A major problem with the suburban lifestyle is its damaging ecological impact. The comparison of low-density suburbs with life in the concrete towers of congested urban conurbations is actually quite misleading; as it turns out, if you want to be kind to the natural environment, the key is to stay away from it. Suburbia fails the environmental friendliness test on a number of counts. Firstly, due to their low population density, suburbs consume natural land at a much higher rate than high-density row housing or apartment buildings. Secondly, they encourage the use of personal motor vehicles, often at a rate of one per family member, at the expense of public transport. It is also much less efficient to provide electricity and water to individual suburban houses instead of individual units in an apartment building. In his comparison of urban and suburban pollution, Edward L. Glaeser concluded that we need to 'build more sky towers – especially in California'. Virtually everywhere, he found cities to be cleaner than suburbs. And the difference in carbon dioxide emissions between high-density cities and their suburbs (for example, in New York) was the highest. Urban residents of New York can claim on average to produce nearly 15,000 pounds of carbon dioxide less than their suburban peers.