1. The artificial manipulation of the environments of the earth; especially, as a means of counteracting global warming.
2. Proposals to deliberately manipulate the earth's climate to counteract the effects of global warming from greenhouse gas emissions.

So far, no large-scale geoengineering projects have been undertaken, nor has a consensus been reached that geoengineering is desirable.

President Obama’s science adviser, Dr. John Holdren, after giving his first round of interviews (April 10, 2009) immediately caused a ruckus by airing his thoughts on geoengineering; the large-scale tinkering with the earth’s climate to chill runaway global warming climate changes that could potentially slow or reverse global warming.

Holdren emphasized that even if he personally thinks it prudent to start evaluating geoengineering options, he still believes that the most pressing concern should be curbing greenhouse gas emissions to prevent global warming from reaching catastrophic proportions.