Even if the Earth did not warm further, coral reefs would continue to die until they no longer existed “on a meaningful scale.” This means that the first “tipping point” for the climate has been reached, researchers write in the second extensive one Global Tipping Points Report that appeared on Monday.
According to the report, if global warming continues, there is a chance of even more tipping points, such as the death of rainforest in the Amazon region and the halt of the Atlantic Gulf Stream.
Scientists speak of a tipping point, or tipping pointwhen a system changes relatively quickly to a new state, as a result of conditions that have gradually changed over a longer period of time. There has been debate among scientists for some time whether such tipping points exist for the warming climate. According to the report’s authors, the rapid decline of coral is the first tangible example on a global scale.
Since 2023, coral reefs around the world have been bleaching due to higher water temperatures. This is the fourth bleaching wave ever identified and hitting 84 percent of all reefs. Bleaching is a defensive mechanism against long-term heat stress, but can also lead to the death of the coral in the long term. The third wave lasted from 2014 to 2017, affected 68 percent of reefs and led to major coral mortality.
Dying rainforest
The “vast reefs as we know them” will continue to die in the current climate until only “small refuges” remain, the researchers write. The coral that is still alive can only be saved if global warming can be reversed in the short term. Previous research estimated that the coral would reach a tipping point in a climate that is on average 1.2 degrees warmer than before the industrial age. The Earth is now structurally above that.
The report points to more possible tipping points. The Amazon forest could die “on a large scale” with just 1.5 degrees of warming. That limit is even lower than established in previous research. The halt of the Atlantic Gulf Stream, which carries warm sea water to the Northern Hemisphere, is a possibility from 2 degrees of warming onwards. That could lead to “much harsher winters” in northwestern Europe.
The report, written by 160 scientists from 87 different institutes from 23 countries, also identifies positive tipping points. Renewable energy generation is growing, as are concerns about climate change. “Even small numbers could overturn the majority,” the accompanying press release states.
On Monday, climate ministers and negotiators will meet in Belém, in the middle of the Brazilian Amazon rainforest, in preparation for the COP30 climate conference in November. It Global Tipping Points Reportwhich is released on the same day, calls on policymakers to take “urgent action.”
Reticent about risks
It is not self-evident that the report will be discussed in Belém, says co-author Manjana Milkoreit of the University of Oslo, at the presentation. The organization “has yet to formally integrate tipping point risks into their work during the COP.” Tipping points have not yet occupied a central place in the authoritative IPCC climate reports.
Max Rietkerk, professor of spatial ecology at Utrecht University, is therefore cautious when it comes to the risk of large-scale tipping points. “We think that in most cases it is really much more complex than there being two states with one tipping point in between,” he says. Since the 1990s, Rietkerk has been conducting research into savannahs that are turning into deserts and is proud of this at the cradle of the current research into tipping points, together with Wageningen ecologist Marten Scheffer.
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Rietkerk recognizes that tipping points exist in small ecosystems, such as clear shallow fens that become completely cloudy in a short time due to algae growth. But he believes this is rare in larger complex systems. In his research into overgrazing of savannas in the African Sahel, he saw that there are many stable intermediate forms between savanna and desert.
Rietkerk expects the same for the tropical rainforest in the Amazon. “It will not be the case that the entire Amazon forest will suddenly turn into savannas. All kinds of intermediate forms are possible in which both savannas and tropical forest occur within one spatial domain.”
The tipping point for coral reefs will not be “one point in time,” acknowledges Melanie McField, a researcher at the Global Tipping Points Report is involved. In the Caribbean, where she has been researching the reefs for thirty years, she sees the change taking place with her own eyes. “It happens all over the world when temperatures reach these thresholds,” says McField. “The temperature increase may differ slightly on certain reefs due to currents, there are delays, but we are in the zone in terms of temperature where it will happen. And it is already starting to happen.”
Bleached coral off Bonaire in 2023.
Photo Science Photo Library
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