The world makes a lot of concrete, more than 9 billion tonnes a year, and is poised to make much more for a population that is forecast to grow by more than 25 per cent by 2050. That makes sand, which is about 40 per cent of concrete by weight, one of the most-used commodities in the world and one that is becoming harder to come by in some regions. But because of the erosive power of ice, there is a lot of sand in Greenland. And with climate change accelerating the melting of Greenland's 1.6 kilometre-thick ice sheet — a recent study found that melting has increased sixfold since the 1980s — there is going to be a lot more. "It's not rocket science," Bendixen said. "One part of the world has something that other parts of the world are lacking." Bendixen is planning a two-year study to answer basic questions about the idea, including its feasibility and the environmental effects of extracting and exporting large amounts of the material. The government of Greenland, a self-ruled territory of Denmark, is studying it as well. It would be up to entrepreneurs, possibly with assistance from the government, to make the idea a reality. Given the potential cost of shipping sand around the world, its feasibility would depend on the price of sand rising.

The need to diversify the economy is a big issue in Greenland. Currently almost all sand is mined within 80 kilometres of where it is used, said Jason C. Willett, a minerals commodity specialist with the U.S. Geological Survey. "Once you move it any distance it then costs too much," he said. The idea also raises questions that go beyond science — about Greenland's economic future, about its potential independence from Denmark and even about the appropriateness of capitalising on climate change. The need to diversify the economy is a big issue in Greenland, where fishing accounts for about 90 per cent of exports and Denmark provides nearly half the government's budget through a block grant. A large sand-exporting industry could help reduce this subsidy, which would be critical to Greenland eventually becoming independent. "The diversification discussion is very important," said Birger Poppel, a political science professor at the University of Greenland. "This could fit into that discussion."

Bendixen has made some hypothetical calculations. If just 15 per cent of the sediment pouring into Sermilik Fjord every year could be extracted, that amount of sand — 2.9 million tonnes — is twice the annual demand of San Diego County in California, one of the most populous in the United States. Sermilik Fjord is only one of a number of places in Greenland with large amounts of sand. And the sand will keep coming as the world keeps warming and the ice sheet keeps melting. "It's like a tap pouring not only water, but sediment," she said. Worldwide, the demand for sand and gravel is relentless and increasing. Mining, usually from open pits or by dredging, is unregulated in many areas and often illegal. In India, for example, sand "mafias" have developed, with gangs stealing sand from a river bend or a beach overnight. A United Nations report this year noted that extraction of sand around the world is exceeding the rates by which it is replenished. Sand removal along rivers and coastal regions often leads to greater erosion and harm to ecosystems, the report said. Work crews will soon begin lengthening the airport's sole runway to handle jets.

In addition to better regulations, the report called for reducing the demand for sand and gravel through improved designs that cut the amount of concrete in buildings and infrastructure. (Lighter designs would also help address a climate change problem: Manufacturing of cement, the reactive ingredient in concrete, is responsible for about 5 per cent of global emissions of carbon dioxide.) Concerns about the supply of sand seem far off in Nuuk, population 17,500, where it is possible to walk from one end of the city to another in less than an hour and where the Greenland government works out of an office building above a shopping centre. But even Nuuk has its sights on expansion. There are plans to build thousands of homes and apartments to accommodate a population that is forecast to reach 30,000 by 2030. More immediately, work crews will soon begin lengthening the airport's sole runway to handle jets, which would help Greenland's nascent tourism industry. Nicolai Mogensen, who runs Nuuk's only concrete plant, is ready. This year he stockpiled extra sand, anticipating the start of the runway project. He currently has about 15,000 cubic yards, a small gray mountain next to the plant. It comes from a nearby fjord, sucked from the bottom by a dredger. Mogensen, who has run concrete plants in Norway, Poland, Germany and Denmark, said he thought Bendixen's idea was a good one. "All these countries are running out of sand," he said.

New York Times