So it comes as a bit of a shock to read in Triumph of the City, the latest book by America's leading urban economist, Professor Edward Glaeser, of Harvard, that cities are a lot greener than the suburbs and countryside.
''Cities are much better for the environment than leafy living,'' Glaeser says. ''Residing in a forest might seem to be a good way of showing one's love of nature, but living in a concrete jungle is actually far more ecologically friendly.
''We humans are a destructive species, even when ? we're not trying to be. We burn forests and oil and inevitably hurt the landscape that surrounds us. If you love nature, stay away from it.''
Anyone who believes global warming is a real danger should see dense urban living as part of the solution. Over the next 50 years, China and India will cease to be poor rural nations, and that's a good thing. They, like the West before them, will move from farms to urban living.
''If billions of Chinese and Indians insist on leafy suburbs and the large homes and cars those suburbs entail, then the world's carbon emissions will soar ? The critical question is whether, as Asia develops, it will become a continent of suburban drivers or urban-transit users.''
Historically, the wealthy managed to combine city and country living by having two homes. Winter months were spent in the city, while hot summers were spent on the country estate.
Less expensive solutions were to surround towns and cities with a green belt. Failing that, big city parks were established. But the emergence of faster, cheaper transportation made it possible to live with trees and work in the city.
Homes and cars account for about 40 per cent of the average American household's emissions of carbon dioxide, half of which is attributable to cars. People could buy more fuel-efficient cars, but the big difference is whether you drive 500 kilometres a year or 50,000, which depends on whether you live in a city or a suburb. Cities are also greener than suburbs because city households use less electricity.
''Smart environmentalism requires thinking through the inadvertent side-effects of different environmental policies and recognising those that actually do more harm than good,'' Glaeser says. The conservationists who keep the San Francisco Bay area free from new construction are preventing development in the greenest part of America. They are consequently increasing development in America's browner areas, such as baking-hot, air-conditioned Texas.
''In older cities like New York, NIMBYism hides under the cover of preservationism, perverting the worthy cause of preserving the most beautiful reminders of our past into an attempt to freeze vast neighbourhoods filled with undistinguished architecture.
''In highly attractive cities, the worst aspects of this opposition to change are that it ensures that building heights will be low, new homes will be few, prices will be high, and the city will be off-limits to all but rich people.''
People seem surprisingly ignorant of how supply and demand work. When the demand for a city rises, prices will rise unless more homes are built. When cities restrict new construction, they become more expensive.
Cities grow by building up or out. When a city doesn't build, people are prevented from experiencing the magic of urban proximity. Preserving a city can, in fact, require destroying part of it, Glaeser says.
The modern desire to preserve Baron Haussman's Paris has helped turn the affordable Paris of the past - with its history of impecunious but ultimately celebrated artists - into a boutique city that today can be enjoyed only by the wealthy.
There is great value in protecting the most beautiful parts of our urban past, but cities shouldn't be embalmed in amber. Too much preservation stops cities from providing newer, taller, better buildings for their inhabitants.
Height restrictions - in Paris, New York and Mumbai - should be of interest and concern to far more of us than just the planning professionals. ''These rules are shaping the future of our cities and our world,'' Glaeser says. ''If the cities' history becomes a straitjacket, then they lose one of their greatest assets: the ability to build up.''
Height, he says, is the best way to keep prices affordable and living standards high.
Glaeser's observations seem of obvious relevance to Sydney and the decisions facing the O'Farrell government. Our sky-high house and unit prices are partly the product of strong demand being met by a woefully inadequate supply of additional houses and units. Now those high prices are contributing significantly to Sydney and NSW's weak rate of economic growth.
The lack of additional supply comes partly from our topography, but mainly from excessive government restrictions on development. But there are limits to how far Sydney can be allowed to sprawl - including the inadequacy of public transport.
Sydney needs to go up, and part of that up is more medium-density housing in north shore Liberal electorates, including the Premier's own.
