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.

CNN: Bill Clinton to cities: Act on climate

With his experience of government, he knew where security was weak, particularly in Ho Chi Minh City, previously Saigon, the capital of defeated South Vietnam.

ECONOMIST: Tran Do, a dissident in Vietnam, died on August 9th, aged 78

Than is Intel's country manager in Vietnam, overseeing a staff of 15 in Ho Chi Minh City (formerly Saigon).

FORBES: Revisiting Vietnam

Abandoned hotel towers in Ho Chi Minh City and Hanoi are monuments to the failure of follow-through that plagues Vietnam.

CNN: Stops and Starts

One leader of the makeover is Son Pham Quang, who runs some of Vietnam's trendiest restaurants, like the Club Opera in Hanoi and the Mandarin in Ho Chi Minh City.

CNN: Stops and Starts