University of Warwick astronomers, in partnership with institutions in Spain, are showing how astronomy tools, that are usually used to study stars, can be repurposed as climate sensors, helping us track how Earth's atmosphere is changing in the face of global warming.
On its journey to Earth, light from stars can change as it interacts with particles in regions containing gas and dust. This effect is especially noticeable when light crosses our atmosphere because the atmosphere introduces lines (like its own "bar code") into the light patterns observed from stars (stellar spectra).
These lines, known as telluric lines, are a nuisance to astronomers, who seek to 'decontaminate' their observations by removing these unwanted features, but a new algorithm called Astroclimes, developed at the University of Warwick, aims to harness the absorption lines left by molecules in the Earth's atmosphere in stellar spectra to measure the abundance of greenhouse gases (GHGs) at night, such as carbon dioxide (CO₂), methane (CH₄), and water vapor (H₂O).
Marcelo Aron Fetzner Keniger, a Warwick Prize PhD Student in the Astronomy and Astrophysics group at Warwick and developer of the Astroclimes algorithm, said: "Monitoring the abundance of GHGs is necessary to quantify their impact on global warming and climate change. Using telluric lines to measure the abundance of GHGs in the Earth's atmosphere has been extensively employed using solar spectra, for example by the COllaborative Carbon Column Observing Network (COCCON). However, since they rely on solar spectra, these measurements can only be carried out during the day, so Astroclimes can hopefully fill the gap with nighttime measurements."
With this in mind, an observation campaign has been carried out this past July at the Calar Alto Astronomical Observatory (CAHA) in Almería, Spain, in collaboration with the University of Warwick, the University of Almería and the Spanish State Meteorological Agency (AEMET).
The main objective of this campaign is to demonstrate the unique potential of combining solar measurements (during the day) and measurements of other stars (at night, using Astroclimes) to study the carbon cycle, the role of GHGs in the current context of global warming, and the reinforcement of observation systems for these gases.
The daytime spectra were measured using a portable FTIR spectrometer (EM27/SUN) from the COCCON-Spain network, temporarily installed at the Calar Alto Observatory. During the night, starlight was analysed using the Astroclimes algorithm on data from the CARMENES spectrograph on the observatory's 3.5 m telescope. The COCCON instrument can derive atmospheric concentrations of GHGs that are calibrated and on par with literature standard and are being used to calibrate the abundances measured with the Astroclimes algorithm.
Marcelo Aron added: "If we can successfully calibrate Astroclimes with the help of COCCON measurements, it could provide a new network for measuring GHG abundances, complementing current networks with nighttime measurements."
The daytime observations taken by the EM27/SUN at about 2,100 m were complemented by a second instrument at sea level located at the University of Almería (UAL). Joaquín Alonso Montesinos, University Professor, and representative of the UAL in the COCCON-Spain project said: "We are grateful to AEMET for counting on us for such an important project, which we believe will be a benchmark in the energy transition."
"The COCCON-Spain national network aims to address the latent lack of atmospheric GHG observations in Spain through the implementation of a network of stations for measurement on a national scale. One of the main objectives of the COCCON-Spain network is to improve current knowledge of GHG sources and sinks, thus contributing to the development of mitigation and adaptation strategies for climate change." emphasizes Omaira García-Rodríguez (AEMET-CIAI), coordinator of the network.
Jesús Aceituno, director of the observatory, concludes, "Calar Alto, with its photovoltaic plant and biomass boiler, aims at reaching energy sustainability. These greenhouse gas detections made with CARMENES demonstrate that an astronomical observatory can also serve to monitor our planet's climate."
