We may have already pushed our planet beyond several tipping points and towards a scenario where the Earth begins “self amplifying” global warming in a series of unstoppable destructive feedback loops, scientists calling for an international emergency response have warned.
More than half of the climate tipping points identified a decade ago are now “active”, with immediate threats including the loss of the Amazon rainforest and the great ice sheets of Antarctica and Greenland, all of which are currently undergoing measurable and unprecedented changes much earlier than expected.
This amounts to an “existential threat to civilisation”, which requires an “emergency response”.
Writing in the journal Nature, the scientists say evidence is mounting that these events are more likely and more interconnected than was previously thought, and could lead to a catastrophic domino effect.
But they say massive emergency action to reduce greenhouse gas emissions will help slow down some of these processes, giving our species more time to adapt and stave off the worst-case scenario of a “hothouse” Earth, in which our planet would be scarcely habitable.
“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,” said lead author Professor Tim Lenton, director of the Global Systems Institute at the University of Exeter.
“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.”
Co-author Johan Rockström, director of the Potsdam Institute for Climate Impact Research, said: “It is not only human pressures on Earth that continue rising to unprecedented levels. It is also that as science advances, we must admit that we have underestimated the risks of unleashing irreversible changes, where the planet self-amplifies global warming.
“This is what we now start seeing, already at 1C global warming.
“Scientifically, this provides strong evidence for declaring a state of planetary emergency, to unleash world action that accelerates the path towards a world that can continue evolving on a stable planet.”
At the moment our planet is on course for disaster – Even if all of the countries signed up to the Paris climate agreement met their emissions goals, we will still see “at least 3C of global warming” by the end of the century, scientists say.
But we are not even on course to meet those objectives.
While we fail to deal with our emissions, the impact is still being felt and triggering irreversible processes.
Permafrost across the Arctic is beginning to thaw on a large scale and release its colossal stores of carbon dioxide and methane – a greenhouse gas around 30 times more potent than CO2.
The Amazon could also soon be beyond saving. Deforestation, combined with climate change, mean the “lungs of the world” are close to a tipping point where the forest dries out and cannot survive. Since 1970, 17 per cent of the Amazon has been destroyed. This tipping point could be hit when deforestation reaches anywhere between 20-40 per cent.
In the Arctic, where temperatures are rising faster than other parts of the world, warming has already triggered large-scale insect disturbances and an increase in fires that have led to the dieback of North American boreal forests, “potentially turning some regions from a carbon sink to a carbon source”, the authors write.
Once a tipping point is hit, it makes the risk of others being hit considerably higher.
But it could plausibly get far worse.
Today, atmospheric CO2 is at levels last seen around four million years ago in the Pliocene epoch, when there were forests growing on Antarctica, sea levels were 20 metres higher than they are today, and global temperatures were 3-4C warmer.
But our CO2 levels continue to spiral out of control, and, the scientists write, we are “rapidly heading towards levels last seen some 50 million years ago”, in the Eocene epoch when temperatures were up to 14C higher than they were in pre-industrial times.
The scientists are calling for the world to “act now” to put the brakes on in order to avoid runaway overheating.
Although future tipping points and the interplay between them is difficult to predict, the scientists argue: “If damaging tipping cascades can occur and a global tipping cannot be ruled out, then this is an existential threat to civilization.”
The scientists are also calling for a greater understanding of how emissions increase the likelihood of causing tipping points to be reached.
To have just a 50-50 chance of global average temperatures remaining 1.5C higher than in the pre-industrial era, the remaining “carbon budget” is 500 gigatonnes (Gt) of CO2 emissions.
As permafrost in the Arctic is already melting, the resultant emissions could take around 20 per cent (100 Gt CO2) off this budget – and that’s not even accounting for the impact of the methane which would be released.
Amazon dieback could release another 90 Gt CO2 and the loss of boreal forests a further 110 Gt CO2.
“With global total CO2 emissions still at more than 40 Gt per year, the remaining budget could be all but erased already,” the article says.
A global departure from the fossil fuel economy is unlikely before 2050, but with the temperature already at 1.1°C above pre-industrial levels, it is likely our planet will cross the 1.5C “guardrail” by 2040. The authors conclude this alone defines an emergency.
“No amount of economic cost-benefit analysis is going to help us. We need to change our approach to the climate problem,” the paper says.
Professor Lenton added: “We might already have crossed the threshold for a cascade of inter-related tipping points.
“However, the rate at which they progress, and therefore the risk they pose, can be reduced by cutting our emissions.”