Green is a simple concept that goes back to sustainability. Human population on earth now threatens to overwhelm the ability of the natural environment to sustain life. Many ways in which we use the planet are dangerous and the volume of use is overwhelming the natural environment. Ninety percent of all energy consumed comes from fossil fuels, which create air pollution, acid rain, and global climate change. We have to decide whether we want life to continue or not. Our choice is to take from the environment—until nothing is left—or to borrow from it. If we borrow, then life on earth is sustainable. Otherwise, we will be one of the last generations of humans on the planet.

In examining our relationship with the natural environment, we have come to understand that some of our practices are not even healthy for humans. The toxins we generate impact the environment of other people and even the environment in our own homes. By developing our green technology, we not only help preserve the natural environment, we also help to clean up the environment in which we all live.

We might divide the motivation to "go green" into three types:

• Practical: Because it helps me.
• Responsible: Because it's fair.
• Purist: Because it's right.

Some people want to be green for practical reasons. They know that the price of energy is going up, and they want to get in front of the price increases so that they can save money in the long run. PVs (photovoltaic systems), better insulation, and buildings that take advantage of natural heating and cooling will all probably save money in the long run. It can be very practical to be "green" if you are prudent about where you spend your money.

Some people know that we are taking too much from the environment and it's hurting our natural surroundings. All the traditional environmentalism is aimed at such goals as preserving habitat, supporting species that are threatened with extinction, and keeping the global climate from wildly changing. Preventing serious environmental damage is our responsibility to others on the planet because everyone draws on the environmental commons.

Some people just recoil at the thought of destroying the beauty and spiritual value of the world. Stomping through that great web of life without concern for its frailty, interconnectedness, and irreplaceable wonder is unjust and uncalled for. Taking a look at what we can personally do to stop wanton destruction appeals to those who care about the world and others in that world.

Of course, there's nothing to say that one person can't have all three motives. In that case, we'd call them really, really, really green!

How green are you already? You can calculate your carbon footprint with the Inconvenient Truth Carbon Calculator, which will tell you how many tons of carbon dioxide your household emits per year.