Many of the observed changes since the 1950s are unprecedented over tens to thousands of years. (hubpages.com)
They can generate anything from a few watts to a few megawatts and provide power for tens to thousands of households at a time. (newscientist.com)
Over thousands of years, the layers of snow build up, forming a flowing sheet of ice thousands of feet thick and tens to thousands of miles across. (nsidc.org)