← Terraforming · Climate intervention
Surface albedo modification
Paint roofs and roads lighter so cities bounce more sun. That can cool streets and cut AC. It is not a global dimmer: cities are about one percent of Earth’s surface.
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Jurisdiction: Cities, buildings, and land-cover proposals (no planetary programme)
Years / status: Surface albedo enhancement (cool roofs, reflective pavements, land-cover brightening); listed in NOAA SRM SoS (July 2024); cool roofs documented by U.S. EPA for urban heat; buildings chapter of IPCC AR6 WG III. Status: research / local practice.
The plan
Raises the reflectivity of ground and building surfaces so more sunlight leaves instead of becoming heat. The practical end is cool roofs, cool pavements, and related land-cover choices. EPA treats cool roofs as an urban heat-island tool: lower roof and near-surface temperatures, less cooling energy in hot seasons. NOAA’s SRM overview lists surface albedo enhancement as a radiation-budget idea alongside SAI, MCB, and CCT: while noting far less research on global deployment than on SAI/MCB.
Construction / status
Cool roofs and light surfaces are ordinary building practice in many hot cities (including long Mediterranean white-wash traditions). There is no planetary albedo programme. IPCC AR6 WG III discusses reflective roofs and related sufficiency measures in the buildings chapter as local mitigation/adaptation: not as a substitute for emissions cuts.
What went wrong, or only partly worked
Documented at building and city scale: cooler roofs, lower indoor heat gain in hot climates, urban heat-island relief where materials and maintenance hold up. Global mean temperature effect of brightening urban surfaces alone is tiny because urban land is a small fraction of the planet. Treat “degrees of global cooling” claims as model curiosities unless tied to a named study with clear assumptions.
Lessons
Winter heating penalties in cold climates; glare; material ageing; rainfall and regional circulation side effects appear in some modelling. Surface brightening does not remove CO₂. Do not sell a white roof as planetary geoengineering: sell it as local heat management that happens to sit on the same shelf family as SRM research.
Sources
U.S. EPA Using Cool Roofs to Reduce Heat Islands; IPCC AR6 WG III Chapter 9 Buildings PDF; NOAA CSL SRM State of the Science Fact Sheet (July 2024); NASEM Reflecting Sunlight research agenda and governance catalog.