New York, Aug 28 (IANS): If the US and Russia waged an all-out nuclear war, much of the land in the northern hemisphere would have below freezing point temperatures in summertime, with the growing season slashed by nearly 90 per cent in some areas, says a study.

"Indeed, death by famine would threaten nearly all of the Earth's 7.7 billion people", said study co-author Alan Robock, Professor at the Rutgers University.

The study, published in the Journal of Geophysical Research-Atmospheres, provides more evidence to support "The Treaty on the Prohibition of Nuclear Weapons" passed by the UN two years ago.

While 25 nations have ratified the treaty so far, excluding the US, it would take effect when the number hits 50.

For the study, the research team used a modern climate model to simulate the climatic effects of an all-out nuclear war between the US and Russia.

Such a war could send 150 million tons of black smoke from fires in cities and industrial areas into the lower and upper atmosphere, where it could linger for months to years and block sunlight, researchers said.

The scientists used a new climate model from the National Center for Atmospheric Research with higher resolution and improved simulations compared with a NASA model used by a Robock-led team 12 years ago.

The new model represents the Earth at many more locations and includes simulations of the growth of the smoke particles and ozone destruction from the heating of the atmosphere.

Nonetheless, the climate response to a nuclear war from the new model was nearly identical to that from the NASA model.

"This means that we have much more confidence in the climate response to a large-scale nuclear war...there really would be a nuclear winter with catastrophic consequences," said study lead author Joshua Coupe.

In both new and old models, a nuclear winter occurs as soot (black carbon) in the upper atmosphere that blocks sunlight and causes global average surface temperatures to plummet by more than 15 degrees Fahrenheit.

According to the researchers, because a major nuclear war could erupt by accident or as a result of hacking, computer failure or an unstable world leader, the only safe action that the world can take is to eliminate nuclear weapons.