The massive emission of greenhouse gases, particularly CO₂, has led to severe damage to the Earth’s ecological environment and poses a threat to human health. Many countries have therefore proposed policies to curb the greenhouse effect. Carbon monitoring is a critical prerequisite for realizing these goals, and tracking carbon emission sources can support the precise implementation and advancement of related policies more effectively. The contribution of fossil fuel combustion to greenhouse gas emissions can be inferred by detecting the abundance of ¹⁴C in carbon dioxide in a specific region. Conventional ¹⁴CO₂ detection methods have significant drawbacks, including complicated operation, high cost and large equipment size. Laser absorption spectroscopy (LAS) offers advantages such as real-time, online in-situ measurement and simple operation, making it suitable for the online detection of isotopes. Among the various LAS techniques, noise immunity cavity enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is the most sensitive. This method integrates frequency modulation spectroscopy (FMS) into cavity enhanced spectroscopy (CES) to suppress the low-frequency noise while increasing the absorption paths, providing a minimum detectable absorption coefficient as low as 10^–13. Additionally, the accumulation of high intracavity laser power in NICE-OHMS can stimulate saturation absorption, which has a narrow spectral width that can mitigate spectral overlap. In this work, we model the spectral signals of ¹⁴CO₂ at different locations and select the transition line of ¹⁴CO₂ at 2209.108 cm^–1 as an optimal measurement target based on the principles of high-intensity and well-resolution. The theoretical analysis of the NICE-OHMS technique is then carried out, and theoretical simulations of a mixed sample of ¹⁴CO₂ and its nearby interfering gases (¹³CO₂, ¹²CO₂, and N₂O), are performed under the simulated experimental conditions. The results of the simulation show that the Doppler broadened spectral signal of ¹⁴CO₂ is covered by the other gases’ signals with a very low amplitude, which is adverse to the detection of ¹⁴CO₂. To eliminate the linear slope of the Doppler broadened signal and to further improve the signal-to-noise ratio, we perform ¹⁴CO₂ spectral measurements by using wavelength-modulated NICE-OHMS (wm-NICE-OHMS). The results of the simulation show that the spectral lines are effectively separated, and the detection accuracy of the ¹⁴CO₂ ratio is greatly improved. Finally, the effects of pressure and modulation index on the ¹⁴CO₂ wm-NICE-OHMS signal are analyzed. The results show that when the pressure is 42 mTorr and the modulation index is 1.07, the signal amplitude of wm-NICE-OHMS reaches its maximum. This work lays a theoretical foundation for the high precision detection of ¹⁴CO₂ in real-time environmental monitoring. The potential for large-scale application of wm-NICE-OHMS in carbon emission tracking is highlighted, providing a more cost-effective alternative to traditional detection methods. Furthermore, the technology is able to suppress spectral interference from other gases and achieve high resolution in ¹⁴CO₂ measurements, which will greatly help monitor and reduce greenhouse gas emissions.