Robert Silverberg 
Time of the Great Freeze 

2650 ADThe Earth has been buried beneath a sheet of ice for 300 years. In cities miles beneath the surface humanity huddles, waiting for release.Dr. Raymond Barnes waits with passion, and listens daily for evidence of life on the still Earth. Finally, a voice from across the void hails his open frequency . . . the surface awaits mankind.But not all men are anxious to return to what was . . . those in power are determined to keep man in his new place, to retain their order of fear and oppression. Barnes and his courageous group of scientists and adventurers are arrested for possession of forbidden technology; the radio is destroyed! Their punishment is swift ejection from the underground city, their only hope is to reach London – 3000 desolate miles across a frozen wasteland!