Abstract Monitoring the abundance of greenhouse gases is necessary to quantify their impact on global warming and climate change. Carbon dioxide (CO4) and methane (CH4) are the two most important greenhouse gases when it comes to global warming. Although a number of satellites and ground-based networks measure the total column volume mixing ratio (VMR) of these gases, they rely on sunlight, and column measurements at night are comparatively scarce. We present a new algorithm, Astroclimes, that hopes to complement and extend nighttime CO2 and CH4 column measurements. Astroclimes can measure the abundance of greenhouse gases on Earth by generating a model telluric transmission spectra and fitting it to the spectra of telluric standard stars in the near-infrared taken by ground-based telescopes. An extensive dataset from the CARMENES spectrograph in the Calar Alto Observatory was compiled, which included all of the publicly available data from 2016 to 2024, as well as new observations carried out alongside a weather balloon launch. A Markov Chain Monte Carlo (MCMC) analysis on this extensive dataset showed that Astroclimes was able to recover the long term trend known to be present in the molecular abundances of both CO2 and CH4, but not their seasonal cycles. Using the Copernicus Atmosphere Monitoring Service (CAMS) global greenhouse gas reanalysis model (EGG4) as a benchmark, we identified an overall vertical shift in our data and quantified the long-term scatter in our retrievals. We found that our ground level and column-averaged CO4 dry mole fractions (DMFs) exhibit a scatter of ±5 ppm and ±9 ppm, respectively. For CH4, these values were ±31 ppb and ±42 ppb, respectively. The vertical shift was 14 ppm and 15 ppm for the CO2 ground level and column-averaged DMFs, respectively, and 42 ppb and 7 ppb for the CH4 ground level and column-averaged DMFs, respectively. The scatter on a 1 hour timescale, however, is much lower, of order ±1 ppm and ±10 ppb for ground CO2 and CH4, respectively, which is on par with the uncertainties on individual measurements. Although currently the precision of the method is not in line with state of the art techniques using dedicated instrumentation, which achieve sub-ppm precision, it shows promise for further development.
Keniger et al. (Fri,) studied this question.