27 November 2019
By Adam Vaughan
A team of influential scientists has warned that the world faces the risk of “an existential threat to civilization” due to mounting evidence that tipping points in the climate and nature are likely to be breached.
Eleven years ago the group cautioned against the dangers of critical thresholds in Earth’s systems being passed and systems tipping into a potentially dangerous state. These include the runaway collapse of ice sheets and Amazon deforestation reaching a level that leads to the drying of the area and death of the entire rainforest.
“We are now a little over 10 years on. The nasty surprise for me was a lot of the things we identified as potential tipping points that many would have thought were far in the future now show evidence of already being active,” says Tim Lenton at the University of Exeter, UK.
In a commentary in Nature, Lenton and his colleagues say changes in the frozen parts of the world are “dangerously close” to tipping points. They point to the area around the Amundsen Sea in West Antarctica, where ice sheets may have begun an irreversible collapse that will lead to 3 metres of sea level rise. “That’s a big wake up call. We may have made some big long-term sea level commitments,” says Lenton.
Other high-risk tipping points include fires in the Arctic and the release of greenhouse gases as frozen ground thaws.
Lenton says that there is now empirical evidence that cascades have begun – where one tipping point makes another one more likely to be passed. He cites the melting of the Greenland ice sheet and the influx of fresh water into the north Atlantic Ocean, which is further weakening an already slowing ocean current in the Atlantic that is key to weather patterns in Europe and Africa. Other research supports this.
Ultimately, this could all add up to a global tipping point where, whatever humanity does, there is no stopping it. The group says such a doomsday scenario is possible but more research is needed.
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The trouble is, it is quite difficult for us to know how close we really are to tipping points. For example, estimates for how many trees the Amazon needs to lose before it is committed to a death spiral of fires and drying range between 20 and 40 per cent of forest cover. The difference is crucial, given 17 per cent has been lost already.
Despite Brazil experiencing the fastest increase in deforestation for a decade, and ensuing fires, the rainforest’s tipping point appears a little way off yet. “At current [deforestation] rates, between 20 and 30 years,” says Carlos Nobre at Sao Paulo University in Brazil.
Measuring tipping points and projecting when they will be reached is difficult, but others agree we are close to them. “We may be at the precipice now with respect to several key tipping points,” says Michael Mann at Penn State University.
While the possibility of a global tipping point might be speculative at this stage, the researchers say its huge impact and irreversible nature mean we need to play it safe. “To err on the side of danger is not a responsible option,” write Lenton and his colleagues.
“Feedbacks and tipping points are the wild cards of the climate system, and they could push us into inevitable climate chaos far faster than heads of government understand,” says Durwood Zaelke at the Institute for Governance and Sustainable Development in Washington DC.
Lenton hopes the renewed focus on tipping points will inject urgency into politics. While local and national governments are declaring climate emergencies – and the European Union is voting tomorrow on whether to declare one – he notes that none have yet delivered the policies to match.
Ironically, the answer to avoiding tipping points in Earth’s system might be positive tipping points in technology or society, such as the protests by schoolchildren in the past year. “I think there is a huge amount to play for,” says Lenton. “We need to get to net zero emissions by 2050, if not before, to limit the risk of tipping other things.”
Journal reference: Nature, DOI: 10.1038/d41586-019-03595-0
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