PREPARE boiling water canner. Heat jars in simmering water until ready for use. Do not boil. Wash lids in warm soapy water and set bands aside.
COMBINE pears, lime zest and juice, sugar and ginger in a large stainless-steel saucepan. Bring to a boil over medium heat, stirring to dissolve sugar. Boil, stirring frequently, until mixture thickens, about 15 minutes. Remove from heat and test gel. If preserves break from spoon in a sheet or flake, it is at the gel stage. Skim off foam. If your mixture has not reached the gel stage, return the pan to medium heat and cook, stirring constantly, for an additional 5 minutes. Repeat gel stage test and cooking as needed.
LADLE hot jam into a hot jar leaving 1/4-inch headspace. Remove air bubbles. Wipe rim. Center lid on jar. Apply band, adjust to fingertip tight. Place jar in boiling water canner. Repeat until all jars are filled.
PROCESS jars 10 minutes, adjusting for altitude. Turn off heat, remove lid, let jars stand 5 minutes. Remove jars and cool 12-24 hours. Check lids for seal, they should not flex when center is pressed.