Tall and resilient, the saguaros of the Sonoran Desert are finding it more difficult to reach maturity as higher temperatures exacerbate drought and leave a trail of young cactus carcasses.

A hotter, drier future awaits U.S. national parks, monuments, historic sites and memorials compared to the nation as a whole, based on the first analysis of climate change impacts across all 417 parks done by UC Berkeley and University of Wisconsin-Madison.

“The desert is becoming warmer,” said Don Swann, a biologist at Saguaro National Park. “We have seen an increase in temperature over the last century and a long-term drought over the past 25 years.”

The findings showed that temperatures in national parks increased at double the national rate, while rainfall decreased across more of the park sites over the past century.

Many national parks happen to be in extreme environments, such as deserts, glacial areas and high alpine settings, and are more vulnerable to the hotter and drier conditions that have already inflicted change on their ecosystems. This includes their small mammal and plant inhabitants that may be brought to extinction at the current rate of change.

It will only get worse with the current rate of greenhouse gas emissions, based on the study’s projections.

From Yellowstone National Park to Mesa Verde National Park, these unique natural and cultural sites set aside to be protected and “unimpaired for the enjoyment of future generations” will bear the brunt of human-caused climate change.

The country could not only lose these unique and irreplaceable ecosystems, but also the tourism revenue that goes hand in hand.

Across all of its locations, the National Park Service boosted more than 331 million visitors in 2017 that spent an estimated $18.2 billion in local regions during their visit, supporting the economy and jobs.

The Southwest will one of the hardest hit areas in terms of rainfall decline, according to the study, which can lead to intensified droughts and wildfires, on top of its natural arid climate.

The cactus-filled landscape of Saguaro National Park is just one of the 22 national parks, monuments, historic sites and memorials designated within Arizona’s borders – more than any other state.

“Once they are adults, saguaros can survive long-term droughts,” Swann said. “However, in the last 25 years, there has been a reduction of young saguaros surviving since they are unable to storage water and rely on wetter soils and cooler temperatures.”

The Grand Canyon is one of the few places on the planet where you are look down into the Earth’s history through millions of years,” park ranger Sharon Cawley said. “It’s gorgeous.”

The Grand Canyon was the nation’s second-most visited park in 2017, boosting about 6.25 million recreational visitors – the largest number recorded.

Along with tourists, poor air quality travels into national parks from outside its boundaries, threatening visitor’s health, scenery, ecosystems and even bank accounts.

Cawley described the park as “a little island” that is impacted and connected to its surroundings on a local, national and even global level.

Even in these sections of perceived untouched nature, the average ozone concentration in national parks is “statistically indistinguishable” from large metropolitan areas, such as Los Angeles, according to a 2018 study published in Science Advances.

Simply put, the number of “bad air days” with unhealthy ozone levels are the same in both cities and parks.

Ground-level ozone is a toxic gas that is formed through a reaction of primary pollutants in the presence of sunlight. These pollutants can be both natural through vegetation emissions and man-made by combustion of fossil fuels.

“The smog produced in Los Angeles blows across the Southwest and, in fact, is one of the major sources of visibility impact in the Grand Canyon,” said Mary O’Rourke, a professor in emeritus in the College of Public Health at the University of Arizona. “This is in addition to what we make in Arizona cities that is not going to stop at the city boundaries. It will blow around the state.”

High pollution days can reduce visibility by 100 miles, according to the National Park Service.

The EPA standards were strengthened in 2015 to 70 parts per billion, based on evidence about ozone’s adverse health effects on both humans and sensitive ecosystems.

Furthermore, the study found that high ozone levels negatively affects visitation to these sites. This ultimately hinders the local economy, decreasing revenue inside the park and its surrounding areas.

It is a vicious cycle: hot, sunny weather draws visitors to national parks, creating more traffic and pollutants for ozone formation, which is exacerbated in the presence of sunlight. In turn, high ozone levels decrease visitation and park health.

“The point is that these places we think of as pristine are not pristine at all,” O’Rourke said. “And who is to fault? All of us.”

Kaite Fletcher is a reporter for Arizona Sonoran News, a service form the School of Journalism with the University of Arizona. Contact her at [email protected].