CO2 acts as a greenhouse gas to trap heat
from the sun.
Natural amounts of CO2 has kept the earth warm to support life - as we know it.
Burning fossil fuels emits excess CO2 to the atmosphere.
This enhanced greenhouse effect traps more heat and leads to global warming.
Methane is also a greenhouse gas and can trap heat 25 times as much as CO2, but since much less methane is being released to the atmosphere, its current CO2 equivalent contribution to global warming is only 14.3%.