‘Cascade’ of changes could threaten human existence
Half of the climate 'tipping points' identified a decade ago are now 'active'
Human civilisation is facing a 'cascade of changes' sparked by global warming that is 'putting its very existence under threat', scientists war n. Experts from the University of Exeter say Earth's climate has hit more than half of the tipping points identified a decade ago as points of no return for climate change.
'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', said lead author Tim Lenton.
The tipping points include reductions in the size of the Amazon rainforest and the great ice sheets of Antarctica. Professor Lenton says they are currently undergoing measurable and unprecedented changes much earlier than expected. Researchers say evidence is mounting that these events are more likely and more interconnected than was previously thought, leading to a possible domino effect. In an article in the journal Nature, the scientists call for urgent action to reduce greenhouse gas emissions to prevent key tipping points, warning of a worst-case scenario of a 'hothouse', less habitable planet.
'A decade ago we identified a suite of tipping points in the Earth system, now we see evidence that over half of them have been activated,' said Professor Lenton.
The authors have proposed a new formal way to calculate whether the planet is in a state of emergency using tipping points to calculate risk.
Co- author Johan Rockström said: ' 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.'
Exiting the fossil fuel economy is unlikely before 2050, but with temperature already at 1.1°C above pre-industrial temperature, it is likely Earth will cross the 1.5°C guardrail by 2040, Professor Lenton said.
The authors conclude this alone defines an emergency. The collapse of major ice sheets on Greenland, West Antarctica and part of East Antarctica would commit the world to around 10 metres of irreversible sea-level rise. Researchers say reducing emissions could slow this process, allowing more time for low- lying populations to move to higher ground. The rainforests, permafrost and boreal forests are examples of biosphere tipping points that if crossed result in the release of additional greenhouse gases amplifying warming, they say.
Despite most countries having signed the Paris Agreement, pledging to keep global warming well below 2°C, current national emissions pledges - even if they are met - would lead to 3°C of warming.
'If damaging tipping cascades can occur and a global tipping cannot be ruled out, then this is an existential threat to civilization', the team claim in their report.
' No amount of economic cost- benefit analysis is going to help us. We need to change our approach to the climate problem.'
Professor Lenton said: '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.'
Though global temperatures have fluctuated over millions of years, the authors say humans are now 'forcing the system'.
'With atmospheric carbon dioxide con
What are the active tipping points?
1. Arctic sea ice
2. Greenland ice sheet
3. Boreal forests
4. Permafrost Atlantic
5. Meridional Overturning Circulation
6. Amazon rainforest
7. Warm-water corals
8. West Antarctic Ice Sheet
9. Parts of East Antarctica
centration and global temperature increasing at rates that are an order of magnitude higher than at the end of the last ice age.'
Will Steffen professor of climate and Earth system science at the Australian National University said the study shows two of the tipping points - coral reefs and Arctic sea ice - may have already been tipped.
'The consequence of activating such a cascade would be an unstoppable slide into hothouse Earth conditions.
'The schoolchildren are right - we indeed have a climate emergency, and an emergency-level response is now needed to ensure that we don’t activate the tipping cascade.'
The research has been published in the journal Nature.