Current state of research: When the climate changes

Tipping points are controversially discussed by scientists. A new report summarizes the current status for the first time and also shows how tipping points could help in the fight against climate change.

Climate research has been discussing tipping points in the Earth system since the early 2000s – at that time, researchers led by Johann Rockström and Timothy Lenton defined nine corresponding points, including the melting of the ice sheets at the North and South Poles, the deforestation of the Amazon rainforest and the weakening of the thermohaline circulation – an important ocean current.

According to the concept, if they tip over, this change will be irreversible. The image of a coffee cup standing on the table is often used by climate research. It can be pushed over the edge of the table for a long time without falling down. At some point it is so far over the edge of the table that it tips over and falls.

New report on tipping points

A new report that “Global Tipping Points Report”, now summarizes the research of the past few years on tipping points. More than 200 researchers from 26 countries worked on the report. The project was led by the University of Exeter and co-financed by the Bezos Earth Fund.

The authors not only come from climate science, but also research social changes. That’s why the new report shows for the first time how so-called “positive” tipping points can counteract climate change. These could, for example, be climate-friendly technologies and behaviors that – according to the tipping point theory – spread faster and faster after a certain point.

According to the report, renewable energies have already reached this threshold by becoming increasingly cost-efficient. Further examples of social tipping elements include e-mobility and plant-based nutrition. The more appropriate image for this would be lined up dominoes. If one topples over, it triggers cascading, possibly positive changes because all the others also inexorably topple over.

Great uncertainty about tipping points

The extent to which tipping points are suitable for communicating climate risks is controversial among researchers. Science disagrees about the number of tipping points in the Earth system. The new report identifies 25 tipping points in the Earth system Potsdam Institute for Climate Impact Research (PIK) writes of 16 such tipping points, for some the tipping has regional consequences, for others it is global. The Helmholtz Climate Initiative mentions on its pages 14.

In its fourth assessment report in 2007, the Intergovernmental Panel on Climate Change (IPCC) also tried to highlight what was already known about the tipping points. Reto Knutti, climatologist at ETH Zurich was one of the authors. He also says: “There were a lot of uncertainties. That’s why the text is kept brief.” One of the best-known climate researchers, Mojib Latif, meteorologist and oceanographer from the GEOMAR Helmholtz Center for Ocean Research, also emphasizes: “The concept of tipping points is only as good as its uncertainty is discussed.”

Uncertainty using the example of AMOC

Latif himself has researched the Atlantic Meridional Overturning Circulation (AMOC). A current system that includes the Gulf Stream, known as the hot water heater of Europe. One published in July Study from Denmark had predicted that this upheaval could collapse as early as the middle of the century. Using simulation models, the research duo calculated that there is a 95 percent probability of a tipping occurring between 2025 and 2095.

When asked about the study, other scientists expressed criticism. One of them is Jochem Marotzke, director at the Max Planck Institute for Meteorology in Hamburg. According to his own statement, he is one of the first Germans to have dealt with overturning circulation in his doctoral thesis in 1985: “We don’t know where we stand with the AMOC. The work of the Danes is an example of the fact that tipping point research always focuses on this depends on what assumptions are made.” Other researchers also emphasize that the statement that the AMOC will collapse this century is not tenable.

Interdependent variables

However, the Intergovernmental Panel on Climate Change assumes that it is very likely that it will weaken by the end of the century. In a 2017 essay, Latif came to the same conclusion. But he wrote that how strong this weakening will be depends on whether and how quickly the Greenland ice cream melts. Latif thus names a fundamental problem in tipping point research: There are many variables that determine each other.

Climatologist Knutti also points out that this is difficult to put into an equation, especially in ecosystems such as the Amazon rainforest. As the temperature rises, the plants in the rainforest evaporate more water, which is predictable. But how do people behave, which areas do they clear, which animal species disappear because of a lack of habitat, and to what extent does this affect the stability of the Amazon? The PIK also writes about a partially unclear study situation in a region that is important for the global climate.

Missing data and technology

Another problem with tipping point research is a lack of data, says Knutti. In fact, climatologist Latif comes to the conclusion that the data situation has continuously improved since the use of drift buoys (ARGO floats) in 2000 and well-placed current observatories since 1995. But observing the ocean is complex and expensive. The ice around the polar ice caps is often observed using satellites. Studies also rely on sea temperatures. In order to combine the data, supercomputers with high computing power are needed.

Ice melting is already underway in West Antarctica and Greenland

Climate researchers largely agree that both the Greenland ice sheet in the north and West Antarctica in the south of the world are considered critical regions. Because as the atmosphere warms, the world’s oceans also become warmer. This leads to the melting of the foothills of the glaciers in West Antarctica that extend into the sea, the ice shelves.

Only recently, a British study came to the conclusion that part of the ice shelf in West Antarctica, the Amundsen Sea, has already reached the tipping point. The PIK also writes that tipping may have already become unavoidable for a glacier in the Amundsen Sea, the Thwaites Glacier. Because once the protective shield of ice shelves is gone, the inland glacier also comes into contact with warmer seas and melts.

We will only recognize tipping when it happens

But it is estimated that it would take at least 500 to 13,000 years for a tipping to occur. These results are very difficult to understand for human time periods, emphasizes Hermann Lotze-Campen, head of the climate resilience research department at PIK. That’s why it’s important to understand: “You won’t be able to say exactly in advance when the tipping point will be reached, but only afterwards!” But one thing is clear: “With every tenth of a degree, the probability that one or more of these tipping points will occur increases.” And averting that is extremely important. Because, as Knutti emphasizes: “It’s like the coffee cup, even if we don’t know when it will fall. We know what happens then: it breaks.”

Consequences of tipping

If the West Antarctic ice sheet disappears completely as a result of this process, the so-called ice-albedo feedback occurs: If there is less or no white snow and no bright ice, less sunlight is reflected and the dark surface underneath absorbs more solar heat. This increases ice melting, in addition to warming caused by man-made greenhouse gases.

The Intergovernmental Panel on Climate Change has concluded that melting of the ice sheet in West Antarctica would cause global sea levels to rise by more than three meters. If all of Greenland’s ice melts, it would be seven meters. And both tipping points, the one in Greenland and the one in West Antarctica, may already have been passed. The PIK defines it for global warming between 1.5 and three degrees.

“Society needs solutions”

But despite these results, according to Marotzke, the image should not emerge that the climate is now “getting out of control and the world is coming to an end.” Latif also emphasizes: “The world doesn’t end at 1.5 degrees.” Panic is not a good advisor. Because even if warming of 1.5 degrees were reached soon, every tenth of a degree above that should be avoided at all costs. Lotze-Campen emphasizes: “But I have the feeling that many people then perceive it as: We can’t do anything anymore anyway.”

For this reason, Latif also rejects disaster communication. As early as 1986, the cover of “Spiegel” showed half of Cologne Cathedral submerged in the rising sea. Caption: “The climate catastrophe”. And nothing has happened since then.

The authors of the “Global Tipping Point Report” also emphasize once again that politics, research and society must now act together. In the best case scenario, this could set in motion further positive levers to tip the scale. It is precisely the uncertainty surrounding the question of when exactly the tipping will occur that demands this.

Latif emphasizes: “It’s like when you’re driving on the highway in thick fog and there’s a traffic jam somewhere in front of you that you don’t know the end of. Then you don’t just rush off like there’s no tomorrow. ” Knutti says research into tipping points in the Earth system is crucial; without it we wouldn’t be where we are today. But what society needs are solutions.