Just to make sure this is understood...

Berkeley CA

Description

Humans did not have to be around to melt ice thousands or millions of years ago because of Milankovitch cycles, which affect the amount of solar radiation hitting the planet's surface. Lest you think that alone can explain the warming now happening, it is too small an effect and takes thousands or millions of years to actually change the climate. The current situation is due primarily to the greenhouse effect caused by carbon dioxide and other greenhouse gases, but mostly CO2. This is happening much more rapidly than previous climate changes. Scientists are sure this stems from human activities, as the CO2 emitted by humans has a different isotopic composition than that from nonhuman sources. Also, the air is cooling more slowly at night now, which rules out any effect from the sun, which obviously is not hitting the earth with light on the night-side of the planet. Finally, the part of the atmosphere closest to the earth is warming, while the one further out is cooling, which is inconsistent with a sun effect, but consistent with a greenhouse effect.