Warning that tipping points may trigger climate cascade

Two massive explosions 13 hours apart tore through a Texas chemical plant yesterday, and one left three workers injured.

The blasts blew out windows and doors of nearby homes and prompted a mandatory evacuation of a 7km radius from the plant in Port Neches in Southeast Texas, about 130km east of Houston.

The initial explosion at the TPC Group plant, which makes chemical and petroleum-based products, occurred around 1am. It sent a large plume of smoke stretching for miles and started a fire.

The three workers hurt during the blast – two TPC employees and a contractor – were treated at hospitals and released. –AP

The planet faces a ‘‘global cascade of tipping points’’ that could lead to an abrupt shift to a warmer world and cause huge disruption to human societies and ecosystems unless nations slash their greenhouse gas emissions.

The warning is contained in an article yesterday in Nature. The authors identified several ‘‘large-scale discontinuities’’ in the climate system that may be underway, and which could trigger further warming.

‘‘If damaging tipping cascades can occur and a global tipping point cannot be ruled out, then this is an existential threat to civilisation,’’ the scientists said.

The ice sheets in West Antarctica may be one of several cryosphere tipping points that were ‘‘dangerously close’’, if they hadn’t already begun an irreversible retreat. These alone would raise sea levels by three metres if melted.

Those in the Wilkes Basin of eastern Antarctica may be similarly unstable, with another four metres of potential sea-level rise if they disintegrated.

‘‘The time to act decisively is now. Any more dithering is irresponsible, as the risks are increasing year by year,’’ said Stefan Rahmstorf, head of Earth system analysis at Germany’s Potsdam Institute for Climate Impact Research, and one of the authors.

‘‘But even once we pass a tipping point – and probably we have done so for the West Antarctic

Ice Sheet – we will need to reduce emissions even more urgently, to slow down the unfolding effects and to avoid passing further tipping points.’’

The interconnected nature of the giant mixing processes that distribute heat around the world’s oceans is a key reason why one region’s changes could reinforce other shifts.

For instance, the melting of

Greenland’s ice sheets is driving an influx of fresh water into the North Atlantic, slowing the Gulf Stream – also known as the Atlantic Meridional Overturning Circulation (AMOC) – by 15 per cent since the middle of the 20th century.

Another outcome is a further heating of the Southern Ocean, resulting in more Antarctic ice melt.

Other effects include drought for the Sahel region because of disruptions to the West African monsoon, and worse fires in the Amazon as that region dries out.

Will Steffen, an emeritus professor at the Australian National University and another author, said some of the processes would add to warming by releasing more carbon dioxide or methane to the atmosphere.

Amazon dieback alone had the potential to release about 90 billion tonnes of CO2 while boreal forests could add another 110 billion tonnes.

Even without including the methane, emissions from melting permafrost could total 100 billion more tonnes of CO2, the report said.

By contrast, humans directly contribute to about 40 billion tonnes of CO2 a year.

We also have a total emissions budget of 500 billion tonnes if the world is to have a 50:50 chance of hitting the Paris climate target of keeping warming to 1.5 degrees.

Entire ecosystems, such as the Great Barrier Reef, were also facing tipping points. – Nine