Climate crisis at 'tipping point', scientists warn
Former Science Editor
Video report by ITV News Science Editor Tom Clarke
"We're in a state of planetary emergency," not the words of breathless campaigners protesting on the streets, or even environment correspondents like me, screaming in their wellies, but a team of distinguished scientists writing in one of the world's leading science journals.
A decade ago, Professor Tim Lenton from the University of Exeter coined the phrase "planetary tipping points" to describe parts of the Earth's interconnected systems that in the past had been pushed from one state, past an irreversible point, into another.
Take the Greenland ice sheet, which we filmed melting earlier this year.
It's now gradually melting because of warming in the arctic. One thing slowing the melting is the 2-3000 metre height of the ice sheet - at that altitude it's too cold to melt. However once it melts below a certain height, it will be impossible for the ice sheet to grow again whatever we do to slow global warming.
Another example is the Amazon rainforest.
It absorbs billions of tonnes or carbon dioxide a year. It also makes its own rainfall as the trees respire moisture into the atmosphere that's then recycled into the forest as rain. Cut too much of the forest down and there isn't enough rainfall to sustain what's left: the Amazon passes a tipping point, dries out, and billions of tonnes of carbon dioxide are released into the atmosphere.
Lenton's team originally described 15 such planetary tipping points.
In the journal Nature today they conclude nine of them are now "active" and based on projected carbon emissions some may reach point of no return within decades.
What's more, some tipping points can push others over the edge.
Freshwater from the melting of the Greenland ice sheet for example could, as it appears to have done in past climates on Earth, shut down major ocean currents in the Atlantic. This in turn could shift rainfall patterns like the African monsoon.
"If damaging cascades can occur and a global tipping point cannot be ruled out, then this is an existential threat to civilisation," they conclude.
Not all scientists agree with the "tipping points" approach - some have even described it as alarmist.
But the authors of the report argue, the risks of ignoring the evidence are so high, "to err on the side of danger is not a responsible option."
It's a gloomy conclusion, but there's still everything to fight for.
Even if we're already on course to exceed some of these planetary boundaries, reducing global warming and deforestation now, could drastically reduce the rate at which these changes happen.
Slowing the speed of "tipping" from centuries, to millennia, would give our ancestors far more time to adapt to the Earth they will inherit.