To combat the predicted effects of climate change, alternatives to emission reductions are under consideration. Global scale atmospheric chemistry or infrastructure projects might reduce the amount of solar radiation being trapped as sensible energy or consume the carbon dioxide (CO2) and other greenhouse gases already present in the atmosphere.
While many approaches are possible, one example of such a project is removal of CO2 from the atmosphere on a large scale. This could be accomplished through seeded gas-phase chemical reactions or through fertilization of the ocean for CO2 uptake. Another example involves application of a layer of reflective chemicals or particles to the upper atmosphere to reduce incident radiation at the Earth's surface. A third idea is to build a large reflective object in between the Earth and sun to block some incident radiation before it reaches the atmosphere.
Geoengineering projects would inevitably alter the climate on a global scale. It will be very important to understand fully the impacts of geoengineering approaches before they are implemented.