How can humans obtain energy without using carbon dioxide-emitting fuels?

Renewable energy takes the energy of the sun and turns it into electricity. Examples of renewable energy are hydropower, solar power, wind, wave and water power, geothermal (using heat from the centre of the earth) and various forms of biofuels.

Nuclear power is non-renewable, but it does not emit carbon dioxide.

The most realistic options for meeting the massive demand for energy in the world today and in the future (currently some 15 terrawatts of power) is either nuclear fission or solar power. All other alternatives simply do not have the capacity to scale up on the level which is required for global implementation (for a detailed analysis of this fact, see the Web Links to the left under "Dr. Nathan Lewis").

While nuclear power could provide sufficient energy to the world carbon free, it would require building a new nuclear power plant every other day for the next 50 years in order to meet demand. Not to mention the problems of national security and the unsolved issues with dangerous nuclear waste that will remain toxic for hundreds of thousands of years.

Solar energy on the other hand has tremendous potential. FACT: MORE ENERGY FROM THE SUN HITS THE SURFACE OF THE EARTH IN ONE HOUR THAN THE ENTIRE WORLD USES ALL YEAR. There are vast supplies of energy in sunlight. The problem with solar energy currently is the cost -- solar cells are simply not economically competitive with other ways of making electricity from fossil fuels (in particular coal). Much more research and development must be done to reduce this cost. The other big problem with solar energy is that currently most solar cells only make electricity, which is difficult to store efficiently. Each night, the sun goes down, and you must have a way to store the energy you will need for the night. Charging and discharging batteries is a very inefficient way to do that. There are solar cells which can produce chemical fuels directly instead of electricity (such as water splitting solar cells that can directly electrolyze water to hydrogen and oxygen). These cells also need a great deal of further research and development before they can be used on a large scale.

See the Related Question links to the left: "What are some alternate sources of energy?"

Most, if not all of the sources of energy listed there are so-called "carbon neutral." Many do not emit any carbon dioxide at all (e.g. solar, geothermal, wind, tides/waves, nuclear), but those that do (biomass) remove as much CO2 from the air as they emit, so that the net is zero.