SAN FRANCISCO, Sept. 13 (Xinhua) -- The Global Climate Action Summit, which brings delegates from city and regional governments, industries and research institutions to western U.S. city of San Francisco to enhance cooperation in tackling climate change, officially opened on Thursday.

At the opening plenary, San Francisco Mayor London Breed called on cities around the world to join hands and address the climate change as she welcomed more than 4,000 delegates from six continents for the summit.

Challenging people, communities, societies and economies around the world to 'step up', the summit is focused on taking ambition to the next level across five key issue areas: Healthy Energy Systems, Inclusive Economic Growth, Sustainable Communities, Land and Ocean Stewardship, and Transformative Climate Investments.

The three-day gathering features more than 25 sessions, 325 affiliate events and 500 major climate commitments.