@58539672: The definition of sustainable is satisfying the needs of the present generation without compromising the ability of future generations to satisfy theirs. Uranium is limited, albeit abundant, in quantity. If we keep exploiting uranium sources, they will be gone in 2000 years. Thus present consumption reduces the amount available to future generations, and in other words, it is unsustainable.
A very promising technology is very extremely plausible. Artificial Photosynthesis could very easily pave the way to a greener and more sustainable future. Similar to how a plant leaf takes in sunlight, carbon dioxide, and water to make glucose, artificial photosynthesis uses the process to take in sunlight, carbon dioxide, and water to make usable fuels such as hydrogen and ethanol. This means the ability to take in CO2, lowering greenhouse gases, and produce usable fuel sources. If we can improve our hydrogen fuel systems (which is quite easy to do really), then our exhaust would be nothing but water, which also happens to be a fuel source for the initial system in the first place.
By implementing solar, wind, geothermal, nuclear, and all other sustainable power methods with techniques like this, we can easily sustain our power and fuel needs, while actually lowering our carbon footprint.
Of course, one thing many people do forget is that all these new technologies still do, and very likely always will, require some non-renewable resources, such as petroleum. Without oil production, we have no plastics to manufacture the necessary components of modern green technologies and computer technologies. Even synthetic oils are often made from natural gas products. That's why I think technologies such as artificial photosynthesis will be the future, as they will actually reverse the negative impact of these required resources.