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Published on November 14, 2007

 To peek into the future, all we have to do is go to Beijing, Athens, Tokyo, or, in fact, just about any city on Earth.

Most of the world's urban areas have already experienced far more dramatic temperature hikes over the past few decades than the 2.6 degrees Celsius increase expected from global warming over the next hundred years.

It's simple enough to understand. On a hot day in New York, locals sprawl out on the grass fields of Central Park, not on asphalt parking lots or concrete sidewalks. Bricks, concrete and asphalt - the building blocks from which cities are made - absorb much more heat from the sun than vegetation does in the countryside. 

Across an entire city, there's much more tarmac than there is grass. So the air above the city heats up. This effect, called an "urban heat island", was discovered in London in the early 1800s.

Today, the fastest-growing cities are in Asia. Beijing is roughly 10 degrees Celsius hotter than the nearby countryside in the daytime and 5.5 degrees Celsius warmer at night. There are even more dramatic increases in Tokyo. In August, temperatures there climbed 12.5 degrees Celsius above the surrounding countryside, reaching 40 degrees Celsius - a scorching heat that affected not only the downtown area, but also covered some 8,000 square kilometres.

Looking at a fast-growing city like Houston, Texas, we can see the real effect of the urban heat island. Over the last 12 years, Houston grew by 20 per cent, or 300,000 inhabitants. During that time, the night-time temperature increased about 0.8 degrees Celsius. Over a 100-year period, that would translate to a whopping 7 degrees Celsius increase.

But, while celebrity activists warn about the impending doom posed by climate change, a more realistic view is offered by these cities' ability to cope. Despite dramatic increases over the past 50 or 100 years, these cities have not come tumbling down.

Even as temperatures have risen, heat-related deaths have decreased, owing to improved health care, access to medical facilities and air-conditioning. We have far more money and much greater technological ability to adapt than our forebears ever did.

Of course, cities also will be hit by temperature increases from carbon dioxide, in addition to further warming from urban heat islands. But we have an opportunity to act. Unlike our forebears, who did very little or nothing about urban heat islands, we are in a good position to tackle many of their effects.

While celebrity activists focus entirely on cutting carbon dioxide emissions, we could do much more - and at much lower cost - if we addressed urban heat islands. Simple solutions can make a vast difference to temperatures.

Cities are hotter than the land around them because they are drier. They lack moist green spaces and have drainage systems that efficiently remove water. In London, the air around the River Thames is cooler than it is a few blocks away in built-up areas. If we plant trees and build water features, we won't just beautify our surroundings, but we'll also cool things down - by upwards of 8 degrees Celsius, according to climate models.

Moreover, although it may seem almost comically straightforward, one of the best temperature-reducing approaches is very simple: paint things white. Cities have a lot of black asphalt and dark, heat-absorbing structures. By increasing reflection and shade, a great deal of heat build-up can be avoided. Paint most of a city and you could lower the temperature by 10 degrees Celsius.

These options are simple, obvious and cost-effective. Consider Los Angeles. Re-roofing most of the city's five million homes in lighter colors, painting a quarter of the roads and planting 11 million trees would have a one-time cost of about $1 billion. Each year after that, this would lower air-conditioning costs by about $170 million and provide $360 million in smog-reduction benefits. And it would lower Los Angeles' temperatures by about 3 degrees Celsius - or about the temperature increase envisioned for the rest of this century.

Compare that to the $180 billion cost of implementing the Kyoto Protocol, which will have virtually no effect.

At the moment, we don't hear much about the smartest choices when it comes to addressing global warming. That needs to change. We do get to choose which future we want.

Bjorn Lomborg

COPENHAGEN

Bjorn Lomborg is the organiser of Copenhagen Consensus, adjunct professor at the Copenhagen Business School, and author of "Cool It" and "The Skeptical Environmentalist".

Copyright: Project Syndicate.

The Nation