“With what I can do, what’s the most important question I can answer?” It was from this reflection that Vinícius Ribau Mendes began to study the impacts of climate change on rainfall in South America. Analyzing sediments taken from the ocean such as sand and mud, the geologist investigates the Earth’s past to understand the present and think of ways to prepare us for the future.
In order to validate predictions and understand how changes in ocean currents affect rainfall, Mendes and his team are reconstructing a picture that has repeated itself twice over the last 20,000 years: the collapse of one of the most energetic sets of ocean currents. of the world.
The project was born at the Federal University of São Paulo, where the researcher teaches, but it is already an international enterprise, with collaborations of scientists from the German universities UniHeidelberg and UniBremen, in addition to USP and the National Institute for Space Research.
More than necessary, research is urgent. Brazil faces the third water crisis in twenty years and the biggest ever recorded in 91 years. In December 2021, more than 95 scientists from national and international institutions signed an opinion article in the journal “Nature” regarding the need for investments in research, soil monitoring and new renewable energy sources. Otherwise, future water crises could compromise the country’s food security and make energy even more expensive.
It is towards this scenario that we are heading if – or very likely, when – the Atlantic Meridional Upturn Cell collapses again. Responsible for the distribution of heat between the northern and southern hemispheres, these currents directly influence summer rainfall in South America. Given the marked reduction in the intensity of these currents, the possibility of collapse in this century is not unrealistic.
“The ocean and the atmosphere control the climate of the continent. This balanced relationship guarantees a rainy summer and a dry winter, as we are used to”, explains Mendes. “A drastic change in rainfall can cause social chaos, impacting agriculture, energy production and water supply in large cities.”
Geological records spanning thousands of years reveal that about 13,000 and 18,000 years ago there were two moments when these same currents stopped. This information is stored in what the geologist calls the “Earth Diary”: marine cores removed more than a thousand meters deep to collect sediments that store records of both sea and continent variations. “By means of layers of sediment deposited continuously over time, we know, with enormous precision, the variations in the volume of rain and in the temperature of the ocean from thousands of years ago”, says the researcher. “Knowing the consequences generated by the collapse of these currents in the past rainfall cycle, we can feed computer climate models and generate better predictions for the future.”
The objective is to build a map of rainfall in South America in these two periods and, thus, make an analogy with the future, if these currents stop again. “Will the rain increase or decrease? It depends. In some places the reservoirs can dry up, while in others they can overflow. Today we see the expansion of agriculture in regions that could be significantly drier in a few decades, so we need planning”, he justifies. Mendes.
The method used in the project is innovative and promises to change the way the area investigates these historical records. The new methodology for measuring precipitation variations in a marine core is based on luminescence, the ability of some materials to emit light when stimulated. This tool allows you to measure characteristics of quartz grains that tell their story on the continent, such as the time they were buried. Since rains and rivers carry these grains to the ocean, their history is directly related to rainfall variations.
This method has shown some advantages over existing ones: it is relatively simple and inexpensive, and it seems that it is more sensitive to rainfall variations. “In studies on the climate of the past, the more techniques we use, the better. It is worth remembering that it is not about replacing what already exists, but complementing it with new information.” To ensure that the project arrives at more accurate results, the same cores are also analyzed using well-established methodologies, such as the technique that uses hydrogen isotopes recovered from organic matter coming from the continent – from leaves, for example.
“Science does not necessarily have to be disruptive and bring up a question that has never been asked. There are important questions that have not yet been answered”, concludes the scientist.
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Pedro Lira is a journalist and social media at Instituto Serrapilheira.
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