326 Big pictures
explore some promising responses for urban regions and their natural systems
to the varied climate-change effects expected.
Vehicle usage, industry, and heating/cooling of buildings, as prime sources
of CO 2 and other greenhouse gases that lead to human-caused climate change,
are concentrated in cities. London and Singapore have some controls on vehicle
usage. Thus solutions must focus on cities to cut down the giant-chimney-like
upward rushing CO 2 flows. Certain German and Swiss cities are seriously invest-
ing in green buildings (Spivey 2002, Dunnett and Kingsbury 2004, Brenneisen
2006). Urban agriculture is growing worldwide (Smit 2006). These are exceptions,
but at the same time possible prototypes. Addressing the much-documented heat
island effect (von Stulpnagelet al.1990,Arnfield 2003), which worsens with both
urbanization and global warming, is particularly relevant now and long over-
due. Certainly many investments and actions by governments, organizations,
and individuals that decrease urban greenhouse-gas sources are warranted to
reduce the proliferating effects of climate change (Gore 2006).
Three broad effects of anthropogenic climate change on urban regions are
(McCarthyet al.2001,Houghtonet al.2001,Climate Change Impacts on the
United States2001,IPCCdraftsummary for Policymakers 2007): (1) temperature
increase, (2) sea-level rise, and (3) extreme weather events. For simplicity, precipi-
tation is included with the first and third effects. Typical effects will be outlined,
though of course variations exist for cities in every corner of the world.
Thetemperature increaseexpected is, in general, a few degrees Celsius (several
degrees Fahrenheit) over a few decades. What does that mean, for instance,
to the now-familiar city and region of Barcelona (Chapter 10 )(Forman2004a)?
Average annual temperature is likely to rise about 2◦C (4.5◦F) by the 2020s,
and 3◦Cbythe 2050s. Temperature increases in summer months will be even
higher. Average annual precipitation is likely to decrease about 10--15 % by the
2020s, and 20 % by the 2050s. An increased frequency and intensity of summer
heat waves, increase in summer drought risk, and greater frequency of intense
precipitation events are likely.
Does that really matter to people, or to the land? Yes. These climatic changes
would significantly squeeze the already limited water-supply system, parch the
soil of the economically and culturally important wine-growing area, scorch
the already-hot summer tourism season causing manifold problems for hotels,
restaurants, and local economies, and produce debilitatingly hot summer condi-
tions for all of Barcelona’s residents. Indeed these effects appear to be imminent.
Temperature increase typically increases evapo-transpiration which dries the
soil and desiccates plants. In built areas, that leaves less shade and less evapora-
tive cooling, i.e., a hotter city. A massive increase in green roofs and other bio-
philic design solutions using drought tolerant plants could reduce the problem,