Some of the world’s earliest known rock art is being destroyed by climate change in the tropics, researchers have warned.
Cave paintings dated to 44,000 years ago, and which are the oldest surviving depictions of hunting and supernatural beings, are "flaking off walls" due to chemical changes caused by rising temperatures.
The painted limestone cave surfaces in southern Sulawesi in Indonesia are being destroyed by chemical processes including salt crystallisation.
These changes are destroying Pleistocene-aged rock art panels at 11 limestone cave sites in Maros-Pangkep, the researchers said.
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Dr Jillian Huntley, from the Griffith Centre for Social and Cultural Research, said she was shocked by the extent of salt weathering on the painted limestone cave surfaces in Sulawesi.
Dr Huntley said: "I was gobsmacked by how prevalent the destructive salt crystals and their chemistry were on the rock art panels, some of which we know to be more than 40,000 years old."
The effects of global warming can be up to three times higher in the tropics, the researchers said.
Dr Huntley said high temperatures and long stretches of consecutive dry days were combining with the retention of monsoonal rains in rice fields and aquaculture ponds to provide ideal conditions for stone decay.
She said: "Our analyses show that haloclasty [salt weathering] is not only chemically weakening the cave surfaces, the growth of salt crystals behind ancient rock art is causing it to flake off the walls – it is disappearing before our eyes.
"In my opinion, degradation of this incredible rock art is set to worsen the higher global temperatures climb.
"The challenges of climate change adaptation for the Indonesian Maritime Continent are complex.
"Understanding the mechanisms of rock art weathering is even more critical in this context. Some of the solutions of looming food insecurity such as the expansion of rice fields and aquaculture ponds can have unintended consequences.
"Holding surface water in these ways enhances humidity, prolonging the seasonal shrink and swell of geological salts, as well as leading to more mineral deposition. All of which leads to rock art degradation.
"We urgently need further rock art and conservation research to have the best chance of preserving the Pleistocene cave paintings of Indonesia."
I Made Geria, director of Indonesia's National Research Centre for Archaeology (ARKENAS), said: "The rock art of Maros-Pangkep provides crucial insight into the world of ancient Indonesia.
"Preserving this art for future generations requires the cooperation and long-term commitment of scientific research institutions, cultural heritage agencies, government authorities, and local communities.
"It also requires us to educate people in Indonesia – and throughout the world – about the urgent need to study and safeguard this irreplaceable evidence of past human civilisation."
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