Climate change can wipe out a species's food source and destroy its habitat, but rising temperatures are having a more surprising effect on green sea turtles that's no less devastating. According to a report in Current Biology [PDF], up to 99.8 percent of the green sea turtles born on certain beaches in Australia are female, a direct result of the area's warmer-than-average temps.
A turtle's sex is determined by its environment. As The Washington Post reports, a clutch of eggs that incubates in sand that's roughly 85°F will produce about 50 percent females and 50 percent males. A few degrees cooler and the batch skews male; a bit hotter and it's majority female.
This evolutionary mechanism tends to balance itself out, but on beaches in northeast Australia, it's being hijacked by climate change. In order to gauge the size of the impact, researchers with the National Oceanic and Atmospheric Administration sampled the nesting beaches along the coast of Australia adjacent to the Great Barrier Reef, the part that has seen the most dramatic temperature rises and coral bleaching. What they found on the warmer northern beaches was the worst-case scenario: 99.1 percent of juveniles, 99.8 percent of subadults, and 86.8 percent of the overall population was female. Data taken from the southern beaches are only slightly less alarming: Turtles hatched in the relatively cooler sands there were still 65 to 69 percent female. According to the study's authors, "the complete feminization of this population is possible in the near future." That would affect the species' future population growth.
Green sea turtles aren't the only species vulnerable to huge sex shifts by way of climate change. Many other reptiles also rely on temperature-dependent sex determination to keep populations balanced. But above-average temperatures can do more harm beyond messing with sex development: It can also kill embryos before they have the chance to hatch. The authors emphasize that figuring out how to regulate sand temperatures at key rookeries will be essential moving forward. If not, the species could face "a population collapse—or even extinction."