MELTING SNOW AND ICE: Ice and snow reflect 40 to 60 percent of the sun’s incoming rays. This has the effect of cooling the planet. But as rising temperatures cause ice and snow to melt, the darker land or water underneath will absorb more heat. This could amplify the greenhouse effect, perhaps by 10 to 20 percent.

THE OCEANS: Water is an excellent heat absorber, and it appears that the oceans can store enough heat to delay the full onset of the greenhouse effect by decades. Just how much delay is difficult for scientists to predict.