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Climate change: what is ‘the point of no return’?

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UN Secretary General Antonio Guterres (front, second from right) with political leaders at COP25

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UN secretary general warns of global crisis as scientists says tipping points are ‘dangerously close’

In Depth James Ashford
Monday, December 2, 2019 - 3:30pm

The world’s leaders and diplomats are gathering at a United Nations climate summit in Madrid today amid growing concerns over the global warming crisis.  

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As the Spanish capital prepares to welcome some 29,000 delegates at the two-week conference of the parties, or COP25, UN Secretary General Antonio Guterres warned that “the point of no return is no longer over the horizon”.

That message is echoed in an article in Nature journal written by a group of leading scientists, who warn that the Earth’s climate is closer to reaching crucial “tipping points” than was previously thought. Here are some of those thresholds.

Ice collapse

Evidence shows that the Antarctic ice sheets are becoming increasingly unstable, and that the Greenland ice sheets could collapse entirely if global temperatures rise by 1.5C - which could happen as soon as 2030 if current trends persist.

Collapsing ice sheets leads to higher sea levels, one of the most dangerous consequences of climate change.

Sea level rises are already having “devastating effects”, forcing mass migration of people to higher ground and coinciding with dangerous hurricanes and typhoons, says National Geographic

Key services such as internet access - which rely on infrastructure in the path of rising seas - may also be hit as a result.

Biosphere boundaries

Climate change threatens to trigger biosphere tipping points, some of the consequences of which are already being felt.

Ocean heatwaves have caused coral bleaching and the loss of half of the shallow-water corals on Australia’s Great Barrier Reef. And there would be “a profound loss of marine biodiversity and human livelihoods” if the global average temperature rises by 2C, according to the report published in Nature.

Deforestation and climate change also risks destabilising rainforests such as the Amazon. The scientists say that “estimates of where an Amazon tipping point could lie range from 40% deforestation to just 20% forest-cover loss”.

About 17% has already been lost since 1970.

Global cascade

The biggest risk is a “global cascade” of tipping points “that led to a new, less habitable, ‘hothouse’ climate state”, says report author Tim Lenton, director of the Global Systems Institute at the University of Exeter.

Evidence suggests that exceeding one tipping point can increase the risk of exceeding others, with such links found for 45% of possible interactions.

Arctic sea-ice loss is amplifying warming in the area, which contributes to an influx of fresh water in the North Atlantic. This in turn contributes to a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), a large system of ocean currents that distribute heat and energy around the world and determine the climate we feel all around the globe.

A further slowdown of the AMOC could destabilise the West African monsoon, triggering drought in Africa’s Sahel region. The phenomenon could also dry the Amazon, disrupt the East Asian monsoon, and cause a heat build-up in the Southern Ocean, which could further accelerate Antarctic ice loss.

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Is it too late?

The scientists behind the Nature article says that the evidence suggests the world is currently in a state of “planetary emergency”.

“We might already have lost control of whether tipping happens,” they write. “A saving grace is that the rate at which damage accumulates from tipping - and hence the risk posed - could still be under our control to some extent.”

“To be honest, I think we know enough climate science to act, yet we are not acting decisively, so we need to put resources into action,” report author Lenton told Vice.

Speaking ahead of COP25, the UN’s Guterres said that the coming 12 months are “crucial”, adding: “It is essential that we secure more ambitious national commitments.” 

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