The replacement of CH₄ by CO₂ in gas hydrate bearing sediments has received great attention since it may enable long-term storage of CO₂ which could mitigate the "Global Warming Effects", and facilitate CH₄ recovery as a potential future energy resource. Elasticity and Stability of CH₄ and CO₂ hydrate are crucial for development of CH₄ hydrate and CO₂ storage in the field.

In this study, molecular dynamics simulations were performed to determine the elastic moduli of CH₄ and CO₂ hydrate for at one hundred pressure-temperature data points, respectively. The conditions represent marine sediments and permafrost where gas hydrate occurs. The Young's modulus and shear modulus of the CO₂ hydrate increase anomalously with increasing temperature, whereas those of the CH₄ hydrate decrease regularly with increase in temperature. We ascribe this anomaly to the kinetic behavior of the linear CO₂ molecule, especially those in the small cages. The cavity space of the cage limits free rotational motion of the CO₂ molecule at low temperature. With increasing in temperature, the CO₂ molecule can rotate easily, and enhance the stability and rigidity of the CO₂ hydrate. This work provides a key database for the elastic properties of gas hydrates, and molecular insights into stability changes of CO₂ hydrate from high temperature of ~5 °C to low decomposition temperature of ~-150°C. Besides, the obtained results are significant with regard to CO₂ storage in the form of CO₂ hydrate in the field.