2023-08-17 20:00:28
A controversy has agitated paleontologists for several decades: the massive extinction of megafauna at the end of the Pleistocene geological epoch, 13,000 years ago, when nearly 70 % species of large mammals have disappeared, was it caused by human activity or by climate change? To this thorny question, a study published Thursday, August 17 in Science offers a half-hearted answer.
As the authors of the article note, California experienced an increase in temperatures as early as 17,000 BC, which caused drought and aridity. In this unstable climate, human activity has however favored the appearance of numerous forest fires which have profoundly upset the local ecosystem. To conduct this research, the remains of 172 specimens of eight different species, ranging from bison antiquus to giant sloths, were studied at the fossil bed of La Brea Ranchin Southern California.
In a few millennia, the climate of Southern California has experienced strong variations. Sea surface temperature increased by 7°C to 8°C between 17,000 and 12,900 BCE, while ambient air temperature increased by 5.6°C between 14 000 and 13,000 BCE. This phenomenon has caused a drought in the region, which the researchers attribute to an increase in evapotranspiration.
Unstable environment
These upheavals then profoundly modify the ecosystem. The oaks and junipers that populated the region give way to a more herbaceous and dry landscape. In short, the fauna is adapting to this new ecology of the place: the researchers note a slight increase in the presence of pines and bushes, which are more resistant to arid temperatures.
These climatic changes lead to a tipping point: hitherto gradual, these fluctuations increased sharply between 13,200 and 12,900 years before our era. The fires then intensified, to such an extent that an accumulation of charcoal, taken from the sediments, was observed. Its presence is multiplied by thirty in a few hundred years. This proliferation of fires is not external to the human presence in the area. Taken as an example, the hunting of herbivores leads to an accumulation of many flammable plant fuels since fewer animals feed on these plants. “Climate change could therefore have […] pushed the ecosystem to an ecological state where human activities can trigger large-scale fires », so says the study.
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