World at risk of heading towards irreversible 'hothouse' state

Christopher Davidson
August 9, 2018

The planet is close to reaching these conditions, and we'll experience a rise in global temperatures by 4-5 degrees Celsius - even if we reduce emissions to reach the target previously set at the global climate deal.

The team considered 10 natural feedback processes, some of which are tipping elements that lead to abrupt change if a critical threshold is crossed.

As large parts of eastern Australia battle drought and Europe is gripped by a heatwave, Professor Steffen said current efforts to combat global warming would not be enough to meet the emission-reduction targets set by governments in the Paris Agreement, which may be insufficient to prevent the unsafe scenario anyway.

The threshold will be reached when average global temperatures are only around 2C higher than they were in pre-industrial times, new research suggests.

"Places on Earth will become uninhabitable if Hothouse Earth becomes the reality", Mr Rockström said.

"These tipping elements can potentially act like a row of dominoes".

"A Hothouse Earth trajectory would nearly certainly flood deltaic environments, increase the risk of damage from coastal storms, and eliminate coral the end of this century or earlier", the study says.

Speaking on RTE's Morning Ireland show this morning, Joseph Curtin, a senior fellow for climate and energy policy at the Institute of worldwide and European Affairs, explained that as sea-ice melts, the sea directly absorbs more of the sun's energy, creating more warming.

That means the Earth faces the potential of runaway global warming at some point in the future.

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The scientists also examined conditions the Earth has seen in the distant past, such as the Pliocene period five million years ago, when Carbon dioxide was at 400 ppm like today.

To state that 2 C is a no-return threshold "is new", said Martin Siegert, co-director of the Grantham Institute at Imperial College London, who was not involved in the study.

"It's rather selective, but not outlandish".

Fossil fuels must be replaced with low or zero emissions energy sources, and there should be more strategies for absorbing carbon emissions such as ending deforestation and planting trees to absorb carbon dioxide.

However, it is not clear whether the world's climate can be safely "parked" near 2C 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.

Soil management, better farming practices, land and coastal conservation and carbon capture technologies are also on the list of actions.

The feedbacks are permafrost thaw, loss of methane hydrates from the ocean floor, weakening land and ocean carbon sinks, increasing bacterial respiration in the oceans, Amazon rainforest dieback, boreal forest dieback, reduction of northern hemisphere snow cover, loss of Arctic summer sea ice, and reduction of Antarctic sea ice and polar ice sheets.

Commenting on the findings, climate researcher Dr Phil Williamson, from the University of East Anglia, said: "In the context of the summer of 2018, this is definitely not a case of crying wolf, raising a false alarm".

"This would be a planet that is not recognisable for us... as we know it", he told Shelagh Fogarty.

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