318Big pictures
be densely peppered with parks and greenspace corridors (Jacobs 1961, Cityspace
1998), so non-urban species can move relatively unimpeded throughout the city
(Chapter4).
Amassive implementation of one of these fine-scale solutions, or several
examples of all the types, could create a city where the packed people daily
encounter and are attuned to the environment. Still, it would be an anthro-
pocentric result. Only shreds of nature could thrive long term. Perhaps only a
massive implementation of all the fine-scale solutions, admittedly an idealistic
goal, could fit the test of urban sustainability.
Asecondsustainability concept takes asystems view of the city,somewhat anal-
ogous to ‘‘urban metabolism” (Sukopp and Werner1983,Haber 1993, Tjallingii
1995,Ravetz2000,Grimmet al.2003). Consider a city as a huge box bulging
with people, and in which some products are manufactured and traces of food
grown. If all the holes in the box are blocked up, the people die, because the
internal production is totally inadequate to sustain the population. Also very
little has been stored in the city to handle such a crisis as plugged-up holes.
Normally the holes of the box are open so huge amounts of things, from food
towater, building materials, vehicles, and people, enter. And immense amounts
leave, including garbage, pollutants, vehicles, and people. The city, as part of a
larger system, is a box with inputs and outputs.
The functioning of Hong Kong, in 1971 a coastal city with four million resi-
dents (Boydenet al. 1981 , McNeill2000), is a vivid example. Its daily atmospheric
inflows and outflows (in thousands of tons) were: oxygen 27 and 0, respectively;
carbon dioxide 0 and 26.5; carbon monoxide 0 and 0.16; sulfur oxides 0 and 0.31;
nitrogen oxides 0 and 0.12; and dust 0 and 0.04. The city’s in-and-out water flows
were: freshwater 1068 and 819; sewage water 0 and 819; and solids in sewage
0and 6.3. Other major inputs and outputs included: petroleum 11.7 and 0; food
6.3 and 0; food waste 0 and 0.8; miscellaneous cargo 18 and 8.1; and people
0.53 and 0.52. The city was a giant sponge, every day absorbing tons of freshwa-
ter, petroleum, food, and cargo goods. And every day it sent tons of pollutants,
sewage, and diverse materials mainly to surrounding areas.
The larger the inputs and outputs relative to production and storage within
thebox,the less stable or sustainable a city is (Tjallingii1995,Forman1995). A
truckers’ or garbage-removal-workers’ strike, or a major breakdown of the water-
supply or sewage-treatment system, causes enormous disruption. All of these
have happened in various cities to the dismay of residents and policymakers
alike. Nevertheless, in addition to reducing population, each of the basic com-
ponents of the city system can be improved. Stability or sustainability can be
enhanced by: (1) decreasing consumption by people within the city; (2) increasing
production in the city; (3) increasing storage in the city; (4) decreasing inputs to
thecity; and (5) decreasing outputs from the city.