At this week’s climate conference in Bonn, Germany, the pressure is on many national governments to continue implementing the Paris Agreement despite the United States’ intention to withdraw. But they’ll have help from the world’s cities.

Bonn is shaping up to be one of the most urban-centered climate summits yet. America’s Pledge, an effort led by Governor Jerry Brown of California and former Mayor of New York Michael Bloomberg to aggregate climate commitments from cities and other “non-Party actors,” will launch its first report, informed by analysis from WRI, on November 11. The Global Covenant of Mayors for Climate and Energy, which counts more than 7,400 cities among its members, or 9 percent of the global population, will announce its 2030 goals. And the Urban Leadership Council, a group of representatives from city networks, the private sector and urban think tanks including WRI, will meet for the first time. These events and more are expected to climax with the Climate Summit of Local and Regional Leaders and the Global Covenant of Mayors Day on November 12 and 13.

It’s fitting that cities are stepping up for climate action—they account for more than half the global population and about 70 percent of the world’s greenhouse gas emissions. But despite their prominence and power, cities can’t do it alone. They need support from leaders at the national and international levels.

Connecting Cities to National Goals

COP23 will prepare the way for next year’s “Talanoa” dialogue, where nations will assess progress towards the targets of the Paris Agreement and countries’ national climate plans, known as “nationally determined contributions,” or NDCs. But while the diplomatic machinery of NDCs was built with national governments in mind, much of the implementation required to see them achieved is at the subnational level, where cities play a big role. How national implementation agendas incorporate individual cities is a major open question.

This kind of cooperative planning between cities and national governments can already be seen in a few places. In China, the central government assigns goals for provinces and cities to achieve the national carbon dioxide intensity reduction target. In Brazil, a new national law will help implement the NDC at the subnational and sectoral levels, too. But these examples are exceptions to the rule.

There is also a limit to how much cities can do on their own. While cities consume and emit a great deal, they do not have full control over their emissions sources. According to a report by the C40 Cities Climate Leadership Group, only a third of a typical city’s assets and functions are directly owned or operated by city government. Cities are sometimes able to manage energy consumption through mechanisms such as transport plans and building codes, for instance, but vehicle fuel efficiency and the carbon intensity of the electrical grid are under the jurisdiction of the national government.

Finance is another example. There are wildly varying degrees of coordination between national and city governments, which sometimes prevents climate funds from reaching municipalities or supporting their priorities. To change this, national policymakers need to recognize the growing role of cities in climate action and formally address it. Finding more ways to fund city-level work on a large scale is critical.

Cities also need technical capacity to put added attention and funding to good use. In the rapidly growing cities of the global south, most of the infrastructurehousing and other services needed to absorb new residents have yet to be built. Decisions made now will influence the sustainability of cities for decades – not to mention economic and social outcomes, which are inextricably linked.

Why It Matters to Get Cities Right

Critics have pointed out that there were similar calls for independent subnational implementation after the United States chose not to ratify the Kyoto Protocol and after climate negotiations failed at COP15 in Copenhagen. The result was that emissions didn’t decline. Mere touting of climate leadership by mayors and advocates will not turn emissions trajectories. Things need to be different this time around.

Simply put, cities must be key drivers towards a more sustainablemore equitable world – or we risk not getting there.

To successfully implement the climate agenda in cities, we need better coordination between city and national planning that produces specific actions, agreement on how to fund them at a large scale and capacity to see them done. It is time for national and city governments to work together, hand in hand, to bend the global emissions trajectory towards sustainability.