Although the days of the Cold War are behind us, the warheads are still piled high and international tensions remain. Nowadays, the world's nuclear arsenals are faced with a new scenario; it’s no longer the US and Russia geared towards mutually assured destruction, it’s now about rogue erratic nuclear states, proxy wars, and much more powerful weapons.

In this light, a new study in Environment Magazine has concluded that even a “small” nuclear war involving fewer than five A-bombs (arguably the most likely scenario in 21st-century warfare) could spark a “nuclear Autumn” that causes widespread damage to land-based and aquatic ecosystems.

The new report by the University of Nebraska-Lincoln looked at data on the 19 types of weapons held in the arsenals of the US, Russia, China, the UK, and France. It concludes that five A-bombs dropped on a city could trigger a nuclear drought. Furthermore, China could cause a nuclear drought with just one of its most powerful nuclear bombs (of which they have 20 stockpiled).

Previous research has said the total destruction of a city around the size of Los Angeles by atomic warfare could throw up 5.5 million tons of ash and soot into the stratosphere for months, thereby blocking out some direct sunlight from reaching the Earth. In turn, this would dramatically reduce the temperature and rainfall around the world.

Of course, nuclear bombs have been dropped in their thousands in the past century alone and we are hardly in a nuclear autumn. However, the issue of a nuclear autumn or nuclear drought is tied to many factors, ranging from the nature of modern war and the potency of the bombs.

As project leader Adam Liska highlights in a statement: "The question is not if a nuclear drought can occur, but what factors increase its probability of occurring and what actions can be taken to mitigate the potentially devastating global impacts?"

Now nine countries have nuclear weapons programs, most armed with bombs significantly larger than those used at Hiroshima and Nagasaki. It’s estimated over 100 of these bombs would be required to trigger a nuclear autumn. It’s also worth remembering that the largest of nuclear weapons testing in the Cold War occurred underground or in remote areas that would not throw up a significant amount of soot.

 All in all, it's a stark reminder to keep your finger off the red button.

"We're losing our memory of the Cold War and we're losing our memory of how important it is to get this right," said co-author Tyler White, a political scientist who specializes in international security and nuclear policy. "Even a conflict that doesn't involve the United States can impact us and people around the world."