Planet Earth ‘cascades’ towards a hothouse, say scientists

A ‘hothouse’ Earth caused by the domino-style collapse of natural systems could already be under way, scientists say.

A “hothouse” Earth caused by the domino-style collapse of natural systems due to climate change could already be under way, scientists say.

A “hothouse” Earth caused by the domino-style collapse of natural systems due to climate change could already be under way, according to a new call for action by scientists.

An editorial in the journal Nature, co-written by Australian National University professor Will Steffen, says more than half of the tipping points that could push the planet towards a hothouse and threaten civilisation are now “active”.

“As soon as one or two clim­ate dominoes are knocked over, they push Earth towards others,” Professor Steffen says.

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“We fear that it may become impossible to stop the whole row of dominoes from tumbling over, forming a cascade that could threaten the existence of human civilisations.”

The Nature article says tipping points such as melting ice, thawing permafrost, changing ocean patterns and forest die-off are useful to help focus attention on a “climate emergency”.

Publication of the report on Thursday comes ahead of a ­planned strike by schoolchildren on Friday and the release of a UN report that says the world is not doing enough to reduce emissions.

 

According to the report, countries will have to increase their carbon-cutting ambitions five-fold if the world is to avoid warming by more than 1.5C.

The Nature editorial says earlier reports by the Intergovernmental Panel on Climate Change had said tipping points were considered likely if global warming exceeded 5C.

But it says that more recent reports by the IPCC had reduced this to warming of between 1C and 2C.

The article says “several cryosphere tipping points are danger­ously close”, but action now could postpone the worst impacts.

“We might already have committed future generations to living with sea-level rises of around 10m over thousands of years,” the article says. “But that timescale is still under our control.”

However, it says “more observ­ational data” and “better models” are needed to “resolve how soon and how fast the ice sheets could collapse”.

Australian National University professor Will Steffen says more than half of the tipping points that could push the planet towards a hothouse and threaten civilisation are now “active”. Picture: Gary Ramage

Researchers say deforest­ation in the Amazon Basin could be nearing a tipping point and the sub-­Arctic boreal forest is increasingl­y vulnerable due to Arctic warming.

Permafrost across the Arctic is beginning to irreversibly thaw, they say.

However, researchers say they “need to improve their understanding of these observed changes in major ecosystems, as well as where future tipping points might lie”.

Nonetheless, the researchers recommend that policymakers err on the side of caution.

“Some economists, assuming that climate tipping points are of very low probability (even if they would be catastrophic), have suggested that 3C warming is optimal from a cost-benefit perspective,” the article says.

“However, if tipping points are looking more likely, then the ‘optima­l policy’ recommend­ations of simple cost–benefit climate­-economy models must align with those of the recent IPCC report.

“In other words, warming must be limited to 1.5C.

“This requires an emergency response.’’

A Polar bear walking on sea ice in the Arctic.

The scientists say improving the ability of models to capture known past abrupt climate changes and “hothouse” climate states — which occurred millions of years ago — should increase confidence in their ability to forecast future changes.

“Some scientists counter that the possibility of global tipping points remains highly speculative,” the Nature article says.

“It is our position that, given its huge impact and irreversible natur­e, any serious risk assessment must consider the evidence, however limited our understanding might still be.

“To err on the side of danger is not a responsible option. If damaging­ tipping cascades can occur and a global tipping point cannot be ruled out, then this is an existential threat to civilisation.

“No amount of economic cost–benefit analysis is going to help us.’’

The scientists conclude: “We need to change our approach­ to the climate ­problem.’’