Scientists writing for the journal, Nature, have warned that the planet has crossed a series of climate ‘tipping points’. They call the risk an ‘existential threat to civilisation’, saying that ‘we are in a state of planetary emergency’. What are climate change tipping points and what effects do they have on the planet? Is it possible that these tipping points can have positive impacts on society?
What is a Climate Tipping Point?
Tipping points are thresholds where a tiny change could push a system into a completely new state and are based on positive feedback loops, whereby an effect of something reinforces the cause. They are caused when particular impacts of global heating become unstoppable, such as the disintegration of the Greenland ice sheet, permafrost loss and coral reef die-off.
In the past, extreme heating of 5C was thought necessary to pass tipping points, but latest evidence suggests that this could happen between 1C and 2C.
The scientists say, “Multiple risks can interact, with one change reinforcing another, and with warming of just a degree or two sufficient to result in dramatic cascading effects.”
The planet has already passed the 1C mark and temperatures will certainly rise further, due to past emissions and because greenhouse gases are still rising. The scientists further warn that one tipping point may fuel others, leading to a cascade, and have called for urgent international action.
When Will We See a Tipping Point for Climate Change
The article comes as the UN warns that the world is currently on track for 3C-4C warming by the end of the century.
The scientists warn that the West Antarctic ice sheet may be in irreversible retreat; a similar situation is occurring at the Wilkes basin in east Antarctica. The collapse of these ice sheets would raise sea levels by many metres. The Gulf Stream current in the Atlantic, which warms Europe, has slowed by 15% since the mid-20th century.
17% of the Amazon rainforest has been lost since 1970. The tipping point where loss of forest leads to it drying out, could lie in the 20-40% range, which could turn some regions from a sink for carbon to a source. In the tropics, corals are predicted to be wiped out by 2C of heating.
A cascade of tipping points could occur because, for example, the melting of Arctic sea ice amplifies heating by exposing dark ocean that absorbs more sunlight. This may increase the melting of Greenland ice and permafrost areas.
Two physical climate tipping points which have received less attention will be discussed.
Examples of these tipping points are starting to be observed, the scientists say. For example, Arctic sea-ice loss is amplifying warming in the region, and Arctic warming and Greenland melting are driving an influx of fresh water into the North Atlantic, where the Atlantic Meridional Overturning Circulation (AMOC) is responsible for bringing warm water to mid-latitude regions and is a key part of global heat and salt transport by the ocean.
The positive feedback is brought about by the current towards the north transporting salty water, which then sinks in the north and flows back to the south to complete the loop. With the melting Greenland ice sheet, the freshwater dilutes the salty water and makes it lighter. This reduces the sinking. With the loop slowing down, less salty water is brought northward and makes the sinking even slower. Rapid melting of the Greenland ice sheet and further slowdown of the AMOC could destabilise the West African monsoon, triggering drought in the Sahel region. The slowdown could also dry out the Amazon, disrupt the East Asian monsoon and cause heat to build up in the Southern Ocean, which could accelerate Antarctic ice loss.
It has been suggested that the AMOC tipping point is unlikely to be reached if the Paris Agreement is adhered to. If this tipping point is exceeded, Europe may experience disrupted rainfall patterns and have knock-on effects for agriculture.