If you burn the plastic now, you get all the CO2 now.
Some plastic last for hundreds of years, so the same amount of CO2 will be released more slowly. An optimistic view is that half of the "CO2" will be trapped for a few additional hundred of years.
A slightly more interesting part is that a part of the emission is methane (that is like 100x worse than CO2), but the article says that the level of methane emission is insignificant anyway.
