There are many current issues that affect the long term sustainability of the built environment. From a land use standpoint, the way the U.S. has developed around sprawl and the automobile has become an issue with sustainability. For example, the separation of uses as the predominate pattern of development after W.W. II has increased the use of energy for transporation of people and goods in turn putting more strain on the environment.
The built environment has a dramatic impact on the hydrological cycle as well. Increased physical development and impervious surfaces mean there are less natural features to absorb rainwater, leading to greater runoff and flooding. The loss of open space results in less water Infiltration into the ground and less evapotranspiration of water and moisture back into the air due to the loss of plants and trees. The quality of our water is diminished due to runoff, seepage, waste/toxins, and groundwater discharge all of which are the result of the built environment.
The total cost on the environment must be accounted for when thinking sustainably. The embodied energy, the energy needed to produce or transport materials, is referred to as the real cost of building or producing something. Each phase of the process requires energy, but not all phases are considered when thinking about usage. For example, the cardboard used to transport building materials when building a house is not accounted for in the total energy used to build the house. However, cardboard is the largest component of construction waste. When we think about sustainability we need to consider all aspects of production, and attempt to reduce energy consumption whenever we can.