Prior to the start of COP16, local governments worldwide moved to the next phase of concrete climate action at the World Mayors Summit on Climate (WMSC2010) in Mexico City on 21 November 2010, convened by Mexico City in conjunction with the World Mayors Council on Climate Change (WMCCC), ICLEI – Local Governments for Sustainability and United Cities and Local Governments (UCLG).

The Global Cities Covenant on Climate (the Mexico City Pact) and carbonn Cities Climate Registry (cCCR) were the most concrete outcomes of the WMSC and were presented in this side event. Local leaders also presented their latest positions with regards to UNFCCC/KP negotiations, paying specific attention to the fact that nations in Nagoya recognized and supported local government action by adopting the "Plan of Action on Subnational Governments, Cities and Other Local Authorities on Biodiversity" at UNCBD-COP10. The desire for a similar outcome at UNFCCC COP16 was addressed.