FunNature & AnimalHuman influence on global droughts dates back a century,...

Human influence on global droughts dates back a century, according to NASA

The dangerous thermal rise that we are experiencing on planet Earth has consequences: the disappearance of animal and plant species, the destruction of glaciers, the rise in sea level … and also, of course, desertification.

Man-made greenhouse gases and atmospheric particles are the main cause of these phenomena, including the risk of global drought.

NASA has only been studying soil moisture since space 1980. But now, for the first time, its science team has linked human activities to drought patterns around the world.

And how did you get it? The clues were hidden in maps of the oldest trees on Earth , in their inner layers.

The tree rings have made it possible to obtain historical measurements of rainfall and temperature and compare them with modern measurements of soil moisture based on satellite data. The thickness of the tree rings indicates wet and dry years throughout their lifespan, providing an ancient record to supplement written and recorded data.

Thus, we have been able to find the “footprints” that show that greenhouse gases have been influencing the risk of drought since the beginning of the 20th century.

The predictions were correct

Models already predicted this human footprint affecting a global pattern of regional drying and wetting characteristic of the climate response to greenhouse gases, and that this presence should be detectable from the early 1900s, and increase over time as as emissions increase.

Indeed. Combining observational satellite data from 1980 along with the plant history present in the tree rings, the researchers verified that the predictions were correct: desertification matched the human footprint of the early 20th century.

They also calibrated their data against climate models that work with atmospheric conditions similar to those of 1850, before the Industrial Revolution increased greenhouse gases and air pollution.

This study is the first to provide historical evidence linking man-made emissions and drought at near-global scales , lending credibility to the models that predicted such a connection.

We have growing evidence of human influence on climate change, and more compelling are the reasons for governments to implement an action plan corresponding to the severity of the situation: we should not allow the global temperature to rise more than 1, 5ºC if we do not want to face a profound planetary transformation that could endanger species, cities or our own life, as we know it.

As if that weren’t enough, according to new research, this greenhouse gas fingerprint is likely to grow stronger in the coming decades.

The story briefly changed between 1950 and 1975, as the atmosphere became cooler and more humid. The team believes this was due to aerosols, or particles in the atmosphere. Before the passage of air quality legislation, the industry expelled large amounts of smoke, soot, sulfur dioxide and other particles that researchers believe blocked sunlight and counteracted the effects of warming greenhouse gases during this period. However, aerosols are more difficult to model than greenhouse gases , so while they are the most likely culprits, the team cautioned that more research is needed to establish a definitive link.

Marvel, K., BI Cook, CJW Bonfils, PJ Durack, JE Smerdon, and AP Williams, 2019: Twentieth-century hydroclimate changes consistent with human influence. Nature, 569, no. 7754, 59-65, doi: 10.1038 / s41586-019-1149-8.

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