The new UK emissions policy takes effect, forcing the country's largest companies to annually publish details of the greenhouse gasses they produce.
Around 1,800 firms listed on the London Stock Exchange, including worldwide known BP and Tesco, will have to release their total emission of greenhouse gases for the year in equivalent tonnes of carbon dioxide, which is the main international standard to measure CO2.
The UK is the first country in the world introducing the policy. The measure will be reviewed in 2015, after which other large British companies could be forced to publish their details as well.
The policy aims to make companies aware of their influence on the environment. Officials estimate that the measure will save 4 million tonnes of carbon dioxide by 2021.