The greenhouse gases such as CO2, allow the earth to maintain its temperature.
The anthropogenic emissions has elevated the temperature from pre-industrial levels.
As those gases are responsible for keeping and re irradiate the heat from the sun, if their concentration grows, as well would the temperature. That is why the countries have made the Paris agreement, to prevent the temperature in the world increase more than 2 degrees from preindustrial levels.
The answer is C.