Moles are not harmful to plants, since they eat insects, not roots, but they do cause unsightly ridges in your lawn where they push up earth above them. They are particularly difficult to combat. Moles can figure out to avoid traps, digging around them. They also don't easily eat poisoned bait because of their mouth structure. Carbon monoxide poisoning can be an especially humane way of treating them, as kind as you can get without resorting to a catch-and-release program.
Determine which raised ridges over the mole tunnels are active. This can be done by stepping on a stretch of raised earth above the tunnel to flatten it, and seeing if it stays flat for several days.
Flatten the ridges of the whole run of active tunnels where the lawn has been pushed up (just by stepping on them). These raised ridges aren't airtight, and would let the gas seep out and be less effective.
Attach a garden hose to your car tailpipe. Seal it, using duct tape.
Insert the other end of the hose in the middle, not the end, of a flattened ridge. Seal around the hose with dirt to prevent gas escaping.
Pump the carbon monoxide from the exhaust directly into the tunnel. Run your car engine for an hour to fill the tunnel.
Make sure to treat all tunnels in your yard by filling each with carbon monoxide multiple times.
Contact a pest exterminator for application of a fumigant, if the above does not work. Fumigants need to be applied by a licensed exterminator.