Since Natural Gas Creates Carbon Dioxide, Why Would It Reduce

Since natural gas creates carbon dioxide, why would it reduce global warming to switch from coal to natural gas?

A) Actually, such a change would not reduce global warming.
B) Because electricity from natural gas plants would cost more and thus it would be used less.
C) Because natural gas plants produce a less polluting type of carbon dioxide.
D) Because mining is not needed in order to obtain natural gas.
E) Because natural gas uses less carbon per joule of energy than does coal.