Last week marked the release of Newsweek magazine’s inaugural environmental ranking of the top 500 largest corporations in America.

The article accompanying the rankings states that “For more than a year, the magazine worked with leading environmental researchers KLD Research & Analytics, Trucost, and CorporateRegister.com to rank the 500 largest U.S. companies based on their actual environmental performance, policies, and reputation”.

Newsweek acknowledges that ranking corporations for sustainability accross different industries is a huge challenge, suggesting that “there’s an inevitable apples-and-oranges element” to it.  For example, the best run mining company is still likelier to cause more environmental damage than the dirtiest financial-services company.  Additional, there is no uniform standard for reporting environmental data, nor is there a requirement to do so.

While discrepancies in available data may make this list more of a rough estimate of green corporate citizenship than the authorative source, Thomas Kuh, managing director of KLD Research (who worked with Newsweek on the rankings) defends the project by suggesting that “One of the purposes of this is to improve the transparency of corporations…and encourage them to provide an even higher level of disclosure”.

The top corporation on the list, Hewlett-Packard, was given high grades for being the first IT company to report GHG emissions associated with its supply chain.  Second place Dell scored well  by becoming carbon neutral in 2008 and leading the industry with product take-back and recycling programs.  Rounding out the top five are Johnson & Johnson, Intel and IBM.