Man-made global warming, caused by the burning of fossil fuels and uncontrolled emissions of greenhouse gases, has become the main factor in worsening droughts in California and the American West, according to a new study.

A team of scientists from UCLA and NOAA has found that while droughts of the last century were primarily caused by decreasing precipitation during natural cycles, an entirely different pattern emerged due to rising temperatures during this century.

Researchers determined that since 2000, human-caused warming has become the dominant force leading to even more severe drought in the western United States. In the case of the intense western drought of 2020 to 2022, scientists attributed 61% of its severity to high temperatures, and only 31% to reduced precipitation.

“For the same precipitation deficit, drought is much stronger today than it was in the 20th century, and it also lasts longer,” said Rong Fu, a UCLA climate researcher and co -author of the study. “This makes the drought more severe and widespread. »

She and her colleagues analyzed data from 1948 to the present in 11 Western states, from California to Colorado. They found that since 2000, human-caused warming has become not only the dominant factor in drought severity, but also in the expansion of drought-affected areas.

Looking at potential future scenarios, the researchers said climate models indicate that an extreme drought like 2020 to 2022 – an event that, without warming, would likely occur once in a thousand years – could occur once every 60 years. by the middle of this century, and potentially an event every six years by the end of the century.

The researchers, including scientists from NOAA’s National Integrated Drought Information System in Boulder, Colorado, wrote that human-caused warming has “ushered in an era of temperature-dominated droughts.”

Shasta Lake fell to low levels as drought conditions persisted in 2021, reducing water supplies across California.

(Brian van der Brug/Los Angeles Times)

“The degree of aridification and intensification of droughts in the region depends on the magnitude of anthropogenic warming,” the researchers write in the report. studypublished Wednesday in the journal Science Advances.

The scientists said their findings, which add to a growing body of research documenting the role of climate change in worsening droughts, highlight the urgent need to reduce emissions linked to global warming while also changing the water and drought management strategies to adapt to the new reality of heat-induced emissions. periods of drought.

They said the results indicate the West will become drier as climate change continues to drive global temperatures higher.

“The degree of drought and severity of the situation depends on our actions. Basically, we control the appearance of droughts in the future. This has not happened in human history,” Fu said. “Future droughts are mainly determined by ambient temperature and the amount of CO2 we emit. It is therefore above all a question of controlling CO2 emissions.

However, the prospects for reducing carbon dioxide emissions in the United States have darkened with the victory of Donald Trump in the presidential election. Trump has pledged to abandon climate initiatives and the Biden administration’s efforts to reduce emissions, and pledged to facilitate more oil and gas drilling.

Trump’s victory could mean closing a window of opportunity to avoid dangerous climate impacts “if we don’t fight back and redouble our efforts to reduce CO2 emissions,” Fu said.

“I am very concerned about the future of the Western United States, the United States as a whole, and the world, particularly because we are at a critical time to limit the catastrophic impacts of climate change,” Fu said. “However, history also shows that our action matters. We must not let the Trump administration decide our future and that of our children and grandchildren.”

The effects of increasing atmospheric CO2 concentrations have become increasingly apparent over the past decade.

Last year was by far the hottest year on record on a global scale. According to NOAAEarth’s average temperature was more than 2.4 degrees warmer than the pre-industrial average. The UN warned in a recent report that without greater action to stop emissions, the world could experience warming of up to 5.6 degrees by 2100, leading to “debilitating impacts on people, the planet and economies”.

With extreme heatpeople in the western United States experienced some of the driest conditions on record. California was ravaged by the three driest years on record from 2020 to 22.

Other scientists have also found that global warming has a major effect on worsening drought conditions.

Researchers using tree rings determined in a 2022 study that western North America was experiencing its driest 22-year period in 1,200 years. They found that this megadrought would not be as severe without global warming, an estimated 42% of its severity was attributable to higher temperatures.

Benjamin Cook, a climate scientist at NASA’s Goddard Institute for Space Studies and co-author of the megadrought study, said the latest study’s methods are robust and the results are similar, although He also said that there is considerable uncertainty in scientists’ future projections. used.

“Drought impacts become more pronounced with warming,” Cook said. “The more warming that occurs, the more we expect drying in this region. And that means more severe, more widespread and more frequent droughts.

Water levels were low in 2022 at Green Mountain Reservoir in Colorado.

(Gina Ferazzi/Los Angeles Times)

Warming contributes to drier conditions by increasing what scientists call evaporative demand. Higher temperatures improve the atmosphere’s ability to hold water vapor, thereby increasing the amounts of moisture that evaporate from the landscape. This makes the land drier and contributes to reduced river flows.

Experts say more intense droughts, accentuated by climate change, will require significant changes in agricultural water use because farms consume most of the water diverted and pumped in the West. about 70% has 80% depending on the region. Along the drought-stricken Colorado River, the federal government has recently funded programs that pay farmers for temporarily reduce water consumption in exchange for payments.

The average flow of the Colorado River, a major water source for seven states and northern Mexico, has declined by about 20 percent since 2000, and scientists have estimated that about half of that flow decline was due to caused by higher temperatures. These declines are expected to continue to worsen as temperatures rise.

The latest study is in-depth and adds to previous research documenting how human-caused warming is causing what scientists describe as: hot drought And aridification in the West, said Brad Udall, a climatologist at Colorado State University.

“They found, like all these other studies, that higher temperatures have been and will be a cause of more severe droughts as global warming occurs in the 21st century,” Udall said. “This means we need to plan for a warmer, drier future. »

Udall said Trump’s victory would likely mean rolling back the Biden administration’s historic climate initiatives and imposing a four-year pause in U.S. efforts to reduce greenhouse gas emissions to levels national and international.

“Unfortunately, the impacts will likely last much longer than four years,” Udall said. “All of this means that the worst outcomes envisioned by this study will be more likely. And, of course, all the other problems linked to climate change, such as increasing floods, monster hurricanes and deadly heat waves, will worsen at the same rate.

Udall said he found it particularly sad that Trump plans to freeze efforts to combat climate change at a time when the country has the science, technology, policy tools and people needed to find solutions.

“We know how to solve this problem,” Udall said. “Much of this activity will now be pushed aside in favor of an anti-science agenda that will further enrich the gigantic corporations that created this problem in the first place. »