From Paris (COP21) to Belem (COP30): Cities at the frontline of climate action

On 23 June 2025, the Global Cities Hub participated in the Mayors’ Summit organized by Anne Hidalgo, Mayor of Paris, marking the 10th anniversary of the Paris Agreement. The event brought together city leaders from across the globe, including Athens, Barcelona, Brazzaville, Douala, London, Milan, Montreal, Nairobi, Phoenix, Rabat, Rio, Taipei, Utrecht, and many other representatives of international organizations, legal experts, and climate scientists. The Summit served both as a celebration of progress and a mobilization ahead of COP30 in December 2025 in Belém, Brazil.

While the Paris Agreement was a landmark in global climate governance, the world remains off-track to meet its central objective of limiting global warming to 1.5°C. According to the latest WMO State of the Global Climate report, 2024 was the warmest year on record since 1850, and key climate indicators continued to worsen. Yet amid these sobering facts, cities stand out as both the largest contributors responsible for over 70% of global greenhouse gas (GHG) emissions, and as crucial actors implementing effective mitigation and adaptation strategies.

As Mayor Hidalgo reminded participants, in many C40 cities, emissions are falling faster than at the national level. In Paris alone, air pollution has dropped by 60% and traffic by 40% since 2015. While 2024 was approximately 1.55°C warmer than pre-industrial averages, Hidalgo pointed out that without the Paris Agreement, this figure could well have doubled.

As the world looks towards COP30, the Summit emphasized the need for cities to work together and adopt even bolder policies, especially in key areas such as housing and mobility. Antonio Costa, President of the EU Council, underlined the importance of multilateral cooperation: “At this moment, when people doubt multilateralism, it is essential to bring Mayors together to find global solutions.”

The Summit also showcased a broad range of city-led climate actions, from reducing traffic and air pollution through enhanced public transport and low-emission zones, to implementing urban greening strategies, biodiversity protection, waste reduction, and circular economy models. The 15-minute city concept emerged again as a flagship example of integrated, people-centred urban planning.

Yet, a key challenge raised by almost all mayors was the persistent lack of access to direct climate finance for cities. Mauricio Rodas, former Mayor of Quito and Head of the SDSN Urban Commission Secretariat, stressed the urgent need to “derisk” funding for cities. To address this, the SDSN Urban Commission has proposed the Green Cities Guarantee Fund, aiming to unlock greater flows of both public and private capital into subnational climate-responsive projects. In addition, the Mayor of Brazzaville highlighted that cities are often sidelined by their national governments in the design of climate policies and projects. The Mayors of Athens and Utrecht echoed this concern, calling for cities to have a seat at the table in international climate negotiations. Another recurring issue was the growing wave of disinformation targeting local climate policies. Mayors agreed on the critical importance of grounding their decisions in science-based evidence, reliable data, and transparent communication with citizens.

As we approach COP30 in Belém, the Paris Summit was a powerful reminder of the ongoing and growing mobilization of cities worldwide. Echoing the words of the UN Secretary-General: Cities are where the climate battle will largely be won or lost.