The buying and selling of greenhouse gas emissions will begin in earnest this week as the Europe Union's trading scheme - the first of its kind in the world - officially began on Saturday, tying companies in a variety of energy-intensive industries to strict limits on the amount of carbon dioxide they are allowed to produce.

Four EU countries have not yet agreed their national carbon emission limits under the scheme, which will help Europe to meet its obligations to cut greenhouse gas emissions under the UN-brokered Kyoto protocol on climate change. Greenhouse gases are blamed for trapping heat on earth, causing global warming.