The Geography of Policy Diffusion

To understand what drives policy development, we need to think about the geographic scales of influence on any given body which may develop and implement policy. A useful framework for this is to think about vertical and horizontal policy diffusion.

• Vertical policy diffusion occurs when a policy mechanism adopted at one scale of governance transfers to others (and this can occur in either direction). An example might be a state adopting ambitious CAFE standards for fuel economy, which are then adopted by the federal government.  In this example, the policy mechanism (CAFE standards) moves from the state to the federal level - or diffuses vertically.
  
  This makes a lot of sense, and not just in issues related to climate change. Sometimes, we try things out at one scale as a bit of a pilot for what it might look like at a larger scale. This was true with the Renewable Portfolio Standards at the state level - that was widely thought to be a testing ground for a national RPS system that never came about.  
   
• Horizontal policy diffusion occurs when a policy mechanism adopted at a scale of governance transfers to other areas at that same scale. An example of this might be a state adopting renewable portfolio standards after seeing a neighboring state do so, or a municipality choosing to set a greenhouse gas emissions reduction target after learning about success in other municipalities around the country. In this example, the policy mechanisms are staying at the same geographic scale, but diffusing horizontally outward to other entities at that same scale.
  
  It's not just policy where we look to our peers to see how they're handling a particular challenge or issue, so this is no surprise that policy creation would follow a similar pattern. Being able to speak to the success of a policy mechanism in a similar application elsewhere lends credibility and can assuage concerns about effectiveness, popularity with constituents, or costs.

Both types of policy diffusion are critical to addressing the global climate challenges we face. Think back to the Clean Power Plan - while inherently a federal policy, it offered states wide-ranging flexibility in how they'd set and meet their targets, including the opportunity to collaborate regionally. This illustrates both vertical and horizontal policy diffusion. The Paris Agreement is another example - it's an international agreement with nationally determined contributions that very likely would require integration and that state and local scales as well. But what if one level of governance isn't as active as others? That's a bit of what were seeing during the Trump Administration. While the federal government in the U.S. wasn't actively seeking to address climate change through federal policy measures, states, municipalities, and businesses were continuing to work in this space and were learning from what their counterparts were doing - a strong example of horizontal diffusion. One common way that policies are actively diffused is through publishing best practices, case studies, and other resources. See e.g. the Resource Library for the Global Covenant of Mayors for Climate and Energy, which is one of the organization identified in Lesson 5. The Horizontal and Vertical Reinforcement in Global Climate Governance article is a good read if you're interested in understanding this better.