# The Wrong Assumptions of the Effects of Climate Change on Marine Turtle Nests with Temperature-Dependent Sex Determination

## TL;DR

This paper argues that using air or sea surface temperatures to predict the sex ratios of marine turtle nests is flawed, as nest temperatures depend more on solar radiation and soil properties.

## Contribution

The study introduces a mechanistic framework that incorporates soil heat dynamics and solar radiation for more accurate predictions of marine turtle sex ratios under climate change.

## Key findings

- Air temperature is a poor proxy for nest temperature due to soil drying and reduced heat conduction.
- Solar radiation and soil properties are more critical than air temperature in determining nest temperatures.
- Current models may misrepresent turtle sex ratios by neglecting subsurface thermal dynamics.

## Abstract

Climate change, caused by the increase in greenhouse gases, is warming the Earth’s atmosphere and oceans. This rise in temperature affects species such as marine turtles, whose sex is determined by the temperature of their nests. Warmer nests produce more females, while cooler ones produce more males. Many studies have used air or sea surface temperature to estimate nest temperature and predict future sex ratios, but this method is questionable. The temperature inside the sand depends mainly on solar radiation and the physical properties of the beach, such as moisture, texture, and heat transfer processes. Air temperature influences the surface but not necessarily the deeper layers, where turtle eggs develop. In fact, higher air temperature may dry the sand, reducing heat conduction and possibly limiting warming at nest depth. Therefore, using air temperature as a proxy can give misleading results, and more accurate models should include soil heat dynamics and solar radiation.

Contemporary climate change, driven by anthropogenic greenhouse gas (GHG) emissions, has raised global temperatures by over 1 °C above pre-industrial levels, profoundly altering Earth’s energy balance. In marine turtles, which exhibit temperature-dependent sex determination (TSD), embryonic sex ratios are highly sensitive to nest temperature. Most studies predicting the effects of climate change on turtle sex ratios have used air temperature or sea surface temperature (SST) as proxies for nest temperature, despite limited empirical validation of this assumption. I question the validity of this approach by examining the physical mechanisms of heat transfer within beach soils, including conduction, convection, and radiation, and how they are modulated by factors such as soil texture, moisture, and solar radiation. The analysis highlights that while GHGs increase air temperature through the greenhouse effect, they do not directly alter incoming solar radiation, the principal driver of subsurface temperature. Furthermore, increased air temperature enhances evaporation and soil drying, reducing thermal conductivity and potentially lowering heat penetration into nesting depths. Consequently, air or SST proxies can misrepresent the actual thermal environment of marine turtle nests, leading to inaccurate or even reverse projections of sex ratios under climate change. A mechanistic approach integrating soil heat dynamics and solar radiation is therefore essential for realistic assessments of TSD responses and conservation planning in a warming world.