Degradation of ancient rock art in Indonesia may be accelerating due to climate change.

The Maros-Pangkep karst, a cave complex in Indonesia, contains Palaeolithic paintings that are between 20,000 and 45,000 years old, including one of the oldest known hand stencils in the world. Anecdotal reports in recent decades suggest that the paintings have been degrading at an accelerated rate. To investigate, at Griffith University in Australia and her colleagues analysed flakes of rock at 11 cave sites in Maros-Pangkep.

They found a high level of sulphur in the rock at all 11 sites, as well as a build-up of calcium sulphate and sodium chloride salts in rock at three of the sites. The salts occur naturally in the rock and form crystals in a process called salt efflorescence, which often happens in wet environments.

“As water washes through the stone or over the top of the stone, it picks these things up, and then when the water dries off and the solution dries off, it drops out the salts,” says Huntley.

The resulting crystals expand and contract with temperature and humidity, exerting a mechanical pressure on the rock that can lead it to flake and fragment, damaging any art painted on the surface.

This finding indicates that salt-driven rock art degradation is widespread in Maros-Pangkep. “It’s a monsoon climate, so you have recharge of water and then you have the dry season, so just naturally this is a perfect environment for salts to form,” says Huntley.

The researchers suggest that the increasing severity and frequency of El Niño-induced droughts – a result of climate change that has led to more consecutive dry days and higher temperatures – as well as the moisture during the monsoon season have provided ideal conditions to accelerate the degradation of the rock paintings.

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A climate model can now reliably predict the strength of the Asian summer monsoon – and tropical cyclone activity associated with it – more than one year ahead of time, which could enable government agencies to make preparations for damaging weather events.

Yuhei Takaya at the Japan Meteorological Agency and his colleagues have developed a climate prediction system that takes into account both historical and up-to-date meteorological measurements to simulate atmospheric changes and temperatures on land and in the ocean. The key to its long-range forecasting is the ability to predict when an El Niño-Southern Oscillation will occur.

“When an El Niño occurs, the Indian Ocean warms during the fall to winter and this persists in the next summer,” says Takaya. The resulting warm conditions in the Indian Ocean have a significant effect on the Asian summer monsoon, he says.

The team’s model was tested using oceanic and climate data gathered between 1980 and 2016. Given meteorological data for a particular year, the model predicts what will happen the following summer, including the sea surface temperature, regional rainfall and a weather pattern known as the western North Pacific monsoon.

“In summer, we have droughts or floods associated with this variability,” says Takaya.

The climate model predicted the strength of the monsoon a year ahead, measuring how linear the correlation is between real and predicted weather patterns with a value of 0.5, where a score of 1 indicates a perfect correlation. It was more accurate at predicting temperatures over South-East Asia than predicting monsoon strength, with a score of 0.75.

Existing climate models used by meteorological centres are usually able to predict weather patterns six months in advance, says Takaya.

Extreme weather events such as heat waves or flooding have significant socio-economic impacts, particularly given that Asia is the world’s most populous continent, says Takaya. “If we can predict the temperature or the precipitation, we can better prepare for these extreme events,” he says.

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If murals or street art are defaced with graffiti, restoring them can be a challenge. But now there is a hydrogel that can remove a layer of graffiti within minutes, without altering the work underneath – even when the art and overlying graffiti use the same type of paint.

Michele Baglioni at the University of Florence in Italy and his colleagues have developed a system that allows cleaning agents to remove just the top layer of paint, which is only a few microns thick.

The team’s technology comprises a cleaning fluid held in a hydrogel, a material that consists of long molecules forming a network that is hydrophilic, meaning it has an affinity for water.

Unlike other gels – such as jam and hair gel – which can spread, change their shape and leave residues in their wake, the hydrogel the team used is made from a network of polymers with a fixed shape.

“The strength of these kind of gels is that they do not leave residues on the surface they clean, which is something that is different from the majority of gels which are used also in [art] conservation,” says Baglioni.

The hydrogel allows only small amounts of cleaning fluid to seep out when it is applied to a painted surface. “This helps in controlling very finely the cleaning action,” says Baglioni.

The cleaning fluid consists mainly of water, with nano-sized droplets of organic solvents as well as detergent-like surfactant materials.

The solvents are targeted at three classes of polymers that are commonly used as paint binders: acrylic, vinyl and alkyd polymers. The solvents cause the paint to swell, allowing it to be removed from a surface.

Depending on the thickness of the paint and its age, graffiti may be ready to be removed just a few seconds or a few minutes after the hydrogel is applied. But each removal operation is unique, and the cleaning material must first be tested on a small area of the graffiti to establish the optimal application time.

“You also have to take into account that sometimes repeated, shorter applications are better than one single long application,” says Baglioni.

The research was presented today at a virtual .