Small suppliers to multinationals are feeling the heat of global warming as an increasing number are being forced by their big-name customers to prove their green credentials.

Household names from a range of industries, including Dell, L'Oréal, PepsiCo, Hewlett-Packard and Reckitt-Benckiser, have announced that they will ask some suppliers to measure and disclose their carbon footprint, which is a measure of the impact of their activities on the environment using units of carbon dioxide.