Jakobshavn Isbræ glacier in western Greenland
Photo: Michael Schwab/Getty Images
The term “tipping point” appears 97 times in the first volume of the current World Climate Report alone.
In September, a new overview study on climate tipping points was published in the renowned journal »Science«.
And at the beginning of December, the OECD published a report in which it warned of "tipping point cascades" and discussed political measures.
The tipping points of the climate system are an issue that not only politics and business, but also every voter should understand in outline.
According to the Intergovernmental Panel on Climate Change, a tipping point is "a critical boundary beyond which a system reorganizes, often abruptly and/or irreversibly."
By “reorganizing itself” we mean that the system goes into a completely different state by itself from the critical point.
Most readers should be familiar with the concept of the upset of ecosystems, especially bodies of water.
There are also tipping points in physics.
If you lean to the side in a kayak, for example, the boat first tries to right itself.
At a certain point, however, there is no more resistance and the boat tips over completely.
It has two stable states: upright or upside down.
Six tipping elements in acute danger
In the professional world, systems with tipping points are called tipping elements.
These include the large ice sheets on Greenland and in West Antarctica, the Atlantic circulation, the Amazon forest and the coral reefs (see graphic below).
Some tipping points have been known for decades.
I have been researching the tipping point of the Atlantic circulation since 1991.
The basic mechanism for the Atlantic tipping point was already described in a study by the famous US oceanographer Henry Stommel, published in 1961.
In 1987, the no less famous oceanographer Wallace Broecker of Columbia University warned in the journal Nature of "unpleasant surprises in the greenhouse" when "abrupt changes in ocean currents are triggered."
Referring to the paleoclimatic data evidence that instabilities in the Atlantic circulation have repeatedly occurred in the history of climate, he wrote: "We are playing Russian roulette with the climate."
The danger that the West Antarctic ice sheet could become unstable and slide into the sea was also described in 1978 by the Antarctic researcher John Mercer - also in "Nature" and with exceptionally clear words for a dry specialist publication.
Its title was: »The West Antarctic Ice Sheet and the CO₂ Greenhouse Effect: A Looming Disaster«.
A historic British-German workshop on tipping points in the Earth system was held at the British Embassy in Berlin in October 2005 and resulted in a first review publication that has since been cited thousands of times in other studies.
Although all of this was many years ago, the topic is more topical than ever.
Together with an international team of experts, the Potsdam Institute for Climate Impact Research (PIK), where I do research, comes to the conclusion in the “Science” study mentioned at the beginning that six tipping points are already more global in the range of 1.5 to 2 degrees Celsius warming likely to be exceeded.
To put this in perspective: Just a few years ago, it was assumed that exceeding tipping points represented a risk with devastating consequences, but with a low probability of occurrence.
Today, the best estimate shows that such events are likely to occur at temperatures below two degrees.
Dangerous domino effects
So what exactly is at stake?
Some of the most important examples of tipping elements, some of which are at risk of warming below two degrees Celsius:
or Atlantic overturning circulation, which also includes the Gulf Stream, is weakening due to increasing precipitation and increasing meltwater inflow from Greenland, because seawater is diluted with freshwater and can no longer sink so easily to the depths.
If the system tilts, this process will run itself: Less and less salty water from the subtropics flows northwards.
The subsidence stops, a layer of fresh water collects on the sea surface, and the current dries up over the course of a few decades.
The result: the cold bubble already observed in the northern Atlantic (see graphic below) is expanding, parts of Europe are cooling down, the sea level is rising by an additional meter along Europe's coasts, marine ecosystems are threatened with collapse, and there are unprecedented weather extremes in Europe.
ice sheet, which is more than 3,000 meters thick
, is losing mass.
As a result, the surface moves further and further down into warmer layers of air.
From the tipping point, the ice is lost: even without further warming, there is total loss.
There is a risk of seven meters of global sea level rise.
It will take about a millennium for the ice to completely disappear.
But in the next 20 years, the system threatens to tip over, which will condemn future generations to abandon most of the coastal cities.
From the tipping point, the
ice sheet begins to slide inexorably into the sea.
In the case of the West Antarctic ice sheet, this point could already have been exceeded, but it is probably between 1.5 and 2 degrees of global warming.
The result would be three meters of global sea level rise over the coming centuries.
The same applies to the two tipping points on the East Antarctic Ice Sheet.
Antarctica is also already losing ice mass.
In the case of
, the tipping point is the freezing point, like that of a lake whose surface is solid at minus one degree Celsius and becomes liquid at plus one degree Celsius.
As the permanently frozen soils of the far north thaw, the biomass in the soil is decomposed, generating more heat that triggers a self-reinforcing process known as the "compost bomb."
In the process, large amounts of the very potent greenhouse gas methane are released, which further fuels global warming without human beings then being able to do anything about it.
creates its own rainfall by recycling water from trees actively collecting it from the ground and evaporating it through their leaves.
The tipping point is exceeded when the forest is cut down too much and/or droughts are too severe due to climate change.
Rain recycling then no longer works, and the forest irretrievably becomes a savannah.
That means devastating loss of animal and plant species, regional climate changes, large wildfires and release of CO₂ that further fuels warming.
have a critical water temperature limit at which they fade and eventually die.
Apparently this tipping point has already been reached.
Since 2015 we have been in the midst of a global coral die-off.
The Intergovernmental Panel on Climate Change (IPCC) estimates that if global warming is limited to 1.5 degrees Celsius, 10 to 30 percent of coral reefs can still be saved; if the temperature rises by two degrees, almost all of them would be lost.
According to the US Ocean Administration NOAA, more than half a billion people worldwide depend on coral reefs for their food supply, income or coastal protection.
But that's not all: At the forefront of research, so-called cascades of tipping points are currently being discussed, which the OECD report also warns about because of their "potentially catastrophic consequences": tipping points that knock over each other like dominoes.
If one subsystem tips over, others will follow.
A classic example: the Greenland ice sheet is tipping.
This leads to meltwater volumes in the northern Atlantic, which bring the Atlantic circulation to a standstill.
This, in turn, is shifting tropical rainfall belts in such a way that the Amazon rainforest is tipping over.
This destabilizes further tipping elements.
Hoping for positive tipping points
There are also positive regional tipping points in a few places.
These include the expansion of the northern coniferous forests and a possible greening of parts of the Sahara, as was the case in the early Holocene.
Above all, however, the hope remains for positive tipping points in human society.
Our energy system is probably just reaching such a point.
According to the International Energy Agency IEA , renewable energies are already the cheapest form of power generation in most countries , including Germany .
They are growing exponentially and, according to the IEA, will overtake coal-based power generation in less than three years.
More than 80 percent of global investments in electricity supply go to renewables, grids and storage.
The tipping point from which the global energy transition will become a sure-fire success has apparently been reached.
However, that is no reason to rest.
With current policies and decades of hesitation, change is happening too slowly.
The OECD report warns: "The existence of tipping points in the climate system means that it is imperative that global temperature rise be limited to 1.5 degrees Celsius." It is currently already at 1.2 degrees.
It would be a planetary tragedy if we had almost prevented the worst - but the catastrophe for humanity still occurs because we procrastinate in the crucial years instead of acting with full strength and determination.