Planet Earth at tipping point of becoming 'Hothouse Earth': Study

A volunteer sprays water as a wildfire burns in the town of Rafina, near Athens, Greece, on July 23, 2018.
A volunteer sprays water as a wildfire burns in the town of Rafina, near Athens, Greece, on July 23, 2018. PHOTO: REUTERS

TAMPA (REUTERS, AFP) - The world is at risk of entering“hothouse” conditions where global average temperatures will be 4-5 deg C higher even if emissions reduction targets under a global climate deal are met, scientists said in a study published on Monday (Aug 6).

The report comes amid a heatwave that has pushed temperatures above 40 deg C (104 Fahrenheit) in Europe and many parts of Asia this summer, causing drought and wildfires, including blazes in Greece in July that killed 91 people.

Around 200 countries agreed in 2015 to limit temperature rise to “well below” 2 deg C (3.6F) 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 deg 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 deg C above the pre-industrial period and rising at 0.17 deg C each decade.

Scientists from the Stockholm Resilience Center, 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 will lead to abrupt change.

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.

Maximising 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.  

The study is available at: http://www.pnas.org/  

What is 'Hothouse Earth'?

"Hothouse Earth is likely to be uncontrollable and dangerous to many," said the article by scientists at University of Copenhagen, Australian National University and the Potsdam Institute for Climate Impact Research in Germany.

Rivers would flood, storms would wreak havoc on coastal communities, and coral reefs would be eliminated - all by century's end or even earlier.

Global average temperatures would exceed those of any interglacial period - meaning warmer eras that come in between Ice Ages - of the past 1.2 million years.

Melting polar ice caps would lead to dramatically higher sea levels, flooding coastal land that is home to hundreds of millions of people.

"Places on Earth will become uninhabitable if 'Hothouse Earth' becomes the reality," said co-author Johan Rockstrom, executive director of the Stockholm Resilience Centre.

Where is the tipping point? 

Researchers suggest the tipping point could come once the Earth warms to 3.6 Fahrenheit (2 deg C) over pre-industrial times.

The planet has already warmed 1 deg C over pre-industrial times, and is heating up at a rate of 0.17 deg C per decade.

"A 2 deg C 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," said the report.

This cascade "may tip the entire Earth system into a new mode of operation," said co-author Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research.

Experts also worry about phenomena like wildfires, which will spread as the planet gets hotter and drier and have the potential to accelerate carbon dioxide buildup and global warming.

How they calculated this 

The "Perspective" article is based on previously published studies on tipping points for the Earth.

The scientists also examined conditions the Earth has seen in the distant past, such as the Pliocene period five million years ago, when CO2 was at 400 ppm like today.

During the Cretaceous period, the era of the dinosaurs some 100 million years ago, CO2 levels were even higher at 1,000 ppm, largely due to volcanic activity.

To state that 2 deg 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.

The study authors "collated previously published ideas and theories to present a narrative on how the threshold change would work," he said.

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

How to stop it 

People must immediately change their lifestyle to be better stewards of the Earth, the researchers said.

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.

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

Yet even if humans stopped emitting greenhouse gases, the current warming trend could trigger other Earth system processes, called feedbacks, driving even more warming.

These include permafrost thaw, deforestation, loss of northern hemisphere snow cover, sea ice and polar ice sheets.

Researchers say it's not certain that the Earth can remain stable.

"What we do not know yet is whether the climate system can be safely 'parked' near 2 C above preindustrial levels, as the Paris Agreement envisages," said Schellnhuber.