More than half of the world's expected nine billion people will live in giant urban expanses by 2030 as cities and their hinterlands occupy an additional 1.2 million square kilometers, thereby tripling in size. That's an additional 1.35 billion people living in cities, suggesting that urban areas that currently occupy roughly 3 percent of the planet's surface will continue to expand. By comparison, urban areas increased by just 58,000 square kilometers between 1970 and 2000.

In new work published in Proceedings of the National Academy of Sciences, urban environment researcher Karen Seto of the Yale School of Forestry and Environmental Studies and her colleagues first divided the global land area into discrete parcels and, using predicted gross domestic product growth, population growth and urban land area cover in 2000, they projected which parcels had a high or low probability of succumbing to citification over the next few decades. Using that model, 1.2 million square kilometers of land have probabilities higher than 75 percent of becoming citified and nearly six million square kilometers have some probability of going urban.

"More than half of the urban land cover on the planet by 2030 has yet to be built," Seto explains. "The expansion of urban areas will have a direct impact on biodiversity hot spots."

Fifty-five percent of that expansion would come from massive urbanization in India and China—a trend that has been growing in recent decades. For example, a megalopolis similar to the urban corridor between Boston and Washington, D.C., in the U.S. is likely to form between Hangzhou and Shenyang in China. But the fastest urbanization is predicted to occur in newly developing regions in Africa, such as the coast of west Africa along the Gulf of Guinea and the shores of Lake Victoria farther south, encompassing Burundi, Kenya, Rwanda and Uganda, among other regions.

This may be bad news, in some cases, for the rich array of plants, animals and microscopic life that also inhabit Earth. The Eastern Afromontane, Guinean forests of west Africa and Western Ghats of India, along with Sri Lanka, are all home to such biodiversity—as well as projected to undergo rapid urban expansion that will encroach on the territory of already endangered amphibians, birds and mammals. Seto and her colleagues project the worst impacts of urban growth to occur in Central and South America.

In addition, such land use change is likely to result in even more of the greenhouse gas emissions that drive climate change, according to the new analysis. An estimated 1.38 billion metric tons of carbon could be released as forest transforms to roads, buildings and homes. As it stands, the world's cities bear responsibility for at least 70 percent of global carbon dioxide emissions. "We need to be more deliberate as a society about how we want urban places to become what they serve for humanity," Seto argues. "Too often, urban expansion is haphazard."

This is not just bad news for animals or the atmosphere, of course. Haphazard urbanization can also ill serve human inhabitants cut off from supplies of clean water or food. And the impact of urbanites is not confined to city limits; a typical Australian from Melbourne or Sydney requires greenhouse gas emissions, water diversion and land use from the entire continent. "Cities have always relied on their hinterlands and other distal places for resources from food and fuel to waste assimilation," the researchers wrote.

10 Comments

1. 1. geojellyroll 07:33 PM 9/18/12

   Huh?
   
   More urbanization means LESS impact on the environment. Cities across the world know that higher density means less use of water, energy, infrastructure, etc.
   
   Rural people use more resources per capita than those in mega cities.
   
   

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2. 2. ultimobo 08:09 PM 9/18/12

   to geojellyroll - yeah density may be more efficient - except for the fact that the most fertile lands tend to be first overbuilt by urban expansion - viz. Orange County in California - as populations naturally gravitate to relatively flat waterside locations, they increasingly occupy the best arable land, requiring more expensive and risky resource-intensive shipping of food grown in more distant locations, with I submit increasing waste, where the average household nows throws out at least $1kpa worth of wasted food. The trend to urban community gardens is an attempt to re-establish the proximity of home and garden.

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3. 3. tharter in reply to geojellyroll 08:33 PM 9/18/12

   Read page 2...

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4. 4. CliffClark 09:01 PM 9/18/12

   to geojellyroll: Cognitive bias is present here. Yes, larger cities may be more efficient. Efficiency is not the appropriate metric. Higher populations living in larger and larger cities require more energy use to transport food to markets, create much larger problems in dealing with waste, and the like. Building cities requires a long-term investment in resources that is not recycled in short- to medium terms. Pollution endemic to large cities takes its toll on the health of human and animal populations, potentially reducing the quality of life. To use only one measure to evaluate the impact larger and larger cities have is more than misleading; it is almost criminal in the way it confuses those people who are still working on developing their critical thinking skills, with the resulting complacency about negative aspects of change or buy-in to untenable and destructive policies. This is deliberate misdirection. Shame on you.

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5. 5. donschandel 11:47 PM 9/18/12

   "10 sauropods would have contributed 7.6 tons (6.9 tonnes) of methane every year, researchers end up with more than 550 million tons (500 million tonnes) of methane produced every year.
   (Cows produce 55 to 110 million tons (50 to 100 million tonnes) of methane each year)"
   above DiscoveryNews.
   So, were does that leave us. No were! We have a lot of poop to go around...

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6. 6. drgray 02:12 AM 9/19/12

   I am wondering how much of these projections into the future have incorporated the ever-present earth anomalies that will ultimately occur in some major and minor size and duration. We have no real way of predicting with much accuracy the asteroid that is headed our way and by the numbers there is at least one if not more on their way. How is our sun going to behave in the future and will we be able to respond with any real viability? Have these unknown variables been factored into this "gigalopolis" projection? What about just plain old human social interaction that could initiate a massive global reduction in population and resources? If we take all of our past history of civilizations growing into oblivion and factor in that potential, will we have our current civilization destroy itself prior to "megalopolis" even being realized? I think that being prepared for some potential future is wise and yet so many variables must factor into this projection into the future that we leave ourselves playing a never ending guessing game. Futuring, as a very new science, is really doing nothing more than some rather sophisticated speculation that must remain open to moment by moment change with regard to the speculated outcome. Just as taking scientific findings regarding carbon, and projecting mankind's ability to create excessive global warming and then finding that we have left so much other factual data out that our projections are flawed in favor of creating wealth rather than health. Something worth pondering with a little more skepticism as I see it.

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7. 7. Common sentences. 03:28 AM 9/19/12

   I like cheese.
   
   
   One must ask, what is its footprint?
   

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8. 8. alan6302 08:35 AM 9/19/12

   cities will make great targets for the coming nuclear war.

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9. 9. jtdwyer in reply to alan6302 11:20 AM 9/19/12

   We probably won't have to wait that long - some avian virus will more likely wipe out all the poor souls crammed into all those little spaces...

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10. 10. Steve3 in reply to geojellyroll 02:27 PM 9/20/12

    Not in the poor developing world. Yes in the USA those rural folks with their V8 pick ups and frequent trips to Dairy Queen and the hardware store rack up CO2. Then of course there's the use of HVAC and with the door being opened by the dogs 200 times a day etc.
    
    But not in the developing world where the growth will be.

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