By the end of this year, more than half of the world's population will live in urban areas for the first time in human history, and it is no coincidence that climate change is now at the forefront of international debate, the top United Nations habitat official said to mark World Habitat Day.

Anna Tibaijuka serves as executive director of UN-HABITAT, the agency which promotes socially and environmentally sustainable towns and cities and adequate shelter for all. "Cities consume upwards of 75 percent of all energy and contribute to an equally substantial amount of greenhouse gas emissions. Cities must therefore be an integral part of any mitigation efforts," she said on World Habitat Day, which is observed on the first Monday in October each year.

The theme of this year's World Habitat Day is "harmonious cities," and the global observance this year is being led from the Angolan capital, Luanda.

The celebrations in Angola are intended to show the world how, after nearly three decades years of conflict, the country is progressing in the establishment of harmonious cities through improvements in urban infrastructure and services, and a new urban development strategy.

Attending the event, taking place for the first time on the African continent, were African housing ministers, particularly those from the Southern Africa Development Community. The celebration featured cultural activities, award ceremonies, and speeches by government officials.

Of the world's 6.7 billion people, there are now more than one billion urban slum dwellers Tibaijuka said, emphasizing the need to ensure that rapid urbanization is accompanied by decent living conditions and efforts to preserve the environment.

"Reducing the contribution of cities to climate change and the vulnerability of cities to the effects of climate change must be viewed as a historical opportunity to improve the living conditions of all women and men, including the most vulnerable segments of our urban populations," she said. "I can think of no better initiative than to combine these efforts to make our cities and towns greener and safer and more equitable."

This year's World Habitat Day comes ahead of the fourth session of the World Urban Forum, set to take place in Nanjing, China, from November 3 to 6. There, UN-HABITAT will release its latest biennial publication "State of the World's Cities."