Several active 'tipping points' of irreversible change in the world's climate system threaten to unleash a global cascade of events that amounts to a planetary emergency, scientists warn.

The concept of tipping points was introduced by the Intergovernmental Panel on Climate Change (IPCC) just over 20 years ago, but researchers now warn that already nine of these vulnerable environmental thresholds are in very real danger of being breached – and much sooner than was ever anticipated.

"A decade ago we identified a suite of potential tipping points in the Earth system, now we see evidence that over half of them have been activated," says climate system researcher Tim Lenton from the University of Exeter in the UK.

"The growing threat of rapid, irreversible changes means it is no longer responsible to wait and see. The situation is urgent and we need an emergency response."

In a new research comment, Lenton and an international team of climate scientists warn that these tipping points – which many assumed were low-probability risks that might only be dangerous if global temperatures rose 5°C above pre-industrial levels – are in fact becoming exceeded at increases of 1–2°C.

"We think that several cryosphere tipping points are dangerously close, but mitigating greenhouse-gas emissions could still slow down the inevitable accumulation of impacts and help us to adapt," the authors write in their paper.

The nine active tipping points identified by the team include warming ice regions in the Arctic, Antarctica, and Greenland, in addition to dramatic changes underway in boreal forests, Atlantic Ocean currents, the Amazon rainforest, warm-water coral systems, and thawing permafrost.

While some of these destabilised systems may appear to be unrelated to one another, the researchers warn increasing evidence suggests the disparate crises are actually linked together – and in fact are part of a global continuum of climate destabilisation that amplifies itself in numerous alarming scenarios.

"As soon as one or two climate dominoes are knocked over, they push Earth towards others," says Earth systems scientist Will Steffen from the Australian National University.

"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."

While acknowledging that we might have already committed future generations to almost unimaginable sea-level rises of several metres, the team argues that the timescale of such effects is still something we can control with our actions today.

"The rate of melting depends on the magnitude of warming above the tipping point," the researchers write.

"At 1.5°C, it could take 10,000 years to unfold; above 2°C it could take less than 1,000 years."

Taking drastic action now to limit carbon emissions won't just mean we put fewer chemicals in the air; it would also mean we could limit feedback systems like permafrost thawing, which threatens to unload its own huge stored reserves of carbon into the atmosphere.

While our understanding of how these tipping points are linked is still emerging, the existing research firmly indicates that betting against climate tipping points is too risky.

One study last year found that "exceeding tipping points in one system can increase the risk of crossing them in others," the researchers say, and determined these cascading links were found for 45 percent of possible interactions.

There's no way of sugar-coating this. The researchers themselves conclude that the planetary emergency we are facing represents an existential threat to civilisation, one which calls for immediate, real action – and now.

"No amount of economic cost-benefit analysis is going to help us," they warn.

"We might already have lost control of whether tipping happens. 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."

The findings are reported in Nature.