You'd expect climate change and protecting endangered species to be among the top environmental challenges facing the U.S.—but antibiotics and nuclear weapons?
They too came up when NBC News surveyed a cross-section of experts who reflect a movement that's evolved since the first Earth Day on April 22, 1970.
There's the general who battled Katrina. The Stanford economist who calls himself a "free market environmentalist." The former lawmaker who helped shape landmark environmental policy. The activist who started Earth Day activities in the U.S. And the lawyer hell bent on turning low-income Americans into environmentalists.
They share some concerns, and a willingness to compromise, but have their own priorities and approaches—proof that there is not just one environmental path.
Prepare and be aware
It was right after Hurricane Katrina hit in 2005 that then Lt. Gen. Russell Honore, head of the military support effort, had his epiphany as he flew over the Gulf of Mexico. "Katrina started off as a natural disaster but then it became manmade," he said of the miles and miles of oil sheens he saw from damaged oil rigs. "That basically scared the hell out of me."
The experience left him convinced that the biggest challenge facing the U.S. is that communities need to be aware of the dangers around them and prepare for the worst—whether that's rising sea levels, drought or potential pollution from nearby industries.
After retiring, Honore turned that conviction into a cause, leading the community outrage in Bayou Corne, Louisiana, when in 2012 an improperly drilled cavern created a sinkhole that forced hundreds to evacuate and has since expanded to 39 acres.
That led to Honore's "GreenARMY"—a loose-knit coalition seeking what he calls "a revolution by the people" in Louisiana. They feel most local and state officials are beholden to business, especially the energy industry. Their battle tactic is to lobby for laws that enforce federal rules. "It's a fight and they see us as the enemy," he said.
For Terry Anderson, an economist at Stanford's Hoover Institution and co-founder of the Property and Environment Research Center, the biggest challenge is to get past such battles by incentivizing change with free market principles.
Anderson's focus has been with the Endangered Species Act. Yes, it helped bring back iconic species like the bald eagle, he said, but it is not having the same success with lesser-known species (think spotted owl) that create property versus habitat battles.
"When landowners see regulations coming they take evasive action to ensure they don't have endangered species habitat," he said.
His goal: change the act "to make endangered species an asset rather than the enemy of private landowners." How? Explicitly allow the law to encourage using taxpayer funds to buy or rent that habitat.
Let science be your guide
Creating a process to independently analyze issues and thus break through gridlock, especially in Congress, is the challenge consuming Phil Sharp.
Sharp, a Democrat who helped craft landmark clean air and water legislation, represented Indiana in Congress from 1975-95. He now runs Resources for the Future, a bipartisan nonprofit whose research is driven by economists.
That process, Sharp said, is based on incentives like those valued by Anderson; being more certain of the benefits and risks of any policy; and above all strong science.
"We have to get smarter about addressing environmental questions, and that means we have to be really sure we're grounded in science," he said, noting that RFF uses that process with issues like fracking, water and nuclear waste.
Give all a reason to buy in
For Kathleen Rogers the biggest challenge is not process or a specific issue, but to "diversify the environmental movement, and to end the status quo by working with community leaders" in areas as varied as women's rights, civil rights, religion and anti-poverty.
A lawyer who recalls environmentalism as "older and mostly white" when she first got started in the 1980s, Rogers now runs the Earth Day Network. The nonprofit not only promotes Earth Day activities, but funds projects year round with a focus on low-income issues like healthier schools—from how they're built to what students eat.
"If the poorest don't have clean schools and communities they won't care about global issues" like climate change, she said.
The even bigger picture
For Denis Hayes, who organized the first Earth Day activities in the U.S., the challenges are eclectic—starting with nuclear weapons.
"Atmospheric nuclear testing was one of the seeds of environmentalism," he recalled, and today's nuclear stockpile "is still the greatest potential threat to the planet."
He also puts environmental health—especially concerns about antibiotics and synthetic hormones—among the top issues.
Climate change is up there too. Hayes echoed his peers in that it comes down to this: not enough action.
It should be a Pearl Harbor moment, where the nation mobilizes as if it were at war, said Hayes, who runs the Bullitt Foundation, which funds green projects in the Pacific Northwest.
No major politician "shares that sense of urgency," he added. "They continue to view climate change as two lines crossing on a graph sometime in the future, ignoring the consequences we have already experienced and the much worse consequences we have already baked into the atmosphere."