Even in subzero Alaska, researchers discover 'urban heat island'

PHOTO/Marion Owen/For the Journal
rozellnedLR.jpg Climate change caused by people is a tough thing to measure in most places, but not in big cities. The clustering of humans, cars, pavement and rooftops makes some cities warmer than surrounding areas. Called "urban heat islands," they exist from Los Angeles to Atlanta to New York. Even Alaska has one.

A few researchers in Berkeley, Calif., have devoted themselves to the study of heat islands. They’ve found that Los Angeles is 6 to 8 degrees Fahrenheit warmer than the surrounding areas. That may not seem like a lot, but those few degrees add up when you multiply them by the cost of air conditioning in millions of homes and offices.

The Heat Island Group, as the researchers call themselves, reports that intense heat absorbed by dark shingles can penetrate buildings, making air conditioners work harder. Members of the research group compared roof surfaces by painting one roof black and another white. The black roof was 70 degrees warmer than the air. The white roof was 18 degrees warmer than the air.

Much of the heat in big cities radiates up from road pavement. Researchers tested fresh asphalt for reflectivity and found that it absorbed 95 percent of solar radiation. Aged asphalt, which is gray rather than black, absorbed 90 percent, and experimental white asphalt soaked up just 50 percent. With the three pavements side-by-side, members of the group measured the following temperatures: new pavement was 123 degrees, faded asphalt registered 115, and the white surface 90. The Heat Island Group concluded that if all L.A.’s pavement were more reflective, the city could save $90 million a year in cooling costs.

While air conditioners are a novelty in Alaska, we have a heat island right here in Fairbanks. In the 1970s, Carl Benson and Sue Ann Bowling of the Geophysical Institute at the University of Alaska Fairbanks drove around town during winter with a temperature sensor mounted on a mast above the car. They measured the warmest temperatures, about 20 degrees above the coolest, in the city center near the Chena River, while outlying areas were coldest. The Chena creates a basin that should hold the coldest air, but the Fairbanks city core, with cars and homes and other sources of manmade heat, was one of the warmest areas in town.

Jan Curtis, the state climatologist for Wyoming who used to work for the Alaska Climate Research Center, compared Fairbanks to Eielson Air Force Base to see how the Fairbanks heat island evolved during the last 50 years. Using long-term temperature records, he and other researchers found Fairbanks’ heat island has grown with the city’s population, while Eielson’s temperatures also increased but not at the same rate as Fairbanks. During the 49-year period Curtis studied, the population of Fairbanks grew by more than 500 percent while Eielson remained almost constant.

Fairbanks, with cold, stable air in winter, is the only place in Alaska where researchers have seen the heat island effect. Anchorage has more than enough people, cars and pavement to warm things up, but the ocean and the Chugach Mountains stir the air and hide any evidence of a heat island.

The staff at the Alaska Climate Research Center studied the Fairbanks heat island to distinguish between a general warming trend felt all over and the local effects caused by a clump of people. The heat island in Fairbanks probably saves people a few dollars in heating costs, Curtis said, but this island still offers little refuge from an interior Alaska winter.

Ned Rozell is a science writer at the Geophysical Institute at the University of Alaska Fairbanks. This column was issued by the Geophysical Institute last month and first appeared in 1999.

01/06/2002 - 8:00pm