Leaders from approximately every country gathered in Paris earlier this month, coming together to sign an international climate change agreement widely hailed as, well, a pretty good start (Vox has a great summary, which I won’t recap here).

The hard(er) part—implementation—comes next, and the national governments that negotiated this agreement are only one star in the constellation of stakeholders that must carry the effort forward. City governments can take action to ensure the commitments made in Paris—which are not strong enough to hold global temperature increases to less than two degrees celsius—grow more ambitious with time.

Transportation, which accounts for nearly a quarter of energy-related greenhouse gas (GHG) emissions globally, must play an important role in bringing about this kind of change. Only 10 percent of the global population accounts for 80 percent of total motorized passenger-kilometers traveled, though that’s poised to change as people in developing countries increasingly take to the road. Emissions in the sector are currently projected to increase more than twofold by 2050, so in order to meet a global 80 percent GHG emission reduction goal by that time, we will essentially have to prevent any transportation-related emissions growth at all. (If you want to get into the weeds of current climate and transportation research, take a look at recent publications from the IPCC, UITP, ITDP, and New Climate Economy.)

Accomplishing this goal will require all the tools in the emissions-reduction toolbox. This means avoiding emissions growth by reducing demand for transportation in the first place; shifting people’s habits to more environmentally friendly kinds of transportation; and reducing the emissions generated by existing practices by improving fuel efficiency, encouraging vehicle electrification, and increasing the uptake of low-carbon fuels.

Within the exhibitor spaces and panel sessions of COP21, the focus remained on supply-side changes that help reduce emissions from existing practices (as I worried it might in my first post on the subject).

But there was also substantial conversation about empowering cities to fight climate change  at the local level. Almost every climate action that a city pursues will require money and expertise. As a result, building implementation capacity through greater access to financing and best-practice knowledge— especially through peer networks such as the C40 Cities Climate Leadership Group and ICLEI—were major focuses of discussion.

In the realm of financing, eight multilateral development banks affirmed their commitment to investing in sustainable transportation. Bambang Susantono, head of the Asian Development Bank, particularly emphasized his organization’s intent to “prioritize bus and metro systems in cities” following the meeting. Separately, a consortium of organizations has come together to create the Cities Climate Finance Leadership Alliance as a means of providing additional investment in low-emission, climate-resilient urban infrastructure. Finally, the Climate Bond Initiative is working to mobilize trillions of dollars in investment, in part through a certification program for low-carbon transportation projects.

Across financing discussions at COP21, a persistent theme was the need for cities to develop a more robust pipeline of investment-grade infrastructure projects. This emphasis is echoed by the Kresge Foundation’s recent work studying three US cities’ abilities to “absorb” and make use of available sources of capital. There was also talk of “bundling” transportation projects across cities to reduce investment risk and allow governments to secure project financing, especially in cities with poor or nonexistent credit. Already, some financial companies in the US offer similar exchange-traded “infrastructure funds,” but the benefits of such funds accrue largely to investors and leave cities themselves out of the conversation.

With regard to knowledge-sharing, peer networks for developing best practices for urban climate action are becoming more solutions-oriented in their actions. C40’s Clean Bus Declaration, for example, serves as a framework for transit providers to commit to introducing low-emission vehicle fleets, and also provides a way for them to pool resources and negotiate bulk purchases with manufacturers, driving down investment costs. This type of procurement-driven collaboration has the potential to lower sustainable technology prices through economies of scale, saving governments and riders money while improving urban air quality.

Some cities are getting involved even further upstream. In Portland, Oregon, for instance, the city council, recently voted to oppose the creation of any new fossil-fuel infrastructure in the city, and in doing so is entering regulatory territory that has generally been reserved for state and federal governments. Nonetheless, mayors and city councillors up and down the West Coast have been signing on in support of similar goals, which seek to keep 80 percent of remaining fossil fuel reserves in the ground in line with the planet’s estimated remaining “carbon budget.”

The optimism and excitement surrounding the Paris agreement better reflect what the agreement represents than what its text actually says—namely, the endorsement of coordinated global climate action across geopolitical borders. With more than two-thirds of global energy use taking place in cities, urban climate action will play a key role in achieving international emissions reduction goals. Though increasingly diverse collaborations, cities are banding together to create a new (albeit informal) transnational governance structure, one focused on the needs of the planet’s nearly four billion city-dwellers. In doing so, cities embody the spirit of the national-level accord reached in Paris, while connecting their actions more directly to their constituents. As the agreement itself acknowledges, to its credit, effectively combatting climate change will require concrete actions and commitments from sub-national actors.

Cities have not been twiddling their thumbs waiting for nations to act. On the contrary, they are reading the Paris agreement as a challenge—not just to hold their countries accountable to their current emissions reduction targets, but to show their countries how much more they can and should ratchet down those emissions targets to become more ambitious moving forward. Commitments thus far don’t give demand-side transportation actions nearly the attention they deserve, and the discussions at COP21 reflected that deficiency. Let’s work together to demonstrate the huge potential for GHG emissions savings that are possible through avoiding transportation emissions growth and shifting behavior to favor more sustainable transportation options.