Food Wastage is third largest source of greenhouse gas emissions after the United States and China

[Ghost Dog]

2. If not done properly, yes:

... Poorly managed compost piles may still create unnecessary amounts of methane. There’s more to composting than just tossing grass clippings, dead leaves and food scraps onto a heap and walking away. The proper balance of air, moisture and organic debris called feedstock ensures thorough decomposition without production of methane gas...

/... http://thegreenenergyblog.com/uncategorized/preventing-methane-gas-composting

Composting is preferable to dumping in landfills, from where methane, if not harvested, will reach the atmosphere.