The wildfire is getting worse. Parts of the United States, say the scientists, is experiencing wildfires three times more often — and four times larger — than in the past 20 years. This summer alone, smoke from wildfires in Canada has turned the skies of North America unearthly, “flames of fire” have been seen in the Mojave Desert and raging fires in Maui have led to disaster.
Records of the distant past can reveal what once caused increased fire activity and what might happen as a result. In a new study published Thursday in the journal Science, a group of paleontologists who analyzed the fossil record at the La Brea Tar Pits, a popular excavation site in Southern California, concluded that the disappearance of sabertooth cats, dire wolves and other large mammals in this region about 13,000 years ago. is associated with rising temperatures and increased human-induced fire activity.
“We point to humans as the main cause of the tipping point,” said Robin O’Keefe, an evolutionary biologist at Marshall University. “What happened in La Brea, is it happening? Well, that’s a very good question – and I think we should figure it out.”
Earth has seen five mass extinction events so far; some scientists have argued that the disappearance of large mammals at the end of the last ice age was the beginning of the sixth. “This is the largest extinction event since an asteroid hit Earth and wiped out all the dinosaurs,” said Emily Lindsey, a paleoecologist at the La Brea Tar Pits and Museum and author of the new study, which added that the loss may represent “the first pulse” in the sixth mass extinction.
Until now, researchers have not been able to determine exactly what caused the disappearance of these animals. The La Brea Tar Pits are one of the few sites in the world with a large enough fossil record for scientists to investigate the question. The pits, which are still active on 13 hectares of land, are filled with bubbling black asphalt that seeped to the surface from within the Earth. Ancient animals stuck in this goo died of exhaustion or predation, and the asphalt fossilized and preserved their remains. “And that’s still happening today,” said Dr. O’Keefe. “You can walk out of La Brea and see a squirrel stuck in tar — I’ve seen it with my own eyes.”
That’s bad luck for animals, but good fortune for scientists: La Brea now boasts the region’s continuous fossil record that stretches back 55,000 years. Examined by Dr. O’Keefe and his team found fossils for eight large mammal species — including the sabertooth cat, American lion and Camelops hesternus, an ancient camel — that lived between 10,000 and 15,600 years ago. Using radiocarbon dating, the team determined that seven of these species went extinct about 13,000 years ago.
To find out why, the researchers analyzed climate, pollen and fire records in the region along with continental human population growth during that time. They found that human occupation began to increase rapidly at the same time that Southern California entered a period of extreme drought and warming. Severe fires occurred, and the crops, once rich in juniper and oak trees, were eventually replaced by grasses and chaparral shrubs.
“What we see is that you have a 400-year long period of very high fires,” said Regan Dunn, a paleobotanist at the La Brea Tar Pits and Museum and an author of the new paper. “And at the end of that time, you’re in a different ecosystem and all the megafauna are gone.”
Described by Dr. O’Keefe describes the conditions as a perfect storm: “You have a bunch of different factors that multiply each other and give you a big increase in fires,” he said. Using a model similar to those that predict stock market trends, the scientists determined that humans were the primary drivers of these fires, both through direct ignition and through the removal of herbivores. , allowing the burning underbrush to spread freely. Climate changes have made it worse, setting the stage for species extinction.
Dr. emphasized Dunn said this pattern cannot account for the dramatic disappearance of large mammals elsewhere in the world at the end of the last ice age. “But to understand the global event, you really have to look at a regional scale,” he said. He added that what happened in Southern California 13,000 years ago “has striking parallels to the environmental and biodiversity crises we face today.”
Climate records during the ice age extinction indicate a warming of about 10 degrees Fahrenheit within 1,000 years, Dr. Dunn, whereas today, temperatures in Southern California have risen about 5.4 degrees Fahrenheit in the past century alone. An increase in fire activity after the arrival of people was also recorded in other locations, including Australiawhere fires have recently taken their own toll on the country’s unique wildlife.
“This study is a good example of how we can use the past to describe the future,” Anthony Barnosky, a paleoecologist at the University of California, Berkeley, who was not involved in the work, said in an email. “And what we’re seeing now — increasing human pressures combined with and actually causing climate change — is like this lesson from the past on steroids.” Dr. added. Barnosky that these changes are not gradual, but fast and catastrophic.
Researchers have noted that it is difficult to match current events with those in the fossil record. “Many of the most threatened wildlife today are the remaining large-bodied mammals that did not disappear” at the end of the last ice age, Dr. Lindsey. But, he added, “because we caused it, we have the power to stop it.”