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What did they do: The researchers, led by Kate Marvel, NASA climatologist, and Benjamin Cook, tree ring specialist at Columbia University, have used large drought atlases in North America, Europe and the Mediterranean, Mexico in Asia, Australia and New Zealand. These drought databases date back to 1400 AD and, in some cases, 1100 AD, based on ring data.
- For this study, researchers constructed a unified global drought atlas, including data from each of the regional analyzes.
- Specifically, they examined atlas records of a measure of drought known as the severity index of the Palmer Drought, which indicates the variability of soil moisture. They used changes in soil moisture to understand the evolution of this metric of drought in the twentieth and twenty-first centuries and to estimate the forced natural variability and internal climate before the industrial revolution.
- For the study, the researchers sought to detect the fingerprint or expected pattern of human-induced drought trends globally, compared to sources of internal variability, such as oceanic climate cycles such as El Niño.
- They used computer modeling to get an idea of the global drought they should expect in a warming world.
"Basically, this article asked the question: to what extent do the observations correspond to those expected by the models during the twentieth century, in terms of hydroclimate? And the answer to that question is that they really fit very well. "
– Co-author of the study Benjamin Cooke in an interview with Axios
What they found: The study found that human emissions of greenhouse gases clearly influence global drought trends from 1900 to 1949, but that emissions of tiny particles called aerosols from coal-fired power plants, cars and mills reduced this signal from 1950 to 1975.
- Since the US Clean Air Act and other air quality laws have reduced this pollution, fingerprints of greenhouse gas emissions have resurfaced, but they are not yet completely separated from the background noise caused by the natural variability of the climate.
- Researchers expect the signal of climate change on global drought trends to become clearer in the coming years, drying up many regions of the world with potentially serious consequences for society.
- The researchers found that parts of North America, Central America, Eurasia and the Mediterranean have become drier, while other regions, such as the United States, have become more dry. India, have become wetter over time.
"What we call the fingerprint in the document basically corresponds to the expected pattern, as if you were looking for fingerprints on a crime scene, you were looking for a particular pattern," Marvel tells Axios.
What they say:
"… the essential physics is pretty clear," says Michael Wehner, a climatologist at the Lawrence Livermore National Laboratory, who did not take part in the new research. "Man-induced temperature increases will lead to drier soils due to an increase in evapotranspiration. The impact on ecosystems and agriculture is clearly detrimental." and raises even more concerns about human interference in the climate system. "
The study is not without its critics, however.
- Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research in Boulder, Colorado, tells Axios that his methods and conclusions are flawed, in part because the computer models used fail to accurately capture one. the main causes of natural climate variability, El Niño and La Niña.
- Trenberth also criticized the research questions pursued in the study, stating that it would have been more appropriate to examine how droughts caused by natural variability have become more intense, more durable and faster to s & # 39; install.
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