-Between 2001 and 2017, the U.S. lost 24 million acres of natural area to the human footprint, about the size of the state of Indiana, according to the report, "How Much Nature Should America Keep," released this week by the think tank Center for American Progress.
The United States should set a goal to protect 30 percent of the remaining natural land by 2030 to avoid the worst effects of climate change and the extinction of wildlife species, the report said.
The South and Midwest lost the most natural area to cities, farms, roads, power plants and other human development in the study. The human footprint in the South grew to cover 47 percent of the region. In the Midwest, 59 percent of all land has been developed for human use.
Scientists from Colorado-based Conservation Science Partners calculated human modification on the U.S. land mass by crunching national data from road networks, satellite imagery of vegetation, energy infrastructure and amounts of nighttime light detected from space, said Brett Dickson, president and chief scientist of the company.
"The national level analysis we did for CAP identified 40 percent of the contiguous 48 states having been developed," Dickson said. "That means 60 percent has not been developed, a pretty good chunk of the U.S."
Only about 12 percent of the U.S. land mass is protected in national parks and conserved open space, and "not a single section of U.S. waters in the Gulf of Mexico, the mid-Atlantic, or the North Pacific" is completely protected from oil and gas extraction, report author Matt Lee-Ashley wrote.
These losses of natural space "pose a direct threat to the nation's clean air and clean drinking water supplies, the prosperity of its communities, and its ability to protect itself from severe weather, floods, wildfires, and other effects of a changing climate," Lee-Ashley said.
"This report does a remarkable job of stressing the importance of committing to such a goal nationally and the urgency we need to be bending the curve of development that's gobbling up wilderness at an alarming rate," said Chase Huntley of the Wilderness Society Action Fund, a political arm of the Wilderness Society advocacy group.
Some 12,000 U.S. animal and plant species "need proactive conservation efforts to avoid a plunge toward extinction," the report said.
Using the same data sets to measure human impact, scientists can also pinpoint the best local land be preserved. Potential areas can be identified by whether land is "ecologically intact" or whether it has existing wildlife corridors, Dickson said.
"That way people can begin to have the debate and discussion with evidence, data and statistics," he said.
The report has the right priorities by focusing on "high value ecosystems," said Kieran Suckling, executive director of the Center for Biological Diversity.
"It's not uncommon that land protection efforts end up protecting sub-optimal habitats, which is politically cheaper," Suckling said. "In this report they really have the right priorities. They are filtering for intact landscape habitats or endangered species and linkage habitats that can connect them."