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July/August 2002 issue	IN THIS ISSUE: Table of Contents Feature: Panic in the woods The Inside Story Editor's Notebook Reverberations À la carte Mosaic Re:Sources

It is common knowledge that cities are warmer than their surroundings, as much as 10°C warmer, in fact. But what, if anything, can be done to reduce the pressure cooker of summer city living? Climatologists studying the problem have several cool suggestions.

The asphalt, concrete and tar in roads, parking lots and roofs absorb the sun's energy and create invisible "urban heat islands," which contribute to health risks, energy costs for air conditioning, smog and local weather oddities.

"The climate in and around cities and other built-up areas is altered," says James Voogt, an urban climatologist at the University of Western Ontario in London. "Urbanization affects surface temperatures, evaporation rates, wind turbulence and precipitation above and downwind of urban areas."

Voogt studies images such as these of Vancouver. They were made using heat sensors mounted on satellites (for the large-scale images) and on helicopters (for the small). Other climatologists monitor near-surface air temperatures using thermometers arrayed across a region.

How to cool cities was the hot topic at the North American Urban Heat Island Summit in Toronto in May, where climatologists, urban planners, architects and others convened to share ideas for mitigating the problem, especially in new urban developments. Painting roofs white, green-roof projects, more trees and parks and improving health-risk alert systems are just some of the ideas to make urban living more comfortable and energy-efficient. For, as we know, it's a pity that the days can't be like the nights, in the summer, in the city.

Islands of warmth Heat sensors on satellites confirm that surface temperatures in Vancouver's city core at 3:30 p.m. on an August day (above) are higher than the rural surroundings and that industrial and commercial zones, major highway intersections, shopping malls and airports tend to be hottest. At 5:30 a.m. the next day (below,left), urbanized areas remain warmer than rural surroundings, due to a slower release of heat from building materials and paved surfaces. The ocean, meanwhile, acts as a heat sink, where temperatures barely change from day to night.

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