Islands of Warmth in a Sea of Cool

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, California 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 freshly rolled asphalt for reflectivity and found that it absorbed 95 percent of solar radiation. Aged asphalt, which is gray rather than black, was found to absorb 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 baked at 123 degrees, faded asphalt registered 115, and the white surface 90. The Heat Island Group concluded that if all L.A.'s pavement was replaced with a more reflective version, the city could save $90 million a year in cooling costs.

While air conditioners are a novelty in most of Alaska, we have a heat island right here in Fairbanks. In the 1970s, Carl Benson and Sue Ann Bowling of the Geophysical Institute drove around town during winter with a temperature sensor mounted on a mast above the car. The warmest temperatures--about 20 degrees above the coolest--were measured 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 of the Alaska Climate Research Center at the Geophysical Institute recently compared Fairbanks to Eielson Air Force Base to see how the Fairbanks heat island has evolved. Using long-term temperature records, he and other researchers found Fairbanks' heat island has grown with the city's population, which increased from 15,000 to more than 30,000 from 1970 to 1990. At Eielson, where the population remained constant, temperatures also increased but not at the same rate as Fairbanks.

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

The staff at the Alaska Climate Research Center studies 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.