Kategorie: News
Highest water temperature for 400 years
Never in the past 400 years has the sea around the Great Barrier Reef been as warm as it is this year. A new study identifies human influences as the primary factor for the warming: "If the situation does not change, we will probably soon witness the demise of one of the great natural wonders of the world," says one of the study authors.
It was the fifth coral bleaching in just eight years, which began in Australia at the start of the year. This is catastrophic for the coral populations of the Great Barrier Reef, as they repel the colourful algae with which they otherwise live together in symbiosis. The result: the corals not only bleach, they also lose the energy suppliers that are often vital for them and subsequently die.
According to climate researcher Benjamin Henley from the University of Melbourne, the main reason for the renewed coral bleaching in Australia was the warmer-than-average seawater. From January to March, the water temperatures off the coast of Australia were higher than in the same period over the past 400 years.
The study shows that there was a steady increase from 1960 to 2024: an average warming of 0.12 degrees per decade was measured in the period from January to March. "The coral bleaching events of recent years were extreme and unprecedented, even over such a long period of 400 years," the climate researcher told journalists on Tuesday. Together with a team, Henley reconstructed the long-term changes in water temperatures around the Great Barrier Reef. To do this, the researchers used temperature data from the past and samples from particularly old coral skeletons. "Based on the nature of the skeletons, we were able to gain new insights into the sea temperature hundreds of years ago."
Humans are mainly responsible
It is obvious that humans are primarily responsible for the rising heat in the sea off Australia's coasts. According to Henley, the data from the study, which the team is currently presenting in the scientific journal "Nature Climate Change", is clear evidence of this. Before the 20th century, water temperatures were still largely stable. Only from 1960 onwards were the researchers able to observe a steady rise, which they attribute to man-made global warming.
Nevertheless, as the researchers themselves point out, there are also uncertainties in the reconstructed temperature data from before 1900: some of the chemical components in the corals that were used to model the temperatures may also have been influenced by other variables such as the salinity of the water. However, additional sampling of coral cores from the region could eliminate these uncertainties in the future.
Corals cannot cope with rising temperatures
The fact that the corals are not coping with the rising temperatures is also shown by the number of coral bleaching events to date. The first time such an event was observed was in 1980 - since then it has occurred more and more frequently. The research team was also able to use the data to show that in the years of the last coral bleaching events (2016, 2017, 2020, 2022 and 2024), it was significantly warmer on average in the months of January to March than in any year of the reconstruction before 1900.
Global problem
However, it is not only the corals of the Great Barrier Reef that are increasingly suffering from rising temperatures. The researchers estimate that 70 to 90 per cent of the world's corals could be lost - even if future climate protection efforts are effective and global warming is reduced to 1.5 degrees.
Should this actually happen, the consequences for the environment would be severe. "It is estimated that up to one million different animal species live on and around coral reefs worldwide. And around half of these are still completely unknown," says Hoegh-Guldberg.
In addition, the large-scale death of coral reefs would also have economic consequences - in Australia alone, tourists visiting the Great Barrier Reef bring several million dollars into the country every year. Coral reefs also generate economic income in other countries and are essential for some people to earn a living.
According to the research team, it is therefore all the more important to drive forward climate protection measures at a global level and, above all, to reduce the amount of greenhouse gases emitted in order to save at least some of the coral species from extinction. "Every fraction of a degree by which we can reduce global warming is important and reduces the risks to the world's coral reefs," says Henley.