We need a sustainable environment and sustainable energy resources to make life sustainable. The social cost of climate change caused by fossil fuels is many times high- er than the cost of preventing climate change. However the damage caused by climate change cannot be compensated for most of the time. In other words getting rid of fossil resources will be the most effective method in meeting the energy demand of human beings. There are still many power plants in the world where fossil fuels are used. In addition considering the fossil fuels consumed in buildings and vehicles the magnitude of the problem becomes more evident. However the transition to 100% carbon-free energy requires a unique engineering effort. Although the ultimate goal of scientists is to achieve sustainability with 100% carbon-free energy this will of course not be easy. This book is a humble effort to bring together different scientific perspectives concerning the carbon footprint of some human activities for a sustainable future and environment.