Melting Snow and Ice Warm Northern Hemisphere

From NASA Earth Observatory:

Snow and ice help control how much of the Sun’s energy Earth soaks up.Bright white snow and ice reflect energy back to space. Because that energy does not get absorbed, it does not go into Earth’s climate. As a result, snow and ice cool the planet. This effect is called a climate forcing because snow and ice directly influence the climate.  

“On average, the Northern Hemisphere now absorbs about 100 PetaWatts more solar energy because of changes in snow and ice cover,” says Flanner. “To put it in perspective, 100 PetaWatts is seven-fold greater than all the energy humans use in a year.” Changes in the extent and timing of snow cover account for about half of the change, while melting sea ice accounts for the other half.