Scientists are warning that a domino effect will kick if global temperatures rise more than 2°C above pre-industrial levels, leading to "hothouse" conditions and higher sea levels, making some areas on Earth uninhabitable.
The report, "Trajectories of the Earth System in the Anthropocene," published Monday in the American Proceedings of the National Academy of Sciences, said "hothouse" temperatures could stabilize 4°C to 5°C (39 to 41 Fahrenheit) higher than pre-industrial levels.
"Human emissions of greenhouse gas are not the sole determinant of temperature on Earth. Our study suggests that human-induced global warming of 2°C may trigger other Earth system processes, often called 'feedbacks,' that can drive further warming -- even if we stop emitting greenhouse gases," lead author Will Steffen of the Australian National University said.
Hotter temperatures could result in sea level rise up to 60 metres from today's shorelines, swamping coastal populations and forcing communities inland. This summer dozens of people have died in wildfires and heat waves from the US to Asia, giving the world an insight into what could lie ahead.
The report says that if the "threshold" -- a theoretical point-of-no-return -- is crossed, this "would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene," referring to the geological age which began at the end of the last ice age, around 12,000 years ago.
Many scientists argue that we have entered a new geological era, the Anthropocene, in which human activity is directly affecting the planet.