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Here’s how city networks can help American cities reduce their carbon footprint

Over the last three years, US mayors have become increasingly convinced that cities should play a strong role in reducing the effects of climate change. Today, two thirds of mayors are willing to expend resources to take action on climate. If the political will exists, the question then becomes: who is offering a roadmap to get there – and what are the next steps?

On top of many head-scratching policy reversals over the past three years, the new presidential administration has refused to take over the baton when it comes to following up on commitments made in international climate negotiations. In the absence of federal leadership and momentum, cities – and especially networks of cities – have entered the race more energetically and are working to close the gap between promised and actual greenhouse gas reductions.

In the report “Cities Joining Ranks” by the Boston University Initiative on Cities we trace the emergence of city networks, systematically review which cities join which networks and take stock of what networks have to offer to their members.

Five out of the ten city-to-city environmental networks we looked at – including C40, Climate Mayors, ICLEI USA, and We Are Still In – were formed since 2014. And the media has caught on to this burst of activity. We find that the number of articles referencing any of the ten networks has increased by 60 per cent in between 2017 and 2016 alone.

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When talking about how climate networks can help cities decarbonise, it is important to keep cities’ big picture challenge in mind. Scientists calculated that, in order to have a reasonable chance to keep average global warming under 2 degrees without needing to resort to geoengineering, global GHG emissions need to be halved in every single decade, starting now. This means cities in high-income countries like the US or UK should be carbon neutral by mid-century the latest. It is an extremely ambitious agenda, but the straw to cling to requires especially wealthy and carbon-intensive cities to act fast.

Small and mid-sized cities in particular need assistance in building capacity to dramatically reduce their carbon emissions. This is where city networks come in providing technical assistance and facilitating best practice exchange.


Mayors confided that the abundance of environmental networks was at times overwhelming as they consider possible memberships. In charting the network landscape, we found encouraging news. By and large, environmental city networks complement each other and allow cities with different levels of ambition and capacity to find peer cities and access tailored assistance. Moreover, the networks are interconnected not only by overlapping memberships, but via joint events and collective advocacy.

Cities which have set their sights high and formulated ambitious decarbonisation plans can use their different network memberships like rungs on a ladder towards achieving their goals. By climbing from one network to another, they can take advantage of the different combinations of technical assistance and membership obligations. My analysis of cities’ joining behavior over time shows that cities appear to follow a very similar pattern that is consistent with gradually ramping up ambition levels.

Close to 80 per cent of American cities with up to one million residents and which have joined at least five environmental networks first became part of ICLEI USA, a network that provides a broad range of technical tools to engage in climate planning. Then they signed on to the tiered commitment process of the US Compact of Mayors, which requires cities to do a GHG inventory, set GHG reduction targets and devise an implementation plan. Thereafter, they joined Climate Mayors, which provided them a national advocacy platform and closer peer-to-peer coordination.

Most recently these cities all committed to uphold the Paris Agreement in their jurisdiction through the “We are still in” movement. The majority have pledged through the Sierra Club Mayors for 100 per cent Clean Energy Initiative to work towards realizing 100 per cent clean and renewable energy in their city.

It is an exciting area for future research to probe deeper into how this joining trajectory has helped cities in practice. For now, it presents a possible roadmap for other ambitious cities to orient themselves as they climb up the ladder of decarbonisation.

Nicolas Gunkel is a research fellow at the Boston University Initiative on Cities and co-author of the “Cities Joining Ranks” report. Previously, he has worked with cities and towns to better collaborate on climate adaptation and he has written about the difficult path for solar in the “sunshine state” Florida.  
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