The Effects of Climate Change on Sea Turtles

The Effects of Climate Change on Sea Turtles

On December 12, 2015, over 90 countries adopted an international agreement called “the Paris Agreement on Climate Change.” This agreement required all signing countries to make significant commitments to resolving climate change. Participants were intended to re-evaluate their pledges in the year 2020 and then strengthen their emissions reductions by 2030. The goal of this Paris Agreement is to move toward emission reductions and a low-carbon environment that will hopefully slow and ultimately stop global warming.

Unfortunately, while all of this rhetoric is being spewed, the earth’s temperature continues to increase. Depending on the source, global temperatures (land and ocean) have increased by approximately 0.85C since 1880 (approximately 0.08C per decade). That said, the rate of global warming since 1980 has more than doubled that number, averaging 0.18C per decade. The nine years between 2013 and 2021 rank among the ten warmest years on record.

So, how does climate change affect different animals? In a study published in 2003 in the journal Nature, it was reported that 80 percent of approximately 1500 species of wildlife studied have shown stress effects from global warming. The key impact that global warming has on wildlife is habitat destruction. Stabile habitats that once supported species’ needs are in flux, no longer able to meet those needs. Temperature extremes and the impact of water, drought, or floods contribute to environmental changes.

While some wildlife populations can move to new locations and adapt, others can’t. To complicate matters, habitat encroachment by humans, housing, agriculture, and industrial development, compete or eliminates potential refuge areas for migrating wildlife.

More adaptable animals, which tend to be those that are labeled “invasive,” are more likely to survive the near-term effects of global warming. Weeds and animal pests, such as the invasive cold-sensitive Burmese Python, slowly migrate toward northern climes. Highly specialized species, such as the eucalyptus-eating Koala, are more susceptible to habitat loss. While it is known that species have adapted to evolutionary change, if the environmental changes occur more rapidly than the species can adapt, extinction may be the outcome.

Lists vary as far as the species most sensitive to climate change and global warming. Typical animals that appear include caribou (reindeer), penguins, polar bears, musk oxen, cold-water fish like trout and salmon, seabirds like puffins and the auklets, possums, butterflies such as European mountain and apollo butterflies, and various amphibians.

Species Impact

However, when it comes to climate change and global warming, the “Canary in the Coal Mine” is the ambassador of our oceans, the sea turtle. There are seven species of sea turtles in the world, and most are critically endangered.

This author lives on a small island in the northern Caribbean. Over the past 29 years, I have witnessed firsthand the effects of climate change and global warming on the environment in which these majestic animals live. From increasing temperatures to loss of habitat, the dynamics of the sea turtle populations in the region have shifted dramatically.
Sea turtles experience Temperature Dependent Sex Determination (TSD) rather than chromosomal dependence, as do many other reptile species. The adage “Cool dudes and Hot Chicks” simplifies the understanding of the dynamics. Eggs incubated in temperatures under 31C render male hatchlings, and over 31C, female hatchlings.

It is a known fact that sea turtles that nest near the equator, where the temperatures are naturally warmer, tend to have a preponderance of female hatchlings. Sea turtles that nest at latitudes farther north and south of the equator tend to have more balanced sex ratios.

Reference Data

Dr. Jeanette Wyneken, a Ph.D. biologist from southern Florida, has been studying sex ratios of Loggerhead Sea turtles (Caretta caretta) as well as other species since the turn of the century. Important to note that 70 percent of all the Loggerheads in the Atlantic ocean originate from the east coast of North America, making them a good model for evaluating hatchling sex ratios.

Starting back in 2002, Dr. Wyneken and her team have performed endoscopic gender determination in approximately ten randomly selected nests per year. As expected, at the beginning of her studies, the sex ratios were skewed toward female hatchlings – not unexpected, considering the majority of her field sites were in Florida. However, since 2011, 100 percent of the greater than 1000 hatchlings that she has evaluated have been female. Dr. Wyneken attributes this to the increasing ambient temperatures as well as the increased temperatures of the nests.

Scientists have been monitoring sea turtle nest temperatures for the past 30 years.

The elevated temperatures not only affect the sex ratios but also there is a direct effect of warmer nest temperatures on the hatching success. The overall number of successful nests has decreased, as well as the viable hatchling percentages of individual nests. In addition, the morbidity and mortality of baby turtles, either in the egg or just as they emerge, have worsened.

  • Cooler nests produce male hatchlings.
  • Warmer nests produce female hatchlings.
  • Even warmer nests tend to produce higher numbers of weak or deformed hatchlings.
  • Hot nests result in hatchling and nest death.
Douglas Mader
Douglas Mader

Depending on the actual temperature of the nest, when during incubation, elevated temperatures occur, and the duration of the heat stress event determines the nature of the morbidity to the hatchling. For instance, mild elevations may cause coagulopathies, or bleeding disorders, in the hatchlings. This is often manifested as blood in the anterior chamber of the eye. Some of these will resolve shortly after emerging from the hot nest.

Douglas Mader
Douglas Mader

Alterations in shell shape and color may be permanent and sometimes lethal effects of excessively warm nests. Deformities, such as cleft palates, double flippers, shell deformities, and even bicephaly (two heads), can also be seen. While some of these animals may emerge from the nest alive, many of their anomalies are incompatible with life.

Douglas Mader
Douglas Mader

Finally, perhaps the greatest threat to coastal animals due to climate change and global warming is sea level rise and the loss of habitat. Sea turtle and shorebird nesting sites are being lost to sea level rise and beach erosion at an alarming rate.

Turtles need to climb higher on beaches to avoid nest flooding with the SLR. With beach erosion, nesting sites are becoming harder to find, resulting in nests being deposited lower to the tide zone. High tides and storm surges are flooding nests that result in the drowning of healthy eggs.

Conclusion and Call to Action

Sexual maturity in sea turtles varies with species and ranges anywhere from 12 to 20 years. The significant decrease in hatchling males may not be appreciated for several decades when current reproductively active males begin to die off.

Unless global warming and its effects can be reversed, there is a likely chance that the elevated temperatures may lead to the extinction of these amazing animals by the turn of the century.

Think globally. Act locally. People can make a difference. One person may think that there is not much they can do to help. That is not true. Reversing global warming is everybody’s responsibility – and if everybody – even half of the people, makes an effort, changes can be made for the better.


  1. Volunteers from the Save-A-Turtle organization survey post-hatching nests to determine the actual hatch count and percentage viability.
  2. This hatchling died in the egg in a hot nest.
  3. This hatchling is displaying a condition called “hyphema,” which is bleeding into the anterior chamber of its eye as a result of coagulation disorders brought on by elevated nest temperatures.
  4. Changes in shell coloration, cleft palates, and double flippers are just some of the effects of excessive incubation temperatures.
  5. Sea turtle nest high and dry on a sandy beach.
  6. Beach erosion has left little usable beach for nesting. This nest is in danger of flooding due to its location.

This article by Douglas Mader was first published by OneGreenPlanet on 20 October 2022. Lead Image Source : Rich Carey/Shutterstock.

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