Small ponds emit a surprisingly large amount of methane compared with larger water bodies. Because ponds are so tiny, they have been difficult to track, and their contributions to terrestrial greenhouse gas emissions are largely unaccounted for. In a new study, Mullen et al. used deep learning to construct a fine-grained map of ponds in Alaska. The counterintuitive relationship between pond size and carbon emissions has to do with the perimeter-to-surface-area ratio. The smaller a pond is, the greater the ratio is. A large perimeter accumulates more decaying leaf litter, sediment, and other terrestrial carbon. Smaller ponds also are shallower, so their carbon loads are more concentrated, and gases generated at the bottom are just a stone’s throw from the surface. Because ponds are so small (<0.01 square kilometer), their size can fluctuate drastically in response to environmental factors like precipitation and permafrost. In the new study, researchers used Planet Labs’ PlanetScope satellites to census ponds in Alaskan boreal and tundra landscapes and tracked them over several years.