Many of them live in urban areas of developing countries.

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In Europe, about half the adult population is currently overweight, and urban areas of many developing countries have a similar prevalence, according to the International Agency for Research on Cancer.

BBC: Breast cancer risk for large mums

One caveat: Estimating population for comparably defined urban areas, particularly in the developing world, can be difficult.

FORBES: The World's Fastest-Growing Megacities

If the methods of reducing a city's carbon footprint are known there is still the question of the means, which vary wildly between the first world urban areas such as Seoul, London and Toronto, and other attendees from cities in the developing world, such as Ho Chi Minh City, Vietnam and Lagos, Nigeria.

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Unlike other developing countries, as of 2007 approximately 76% and 24% of Peruvians lived in urban and rural areas, respectively.

UNESCO: Country Profile: Peru