Two weeks ago, in the quiet of an Arctic ice field, something unusual happened: A 360-foot-long nuclear submarine broke through the thick ice and surfaced. The USS Hartford, part of the Atlantic Fleet, pushed through the ice, its conning tower standing like a black monument in a vast landscape of blinding white.

It wasn't alone. Nearly two dozen U.S. military personnel, parachuted and flown in by helicopter from bases in Alaska, were waiting for the Hartford to make its grand entrance. The entire scene was part of ICEX 2016, or Ice Exercise 2016, designed to prepare the U.S. military to fight north of the Arctic Circle.

The Arctic has traditionally been a low military priority for everyone. Its climate, particularly during the winter, makes it unfriendly to human life. The prevalence of ice and lack of dry land makes stationing forces there difficult. Military outposts are generally limited to arctic research, early warning, and meteorological stations.

Generally speaking, it's not worth fighting over.

Global warming is changing that. Rising temperatures are contributing to a decline in Arctic sea ice. Less ice means previously unreachable resources — particularly oil and natural gas — can now be accessed and a new ice-free Arctic shipping route servicing the northern hemisphere appears downright likely.

Nobody is sure what riches lie under the freezing waters, but the U.S. Department of Energy estimates 13 percent of the world's undiscovered oil — or 90 billion barrels — lies waiting under the Arctic. That's enough to keep the entirety of human civilization chugging along for 2.5 years. The DoE also estimates the Arctic holds 30 percent of the world's undiscovered natural gas.

Under international law all countries have exclusive use of the resources in and under the ocean within 200 miles of their territory. A Norwegian island just a mile wide, for example, would grant Norway all the resources within a 200-mile radius. Similarly, the continental shelf extending from dry land into the ocean grants the country occupying it resources underneath.

Only a handful of countries have direct claims to Arctic territories. Canada, Denmark, Finland, Iceland, Norway, Russia, Sweden, and the United States all have land north of the Arctic Circle. Even China is also trying to get in the game, but its quest for influence in the region has been hobbled by the fact that it doesn't actually have any territory there.

Russia is staking its claim to the Arctic and is being more than a little unreasonable about it. In 2007 Russian robotic submarines planted the national flag under the North Pole. Russia claims the North Pole on the grounds that the Lomonosov Ridge, an extension of Russia's continental shelf territory, passes underneath the pole.

Russia is preparing to back its claims up, too: As of 2015, it had established six new bases north of the Arctic Circle, including 16 deepwater ports and 13 airfields. Russia has deployed advanced S-400 long-range surface-to-air missiles, as well as "Bastion" supersonic anti-ship missiles, to protect Arctic bases. The vastness of the Arctic means these weapons don't threaten other countries, but they do create fortified bases that will allow Russia to springboard ships, planes, and Arctic-trained troops into contested territory.

Sometime this year Russian airborne forces are expected to conduct large-scale exercises in the area.

In all fairness, Russia does have a very large amount of territory north of the Arctic Circle, and it has a right to defend itself. Viewed in a neutral context, the exercises and base-building are typical measures of self-defense. However Russia's grandiose claims to the North Pole, aggression in the Ukraine, and the repressive government of Vladimir Putin add a menacing subtext to these new military developments.

The U.S. has no major bases north of the Arctic Circle line, but is practicing to go there if necessary. Late last year, a combined Army and Air Force exercise temporarily deployed Stryker combat vehicles to Deadhorse Alaska, one of the northernmost communities in the United States. The Navy is in talks to base sub-hunting planes in Iceland, and some of the first operational Air Force F-35 Joint Strike Fighters will be based in Alaska. Both locations are just south of the Arctic Circle.

What would war in the Arctic look like? It would be two wars: one against the human enemy, which would often be hundreds of miles away and seldom seen, and another, constant war against the elements. Both would be trying to kill you. War would mostly be conducted by aircraft and submarine, the better to avoid actually operating on the ice.

The weather and the flat, featureless terrain would mean long-range subs and planes that pack plenty of firepower would play decisive roles. Unmanned, autonomous drones that can survive the harsh weather would be particularly useful. Large numbers of ground forces would be difficult to manage, so small Army, Navy, Air Force, and Marine units trained to parachute, ski, or infiltrate by submarine would be used to attack and defend isolated Arctic bases. Search and rescue, to recover pilots shot down in such a bleak, hostile environment, would be a must.

The Arctic is a big, harsh place, and everyone would prefer to stay out of it as much as possible. But climate change is making the region more useful to everyone — and that means developing the ability to claim it or at least deny it to someone else. A war in the Arctic could be the first conflict generated by humanity’s impact on the environment — but it wouldn’t be the last.

The Arctic is a big, harsh place, and everyone would prefer to stay out of it as much as possible. But climate change is making the region more useful to everyone — and that means developing the ability to claim it or at least deny it to someone else. A war in the Arctic could be the first conflict generated by humanity's impact on the environment — but it wouldn't be the last.