When we talk about public lands, national parks and monuments tend to get most of the attention. But state parks actually see more visits each year. In 2017, people made 2.5 times as many visits to state parks than national ones, for a cumulative 807 million trips.

If visits continue to grow as they have been in recent decades, we might soon overwhelm the budgets of the 50 states’ respective park systems, according to a new study published Monday in the Proceedings of the National Academy of Sciences. And a warming climate will only add to these costs.

The findings are based on extensive data collected since 1984, when, scientists began cataloging information on the attendance, spending, and operations of the approximately 18.7 million acres of state parks in the United States. Based on this, the study authors found that attendance is growing by an average of 6.6 percent each year.

If visits continue to grow like they have been, the average operating costs of state parks could increase by over tenfold by 2050, from an average of $432 per acre to $5,380.29 per acre. Attendance increases the costs of maintaining parks more than any other factor. Extra visits demand more labor and staff to enforce rules, maintain facilities, and provide visitor services. A one percent increase in visits costs a state park $21.16 per acre.

“We were really shocked when we saw that by the time we project the numbers to 2050, there’s an order of magnitude difference in operating costs and what it will cost to maintain the current level of outdoor recreation quality,” says Jordan Smith, director of the Institute of Outdoor Recreation at Utah State University and lead author on the paper.

The scientists also used the park data to correlate temperature and operating costs. Using this relationship, they estimate how climate change could affect these costs under three emissions scenarios. They found that the more we warm the planet, the more expensive it will be to manage the parks. Under a high emissions scenario, similar to the current path we’re on, operating costs go up by $238.28 per acre in 2050.

As temperatures warm, access will increase at parks. Roads and locations that close in snowy conditions will open sooner in the year, lengthening the recreation season. That means parks will need more staff and resources to accommodate visitors. In parks especially far north, such as in Alaska, warming temperatures will bring more cycles of freezing and thawing in spring, requiring additional maintenance as buildings and roads flex and crumble over the shifting soil. But warmer parks aren’t safe either; in Texas, Louisiana, and Florida, sea level rise will lead to more flooding, increasing the costs of maintaining parks.

“Our results suggest a dire future for America’s state park systems,” the researchers write in the study. Since 2006, funding for state parks as a whole has actually gone down. Currently, park funds come mostly from state budgets and entrance fees. But Smith says that on average states dedicate only 0.15 percent of their budgets to their parks. “That’s really surprising when you think about how much benefit these park systems provide to the general public,” says Smith, who has already sent out the findings to legislators and outdoor recreation professionals across the country. “We make the case in the paper that it’s not too big of a stretch to say that that state legislators should put a little bit of money into their state parks.”

The “dire future” described in the study might be an exaggeration, though, according to Margaret Walls, a senior fellow at Resources for the Future, a nonprofit research organization focused on natural resource economics and policy. “OK, so visitation is going to go up—that’s not a bad thing for the state parks systems,” she says, “the state park systems get about 40 percent of their money from entrance fees and user fees, so when more people come in, more money comes in.”

Even with user fees, though, there will still be a gap in funding if the scenarios in the paper play out. Walls adds that in recent years states have moved away from using their general revenues to fund parks and instead tap into a variety of taxes and fees, including those on lottery proceeds, registration of ATVs and snowmobiles, and state park-commemorating license plates. Smith says states are also considering corporate sponsorship programs and taxes on outdoor recreation gear to help fund their parks. “The main message [of the study] is to put states on alert that costs are going to go up in the future, and they need to be ready to fund their systems,” says Walls.