CNN  — 

Twenty days of lethal heat per year. Collapsed ecosystems. And more than 1 billion people displaced.

Those are all probable scenarios that could devastate societies by 2050 if swift and dramatic action isn’t taken to curb climate change, according to a think tank report backed by a former Australian military chief.

The paper, by the Melbourne-based Breakthrough National Center for Climate Restoration, is not a scientific study, but an attempt to model future scenarios based on existing research.

It paints a bleak future in which more than a billion people are displaced, food production drops off and some of the world’s most populous cities are left partially abandoned.

Its foreword is written by Chris Barrie, a retired admiral and former head of the Australian Defense Force, who said that “after nuclear war, human-induced global warming is the greatest threat to human life on the planet.”

“A doomsday future is not inevitable,” he notes. “But without immediate drastic action our prospects are poor.”

Andrew King, a climate science lecturer at the University of Melbourne who was not involved in the report, said its findings were “plausible,” although he did not expect human civilization to end in 2050.

“Without a doubt (climate change) is a huge threat to human civilization,” he said. “It’s the details that we need to pin down.”

King said that while he expected all of the issues mentioned in the paper to be occurring by 2050 – such as displacement of people and food shortages – it remained to be seen how widespread they would be.

He noted that there were many factors aside from climate change that could have an impact on global security and how humans react to altered conditions, such as population growth and inter-governmental action.

Dire warnings

The future predicted by the report is one of potential global catastrophe.

Authors David Spratt and Ian Dunlop, both longtime climate researchers, warn that climate change at present poses a “near-to-mid-term existential threat to human civilization.”

They drew on existing scientific research and “scenario planning” to forecast that if global temperatures rise 3 degrees Celsius by 2050, 55% of the world’s population across 35% of its land area would experience more than 20 days of lethal heat per year, “beyond the threshold of human survivability.”