Tree Rings Confirmed Climate Change
A study of annual rings on tree sections over the past 600 years has shown that extreme climate change began in the middle of the last century. The results are available in the journal Proceedings of the National Academy of Sciences.
Annual tree rings are a natural "document" that tells about the climate on the planet in a particular period. Working on the creation of the South American drought Atlas (SADA), scientists analyzed how the humidity of the soil in which trees grow has changed over the past six centuries.
It turned out that until the 1930s, droughts in South America were repeated with a certain frequency, then the intervals between dry periods increased, and since the 1960s, large-scale droughts were regularly observed once a decade. At the same time, the climate began to change in the direction of warming.
The new edition of SADA covers climate change in Argentina, Chile, Uruguay, Paraguay, most of Bolivia, southern Brazil, and Peru using data collected from 286 tree sections. The data obtained are supported by historical archival records.
According to the first author of the article, paleoclimatologist Mariano Morales of the National Research Council for science and technology of Argentina, prolonged droughts in recent decades have led to a difficult situation in agriculture in these and neighboring countries, and today the situation is such that many state food systems are at risk of collapse.
The authors note that extreme climate changes in time are associated with the activation of human activity in the region, although it is not possible to write off everything only on the anthropogenic factor.
"Our Atlas alone does not provide evidence of how much the observed changes are related to natural climate variability or warming caused by human activity," Morales says.
"We do not want to attribute all climate changes to humans indiscriminately. Many natural variability factors can mimic human impact," supports another author of the study, paleoclimatologist Edward cook (Edward Cook) from Columbia University.
Interestingly, the picture is not the same across the continent: while parts of Argentina and Chile experienced one of the worst droughts in history, the South-Eastern part of South America experienced abnormally wet conditions.
And it is more likely that the leading role still belonged to natural causes, among which the researchers identify three main ones: cyclical shifts in sea surface temperatures over the Pacific ocean and the Atlantic; changes in the belt of westerly winds around Antarctica, called the southern ring mode; and the phenomenon of Hadley cells, in which atmospheric circulation transfers warm and humid air from the equator to the poles, reducing the latitudinal temperature gradient.
All these phenomena are amplified against the background of global warming associated with anthropogenic greenhouse gas emissions.
"This is consistent with the idea that both wet and dry anomalies increase with global warming," said climate scientist Jason Smerdon of Columbia University, who also took part in the study.
Scientists hope that their results will allow us to better understand the relationship between natural and anthropogenic factors and predict long-term climate change.