The tipping point is that magic moment when an idea, trend, or social behavior crosses a threshold, tips, and spreads like wildfire. Just as a single sick person can start an epidemic of the flu, so too can a small but precisely targeted push cause a fashion trend, the popularity of a new product, or a drop in the crime rate.
Politicians, economists and even some natural scientists have tended to assume that tipping points1 in the Earth system — such as the loss of the Amazon rainforest or the West Antarctic ice sheet — are of low probability and little understood. Yet evidence is mounting that these events could be more likely than was thought, have high impacts and are interconnected across different biophysical systems, potentially committing the world to long-term irreversible changes.
Here we summarize evidence on the threat of exceeding tipping points, identify knowledge gaps and suggest how these should be plugged. We explore the effects of such large-scale changes, how quickly they might unfold and whether we still have any control over them.
In our view, the consideration of tipping points helps to define that we are in a climate emergency and strengthens this year’s chorus of calls for urgent climate action — from schoolchildren to scientists, cities and countries.
The Intergovernmental Panel on Climate Change (IPCC) introduced the idea of tipping points two decades ago. At that time, these ‘large-scale discontinuities’ in the climate system were considered likely only if global warming exceeded 5 °C above pre-industrial levels. Information summarized in the two most recent IPCC Special Reports (published in 2018 and in September this year) suggests that tipping points could be exceeded even between 1 and 2 °C of warming (emphasis added).
Rain has fallen on the summit of Greenland's ice sheet for the first time in recorded history, heightening concerns about the already precarious condition of its ice.
An unprecedented 7 billion tons (6.3 billion metric tons) of water pelted the ice sheet last Saturday (Aug. 14), falling as rain and not snow for several hours. This was the third time temperatures at the summit had risen above freezing in less than a decade, according to recordings taken by the National Science Foundation's Summit Station.
The rain, which occurred over two days from Aug. 14 to Aug. 15, was also accompanied by the melting of up to 337,000 square miles (872,000 square kilometers) of ice, according to the U.S. National Snow & Ice Data Center (NSIDC).
"There is no previous report of rainfall at this location, which reaches 3,216 meters (10,551 feet) in elevation," NSIDC researchers said in a statement, adding that the amount of ice lost in one day was the same as the average ice lost across a typical week for the same time of year (emphasis added).