The images of bison and deer and other more schematic ones captured by Upper Paleolithic artists, the oldest dating back 35,000 years, in the Altamira cave (Cantabria) will deteriorate in the coming years if protective measures are not taken in the face of rising outside temperatures and the resulting increase in the concentration of CO2 inside the cave, according to the forecasts of the scientists working on its conservation.
A mathematical model resulting from a study carried out by Spanish and French researchers has been revealed as an effective tool for the conservation of parietal rock art in the face of the threat of global warming, which adds to the risk already posed by visits to prehistoric sanctuaries.
More information
The work of the interdisciplinary team made up of scientists from the National Museum of Natural Sciences (MNCN), the Geological and Mining Institute (IGME) – both belonging to the Spanish National Research Council (CSIC) – and the universities of Alicante, Almería and the Centre for Space Studies of the Biosphere (CESBIO) in Toulouse aims to project future scenarios of a higher concentration of carbon dioxide (CO2) in the Altamira cave, a reflection of the increase in the same compound outside and the main cause of rising temperatures on Earth.
Bison from the Altamira caves in Cantabria.Wikipedia
For Roberto Ontañón, director of Caves of Cantabria and the Prehistory Museum of Santander“This model provides those of us who manage the conservation of rock art with a tool that goes beyond the capabilities of our measuring equipment; for example, to determine how many people can enter a cave without altering its environment.” Currently, visits to Altamira are restricted to five people per week, but it is very likely that in the near future this quota will be eliminated, in the same way as happens in other jewels of Paleolithic art, such as the cave of Lascaux in the French Dordogne.
Regarding the threat of global warming to the paintings and geological treasures in caves, Ontañón says that the increase in CO2 also causes the water that enters the cavities by filtration to become more corrosive due to greater acidification.
The painted hands in the Lascaux cave.Getty Images
The first measures that could be taken to protect the ochre and black of the bison and deer of Altamira should consist of “protecting the exterior and surroundings of the cave and not modifying the external soil, since this causes the lifting of particles that favour the dispersion of microorganisms towards the interior of the cave”, according to Sergio Sánchez Moral, researcher of the Geology department of the MNCN. Ontañón, for his part, adds the need to limit sunlight and the installation of antechambers “that make the caves deeper”. Because a medium-term solution is to “insulate the caves more”, he affirms.
Outside temperature
Global warming also poses a challenge to the natural process in underground cavities and galleries, where CO2 concentrations depend largely on environmental conditions outside. And the challenge is even greater when it comes to caves that preserve masterpieces of prehistoric art on their rock walls, since paintings are the most vulnerable forms of cave art to the risk of corrosion. In addition to Altamira, in the subsoil of the Cantabrian coast there are hidden caves with some of the most important parietal paintings from the Upper Palaeolithic, such as El Castillo, La Pasiega or Las Monedas, in Puente Viesgo, or El Pendo, a few kilometres from Santander.
“Between 1996 and 2012 we measured and collected data on the temperature and humidity of the cave’s exterior floor and compared them with data obtained on the temperature and CO2 concentration in the rooms and galleries of Altamira. Using this data and advanced techniques, CESBIO scientists have designed a mathematical model that predicts the dynamics of carbon dioxide concentration inside the cave,” explains Sergio Sánchez Moral.
The model also incorporates a series of data obtained from time series of satellite images, which has made it possible to simulate variations in the concentration of CO2 in what has been called the Sistine Chapel of Paleolithic Art under different climatic conditions and to compare the results with real data.
Other paintings at Lascaux.
According to Sánchez Moral, the study addresses not only the interrelation between climate, soil and rock and their impact on the environmental conditions of a cave that houses paintings created by artists thousands of years ago, but also the impact caused by human activities and the foreseeable deterioration that will result from global warming.
“This tool provides us with fundamental information about the interaction between the external and subterranean climate, which is the key to maintaining the environmental stability of the cavity and, therefore, to preserving the valuable cultural heritage it houses,” continues the researcher from the National Museum of Natural Sciences, who highlights the success of being able to explain a natural process through an abstract mathematical pattern.
The Spanish researchers took data on temperature and CO2 concentration during the years when Altamira was visited by up to a thousand people a day and compared them with the behaviour of these parameters in the cave in its natural state obtained in subsequent years. In this way, they were able to reconstruct the past and measure the impact of human activity in the cave, which was particularly intense during the period 1950-1970.
Soledad Cuezva, a geologist at the MNCN who participated in the study, confirms that the results obtained leave no room for doubt about the enormous impact of the high influx of visitors during that period of the last century, when outside temperatures were also lower. “This caused a large amount of CO2 to accumulate inside, favouring condensation processes on the roof and the subsequent corrosion of the rock that supports the paintings, which is why it was essential to take measures to reduce the impact that the visits were having,” says Cuezva.
This researcher adds another danger to the cave ecosystem due to the entry and dispersion of microorganisms that not only attack the paintings, but also “the spectacular mineralizations that some of them contain,” which are sometimes reflected in beautiful veins of color in the rock, which can be admired in caves such as El Castillo. According to this scientist, “this mathematical model tells us that there will not only be higher concentrations of CO2, but also an increase in the oscillation of maximums and minimums, which will cause greater instability and may result in an intensification, not only of the corrosion processes of the rock, but of mineral precipitation that covers the paintings.”
The study used a global modelling technique to reconstruct the past and its results allow for the establishment of measures to continue preserving Altamira’s cultural heritage and which will be applicable to other underground cavities, anticipating the climate changes that will foreseeably modify their environmental conditions.
Dynamic equations
The method of the work was based on the development of dynamic equations that control the temporal and spatial variability of the exchange flows of gases, energy and matter between the external environment and the underground environment. This approach has allowed the Toulouse scientists, led by mathematician Sylvain Mangiarotti, to design the model that simulates and analyses the interactions between these factors and takes into account both internal and external influences on the microclimate of the cave.
The algebraic formulation of the obtained models confirmed that the main drivers of the cave microclimate are the outside temperature, the soil-rock humidity and the human activity inside.
Visitors at the replica of the Altamira cave, in 2023.Alamy Stock Photo
Cuezva says that the environmental conditions of each cave are different and the model obtained is suitable for the predictions in Altamira, “but the method followed to achieve it is applicable to other underground cavities, so our work is having a great international impact in dealing with the same threats in other prehistoric sanctuaries.”
Researchers point out that cave paintings are, in general, the reason that arouses society’s interest in preserving cave ecosystems, but, beyond their cultural importance, caves are environments in which species adapted to very specific environmental conditions survive and which contain geological formations, speleothems such as stalactites and stalagmites, which allow us to glimpse the climate of the past. “Protecting both the biology and the geology of these spaces requires developing sustainable management practices,” concludes Cuezva.
All the culture that goes with you awaits you here.
Subscribe
Babelia
The latest literary releases analysed by the best critics in our weekly newsletter
RECEIVE IT
