Surface, not exhaust: a multi-sensor satellite test bounds the local thermal footprint of hyperscale data centres

Jiawei Jing 

Whether hyperscale data centres (DCs) warm their surroundings has become a live policy question with directly conflicting answers: a coarse-resolution satellite preprint attributes ~2 °C of land-surface warming to facilities worldwide (Marinoni et al 2026), while peer-reviewed mobile transects near Phoenix measure +0.7-0.9 °C of near-ground air warming within a few hundred metres downwind (Sailor et al 2026). Prospective models of anthropogenic-heat impacts exist, but none has been tested against long-term observations — and no major DC market requires any assessment of local temperature impact before construction. Here we provide the first ex-post, controlled satellite test, for Japan’s largest DC concentration: the Inzai and Tama clusters of Greater Tokyo, whose staggered build- out (twelve facilities, 2011-2025) provides a clean three-phase (pre/construction/operation) event study plus independent replication. Combining daytime Landsat surface temperature (2013-2026), 70 m day/night ECOSTRESS, 1 km MODIS composites, matched pre-2013 controls, facility-level energy disclosures and explicit minimum-detectable-effect analysis, all gated by an energy-balance ceiling (~0.35 °C attainable at cluster scale at night), we find three things. Commissioning cools the daytime surface by 1.8-2.2 °C — significant under all three reference types, a surface radiative-property signal (albedo and emissivity) opposite in sign to the viral claim. Deep-night facility-scale changes are indistinguishable from zero (bounded below ~0.6-1.2 °C), and the cluster-scale night bound (0.24-0.29 °C, autocorrelation-corrected, pooled two-platform record) closes beneath the physical ceiling; +2 °C would require 6-43 times the available waste heat. And one energy-balance framework reconciles the conflicting literature: near-source air warming is detectable where heat-rejection density is high and climates dry; kilometre-scale surface warming from waste heat is not physically attainable. The protocol supplies the ex-post verification tool that current siting regimes lack.