Planet at risk of heading towards irreversible 'hothouse' conditions, new report says

The world is at risk of entering "hothouse" conditions with average temperatures 4-5 C higher even if emissions reduction targets under a global climate deal are met, scientists say in a new study.

The report, published Monday in the Proceedings of the National Academy of Sciences, comes amid a heatwave that has pushed temperatures above 40 C in Europe this summer, causing drought and strengthening wildfires, including blazes in Greece in July that killed 91 people. It is suspected that the Greek blazes resulted from arson.

Around 200 countries agreed in 2015 to limit temperature rise to "well below" 2 C above pre-industrial levels, a threshold believed to be a tipping point for the climate.

However, it is not clear whether the world's climate can be safely "parked" near 2 C above pre-industrial levels or whether this might trigger other processes which drive further warming even if the world stops emitting greenhouse gases, the research said.

Currently, global average temperatures are just over 1 C above the pre-industrial period and rising at 0.17 C each decade.

Scientists from the Stockholm Resilience Centre, the University of Copenhagen, Australian National University and the Potsdam Institute for Climate Impact Research said it is likely that if a critical threshold is crossed, several tipping points would lead to abrupt change.

There will be uninhabitable places on Earth

Such processes include permafrost thaw; the loss of methane hydrates from the ocean floor; weaker land and ocean carbon sinks; the loss of Arctic summer sea ice and the reduction of Antarctic sea ice and polar ice sheets.

"These tipping elements can potentially act like a row of dominoes. Once one is pushed over, it pushes Earth towards another," said Johan Rockström​, co-author of the report published in the Proceedings of the National Academy of Sciences and executive director of the Stockholm Resilience Centre.

"It may be very difficult or impossible to stop the whole row of dominoes from tumbling over. Places on Earth will become uninhabitable if 'Hothouse Earth' becomes the reality," he said.

It may be very difficult or impossible to stop the whole row of dominoes from tumbling over. Places on Earth will become uninhabitable if 'Hothouse Earth' becomes the reality- Johan Rockström​, co-author of the report

Maximizing the chances of avoiding such a hothouse state requires more than just reducing greenhouse gas emissions, the report said.

For example, improved forest, agricultural and soil management; biodiversity conservation and technologies that remove carbon dioxide from the atmosphere and store it underground are needed.

Commenting on the research, some experts said uncontrolled warming is still uncertain but not implausible.

"In the context of the summer of 2018, this is definitely not a case of crying wolf, raising a false alarm: the wolves are now in sight," said Phil Williamson, climate researcher at the University of East Anglia.