San Francisco has a mandatory recycling law. This was allegedly done to prevent landfills from releasing methane. They might seem to have a point except that composting could interfere with carbon burial (earlier discussed here).
If they really want to use garbage policy to lessen the greenhouse effect, they should char the garbage enough to stop decay (maybe they could use solar power for that) and then throw it in the landfill anyway. On the other hand, this doesn't require passing laws that tell ordinary citizens what to do, so professional busybodies won't get off on this policy.