美国国家公共电台 NPR How Climate Change Is Affecting Alaska's Military Radar Stations（在线收听）

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A document by the Defense Department has a simple title, "Report On Effects Of A Changing Climate To The Department Of Defense." The Pentagon paper lists dozens of military installations that are more vulnerable to wildfires, flooding and drought. In Alaska, the U.S. military has to think about the shifting ground beneath its feet. Alaska Public Media's Zachariah Hughes traveled to 1 of 15 remote radar sites that scan the airspace over the Arctic.

ZACHARIAH HUGHES, BYLINE: Getting out to the military's radar station at Tin City starts with a flight from Anchorage's Joint Base Elmendorf-Richardson in a small Air Force plane - 630 miles, the pilot tells us.

UNIDENTIFIED PILOT: Our flight time today is just a couple hours, so hopefully everyone would be good there.

HUGHES: Early in the 20th century, Tin City was a small mining town. But since the 1950s, it's been the site of a long-range radar that's supposed to watch for Soviet bombers. It used to take well over a hundred airmen to manage it. Over time, though, improved technology has whittled down the number of personnel to just four private contractors.

(SOUNDBITE OF DOOR SHUTTING)

HUGHES: After the flight, we'd take a quick drive to the building where the site technicians sleep, eat and give safety briefings to the occasional visitor.

JEFF BOULDS: If you got your warm gear, you'd have to bring it with you. There's no way of getting out of that.

HUGHES: Jeff Boulds, a mustachioed Montanan with graying hair, gets ready to take us from down here at the lower camp site up a steep mountainside to see the radar itself.

BOULDS: You're not going up to the top camp without some kind of arctic gear. Other than that, welcome to Tin City.

HUGHES: What comes next is a half-hour trip up snowy switchbacks that look like they're about to drop away at every single turn. Workers make the 2,300-foot ascent in a treaded vehicle called a PistenBully. It looks like a cross between a bulldozer and a tank.

We going in that?

BOULDS: Yes.

HUGHES: Get out.

Running these radar sites has never been easy to do, but now it's getting even less manageable. Coastal erosion driven by warming seawater is nibbling away at land around vital infrastructure that support basic operations. Runways used for resupply are in jeopardy, and permafrost beneath some buildings is thawing. Colonel Daniel Lemon is the Air Force commander in charge of remote radar sites stretching from the Pacific to the high Arctic.

DANIEL LEMON: Climate change is happening, and there is erosion going on on the North Slope of Alaska. That's a fact. We know that's a fact. I don't know what's causing it, but we have to do something about it. It is impacting our mission.

HUGHES: So far, 3 of the 15 radar stations in Alaska, all of them along the Arctic coastline, are grappling with climate-driven threats to infrastructure. The installation at Tin City, perched here on a hill overlooking the Bering Strait, is not yet one of them. However, environmental changes are undeniable. During our visit, the strait was completely free of sea ice - a month later than freeze-up used to begin.

BOULDS: Sixteen degrees right now.

HUGHES: This is the most western point of the North American continent. From the radar site, the Russian mainland is only 48 miles away - blocked today by clouds. The radar building itself is covered with ice.

All the metal out here has - I mean, it looks like Hoth in "Star Wars." There's just snow crystals and totally wind-strafed buildup on everything.

Inside the radar building, most of the equipment is classified and looks like the kind of metal filing cabinets and fluorescent lighting that you'd find in an accountant's basement - albeit with an unsettling hum.

BOULDS: If you can hear...

(SOUNDBITE OF RADAR HUM)

BOULDS: ...That's the radar rotating right now.

HUGHES: Everything at Tin City - from the runway for the plane, to the cafeteria that keeps Boulds fed - it all exists so that this machine can keep spinning. For the military, maintaining sovereignty over U.S. airspace means being able to know what's moving through it, even at the remote fringes of the continent. The military is already spending big to slow down impacts from a warming Arctic. Colonel Lemon says that at another site, about 200 miles to the north, waves from the encroaching Chukchi Sea were washing over the airstrip.

LEMON: So we have a $47 million seawall project. They're actually building a seawall to protect that runway.

HUGHES: Tens of millions of dollars to protect one runway at one site, and it's only the start. A 2014 government report found that the installations are seeing erosion that the Pentagon didn't expect until the year 2040. Other sites will need boulders barged in for fortifications of their own. And while the military acknowledges the problem, there is no comprehensive plan yet for how to keep the radar spinning. For NPR News, I'm Zachariah Hughes in Tin City, Alaska.

(SOUNDBITE OF NIKLAS PASCHBURG'S "SONAR")