By Renata Nagai
What stories can the oceans tell us?
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“Live in the present, plan for the future and forget the past: what is past is past.” How often do we not come across this type of advice (especially in advertisements)? We live in a society that lives in the present, looks to the immediate future, and ignores the past. However, when we encounter a new situation, it is the sum of our experiences that shapes our response and makes us adaptable. Climatologists apply the same logic to improve our ability to predict, respond, and adapt to global climate changes that are expected in the next eighty years: looking at past climates. But where is this information stored and how can it be accessed?
Just as our personal memories are not only in one part of the brain, climate files are stored in different places in the geological record – they are in the growth rings of trees, in the layers of ice, in the polar caps and in the mountains, in the deposited ones Sediments. in the deep ocean. Each of these files represents an isolated point in space with latitude and longitude and stores information about different environmental conditions and in different time slices. Until recently, timing and getting data from these files was a major challenge. Thanks to technological and analytical advances, we can now reliably determine the time of climatic events and determine how hot or cold the temperature of the planet was.
For the past decade, science has tried to develop statistical tools that can be used to unify climate memories from different sources. As if each record were a pyramidal cell containing certain pieces of climate memory, and the connection between these files formed a kind of neural network that allowed scientists to access the climate response to natural or man-made changes on a global scale. These new syntheses look at specific moments in the past: the recent past before the industrial revolution and the past past millions of years ago when the concentration of CO2 in the atmosphere was similar to that projected by the Intergovernmental Panel on Climate Change (IPCC) for the year 2100.
For example, recent global syntheses suggest that climatic events that occurred in the past and were recognized as global effects, such as the Little Ice Age and the Medieval Warm Period, were likely to have regional, greater effects on the northern hemisphere. Since the industrial revolution, however, an increase in the global average temperature has been recorded in all climate archives, which only increases the role of humans in climate change.
However, it is curious to note that if, on the one hand, we make progress in understanding the effects of future climate change at the global level, on the other hand, we find that we still do not understand well these effects on smaller regional regions and local spatial scales. For example, in the last week of February 2021, a paper published in Nature Geoscience won the media by reporting that global warming has fueled the weakening of the South Atlantic circulation in unprecedented ways over the past thousand years, which can lead to instability in the entire climate system.
What does this mean for the temperature of the Atlantic waters that bathe the Brazilian continental margin? Knowing that sea surface temperature affects rainfall patterns on the South American continent and the diversity of fish species of commercial interest, what are the consequences of these changes for our own food security? The answer to these questions could lie in memories of the climate stored in marine sediments. And just as our memories define our understanding of the world and help us predict what is to come, climatic memories can help us understand how the planet responded to changes in the past, and thus help us see the future more clearly.
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Renata Nagai is an oceanographer and professor at the Federal University of Paraná.
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