Keeping global warming to within 1.5-2°C may be more hard than previously assessed, according to researchers.
Global warming could result in average temperatures almost 10 degrees higher than they are now and rising seas of up to 200 feet, according to a new paper.
Steffen said nations needed to work together to greatly accelerate the transition towards an emission-free world economy.
Steffen said that if the temperatures increased two degrees due to human activities, a process known as feedback would be activated in the Earth's system, which could aggravate global warming even if greenhouse gases are no longer emitted.
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.
The authors of the study published to Proceedings of the National Academy of Sciences identified a number of natural feedback processes that could turn carbon sinks into carbon engines.
Such a rise would cause areas with permafrost to thaw, creating sea level rises, while methane on the ocean floor may be released with ocean and land carbon sinks weakening.
He said: "Once one is pushed over, it pushes Earth towards another. It may be very hard or impossible to stop the whole row of dominoes from tumbling over", said Johan Rockstrom, Executive Director of the Stockholm Resilience Centre in Sweden.
That's the alarming warning from an global team of scientists, including Australian National University professor Will Steffen, in a study published on Tuesday. In particular, we address tipping elements in the planetary machinery that might, once a certain stress level has been passed, one by one change fundamentally, rapidly, and perhaps irreversibly.
"A 2ºC warming could activate important tipping elements, raising the temperature further to activate other tipping elements in a domino-like cascade that could take the Earth System to even higher temperatures", claimed the report.
"What we do not know yet is whether the climate system can be safely "parked" near 2ºC above pre-industrial levels, as the Paris Agreement envisages", shared Schellnhuber. But the HFC phasedown can help mitigate the risk, the researchers find.
Avoiding this scenario requires not only the reduction of carbon dioxide and greenhouse gas emissions into the atmosphere but also enhancement of existing biological carbon stores, warns the Stockholm Resilience Centre, a research institute specialising in sustainable development and environmental issues. Critically, the study emphasizes that these measures must be underpinned by fundamental societal changes that are required to maintain a "Stabilized Earth" where temperatures are ~2°C warmer that the pre-industrial. "We totally hand over our fate to an Earth system that starts rolling out of equilibrium".