Cities across the globe are experiencing a surprising side effect of climate change—a surge in rat populations. As global temperatures rise, urban environments are becoming more hospitable to these resilient creatures, causing a boom in their numbers that presents growing challenges for public health and city management. Scientists studying urban rat trends have found that warming climates, combined with factors like dense human populations and shrinking green spaces, create a perfect storm for these rodents to thrive. Rats are highly adaptable and opportunistic, often capitalizing on human-generated waste and shelter. Warmer winters in urban areas mean rats face fewer challenges in surviving harsh weather, extending their active foraging and breeding seasons significantly. This longer reproductive window leads to quicker population growth. For example, cities such as Washington, D.C., New York, San Francisco, and Toronto have reported substantial increases in rat sightings, with some experiencing growth rates several times higher than others.