On May 30, 2007, California Governor Arnold Schwarzenegger and Ontario Premier McGuinty signed a Memorandum of Understanding on climate change, agreeing to coordinate efforts.

Ontario and California agreed to:
• Coordinate efforts to switch to clean energy technologies, promote green buildings and increase efficiency;
• Collaborate on energy efficiency programs;
• Work together on national, North American and international emissions trading;
• Explore market-based mechanisms, such as expanding the Western Regional Climate Action Initiative to encourage an effective carbon market; and
• Coordinate policies requiring transportation fuel producers to reduce carbon emissions by 10% by 2020 - the equivalent of removing 700,000 cars from the roads.