Climate-Related Local Extinctions Are Already Widespread among Plant and Animal Species

For most of the last decade, the conversation about climate change and extinction has been framed in the future tense. Species will be lost, populations will collapse, and ranges will shrink. Then, John Wiens went back through hundreds of published range-shift studies and found that the losses aren't coming. They're already here, already counted, and already in the data. We just hadn't looked at the right column of the spreadsheet. Here's the insight that drove his study. Biologists have been documenting for years that species are moving toward cooler places as climates warm, shifting poleward and climbing to higher elevations. That's the headline story. But those same studies also surveyed populations at the opposite end of each species' range: the warm edge, the lower-latitude or lower-elevation boundary where conditions are already hottest. And at those warm edges, populations were vanishing. Not moving. Vanishing. The data on those disappearances was sitting inside the published literature, embedded in range-shift studies, largely uncounted. Wiens combed that literature systematically. He ran multiple searches of Web of Science, using terms that combined "global warming" or "climate change" with "local extinction," "contraction," or "range shift." He applied strict inclusion criteria. A study had to resurvey specific localities at two or more discrete time points over at least ten years, and it had to link its findings to climate change through statistical analysis. Broad distributional trends without site-level resurveys didn't qualify because those can't unambiguously document that a specific population is gone. The average study duration in the final set was about fifty years, with a range of fourteen to one hundred and fifty-nine. That rigorous filter produced a dataset of twenty-seven studies and nine hundred and seventy-six unique species. The headline number is forty-seven percent. Nearly half— four hundred and sixty out of nine hundred and seventy-six species — had already lost populations at their warm edges due to climate change. Let that sit for a moment. This isn't a model projection. This is documented disappearance, compiled from field resurveys, under the modest warming the planet has already experienced. And the losses are not evenly distributed. They fall harder on certain groups in ways that reveal why some populations fail while others hang on. The geographic gap is the most striking. Tropical and subtropical species showed local extinctions in fifty-four and a half percent of cases. For temperate species, it was thirty-nine percent. That thirteen-point gap makes biological sense. Tropical species have evolved in environments where temperature barely varies across seasons. Their thermal niches are narrow. A small absolute temperature increase is, for them, a much larger relative perturbation. Temperate species have broader thermal tolerances built from enduring cold winters and hot summers. They have more buffer. Tropical species, under even modest warming, are already running out of room. Biology also predicts the gap between animals and plants. Fifty percent of the seven hundred and sixteen animal species surveyed had warm-edge local extinctions. For plants, it was thirty-nine percent of two hundred and sixty species. The contrast is especially sharp in temperate systems. Only eight and a half percent of temperate plant species showed warm-edge losses, compared with thirty-nine percent of temperate animal species in the same studies. Plants can't run, but they can sometimes persist in place by tolerating slightly warmer conditions or by germinating in microsites where temperatures are cooler. Animals face direct physiological stress and often need to move or adapt quickly. Then there's freshwater. The freshwater signal is the most dramatic in the entire dataset. Seventy-four percent of thirty-one freshwater species had warm-edge local extinctions, compared to forty-six percent of terrestrial species and fifty-one percent of marine species. Wiens offers a clear mechanism. Freshwater habitats can be fundamentally altered or eliminated by changes in precipitation. A drought doesn't just warm a river; it can remove it. Marine species can buffer temperature by moving within the water column. Freshwater fish can't do that. Wiens is careful to flag a caveat. That seventy-four percent figure comes largely from a single study of European fishes, so it should be read with appropriate caution. But the directionality is telling. Now, the natural pushback. If a species is losing populations at its warm edge, can't it just shift its range — move uphill, move north, and survive? This is where Wiens's analysis gets uncomfortable. The answer, for a striking fraction of species, is: not fast enough or not at all. He documents three failure modes. First, niche shifts. When climate changes, a species can theoretically evolve new thermal tolerances, staying put by adapting. But transplant experiments in plants, phylogenetic analyses of niche change rates in plants and animals, and projections based on heritability and temperature tolerances in lizards all point to the same conclusion: niche evolution is usually too slow to keep pace with rapid anthropogenic warming. The forty-seven percent local extinction rate is itself evidence of this. Those populations didn't adapt in place; they were lost. Second, dispersal. Even species that could theoretically track their climate niche often can't get there. Agriculture, roads, and urbanization fragment the landscape. Islands, peninsulas, and mountaintops create geographic dead ends where there's simply no suitable habitat to move into. And even without barriers, dispersal may be too slow relative to the pace of change. Third, the pattern of who survives matters. Among nine hundred and four species with paired edge data, cool-edge expansions occurred in three hundred and sixty-seven species — so about forty percent were successfully colonizing new territory upslope or poleward. But that expansion at the cool edge doesn't save the populations already lost at the warm edge. Wiens notes that fifty-four species, about six percent, expanded at both warm and cool edges simultaneously. For the rest, the math wasn't working in their favor. Here is what makes this finding particularly sobering. The warming we've experienced so far is modest — a fraction of what climate projections anticipate over the coming century. Wiens cites an expected increase of roughly two-fold to five-fold in warming over the coming decades. If forty-seven percent of surveyed species are already losing populations under current conditions, the trajectory implied by that multiplier is stark. The losses already recorded aren't the warning signal. They're the beginning of the record. There's also a methodological point that deserves emphasis. The data Wiens used already existed. It was published, peer-reviewed, and sitting in the literature. What was missing wasn't field surveys; it was someone systematically asking: what happened at the warm edge? Range-shift studies were designed to document where species moved. Nobody had gone back and counted where they didn't make it. That's why the local extinction framing matters so much. Local extinction — a population gone from a site where it previously occurred — is distinct from global extinction. A species can suffer dozens of local extinctions and still exist. It might even look fine in broad distributional summaries. But local losses erode genetic diversity, sever ecological relationships, and remove exactly the populations closest to physiological limits — the populations most likely to signal what's coming for the species as a whole. Wiens argues explicitly that patterns of present-day local extinctions from range-shift studies should be part of the evidence used to predict species persistence in the future. Not as a supplement. As a core data source. The losses documented here are already affecting species people depend on. Among those showing warm-edge population losses are grasses, including wheat, rice, and corn. This isn't only a story about biodiversity in the abstract. What Wiens has shown is that the archive of climate-related population loss is larger than we recognized, broader than any single taxonomic group, and already measurable in the data we've been collecting. The question was always there. The answer was already in the spreadsheet. Nearly half the species surveyed have paid for our inattention with populations that are gone. This lecture was created by ennepō. Go to https://ennepo.ai to Discover, Create and Follow the latest research in your field. Read when you can. Listen when you want to.