Sustainability is actually a huge concept that covers almost everything that can run out or die. Money, life, and production are all areas in which sustaining is important. In the area of environmentalism it tends to focus on areas such as energy, fresh water, and raw materials.
How long can we continue to do a particular activity before we run out of what we need to continue the activity? There are renewable resources and non-renewable resources. If we plant a tree and cut down a tree (and wait 30 years) we have a renewable resource. If we mine the silver however it will not return so minerals are non-renewable.
Most current methods of energy production are based on removing a resource from the earth and then converting it to energy. Coal and oil are the primary sources of energy that we use today. These items will run out eventually because they take so long to form. Using other forms of energy such as nuclear power and solar energy can supplement our current energy needs.
Clean water is vital for life. In order to maintain our way of living we need to keep our water clean and free of waste products. As pollution fills our water sources and the water that is easiest to get to from beneath the surface of the earth is consumed the sustainability of our water supply can be in question. Keeping pollution from entering the water supply as well as finding ways to save water will be a great help in having enough clean water for the future.
Clean air is something that should be available for all people. As the air gets polluted by waste from industry and automobiles powered by toxic fuels the air quality begins to suffer. This is most noticeable in large cities when the smog in visible. Trees and other plant life clean the air as they go about their cycle of life but they cannot do it as quickly as we can fill it with waste. Not pumping as many noxious fumes into the atmosphere in the first place plays an important role in maintaining the air quality.
Raw materials are required to build and maintain all parts of the human civilization. From the food we eat to the clothes on our backs we need to conserve and recycle raw materials as much as possible in order to have what we want in the future.
The sustainability of our culture is in question. Do we have the necessary drive to keep from running out of the things that we need for existence?