The fact that something is physically and logistically possible doesn’t, however, tell you whether it’s the right thing to do. And there are a growing number of thinkers arguing against this hyperdense vision of the future — particularly in the context of fast-urbanising nations such as China. Here, rapidly built high-rise neighbourhoods are often poorly linked to transport systems, and do not provide adequate access to the services people need. “You can have vertical sprawl,” says Altman at Fivesquares. “If it’s all high-rise city, if it’s not linked to transport networks, if we haven’t learnt to mix uses and create places that feel humane, then that’s going to be a problem. Planning can get sacrificed because it’s all happening so quickly.”
Even where hyperdensity is done thoughtfully, the environmental case is not necessarily a slam dunk. First, cities should not be thought of as benign in themselves: as LSE’s Power pointed out in 2000, they are “particularly harmful to the environment”, using three-quarters of the world’s energy in 2% of its land surface. Moreover, each city dweller uses more resources than the global average, not fewer: a recent research paper on megacities published in the Proceedings of the National Academy of Sciences found that while the 27 largest cities hold 7% of the global population, they use 9% of the world’s electricity, 10% of its petrol and produce 13% of its waste.
The reasons for this high energy use are not fully known. Mark Bessoudo, a sustainability specialist at WSP in Toronto, points out that high-density areas depend upon low-density hinterlands. “What’s not often taken into account,” he says, “is the fact that to keep them running, these cities also require industrial lands, ports, suburbs. In other words, the environmental benefits of a city’s dense urban core can be outweighed by the resource-inefficient yet essential areas on its periphery. They’re two sides of the same coin.”
Others believe that the heavy transport and other infrastructure needed for hyperdense cities is not as efficient as assumed, in part because it has to be run constantly, including at times of low demand. Hyperdensity also results in much less roofspace per dwelling for the kind of solar energy generation that could otherwise power new homes.
These doubts combine to limit the importance that hyperdensity’s supporters, such as Sharro, can place on environmental arguments. “A lot of people who are in favour of the sustainability agenda are quite sceptical,” he admits. “We need to be really careful about making [sustainability] claims. Because whenever they’ve been made in the past, they’ve been open to critique.”
If the sustainability argument isn’t clearly supportive of hyperdensity, there are others that are decidedly negative. One centres around the social implications of the commercial business model that often delivers high-rise. Duncan Bowie, an urban policy academic at the University of Westminster and adviser to former London mayor Ken Livingstone, says that the density of new development in the city has ramped up in recent years to 150 homes per ha, with as much as 60% provided in developments that are above the density levels recommended in the city’s guidelines.
The upshot, says Bowie, is simply that land has become more and more expensive, which then enables developers to argue that they can’t provide social or affordable housing.
Last year, Bowie told the London Assembly (an elected body that scrutinizes the activities of the mayor): “Bluntly, when you get to very high densities, you do not get family units and you generally do not get affordable housing. We have to recognize that there are quite negative consequences of pushing hyperdensity to the extent we are. We have to … look at what type of housing we are actually trying to build.”
If hyperdensity has the potential to be socially exclusive, others argue that it can be psychologically problematic too. There are many studies connecting urban environments to negative impacts on our mental state. These include a comprehensive 2004 study by Kristina Sundquist, published in the British Journal of Psychiatry, which found an association with depression and psychosis: the more densely populated the area, the greater the association, with those in the densest areas up to 77% more likely to develop psychosis.
Now some, such as Canadian neuroscientist Colin Ellard, director of the Urban Realities Laboratory at Waterloo University in Ontario, are starting to draw measurable connections between these negative effects and the physical make-up of cities. Ellard says his tests, which use virtual reality to chart people’s reactions to a variety of environments, show that “high-density settings in which we’re surrounded by very tall and oppressive structures … can have a substantial effect on your mood”.
One of the most important voices in the density debate is architect Jason McLennan, creator of the Seattle-based Living Future Institute and a former winner of the Buckminster Fuller Prize. He argues that the idea of living your life high above ground, in artificial environments with limited access to natural light, goes against the grain of people’s natural affinity with nature — known as biophilia — and their circadian rhythms, as well as research linking behavioural problems to lack of access to nature. “There is increasing evidence that children shouldn’t spend time in high-rise environments where they don’t see faces,” he says. “Studies are linking stress levels and how the brain fires when you deprive it of that kind of sensory impact.”