Firms guilty of overstating their green credentials can expect to face fresh criticism following the launch of a new website that provides consumers with an opportunity to evaluate the green claims made in companies' adverts.

The Greenwashing Index has been launched by US marketing agency EnviroMedia Social Marketing and allows users to post adverts and then rate them against a set of greenwashing criteria.

The criteria, which were developed in conjunction with the University of Oregon School of Journalism and Communication, cover whether the ad uses misleading words or graphics, makes vague or unprovable claims, overstates a product or services' green credentials or leaves out relevant information.

Visitors will be able to rate adverts based on the criteria and generate scores that will range from "good", to "pushing it", to "total greenwash".

EnviroMedia president Kevin Tuerff said he hoped the Index "will help eradicate bad environmental marketing claims and, at the same time, shine a positive light on companies making measurable reductions in carbon emissions related to climate change".

The site was launched as the US Federal Trade Commission (FTC) today hosts the first in a series of public workshops designed to review its environmental marketing guidelines.

The review of its so-called green guides had been scheduled for 2009, but late last year the FTC said it would be pulling the review forward in response to growing public concern over green marketing campaigns. The commission is to undertake a series of workshops over the coming months and could update its marketing guidelines to firms based on the results.

In related news, the UK Advertising Standards Authority today upheld a complaint from Friends of the Earth over an advert from the Malaysian Palm Oil Council that claimed its palm oil was " sustainably produced".

The ad, which appeared on BBC World last year, also claimed that palm oil production benefited the environment.

The ASA fully upheld Friends of the Earth International’s complaint that the advert was misleading on the grounds that palm oil production had resulted in widespread deforestation.

The watchdog ruled that the adverts were misleading, "because there was not a consensus that there was a net benefit to the environment from Malaysia's palm oil plantations".