BLOOM: Beryllium-Linked Optical Overcoating Medium

As global warming accelerates beyond the pace of decarbonization, immediate and scalable cooling strategies are urgently needed. We present the BLOOM Medium, an encapsulated beryllium nanocoating that forms a highly reflective, durable surface layer across urban infrastructure. By coupling ultra-high solar reflectance with long-term environmental safety, this surface-based approach achieves rapid temperature reduction without atmospheric deployment or global treaties. It is not the sky we must change, but the light upon the ground. Applied to urban surfaces, BLOOM mitigates urban heat island effects, reducing local surface temperatures by up to 4 °C. Climate simulations further show that covering 20% of global urban land could lower the global mean temperature by nearly 0.5 °C and cut cooling energy demand by 18–25%.