossil-fuel burning power plants and infrastructure built in this decade will produce energy and emissions for up to 50 years. “Even if policy leaders decide in the future to reduce reliance on carbon-emitting technologies, it may be too late.”

The board said it was concerned that some policymakers deny the existence of global warming in the face of overwhelming scientific evidence. Republican presidential candidates Rick Santorum and Ron Paul have called it a hoax.

The board recommended that countries reduce carbon dioxide emissions through tax incentives and regulations; retire older coal-powered plants and require new ones to capture the carbon dioxide they produce; and invest in alternative energy.

In a survey by Stanford University, 83 percent of respondents said they believe global warming is happening. That includes majorities among both Democrats and Republicans.

The Bulletin of the Atomic Scientists was founded by scientists who built the atomic bomb and created the Doomsday Clock in 1947 to publicize threats to humanity and the planet. The Bulletin’s board of directors, in consultation with its board of sponsors, which includes 18 Nobel Laureates, makes the decision to move the hand of the clock.