Warning: The people of the world, within ten (10) years time, need to reduce carbon emissions to prevent global warming and save the planet.
Carbon emissions, carbon footprints, greenhouse gases, climate change or global warming are just few phrases which we find to have been part of our normal daily life. It is unfortunate that its only the obvious that people see. Sustainability is not only about climate change.
On the net, there are several definitions which we can find about sustainability:
Sustainability - the ability to maintain balance of a certain process or state in any system. It is now most frequently used in connection with biological and human systems. In an ecological context, sustainability can be defined as the ability of an ecosystem to maintain ecological processes, functions, biodiversity and productivity into the future.[Source]
Sustainability - the development that meets the needs of the present without compromising the ability of future generations to meet their own needs.[Source]
Sustainability - our responsibility to proceed in a way that will sustain life that will allow our children, grandchildren and great-grandchildren to live comfortably in a friendly, clean, and healthy world. 
At present times, sustainability is considered to be an important aspect in project implementation. From concept definition, detail design, construction to operation, sustainability plays a big factor in assessing the feasibility of projects. Resource sustainability, impact to environment and climate, or impact to the community need to be assessed in every aspect.
Incorporating sustaibility in every aspect of the project will provide a greater advantage of winning the bid.