Mayors from all over the world have gathered in the South African city of Johannesburg to participate in many exciting events at the Summit of the C40 Cities Climate Leadership Group, an international group of mayors created in 2005.

Amongst the events were the launch of the Climate Action in Mega-Cities 2.0 report and a discussion about the role of measurement and smart data in advancing city climate agendas.

The report details the actions taken by reporting cities since 2011. 41% of these actions are taking place at a citywide scale; and there is a 500% increase in cities implementing bike-sharing schemes over just two years, as well as a doubling of the number of cities reporting BRT systems.

I have uploaded an infographic about this.

Bill Clinton sent a message to the C40, in which he praised Michael Bloomberg's "evidence-based approach" to tackling climate change while mayor of New York City. View it watchable below.

The summit has also seen the launch of a new C40 city directors programme which includes three new African cities, Dar es Salaam, Nairobi and Cape Town, bringing the total number of C40 cities to 66.

A ceremony welcoming for new African cities to C40

Over half of these mayors have signed a letter urging the United Nations working group on sustainable development goals to include a specific urban goal targeted in cities' performance among the overall goals.

“As a global mayor, and one whose city will forever be linked to the global sustainable development agenda, I cannot stress enough the fact that without an urban goal the Sustainable Development Goals will be incomplete,” said Mayor Paes of Rio de Janeiro.

It was also announced that Houston had committed to read deuce greenhouse gas emissions by the city by another's 10%, following the successful reduction of emissions by 26% since 2007. "You can’t manage what you don’t measure,” said Mayor Parker. “Our achievement is impressive, but we must not stop there."

Christiania Figueres, the UNFCCC Executive Secretary, yesterday also told the assembly that cities were at the forefront of action in international climate agenda. Michael Bloomberg was welcomed as the new UN evangelist on this area. he was appointed by Ban Ki Moon to this role last week. "(Ban) probably is a little bit frustrated that the nations of the world haven't come together," Bloomberg said before the meeting. Bloomberg is also president of the C40 board.

City mayors also attended working sessions for their networks and there was a discussion on climate proofing cities with examples from cities as varied as Addis Ababa, Rotterdam, Venice and Philadelphia. Ironically Rome's mayor Ignazio Marino was prevented from attending because of extreme flooding in his city.

Today there is discussion on healthier, wealthier cities report that was released by C40 and the Climate Disclosure Project last June.