Manchester, Mar 17: The consequences of a nuclear war have been well-explored by science. Beyond immediate death and destruction, a famine and climate disaster beckons.
Over the past 30 years, fear of nuclear Armageddon' had faded from its peak at the height of the Cold War.
The world's nuclear weapon stockpile has shrunk to about one-fifth the size it was in 1990 and while threats have persisted, they have typically been from rogue states (such as Iran and North Korea) in cases where escalation to global conflict was deemed unlikely.
Those fears have been re-awakened by Russia's nuclear posturing.
Russian President Vladimir Putin put his nation's nuclear forces on a state of high alert during the invasion of Ukraine, marking a change of direction that risks a return to when the world's nuclear superpowers were on the brink of conflict during the Cold War.
In the remote scenario that the conflict in Ukraine escalates to nuclear exchange, the consequences would be dire and not just because of the enormous and horrific death toll.
Even a limited nuclear conflict in Ukraine that sees just one percent of the world's nuclear stockpile exchanged is likely to bring devastation to the climate that would spread suffering and death globally.
It has been termed nuclear winter'. Younger generations may think of a scene from the Fallout video games.
But those who lived through the 1980s, a decade marked by renewed international tensions and crises, the largest global nuclear stockpile ever recorded in history, and books and films imagining nuclear doomsday, will remember what it was like to be on the cusp of nuclear catastrophe and an environmental disaster.
The climatic effect expected from a nuclear war was first studied in 1982 by the Dutch atmospheric scientist Paul Crutzen and his British colleague John Birks. They were concerned that a nuclear exchange could produce many fires with smoke so thick that it would produce an atmosphere-engulfing layer that reduced sunlight penetration, a concept they called nuclear twilight' (or nuclear dawn).
A year later, five scientists based in the United States including the atmospheric scientist Richard Turco and the astronomer Carl Sagan took to better understanding these predictions through computer modelling.
Their conclusions suggested that nuclear-induced climatic effects would last much longer than first expected, resulting in what they dubbed a nuclear winter.
Enough sunlight would not penetrate the dark blanket of smoke to keep temperatures high on the ground, causing a harsh winter in any season .
Disruptions from dust and soot would then be followed by longer term shifts in the atmosphere that were partly unpredictable, and then patterns resulting in a global cooling.
The concept of nuclear winter shocked many when published for the first time, fuelling the nuclear protest movements that were already sweeping across Europe and the United States. It divided the scientific community too, seeming exaggerated in its predictions to some climatologists.
Although at one point labelled Soviet-inspired propaganda, nuclear winter actually propelled scientific collaboration across the Iron Curtain as Russian scientists confirmed and refined the Americans' computer modelling predictions. One, Vladimir Alexandrov, mysteriously disappeared shortly afterwards.
The nuclear disarmament of the 1990s made the concept of nuclear winter fade from the public view, but atmospheric scientists have continued work on computer models, often energised by new, emerging nuclear threats and technology.
Turco and two contributors of the early nuclear winter study, Alan Robock and Owen Toon, continued to actively research the potential global consequences of local conflicts fought with nuclear weapons.
They focussed especially on the case of India and Pakistan, concluding that even a limited nuclear exchange in which 50 Hiroshima-size nuclear bombs were detonated would have global ramifications.
Using volcanic eruptions as a proxy to understand how smoke would spread across the globe, they further refined the early prediction on limited exchange.
The conclusions they recently reached are troubling: in particular, they envisage that reduced sunlight over a significant period of time would impact on agricultural production and substantially reduce our ability to survive a nuclear war.
More people could die outside the target areas due to famine, Robock predicts.
The dire consequences of a nuclear winter has not stopped Putin's threats, nor has it seen disarmament efforts bolstered. In recent years, world leaders have done the opposite.
Both Putin and former US President Donald Trump invested in modernising their country's nuclear weapons and instigated the end of the Intermediate-Range Nuclear Forces Treaty (the INF); one of the pillars of nuclear disarmament.
Since it was first signed in 1987, the INF has been important in preventing nuclear escalation, limiting the use of medium and intermediate-range nuclear missiles.
As a tool to temper crisis points, its demise makes the result of any nuclear missiles being fired in Ukraine even worse, especially given the technological capacity of modern nuclear arms.
Weapons such as the recently tested Russian hypersonic missile Zyrcon, which can evade early warning and defence systems, are some of the flexible deployment innovations that are changing traditional ideas of nuclear security.
These weapons are also much more powerful than their predecessors, with some releasing between one and five megatons (the US nuclear warhead B-83 and the Chinese Dong Feng-5, respectively).
A megaton bomb, which is the equivalent of one million tonnes of TNT, is about 50 times more powerful that the two bombs used on the Japanese cities of Hiroshima and Nagasaki.
Fifty one-megaton nuclear bombs could kill 200 million people. If used on a large city like London, it is estimated that a single five-megaton missile would produce two million fatalities.
Whether this bothers anyone at the Kremlin is unclear. But to other world leaders, the situation in Ukraine offers an opportunity to reflect on whether nuclear disarmament has been pursued strongly enough in recent years.
Many have shied away from the Treaty on the Prohibition of Nuclear Weapons, and may ponder whether they have shown enough opposition to nuclear weapons enthusiasts, such as Trump and Putin, when they each abandoned the INF.
One could argue that it is all over overestimated: the nuclear winter predictions, the forecasted casualties over nuclear war, the impacts on global health and the environment from an exchange of bombs and so on. But no one wants to be in a position to find out.