New York, United States - The mushroom clouds of nuclear explosions cast a long shadow over the 20th century. The fungal smoke stacks provoked fear of an atomic apocalypse and became a rallying symbol for anti-war activists.
Their fright factor may be waning. The Cold War arms race was over by the time millennials were born. For the Instagram generation, cyber-strikes and hijacked jets hitting skyscrapers weigh heavier on the mind.
"Nuclear weapons kind of faded down once, like, the issue of terrorism and 9/11 happened," New York high school pupil Lucy Li, 16, told Al Jazeera. World War II was a long time back, she said. "Terrorism is the main focus and worry right now."
This month, Li and other teens visited the United Nations headquarters to learn about the 1945 bombing of Hiroshima from survivor Setsuko Thurlow , 84, who relived harsh childhood memories of the blast, infernos and relatives dying from radiation sickness.
Thurlow worries that the strike, which claimed some 140,000 lives by the end of the year, was too-quickly forgotten. People "went back to sleep", she told Al Jazeera. "We gotta clean up this mess before we pass on the planet to the next generation."
Lecturing youngsters is only half the battle. Downstairs at the world body, diplomats were hatching plans to outlaw nuclear weapons, of which there are more than 15,000 globally, owned by nine countries .
Many nations abhor the weapons, saying any nuclear strike would kill masses of civilians and automatically constitute an atrocity. Like mustard gas and land mines, they are inhuman and should be banned , they say.
For several years, Austria, a landlocked European nation, has built support for a push against Russia and the United States - which have the lion's share of nuclear weapons - and other nuclear powers in a bid to declare the weapons illegal.
On September 21, Austria's Foreign Minister, Sebastian Kurz , told the UN General Assembly that Austria "will table a draft resolution to convene negotiations on a legally-binding comprehensive instrument to prohibit nuclear weapons".
Diplomats familiar with the talks told Al Jazeera that Austria, Mexico and others will shortly release a UN General Assembly resolution that already has the support of more than 120 of the UN's 193 members.
The document is still being drafted in Geneva, but is expected to arrange a confab aimed at creating a nuclear weapons treaty akin to legal prohibitions on chemical weapons , landmines and cluster bombs .
"We all agree that the humanitarian consequences of the explosion of nuclear weapons would be unacceptable," said Kurz. "Experience shows that the first step to eliminate weapons of mass destruction is to prohibit them through legally-binding norms."
In some ways, he is preaching to the converted. The five legally-recognised nuclear-armed states - the United States, Russia, France, China and Britain - known as the P5, have long vowed to ditch their doomsday arsenals under the Non-Proliferation Treaty .
In 2009, US President Barack Obama called for a world without nuclear weapons while in Prague. His New START deal with Russia, ratified the next year, cut the number of deployed strategic nuclear warheads to 1,550.
In his UN address this month, Obama spoke of his "unique responsibility" to scrap nuclear weapons and on September 23 the UN Security Council passed a resolution supporting a 20-year-old treaty against nuclear test blasts.
But progress is too slow for Austria and others. Despite talk of disarmament, the US will spend some $1 trillion over three decades to modernise its nuclear arsenal. Britain plans to renew its missile-launching submarines.
Prospects for more US-Russia deals are bleak, given the rows over Ukraine and Syria. Donald Trump, the Republican presidential nominee in this year's White House race, even suggested that Japan and South Korea acquire the weapons .
Meanwhile, the nuclear-toting states outside the NPT - Pakistan, India, North Korea and also Israel, which neither confirms nor denies its stockpiles - answer to nobody. Some fear that Iran will join them after its 10-year deal with the US and others expires.
North Korea came closer to being able to launch nuclear warheads at neighbours this month with its fifth test blast . Pakistan is deploying small, tactical nuclear weapons to deter India that could be stolen or misused.
The UN calls for a world free of nuclear weapons and marks September 26 as the International Day for the Total Elimination of Nuclear Weapons , but has largely shelved the issue to focus on more-likely gains against poverty and climate change.
Thomas Countryman, the US State Department's point man on nuclear arms, called Austria's effort "meaningless" and "dangerous". Pyongyang's recent test blast showed why the US should retain its deterrent advantage, he said.
"The international security environment needs to evolve in a way that gives the Russian Federation and the United States first, and later other nuclear weapon states, the confidence to negotiate further reductions in their nuclear arsenals," Countryman told Al Jazeera.
"That is not something that can be accomplished by outside pressure from other states or from NGOs."
Opinions are mixed on whether Austria will achieve anything beyond a UN General Assembly resolution, which carry moral, not legal, force. Joseph Gerson, an anti-war activist, predicted an "intense fight" between the P5 and smaller UN members.
"It's the many against a few, but the few have considerable power," Gerson, from the American Friends Service Committee, a Quaker group, told Al Jazeera. "The US has sent out a demarche to quite a number of countries telling them not to push on this."
Kenneth Luongo, president of the Centre for a Secure Nuclear Future, a policy group, doubts that the US or Russia will yield to pressure. Their generals, however, may scrap some costly nuclear arms for weapons better suited against armed groups and other, more urgent, threats.
Global risk analyst Ian Bremmer, president of the Eurasia Group, says the threat of nuclear brinksmanship has subsided, while cyber-strikes are ever-more menacing and available to many more than the nine nuclear powers.
While envoys negotiate between governments, the activists continue campaigning, though without the frequent "Ban the Bomb" marches that once drew big crowds in western cities but dwindled from the 1980s onwards.
Hidenori Watanave, a Harvard University scholar, is building an online archive of survivors' testimonies from Hiroshima . Youngsters can use it to become "storytellers about the atomic bomb" via Facebook-style sharing, once Thurlow and others like her are gone, he told Al Jazeera.
His project and other efforts are having an impact, however limited. After the UN class, pupil Li grappled with a question that vexed even Robert Oppenheimer, the physicist behind America's nuclear project, seven decades ago.
"I feel like they were created in this race to show who is the No 1, like, most powerful country in the world," Li said. "What I don't get is why you would create a weapon that could destroy the world in a few seconds, just for the sake of power."
Follow James Reinl on Twitter: @jamesreinl