Natural Gas Environmental effects

What are the environmental effects of harvesting, refining, and burning natural gas? I know burning it produces water and apparently it is cleaner than other fossil fuels. Where are our natural gas deposits that are feasible to extract? What is the risk of environmental damage? I'm concerned that using natural gas will be an improvement over other fossil fuels, environmentally speaking, but may still cause damage, some or all of which may be irreversible in the short/medium terms (a few decades or less).