(CNN) -- If you fix the cities, do you fix the problem? With 50 percent of the entire human race currently living in cities and responsible for emitting up to 80 percent of all global carbon dioxide (CO2) emissions every year, they certainly don't seem a bad place to start.
Multi-storeyed residential buildings stand behind an expanse of slums in Mumbai.
The Tyndall Centrer for Climate Change Research says "the fate of the Earth's climate" basically hinges on what we do with our cities from now on. But the fate of the world's cities largely hinge on what the developing world decides to do with their own growing metropolises in the next 20 years.
According to the World Resources Institute (WRI), urban populations in the developing world are growing at 3.5 percent per year, compared to less than 1 percent growth rates in developed world cities.
UN-Habitat says that a staggering 95 percent of the expected global population growth we will see over the next 2 decades will be absorbed by cities in the developing world.
What that means is by 2030 another 2 billion people from the developing world will be living in cities (only 100 million from the developed world meanwhile will be doing the same). Currently 75 percent of world's poorest people -- 1 billion -- live in cities.
Higher density, lower standards
Whether the new wave of migrants will find a better life in cities remains to be seen. More than 70 percent of city dwellers in the developing world (that's around 900 million people) live in slum-like conditions, according to the World Health Organization (WHO).
And that number is predicted to more than double to reach 2 billion slum-dwellers by 2020.
The health risks for people living in slum-like conditions will come from every corner and will include increased mortality rates from heat waves; higher risk of exposure to flash floods, mudslides and landfalls; and more frequent exposure to waterborne and infectious diseases (notably dengue fever).
When it comes to poor cities, bigger is by no means always better. According to UN Habitat, the mega-cities of the future, (those with more than 10 million residents) will be "giant potential flood and disaster traps" if insufficient action is taken on behalf of their residents.
Already, 75 percent of the world's 21 mega-cities are based in the developing world, and by some estimates, 27 of the 33 mega-cities expected to exist by 2015 will be in developing countries.
Cities have always traditionally been the centers of the world's wealth, and the World Bank says that as much as 80 percent of the future economic growth of the developing world will come from its cities.
But the United Nations Environmental Program me (UNEP) has also recently said that population growth in the cities of the developing world "has outpaced the ability to provide vital infrastructure and services".
Rapid economic growth brings substantial problems of its own -- notably increased pollution. Already, 16 of the 20 most polluted cities in the world are in China, which is arguably undergoing the most rapid industrial and economic transformation the world has ever seen.
Today urban air pollution prematurely kills 1 million people a year, the majority disproportionately located in the developing world.
The pollution is not, as some might expect, always transport-related. Some of the most potent and deadly forms of pollution affecting city residents in the developing world are entirely industrial in their nature.
In 2007 the Blacksmith Institute came up with an unranked list of the top 10 most polluted cities in the world. Without exception the sources of that pollution were industrial -- factories pumping out chemicals into the atmosphere and into water supplies.
The pollutants in question amongst the cities in this top 10 were predominantly made up of toxic chemicals, lead, radioactive materials (one of the cities is Chernobyl) and airborne particulates.
Toxic pollution is a particular disease of the developing world's urbanites, affecting more than 1 billion of its citizens. The World Bank says that as much as 20 percent of all the health problems in the developing world can be attributed to environmental factors, particularly pollution.
Mercury levels in the groundwater in Vapi, India, one of Blacksmith's top 10 polluted cities, is a breathtaking 96 times higher than WHO standards. And if you live in Sumgayit in Azerbaijan, also on the list, where "genetic mutations and birth defects are commonplace", you have between a 22 percent to 51 percent higher chance of getting cancer than if you lived anywhere else in the country.
Clean transport takes a backseat to growth
Transportation-related pollution just rubs salt into the wound in these parts of the world. And unless dramatic changes take place in world's cities' transport systems, things will go from bad to worse.
Globally, according to Pew Center on Global Climate Change, emissions from transportation are "rising faster... than any other sector."
In the next 30 years, China alone will have around 752 million urbanites, all needing to get around town. Currently, less than 1 percent of Chinese own a car.
According to World Watch, the Chinese adopting the American "car-centered model in these places would have disastrous consequences".
It gives an example: If each of those 752 million city dwellers copied the transportation habits of your average resident of San Francisco in 1990, the actions of that one country would result in 1 billion additional tons of carbon emissions a year -- the same amount that was released worldwide by all road transport in 1998.
Clean public transport systems then are being increasingly seen as a necessity all over the world, but particularly in the developing world. Pew says that challenges that motorization presents the developing is "unprecedented" and warns that "there is little time or money to build public transportation systems or to expand roads to handle the new traffic."
How well these cities will cope with their particular problems could largely be down to the local officials in charge, if the experiences of London, New York and Bangkok are anything to go by.
City officials in Bangkok were ultimately responsible for reducing the city's air pollution levels by 20 percent to 50 percent, even with a 40 percent increase in vehicles, according to The Economist and they managed this by imposing stricter rules on motor-related pollution and introducing unpopular but effective taxes. E-mail to a friend
Sources: UN IPCC; UNEP; UN Habitat; Tyndall Center for Climate Change Research; Economist; World Resources Institute; Climate Change and Developing-Country Cities: Implications For Environmental Health and Equity; E Magazine; World Watch; Pew Center on Global Climate Change