A fresh study on the global impact of a nuclear war has concluded that any conflict would plunge the world into darkness, cause temperatures to plummet and wipe out much of the world's sea life.

Researchers at Louisiana State University ran multiple computer simulations to assess the impact of global and regional nuclear conflicts on the world's oceans. They found that in all scenarios, firestorms would release soot and smoke into the upper atmosphere, blocking out the sun and forcing temperatures to fall by an average 13 degrees Fahrenheit in the first month.

That, in turn, would cause ocean temperatures to fall and sea ice to expand by more than six million square miles, blocking major ports including China's Tianjin, Copenhagen and St. Petersburg. Researchers said changes to Arctic sea ice would likely last thousands of years, describing the event as a "nuclear little ice age."

The study comes after the specter of nuclear war was raised following Vladimir Putin's invasion of Ukraine, with Russian Foreign Minister Sergei Lavrov warning in April that there was a "serious" risk of nuclear war.

Lead author, assistant professor Cheryl Harrison, said: "It doesn't matter who is bombing whom. It can be India and Pakistan or NATO and Russia. Once the smoke is released into the upper atmosphere it spreads globally and affects everyone."

The simulations examined what would happen to the Earth if the US and Russia dropped 4,400 100-kiloton bombs on cities and industrial areas, and, separately, if 500 of the same-sized weapons were detonated in an India-Pakistan conflict.

In the largest scenario, ocean recovery would likely take decades at the surface, and hundreds of years at depth.