Environment Canada or the people who negotiated the agreement would be in a better position to answer that question.
This is how I understand it; if Canada were to fall short of its 300-megaton objective at the end of the 2008-2012 period, there would be a new round of negotiations to cover the following five years. According to the Kyoto Protocol, Canada or any other country that does not meet its target will be subject to a 30% penalty. For example, if Canada has not met its 300-megaton commitment, the target will increase by 30%, which will lead to a 390-megaton deficit.