The Collaborative International Dictionary of English v.0.48:

Soberly \So"ber*ly\, adv.
   In a sober manner; temperately; cooly; calmly; gravely;
   seriously.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Soberly \So"ber*ly\, a.
   Grave; serious; solemn; sad. [Obs.]
   [1913 Webster]

         [He] looked hollow and thereto soberly.  --Chaucer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

soberly
    adv 1: in a grave and sober manner; "he walked soberly toward
           the altar" [syn: gravely, soberly, staidly]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "soberly":
   calmly, composedly, conservatively, coolly, decorously, demurely,
   dispassionately, earnestly, equably, evenly, formally, grandly,
   gravely, grimly, imposingly, in balance, in moderation, in reason,
   judiciously, loftily, magisterially, majestically, moderately,
   nobly, prudently, regally, restrainedly, royally, sedately,
   serenely, seriously, sober-mindedly, sobersidedly, solemnly,
   somberly, soothingly, staidly, stately, steadily, subduedly,
   temperately, thoughtfully, tranquilly, venerably, with dignity,
   within bounds, within compass, within reason, worthily