The effects of human-made climate change became increasingly clear in 2018: devasting wildfires, scorching droughts, and mammoth hurricanes. However, the effect of rising global temperatures goes much further than longer summers and extreme weather – it could have disastrous and unforeseen consequences for all kinds of life on Earth.
A new study has found that up to 93 percent of green turtle hatchlings could be female by 2100 as a result of climate change, as reported in the journal Global Change Biology last month.
Along with many other reptiles and some fish species, green turtles undergo temperature-dependent sex determination. While in the egg, the external temperature in the nest determines whether the embryo develops into a male or a female. In many turtle species, eggs from cooler nests hatch as males, while eggs from warmer nests hatch as females. The sex ratio of wild green turtles is currently pretty well balanced, with 52 percent of hatchlings produced being female.
However, as this study shows, rising global temperatures will increase the temperature of more and more nesting sites, causing a shift in this ratio and sparking widespread “feminization” of the species. This could hold some advantage in the short term, leading to more females nesting and a boom in the populations, but eventually, the rise in temperatures will catch up with the turtles and approach “lethal levels”.
Scientists from the University of Exeter in the UK and the Marine and Environmental Sciences Centre in Portugal created a number of modeled scenarios based on predictions from the United Nations' recent IPCC report and data they gathered from a turtle nesting site in Guinea-Bissau, Africa. Their estimate suggests rising global temperatures will result in between 76 to 93 percent of hatchlings being female by the end of the century.
Not only this, they predict that over a third, between 33 to 43 percent, of current turtle nesting areas could be submerged due to rising sea levels.
“Our results suggest the nesting population of green turtles the Bijagós Archipelago, Guinea-Bissau, will cope with the effects of climate change until 2100,” lead researcher Dr Rita Patricio said in a statement.
“Cooler temperatures, both at the end of the nesting season and in shaded areas, will guarantee some hatchlings are male. Although rising temperatures will lead to more female hatchlings – and 32-64 percent more nesting females by 2120 – mortality in eggs will also be higher in these warmer conditions. As temperatures continue to rise, it may become impossible for unhatched turtles to survive.”
Shockingly, this feminization effect has already been seen in certain populations of wild turtles. A study last year found that 99.1 percent of the juvenile green turtles at the northern end of the Great Barrier Reef were female. The findings were so severe in this neck of the woods that the researchers even argued the “complete feminization of this population is possible in the near future”.