Tipping Points Explained
What are Tipping Points?
At present we are able to prevent climate change from getting worse by reducing our emissions of greenhouse gasses, but that will not always be the case. At some point if we continue business as usual the rising global temperature will trigger feedback loops within the earth's climate system which may lead to a series of cascade reactions and the nightmare scenario of runaway global warming. If this happens then preventing climate change is no longer within our control, even if we reduce our emissions of greenhouse gasses to zero.
The various feedback loops that can cause runaway global warming are known as tipping points. As each tipping point is reached the global climate goes through an abrupt and permanent shift. Scientists do not yet know when these tipping points may be reached, or how they might cascade, with one tipping point causing another, and so on like a line of domino's. For these reasons it is important to understand what tipping points are, and when they are likely to be reached, so that we can avoid them and prevent runaway global warming.
The Amazon
The amazon rainforest sequesters CO2 from the air into its soils and plants. If global warming exceeds 3.5C however (it is currently at 1.1C) the combination of deforestation and climate change will likely trigger a massive die-back of the amazon. This will transform the amazon into a dry savannah, turning it into a net emitter of CO2 and thereby accelerating global warming. Once this has happened, it cannot be reversed.
Recent findings, based on three decades of satellite data [1], show that this process has already begun, with 75% of the forest having lost stability.
The amazon is home to one out of every ten species known to science, and is a huge storehouse and absorber of carbon. Its loss, scientists say, would be devastating to the climate and to biodiversity.
North Atlantic Ocean Circulation (The Gulf Stream)
One of the main tipping points in the climate system is the gulf stream, an ocean current that brings warm water from the Gulf of Mexico to the ice sheets in the Arctic. The rising ocean temperature and the melting Arctic ice are weakening the strength of the Gulf stream, and threaten to cause it to collapse altogether. A recent study showed that the gulf stream was at its lowest ebb for the past 1,600 years [2], but most studies suggest that any tipping point is not likely to occur this century.
The film The Day After Tomorrow depicts the slowdown of the Gulf Stream and a catastrophic freeze that ushers in a new mini ice age for northern Europe and America. Although the film is exaggerated, the actual result of a collapse of the gulf stream would lead to lower temperatures across northern Europe by at least several degrees, even with global warming, as well as disrupting the rains that billions of people depend on for food around the world. Other effects are an increased instability on the Antarctic ice sheet and the Amazon rainforest.
Sudden Thawing of Northern Permafrost - the Ticking Climate Bomb
Permafrost is land that remains frozen, either at soil level or underneath the spoil, though it may not be covered in snow or ice. Because the soil is frozen the permafrost has trapped within it huge amounts of CO2 and methane, the two most common greenhouse gasses.
The sudden thawing of the Northern permafrost, such as the Siberian permafrost, is one of the major 'cascade'' tipping points, in that once the collapse of the permafrost is underway it will lead to the vast release of the CO2 and methane trapped within it, which in turn will accelerate climate change and lead to other tipping points being triggered. For this reason, it is often referred to as the 'ticking climate bomb'.
The western Siberian permafrost is especially vulnerable, as it has warmed by 3 or 4C in the last 40 years, one of the fastest rates of warming in the world behind the Barents Sea (see below), and has already begun melting for the first time since the ice age. A recent study [3] showed that the permafrost is on a precipice and by as soon as 2040 the climate may no longer be able to sustain it, causing a collapse. This could lead to a doubling of greenhouse gasses in the atmosphere which would lead to catastrophic levels of global warming.
Sudden Collapse of Greenland, Arctic, and Antarctic Ice Caps - Unstoppable Sea Level Rise
Unlike the Arctic ice cap, the ice caps in Greenland and the Antarctic ice sheet are on land. This means that as they melt they will cause a direct rise in sea level. A collapse in these ice sheets would therefore cause an irreversible and unstoppable rise in global sea levels. Greenland and Antarctica are currently losing ice six times faster than 30 years ago, and Greenland's ice sheet has been shrinking continuously for the last 25 years. If global warming triggers a complete melt of the Greenland and West Antarctic ice sheets (a smaller and more vulnerable part of the larger Antarctic ice sheet), global sea levels would rise by at least 10m. The collapse of the entire Antarctic ice sheet would see that figure rise to at least 65m. That would see most of Swansea Bay and the river valleys that feed into it, for example, including Swansea itself, under tens of metres of water.
The Arctic ice sheet is also showing signs of collapse, and it is possible that we will soon experience a complete melting of the Arctic ice sheet during the summer seasons. Although the melting of the Arctic sea ice will not cause sea levels to rise, its melting, along with the melting of the Greenland and Antarctic ice, will mean that light from the sun will no longer be reflected back into space by the white ice, but will instead be absorbed by the land and the sea, causing an ever faster chain of global warming that will be irreversible.
It is in the polar regions where the first tipping points are likely to be reached, and some researchers suggest that the signs of destabilisation that would precede a collapse in the ice sheets are already being seen. The image below, for example, shows the change in the extent of summer Arctic ice over the last few decades.
Abrupt Sea Ice Loss in Barents Sea
The Barents Sea is situated above Norway, Sweden and northwestern Russia. It is warming at the fastest pace of anywhere else in the world, some 5 to 7 times faster than the global average [4]. This is likely to lead to a permanently ice free sea in the coming decades, leaving it more like the Atlantic than an Arctic sea. This will have serious repercussions, and scientists are saying it is a harbinger of what will happen in the Arctic. The Barents Sea shields the Arctic from warmer waters reaching it, and so the loss of sea ice here will result in faster warming for the Arctic ice cap.
The melting of the sea ice in the Barents Sea will also lead to more extreme weather events across the northern hemisphere, and is even leading to a more rapid warming of the Tibetan Plateau. Perhaps most seriously however, is the fact that the loss of the sea ice will lead to a much greater amount of energy from the sun being absorbed by the ocean instead of being reflected back into space by the ice, leading to faster and more abrupt global warming.
Coral Reef Die-off
Coral reefs are havens of spectacular beauty and biodiversity, but they are also very sensitive to ocean temperatures, and when the ocean temperature becomes too warm for them they 'bleach', and then die-off. This makes them very vulnerable as emissions of greenhouse gasses continue to rise and the world's oceans continue to warm.
The dying off of the world's coral reefs are being reported all over the world. The UN Status of Coral Reefs of the World 2020 report [5] provides the most detailed scientific picture to date of the toll elevated ocean temperatures have taken on the world’s coral reefs. It showed, for example, that between 2009 and 2018 some 14% of the world's coral reefs were lost, and that without action to limit global warming to 1.5C, up to 90% of the world's coral reefs will be gone by 2050. When you consider that 25% of all marine species depend on coral reefs, you can begin to see just how devastating this will be on marine biodiversity, and on the 500 million people worldwide that depend on coral reefs.
[1] https://www.nature.com/articles/s41558-022-01287-8
[2] https://www.nature.com/articles/s41586-018-0007-4
[3] https://phys.org/news/2022-03-permafrost-peatlands-approaching.html
[4] https://www.nature.com/articles/s41598-022-13568-5
[5] https://www.unep.org/resources/status-coral-reefs-world-2020
