IT companies and calculating environmental impact

Typically for an IT companies, the impact to environment from their operations or products is relatively very low. Whatever it is, comes from following -
1. IT Servers and user computers
2. Facilities/ Offices
3. Use of products (like some hardware) at customer' end

Look at these links from leading IT companies on how their operations cause environmental impact and what steps have they taken to mitigate the same - 

1. Apple's environmental impact 

2. SAP and Greening of Service Business