This thesis aims to provide the reader with an overview of climate change caused by the greenhouse effect by analysing policies and strategies adopted by countries, both presently and historically, with a focus on the situations in Europe and Australia. The main character of the work is going to be introduced, the CO2, and one of the main method to deal with it is deeply discussed and evaluated in detail: the Carbon Pricing. Following this, comparisons among countries are made, highlighting differences and calculating key performance indicators to determine which country has been the most polluting now and in the past.