The heat would just travel back into space. Thankfully atmospheric greenhouse gases trap heat in the lower atmospheric layers and in the earth's surface. The gases are water vapor, methane, carbon dioxide, CFC's, and NO 2 . As the gases absorb outgoing radiation, they heat up and their warmth radiates back down to the earth's surface. Increased heat results in increased evaporation.
Hotter air holds more water vapor, creates feedback loop so the earth gets warmer.
A carbon dioxide molecule may last in the atmosphere up to 100 years. Atmospheric carbon dioxide is released from fossil fuel, cattle, cement, burning biomass, as well as other means. Principal ingredient of natural gas. Generated by bacteria in rice paddies, decomposing garbage, cattle, and ruminant animals. Fossil fuel production, landfills, pipeline breaks, as well as, other means.