The Missouri River floodwater surging on to the air base housing the U.S. military’s Strategic Command overwhelmed round-the-clock sandbagging by airmen and others. They had to scramble to save sensitive equipment, munitions and dozens of aircraft.

Days into the flooding, muddy water was still lapping at almost 80 flooded buildings at Nebraska’s Offutt Air Force Base, some inundated by up to 7 feet (2.1 meters) of water. Piles of waterlogged corn cobs, husks and stalks lay heaped everywhere that the water had receded, swept onto the base from surrounding fields.

Though the headquarters of Strategic Command, which plays a central role in detecting and striking at global threats, wasn’t damaged, the flooding provided a dramatic example of how climate change poses a national security threat, even as the Trump administration plays down the issue.

It is also a reminder that the kind of weather extremes escalating with climate change aren’t limited to the coasts, said retired Rear Adm. David W. Titley, founder of both the Navy’s Task Force on Climate Change and the Center for Solutions to Weather and Climate Risk at Penn State University.

“We probably do need some walls—but they’re probably levees,” Titley said, in a reference to President Donald Trump’s proposal to take money from the military construction budget to fund a wall at the U.S.-Mexico border. “I would say those are the kinds of walls we need.”

The late-winter floods that have swept over Plains states starting last week—breaching levees, halting Amtrak trains, and killing at least three people—are also the second major inundation in less than a decade to hit the air base outside Omaha.

It would takes weeks or more for scientists to determine if the Plains flooding, or any weather disaster, was caused or worsened by climate change, which is occurring as emissions from coal, oil and gas alter the atmosphere. But federal agencies and scientists around the world agree that climate change already is making natural disasters more frequent, stronger and longer.

The military has warned in a series of reports under past administrations that climate change is a security threat on many fronts. That includes “through direct impacts on U.S. military infrastructure and by affecting factors, including food and water availability, that can exacerbate conflict outside U.S. borders,” the federal government’s grim climate report said last year.

But Trump has belittled his own government’s warnings. During a January cold spell, he tweeted his wish for “a little of that good old fashioned Global Warming!” In response to security warnings on climate change, the Trump administration has allowed a physicist who rejects scientific consensus on manmade climate change to start organizing a White House panel to make its own determination.

Responding to an AP inquiry, the White House’s National Security Council did not directly address whether the administration sees climate change as a national security threat, but said it takes the issue of climate change seriously.

But the Trump White House’s national security strategy mentions climate only in the context of “countering an anti-growth energy agenda” for fossil fuels.

Department of Defense spokeswoman Heather Babb said the department “works to ensure installations and infrastructure are resilient to a wide range of challenges, including climate.”

“DOD will focus on ensuring it remains ready and able to adapt to a wide variety of threats—regardless of the source—to fulfill our mission to deter war and ensure our nation’s security,” Babb said.

Under the Trump administration, unlike in previous administrations, the Pentagon has offered little public comment on climate change as a security threat. The Pentagon’s guiding star of defense planning, known as the National Defense Strategy, does not even mention climate change.

That leaves it to former military leaders to raise the alarm about how climate change could affect national security. Retired Brig. Gen. Gerald Galloway said that worsening bouts of weather— floods cutting off troops’ way in and out of bases, high waves complicating landings, heat waves depriving aircraft of the lift they need to fly—are all problems the military could be dealing with.

Military bases are launch platforms and you “can’t fight a war unless you’ve got a place to leave from,” said Galloway, a member of the Center for Climate and Security’s advisory board.

Titley predicted Offutt Air Force Base would prove the latest military installation to have racked up $1 billion or more in damage. Hurricanes struck North Carolina’s Camp Lejeune in September and Tyndall Air Force Base in Florida in October.

The current political atmosphere discourages any big efforts building up base defenses against climate change, said Titley, who also served as chief operating officer of the National Oceanic and Atmospheric Administration.

Defense Department officials “by and large know what they need to do, but it’s very hard for them to do. White House dynamics are the White House does not want to hear about it,” he said.

“The Pentagon is really between a rock and a hard spot here,” Titley said.

Earlier heavy flooding at Offutt has prompted the base to start raising its levee by 2 feet this year, said Maj. Meghan M. Liemburg-Archer, spokeswoman for Strategic Command.

Sandbagging had held back 2011 floods at the base. The flooding that poured in starting March 15 was worse, Norton, the base’s support group commander, said.

“It was all hands on deck,” Norton said. “All through the night, we worked. It was thousands of people, in total, working to sandbag, move in huge Hesco barriers; a whole host of people clearing equipment out of facilities, moving munitions … even crews doing things like disconnecting power. It was a massive effort.”

More than 30 aircraft were towed to higher ground or flown to other locations. Crews hauled out loads of equipment, engines and tools.

By Saturday, the flood had rolled over a third of the base, swamping more than 1.2 million square feet of buildings.

Though Strategic Command headquarters escaped flooding, it had to cut staff to a minimum as high water blocked roads. The command holds down a range of responsibilities, including global strike capacity, missile defense, nuclear operations and strategic deterrence.

Inundated buildings include the 55th Wing headquarters, the massive Bennie L. Davis Maintenance Facility and a building that houses the 55th Wing’s flight simulators.

About 3,000 feet of the base’s 11,700-foot runway is submerged.

“The good news is that no one on the base was injured,” Norton said. “We know how lucky we are.”

Touring Offutt, the base’s fire chief, Dave Eblin, kicked one of the soggy corn cobs strewn throughout the base. Asked whether there had been some type of fodder silo that ruptured nearby, Eblin just laughed.

“No, it came in from the fields. Miles of corn fields around the base,” he said, nudging at the cob underfoot. “It clogs everything: engines, boat motors. It’s everywhere.”

(Knickmeyer and Burns reported from Washington. AP science reporter Seth Borenstein contributed, also from Washington.)