Cities and Nations Must Collaborate to Fight Climate Change

At the beginning of the twentieth century, around 15 percent of the global population lived in cities. Today, more than half do. People have migrated toward urban centers, attracted by the professional and personal opportunities offered there. The number of cities continues to grow, and so do the cities themselves: Sao Paulo, Tokyo and Delhi now have more than 10 million inhabitants each. By 2050, three-quarters of all people are expected to live in cities.

While this tremendous growth presents its fair share of challenges, it also presents significant opportunities to drive positive change and shape our collective futures. This is especially true of climate change.

Cities consume more than two thirds of the world's energy, and they are responsible for 70 percent of global greenhouse-gas (GHG) emissions. But by the same token, the vast resources and dynamic economies of cities enable them to also be a key part of the solution to climate change.

From Rio to Paris to Istanbul to Durban to Seoul, city mayors are already making great progress in reducing greenhouse-gas emissions and minimizing climate risks. Mayors are held directly accountable by their constituents, and therefore are often able to act quickly and decisively -- we are neither stymied by international debate nor beholden to bureaucrats. We have a vision for the Road to Paris CoP 21 and beyond; we are mobilizing citizens and putting pressure on national leaders to also deliver concrete results.

Problems like climate change demand bold solutions that are also financially viable, and it is the responsibility of mayors to find and implement them. That is why cities around the world have voluntarily chosen not only to set ambitious emissions-reduction targets, but also to work collaboratively to help each other achieve their respective goals.

When one city raises the bar, whether through a groundbreaking recycling initiative or a successful buildings-retrofit program, the solution provides a blueprint from which other cities can learn. For example, Santiago de Chile's new public-transport system was inspired by Bogota's Transmilenio, which itself was influenced by Curitiba's rapid-transit bus system. Likewise, Rotterdam's flood-prevention measures have been implemented by other delta cities around the world, from Ho Chi Minh City and Jakarta to New Orleans.

Mayors all over the world are taking action individually on climate change, but for these changes to be truly meaningful, they must also be collective. That is why innovative, like-minded local governments have joined cities networks such as ours to fight climate change together. Through these networks, cities have forged winning partnerships and collaborations with keys actors in the climate agenda, including national governments, international agencies, businesses and non-governmental organizations around the world.

Together, we have been stepping up the pace of climate action. Now recognized as "governmental stakeholders," cities and our networks are actively engaged in negotiating for a new international climate treaty. Today, cities have a voice on an international scale -- 108th mayor of New York Michael Bloomberg was recently named United Nations Secretary-General Special Envoy for Cities and Climate Change. By demonstrating our achievements and the power of collaboration, we hope to inspire world leaders to jointly increase their climate action.

United Nations Secretary General Ban Ki-moon's UN Climate Summit on September 23, 2014, will signify a new milestone in the journey of globally-coordinated local climate action, and an important step on the road to CoP 21 in Paris in 2015.

At the Summit, we will come together with bolder commitments, higher ambitions and bigger initiatives on finance, resilience, carbon pricing, transport, waste, energy and buildings. Each of these initiatives is born out of an unprecedented collaboration among cities, and will add critical support on the collective road to Paris in 2015.

We know that there is no president, minister, mayor, CEO or citizen who can meet the challenge of climate change alone. If we are to confront the issue successfully, we need to collaborate. As our soon-to-be launched initiatives will show, we are committed to acting urgently and cooperating intensively to help ensure that we reach a meaningful climate agreement that will limit the world to a rise in temperature of less than two degrees Celsius. Leaders of nations and cities, it is time we tackle climate change together.

This post is part of a month-long series produced by The Huffington Post in conjunction with a variety of events being held in September recognizing the threats posed by climate change. Those events include the UN's Climate Summit 2014 (to be held Sept. 23, 2014, at UN headquarters in New York) and Climate Week NYC (Sept. 22-28, 2014, throughout New York City). To see all the posts in the series, read here .