Sharon Harlan
Arizona State UniversityWhat do we know: What does Sociology bring to the table for studying the human dimensions of global
climate change?
I begin with a few observations about climate and climate change that seem most salient to me from a sociological
perspective, although they do not all derive from sociological studies. My choice of these particular observations
is influenced by my immersion in an interdisciplinary research environment in which I collaborate with
biophysical scientists on studies of urban socio-ecological systems. Similarly, my views of what sociology can
contribute to studying global climate change, and how sociologists can most effectively participate in influencing
public responses, are also situated in my recent experiences of researching the relationships among climate,
landscapes, and human health in cities.
- Climate changes are occurring globally at multiple spatial and temporal scales. For example, it is widely
accepted that the global average temperature has risen 0.5oC since the 1970s (McMichael et al. 2006). In
roughly the same time period, however, changes in nighttime city temperatures compared to surrounding rural
areas have been several times larger and most estimates of current differences at the urban-rural interface
range from 1 – 3oC (Voogt 2004). Seasonally and in some cities, the temperature increases are much larger.
Not only are cities experiencing chronic temperature increases, but global and urban warming are jointly
responsible for more extreme heat events in cities. Those acute events are longer in average duration than they
have been in the past and are also projected to be more frequent and intense in the future (Meehl and Tebaldi
2004). - Human systems and non-human systems are interacting at multiple scales to cause the socio-ecological
changes that affect climate. Just as greenhouse gas emissions and land-use transitions are widely accepted
as major causes of global warming (Kalnay and Cai 2003), temperature increases in and around cities have
anthropogenic sources. The urban heat island (UHI) is primarily attributable to the replacement of naturally
vegetated land cover with buildings and vast expanses of impervious surfaces that increase heat-absorption
and heat-storage capacity (Voogt 2004). The UHI effect is also heightened by vehicles and energy use in
urban households and industries that release heat near the ground. The UHI effect is spatially distributed
unevenly over urban landscapes, resulting in substantial intra-city heterogeneity in climate variables, such as
temperature and humidity (Stabler et al. 2005). Thus, urbanization contributes to meso- and micro-climate
changes and these changes are more intense and variable within cities. - Climate and climate changes have important and unequal effects on the vulnerability of different groups
of people that can be measured and perhaps explained by similar processes of social stratification at the
global level and the very fine resolutions of individual neighborhoods and households in single cities.
For example, the distribution of temperature, similar to many other environmental hazards in cities, is
substantially correlated with the social class and race/ethnic composition of urban neighborhoods (Jenerette
et al. 2007). In Phoenix, Arizona, affluent whites are much more likely to live in neighborhoods that have
lower average temperatures and where they are exposed to many fewer hours of extremely high temperatures
than low-income and Latino residents (Harlan et al. 2006). Intra-regional correlations between population
characteristics and local differences in temperature and hours of exposure are primarily explained by
vegetation cover and open spaces in the neighborhoods.