Legal Models for Public-Private City Greening Partnerships

• Pages: 10485-10492
• Date: 01 September 2025
• Published date: 01 September 2025
• Author: Daniel J. Metzger

COMMENTS

SEPT/OCT 2025 ENVIRONMENTAL LAW REPORTER 55 ELR 10485

LEGAL MODELS FOR PUBLICPRIVATE

CITY GREENING PARTNERSHIPS

by Daniel J. Metzger

Daniel J. Metzger is a Senior Fellow at the Sabin Center for Climate Change Law at Columbia Law School.

Cities are signicantly hotter tha n their surrounding

areas. at dierence, known as the “urban heat

island” eect, is driven in signicant part by the

dark-colored buildings, sidewalks, roadways, and simi-

lar surfaces that dominate urban spaces, absorbing solar

energy and later radiating it outward as thermal energy

that heats the nearby air.1 Reduced vegetation in urba n

environments compounds the issue.

But there are straightforward tools available today

to combat this phenomenon—replacing dark-colored

roong and pavement with more reective alternatives,

expanding the tree ca nopy, and installing other vegetative

features like bioswale s, rain gardens, and urban meadows.

Called here “smart surfaces,” these tools are a group of

technologies and design priorities that aim to mitigate

the eects of climate change, especially extreme heat,

excessive rainfall, and ooding, in a cost-eective way by

increasing the reectivity, permeability, and vegetation of

certain urban areas.

is Comment suggests and describes one avenue

through which cities and local community-based orga-

nizations (CBOs) could tackle extreme heat: partnering

with one another to transform paved surfaces into green

or reective ones. Partnerships of this kind could combine

the resources and desire to create green spaces that non-

governmental groups oer with cities’ large portfolios of

property. Although there appear to be no such programs

currently operating that are expressly designed for smart

surfaces, the examples of comparable, existing programs

1. Francisco J. Doblas-Reyes et al., Linking Global to Regional Climate Change,

in C C 2021: T P S B. C

 W G I   S A R   I-

 P  C C 1363, 1454 (Valérie Masson-

Delmotte et al. eds., Cambridge Univ. Press 2021), https://www.ipcc.ch/

report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter10.pdf:

[T]hree main factors contribute to [the urban heat island eect’s]

development .. .: (i) three-dimensional urban geometry includ-

ing building density and plan area, street aspect ratio and build-

ing height; (ii) thermal characteristics of impervious surfaces; and

(iii) anthropogenic heat release, either from building energy con-

sumption, especially waste heat from air conditioning systems, or

as direct emissions from industry, trac, or human metabolism.

described below explain models for how this could work in

a variety of settings.

I. Background

A. Tackling Urban Heat With Smart Surfaces

Smart surfaces work by increasing outdoor surfaces’

reectivity and permeability. For example, roong mate-

rials with high reectivity decrease the amount of solar

energy translated into indoor spaces, directly reducing

heat stored and obviating some of the need to operate

air conditioners that exacerbate urban heat by tra nsfer-

ring indoor heat outside. Trees and other forms of vegeta-

tion are more reective than asphalt surfaces and further

reduce urban heat through evaporative processes.2 Across

a whole city, smart surfaces strategies can oer signicant

cooling in a cost-eective way.3 ese are proven, rapidly

implementable ways that cities can increase livability,

adapt to the changing climate, and move toward meeting

mitigation goals.4

On individual buildings and in particularly hot neigh-

borhoods, the eect of smart surfaces can be even more

pronounced than in the city at large. at is particularly

important because the zoning r ules (both past and present)

that have caused and still contribute to segregation have

increased the density of low-income neighborhoods with-

out preserving features that maintain livability in those

areas, like dense tree canopy. As a result, those neighbor-

2. Joseph L. Moss et al., Inuence of Evaporative Cooling by Urban Forests on

Cooling Demand in Cities, 37 U. F  U. G 65 (2019),

https://www.sciencedirect.com/science/article/pii/S1618866717304661;

Athanasios Paschalis et al., Urban Forests as Main Regulator of the Evaporative

Cooling Eect in Cities, 2 AGU A e2020AV000303 (2021), https://

agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020AV000303.

3. G K  R J, S S C, C C,

S C C,  E E: C  B-

  S S A  B 18 (2021), https://

smartsurfacescoalition.org/s/Baltimore-Draft-Document92022_Reduced.

pdf.

4. Gabriella Mickel, Reimagining Parking: Unlikely Spaces for Climate Resil-

ience, Y E’ R. (Jan. 2, 2024), https://environment-review.yale.edu/

reimagining-parking-unlikely-spaces-climate-resilience. Many of the ben-

ets smart surfaces oer are adaptation ones, like dealing with extreme heat

events, changing rainfall patterns, and increased severity of storms. But by

increasing the energy eciency of spaces and reducing heat overall, smart

surfaces also reduce energy demand—primarily the demand created by air

conditioning—and so can reduce carbon dioxide emissions.

Author’s Note: Thanks to all my colleagues at the Sabin

Center for workshopping the idea for this Comment, and

to Amy E. Turner, Romany Webb, and Brittany Gentry for

their invaluable editorial help.

Copyright © 2025 Environmental Law Institute®, Washington, DC. Reprinted with permission from ELR®, https://www.eli.org