The world is at increased risk of triggering multiple climate “tipping points”, causing cascading effects that are likely to lead to irreversible and uncontrollable impacts on the Earth, according to an assessment by leading climate scientists.
There is an increased likelihood that tipping points could be crossed if average global temperature rises beyond 1.5 degrees, the analysis published by research journal Science concludes. Containing temperature rise to 1.5 degrees is the more demanding of Paris Agreement targets.
The most immediate tipping points the scientists have identified are: the collapse of Greenland and West Antarctic ice sheets; a widespread abrupt permafrost thaw releasing vast amounts of methane; the weakening of convection in the Labrador Sea, and a large die-off of tropical coral reefs around the equator. Permafrost is most concentrated in the Arctic beneath large parts of Alaska, Canada and Siberia.
The planet may have already left a “safe” climate state when temperatures exceeded 1 degree warming, it finds — current global average temperatures are 1.1 to 1.2 degrees above pre-industrial levels.
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[ Risk of passing multiple climate tipping points escalates ‘above 1.5 degrees of global warming’ ]
[ Climate system Q&A: What are the ‘tipping points’? ]
Human-induced carbon emissions have been pushing up Earth’s temperature through the greenhouse effect, and much more warming is expected in coming decades if carbon levels in the atmosphere are not reduced.
Warming may not always be steady — passing a “tipping point” can cause sudden or irreversible change, warns the group led by Dr David Armstrong McKay of Stockholm Resilience Centre.
Scientists are now worried the Earth is approaching some climate tipping points sooner than had been anticipated, beyond which rapid and difficult-to-reverse climate changes may occur — a scenario confirmed in the most extensive evaluation of tipping points published on Thursday.
Co-author Johan Rockström, co-chair of the Earth Commission and director of Potsdam Institute for Climate Impact Research, said: “The world is heading towards 2-3 degrees of global warming. This sets Earth on course to cross multiple dangerous tipping points that will be disastrous for people across the world.
“To maintain liveable conditions on Earth, protect people from rising extremes, and enable stable societies, we must do everything possible to prevent crossing tipping points. Every tenth of a degree counts,” he added.
Co-author Prof Tim Lenton, director of the Global Systems Institute at the University of Exeter, said their new work “provides compelling evidence that the world must radically accelerate decarbonising the economy to limit the risk of crossing climate tipping points. To achieve that we now need to trigger positive social tipping points that accelerate the transformation to a clean energy future”.
“We may also have to adapt to cope with climate tipping points that we fail to avoid, and support those who could suffer uninsurable losses and damages,” Prof Lenton added.
Scouring paleoclimate data, current observations and outputs from climate models, the international team concluded that 16 major biophysical systems involved in regulating Earth’s climate ‑ so-called “tipping elements” — have the potential to cross tipping points where change becomes self-sustaining.
That means even if global temperatures stop rising, once the ice sheet, ocean or rainforest has passed a tipping point it would carry on changing to a new state, Prof Lenton explained. How long the transition takes varies from decades to thousands of years depending on the system.
Profs Rockström and Lenton are co-hosting a global conference at the University of Exeter on September 15th to consider how to improve warnings of the imminent risks of catastrophic climate tipping points and to accelerate positive tipping points to avert the climate crisis.
