New research from the Columbia Climate School reveals how the loss of air-quality monitoring, urban planning gaps, and historical climate patterns shape our modern world.
When the U.S. government suspended its global air-quality reporting program in 2025, the impact was immediate and measurable. For more than a decade. embassies and consulates served as independent. publicly available sentinels of environmental health in cities across the globe. According to new research from the Columbia Climate School. that silence had consequences: aerosol pollution in those cities rose by approximately 33%.
Researchers tracked this shift across 46 cities using satellite observations. comparing current levels against the data collected before the program’s shutdown. They identified an increase of roughly 1.9 micrograms per cubic meter of PM2.5—the microscopic particles capable of penetrating deep into human lungs. These surges were most persistent in regions that lacked an alternative national monitoring system. As lead author and assistant professor Zoey Zhou notes, public access to trusted data is a critical mechanism for accountability. For Zhou, the trend is concerning, as it mirrors a broader move in the U.S. and internationally to shutter programs that collect essential climate and environmental intelligence.
The implications of data gaps extend well beyond the sky. A new study targeting urban deprivation suggests that hundreds of millions of people currently live in “invisible” neighborhoods—densely built. poorly connected areas that often escape the notice of global policy makers. By mapping 5,132 cities across Africa, Asia, and Latin America, researchers estimated that 395 million people live in these conditions. The problem is particularly acute in Africa, where 43.6% of urban residents live in deprived areas. Most significantly, over one-third of these individuals—136 million people—reside in small and medium-sized cities with fewer than 1 million residents. These smaller hubs are frequently excluded from urban data discussions despite absorbing a massive share of the world’s population growth.
Dana Thomson. a co-author of the urban study. notes that these smaller cities often lack the resources to manage rapid expansion. Her team utilized a machine-learning model trained on data from large centers like Nairobi. Mumbai. and Mexico City to identify these vulnerable communities. Without neighborhood-scale data, the path to directing essential services and resources to those in need remains blocked.
Looking back helps clarify the stakes of these modern challenges. A newly published study by Sam Anderson and Shawn Chartrand reconstructs a massive 1941 North American heat wave to compare it with the record-shattering event of 2021. Though the 1941 event was 1.7°C cooler, it occurred in a vastly different climatic and social era. By reviewing 357 issues of 25 newspapers alongside climate and mortality data, researchers found the 1941 event caused 344 heat-related deaths. While the 1941 tragedy saw a higher incidence of drowning as a result of the heat. 2021 deaths were largely linked to indoor exposure in British Columbia. This comparison underscores a fundamental reality: the human cost of climate extremes is determined as much by our infrastructure. technology. and social policy as by the weather itself.
The sequence is clear: whether through the loss of air-quality sensors, the invisibility of small-city deprivation, or the historical echoes of past heat waves, our ability to manage the future depends entirely on the transparency and accuracy of the evidence we choose to keep in sight.
Other recent developments from the Columbia Climate School include new frameworks for utilizing Earth-observation data in humanitarian decision-making and collaborative strategies for navigating the surge of subsea data collected at sea.
Columbia Climate School air quality urban deprivation climate change heat wave environmental data global policy research