The impact of urbanization on climate change, and in turn how climate change affects the disruption of cities, is the focus of the World Habitat Day, which falls on Monday.

Now in its 25th year, the UN initiative examines how mankind can make its towns and cities better places, while promoting the basic rights of all people to have adequate shelter.

As the planet gets set to welcome its 7 billionth resident this month, and with more than half of them being city dwellers, UN-Habitat, organizer of World Habitat Day, believes the rapid urbanization, and the climate changes associated with it, is one of the greatest challenges facing human beings today.

According to Cities and Climate Change: Global Report on Human Settlements 2011, the UN Habitat report released earlier this year, by 2050 there could be as many as 200 million "enviro-refugees" worldwide, forced from their homes by rising sea levels and increasingly frequent droughts or flooding.

In addition, about 60 million people currently live in areas that are 1 1 meter above sea level. That number is forecast to rise to 130 million by the end of the century and major coastal cities like Shanghai, Tokyo and New York could face serious threats from storm surges with the rising sea levels.

Ahead of the Global Observance of World Habitat Day, to be hosted on Monday in Aguascalientes, Mexico under the theme of Cities and Climate Change, UN Secretary-General Ban Ki-moon wrote in a statement that experts are predicting by 2050 the global population will increase 50 percent from what it was in 1999.

He noted that scientists have said by that time, "global greenhouse gas emissions must decrease by 50 percent compared to levels at the turn of the millennium."

"I call this the '50-50- 50' challenge. Rising sea levels are a major impact of climate change -- and an urgent concern ... The nexus between urbanization and climate change is real and potentially deadly," Ban wrote.

"Cities are centers of industrialization and sources of emissions, but they are also home to solutions. More and more municipalities are harnessing wind, solar and geothermal energy, contributing to green growth and improving environmental protection," he added.

In Vancouver, a city that hosted one of the early Habitat conferences in 1976, Rob Sienuc, principal of Broadway Architects, said his profession is cognizant of the implications of the rapid urbanization and is acting accordingly.

"We've turned a corner. We're changing our attitude toward the way we build cities, particularly here in North America. It's really starting to happen. But there is still a long way to go. Like anything, it's changing our attitude to the way we live. Too much consumption causes the problems we have here. It causes our pollution problems and everything else," said Sienuc.

Many of Sieniuc's projects, ranging from schools to purpose-built communities, are in Canada's far north in the Yukon and the Northwest Territories, where the winter temperatures can get as low as -55 degrees Celsius. With such extreme conditions, all his designs are planned and created in a sustainable environmental design, starting with the land, community and building.

"That's the order. We have to respect the balance of nature. We have to be in balance with nature basically. It starts at that point so anything we do in terms of an imprint on the environment we got to be respectful so we are not actually affecting the eco-systems. It's an ecology thing first, a community thing second, and to me, it's a building thing third. That to me is sort of the importance. We got to remember that," he said.

Of particular interest and concern to Sieniuc are energy sources. He considered that heavy reliance on fossil fuels, particularly coal, has been a big part of the world's pollution problems. In addition, the established economic powers have exported their problems to developing countries, hence the daily traffic chaos found in most big cities around Asia.

As a supporter of geo-exchange, and other renewable energies, such as solar and wind, he suggests the energy of the Earth can be harnessed by drilling down 60 to 100 meters. That far down there is a constant temperature that can be harnessed anywhere on the planet, be it Africa or the Arctic.

"I do a lot of work up north. The effects up there are very dramatic. Climate change effects are very dramatic. The cost of energy is very dramatic and you see these changes and the communities up there have to address them now because it's very, very costly," Sieniuc said.

"If we don't address them we're going to end up at a point where it's just going to become too much money to rely on that kind of energy to heat our homes, heat our buildings, schools and everything else. So we have to change the way, just change our approach to energy and what we use for energy."

Sieniuc added he has seen the effects of pollution first hand, even in the remote Yukon, an area of about 35,000 population and with little industry. The population have floated in from other parts of the world and settled down.

"When you are talking about Habitat Day, it truly is, it's a global thing and it's a global responsibility stewardship that we all have," he said.

"I use the term enviro-citizen. We are really enviro-citizens of the world and we got to be respectful of water across the border. We have to be respectful of the air, all those things, because that is the only way we are all going to be able to live together in future as the population grows and we have more and more demands on the Earth."