A new study published in Science has warned that the Earth is on the verge of crossing five dangerous climate tipping points that could have disastrous consequences for the planet and humanity. The study, which synthesizes more than 200 research papers, identifies 16 potential tipping points that could trigger self-reinforcing feedback loops in the climate system, leading to irreversible changes.
Climate tipping points are thresholds in the Earth’s climate system that, once crossed, could lead to large-scale and often abrupt changes in the state of the system. For example, the melting of the Greenland ice sheet could eventually raise the global sea level by about 7 meters, flooding many coastal areas and displacing millions of people. The collapse of the Amazon rainforest could alter the regional and global climate, affecting biodiversity and rainfall patterns.
Some of these tipping points are interconnected, meaning that crossing one could increase the likelihood of crossing another, creating cascading effects. For instance, the loss of Arctic sea ice could accelerate the warming of the Arctic region, which could in turn trigger the thawing of permafrost, releasing large amounts of greenhouse gases into the atmosphere.
Which tipping points are at risk of being crossed?
The study estimates the likelihood of crossing each of the 16 tipping points at different levels of global warming, based on the best available scientific evidence. It finds that five of them may already be triggered at the current level of warming, which is about 1.1°C above the pre-industrial average. These are:
- The collapse of the Greenland ice sheet, which could raise the global sea level by about 7 meters over hundreds to thousands of years.
- The collapse of the West Antarctic ice sheet, which could raise the global sea level by about 3 meters over hundreds to thousands of years.
- The widespread and abrupt thawing of permafrost, which could release large amounts of carbon dioxide and methane into the atmosphere, amplifying the greenhouse effect.
- The collapse of convection in the Labrador Sea, which could weaken the Atlantic Meridional Overturning Circulation (AMOC), a system of ocean currents that regulates the climate of the North Atlantic region and beyond.
- The massive die-off of tropical coral reefs, which could reduce the biodiversity and productivity of marine ecosystems, affecting fisheries and coastal protection.
The study also finds that four of these tipping points move from being possible to likely at 1.5°C of warming, the lower limit of the Paris Agreement. These are:
- The loss of the Amazon rainforest, which could alter the regional and global climate, affecting biodiversity and rainfall patterns.
- The shift of the boreal forest, which could change the albedo and carbon storage of the northern regions, affecting the global energy balance and climate.
- The disruption of the Indian summer monsoon, which could affect the livelihoods and food security of billions of people in South Asia.
- The emergence of multiple breadbasket failures, which could reduce the global food production and increase the risk of famines and conflicts.
At 1.5°C of warming, five more tipping points become possible, according to the study. These are:
- The loss of the Arctic summer sea ice, which could accelerate the warming of the Arctic region and affect the wildlife and indigenous communities.
- The destabilization of the East Antarctic ice sheet, which could raise the global sea level by tens of meters over thousands of years.
- The activation of the Arctic methane hydrates, which could release large amounts of methane into the atmosphere, amplifying the greenhouse effect.
- The slowdown of the El Niño–Southern Oscillation, which could alter the variability and extremes of the global climate.
- The onset of irreversible Sahel greening or browning, which could affect the vegetation and rainfall of the semi-arid region in Africa.
The study also identifies six tipping points that require at least 2°C of warming to be triggered. These are:
- The collapse of the AMOC, which could cause drastic changes in the climate of the North Atlantic region and beyond.
- The transition of the Antarctic Circumpolar Current, which could affect the ocean circulation and heat transport around Antarctica.
- The breakdown of the West African monsoon, which could affect the water availability and agriculture of millions of people in West Africa.
- The shift of the Southern Ocean carbon sink, which could reduce the ocean’s ability to absorb carbon dioxide from the atmosphere, enhancing the greenhouse effect.
- The emergence of a snowball Earth, which could result in a global glaciation and a radical transformation of the climate and life on Earth.
- The initiation of a runaway greenhouse effect, which could make the Earth uninhabitable for humans and most other species.
Why is it important to avoid crossing tipping points?
The study warns that crossing tipping points could have severe and irreversible impacts on the Earth’s climate system, biodiversity, and human welfare. Some of these impacts could occur within decades, while others could take centuries or millennia to unfold. However, once triggered, some of these tipping points could be impossible to reverse, even if the global warming is stopped or reduced.
The study also emphasizes that the current level of warming is already risky and that the Paris Agreement goal of limiting the warming to 1.5°C is crucial to avoid crossing more tipping points. The study urges for urgent and ambitious actions to reduce greenhouse gas emissions and enhance the resilience of the climate system and society.
The study concludes that “the Earth may have left a ‘safe’ climate state beyond 1°C global warming”, and that “to maintain liveable conditions on Earth and enable stable societies, we must do everything possible to prevent crossing tipping points”.
