The loss of nesting beaches and feeding habitats plus the skewing of sex ratios as temperatures and sea levels rise does not bode well for the future of the sea turtle.
The sex of a sea turtle is not determined by its genetics, as is the case for us, but by the temperature of the nest. This is known as ‘environmental sex determination’ or ESD. Each species has a significant temperature, for example 30°C, which acts as a borderline between the sexes. In general, if the incubation temperature of the nest is above this significant temperature, the eggs will hatch into females. If the temperature in the nest is cooler, males are hatched.
Where genetics determines the sex of an animal, the ratio of males to females is normally close to 1:1. In the case of sea turtles, however, it is possible to have an entire nest hatch as either males or females, depending on the nest’s location. For example, a nest positioned in the shade will experience cooler temperatures than one exposed to the sun all day long, and would be more likely to produce many males.
One of the threats global warming poses to sea turtle populations is the rise in average temperatures. Even a slight rise in temperature could drastically skew the sex of many nests towards females, reducing the number of males hatched and therefore reducing the potential for fertilization of the next generation of eggs.
A second threat to sea turtles from global warming comes from sea level rise. Adequate nesting beaches are already in decline due to the expansion of coastal development. Rising sea levels mean that over time even more beaches will be lost to the sea, therefore there will be fewer locations for turtles to nest.
Global warming is also associated with an increasing frequency of extreme weather events. These have the potential to damage nesting beaches; destroy coral reefs and cause other alterations to critical sea turtle habitats.