Earthshine Decreasing 

The reason we are able to see a new Moon is because it is lit by reflected light from the Earth - earthshine. The amount of earthshine is controlled by the Earth's albedo - the higher the albedo the more earthshine. In the last ice age the albedo was high as ice is a good reflector. Cloud cover acts in the same way. 

The source of the light is, of course, the Sun. And with light comes heat. Generally 30% of the solar energy hitting the Earth is reflected - the albedo at work.

How do you measure the albedo? THIS ARTICLE based on THIS PAPER tells you how and it is based on measuring earthshine. (Jokes about moonshine will not be tolerated!) The investigators have been measuring earthshine on the moon since 1998 and have found that it has decreased by an amount indicating a 0.5% decrease in the albedo. A decrease in the energy reflected out indicates an increase in the energy received by the Earth.

In the ice ages high albedo encouraged cooling; now the decreasing albedo is increasing global warming.

Surprisingly the change in the albedo is attributed to a shortage of low altitude clouds over the eastern Pacific.