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1. Analytical Models of Instantaneous Radiative Forcing Across Opacity Regimes

   https://doi.org/10.1175/JCLI-D-25-0233.1  

   Czarnecki, Paulina; Polvani, Lorenzo M; Pincus, Robert (October 2025, Journal of Climate)

   Radiative forcing by carbon dioxide depends on the difference between surface and stratospheric temperature scaled by the logarithm of its concentration (Wilson and Gea-Banacloche 2012; Jeevanjee et al. 2021). This relationship arises due to the cooling-to-space theory or theτ= 1 law, where all emission of infrared radiation originates from the atmospheric pressure level where the gas reaches sufficient optical thickness (in the case of CO₂, in the stratosphere). Here we develop theoretical understanding of forcing by other well-mixed greenhouse gases including methane (CH₄), nitrous oxide (N₂O), and chlorofluorocarbons (CFCs). Radiative forcing by an optically thin absorber (e.g., CFC-12) is governed by emission throughout the troposphere and scaled by the total change in gas concentration, such that a linear increase in gas abundance yields a linear increase in forcing. We examine the factors that control the magnitude of radiative forcing, demonstrating analytically that CFC-12 is a stronger per-molecule absorber than CO₂due to its larger average cross-section, rather than its band width or spectral position. Application in idealized atmospheres with simplified lapse rates illustrates how radiative forcing by optically thin gases depends almost linearly on lapse rate. Finally, gases that are both optically thin and optically thick across their absorption spectrum, such as N₂O and CH₄, can be understood as a combination of the two regimes, yielding a super-logarithmic relationship to concentration. Our theory is in excellent agreement with full-physics line-by-line calculations in atmospheres with and without spectral overlap by water vapor 

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2. A Radial Decrease in Kinetic Temperature Measured with H ₂CO in 30 Doradus

   https://doi.org/10.3847/1538-4357/ad47bf  

   Indebetouw, Rémy; Wong, Tony; Madden, Suzanne; Sewiło, Marta; Roman-Duval, Julia; Chevance, Mélanie; Rubio, Monica (July 2024, The Astrophysical Journal)

   Abstract Feedback from star formation is a critical component of the evolution of galaxies and their interstellar medium. At parsec scales internal to molecular clouds, however, the observed signatures of that feedback on the physical properties of CO-emitting gas have often been weak or inconclusive. We present subparsec observations of H₂CO in the 30 Doradus region, which contains the massive star cluster R136 that is clearly exerting feedback on its neighboring gas. H₂CO provides a direct measure of gas kinetic temperature, and we find a trend of decreasing temperature with projected distance from R136 that may be indicative of gas heating by the stars. While it has been suggested that mechanical heating affects H₂CO-measured temperature, we do not observe any correlation betweenT_Kand line width. The lack of an enhancement in mechanical feedback close to R136 is consistent with the absence of a radial trend in gravitational boundedness seen the Atacama Large Millimeter/submillimeter Array CO observations. Estimates of cosmic-ray flux in the region are quite uncertain, but can plausibly explain the observed temperatures if R136 itself is the dominant local source of energetic protons. The observations presented here are also consistent with the H₂CO-emitting gas near R136 being dominated by direct radiation from R136 and photoelectric heating in the photodissociation regions. 

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3. Theory cracks old data: Rovibrational energy levels of ortho H ₂ –CO derived from experiment

   https://doi.org/10.1126/sciadv.adj8632  

   Stachowiak, Marcin; Grabowska, Ewelina; Wang, Xiao-Gang; Carrington, Tucker; Szalewicz, Krzysztof; Jankowski, Piotr (February 2024, Science Advances)

   Measurements of rovibrational spectra of clusters provide physical insight only if spectral lines can be assigned to pairs of quantum states, and further insight is obtained if one can deduce the quantitative energy-level pattern. Both steps can be so difficult that some measured spectra remain unassigned, one example isorthoH₂–CO. To extend the scope of spectroscopic insights, we propose to use theoretical information in interpretation of spectra. We first performed high accuracy, full-dimensional calculations of theorthoH₂–CO spectrum, at the highest practically achievable levels of electronic structure theory and quantum nuclear dynamics. Then, an iterative, theory-guided method developed here allowed us to fully interpret the spectrum oforthoH₂–CO, extending the range of van der Waals clusters for which spectroscopy can provide physical insights. 

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4. Impacts of Carbonate Buffering on Atmospheric Equilibration of CO ₂ , δ ¹³ C _DIC , and Δ ¹⁴ C _DIC in Rivers and Streams

   https://doi.org/10.1029/2023GB007860  

   Winnick, Matthew J.; Saccardi, Brian (February 2024, Global Biogeochemical Cycles)

   Abstract Rivers and streams play an important role within the global carbon cycle, in part through emissions of carbon dioxide (CO₂) to the atmosphere. However, the sources of this CO₂and their spatiotemporal variability are difficult to constrain. Recent work has highlighted the role of carbonate buffering reactions that may serve as a source of CO₂in high alkalinity systems. In this study, we seek to develop a quantitative framework for the role of carbonate buffering in the fluxes and spatiotemporal patterns of CO₂and the stable and radio‐ isotope composition of dissolved inorganic carbon (DIC). We incorporate DIC speciation calculations of carbon isotopologues into a stream network CO₂model and perform a series of simulations, ranging from the degassing of a groundwater seep to a hydrologically‐coupled 5th‐order stream network. We find that carbonate buffering reactions contribute >60% of emissions in high‐alkalinity, moderate groundwater‐CO₂environments. However, atmosphere equilibration timescales of CO₂are minimally affected, which contradicts hypotheses that carbonate buffering maintains high CO₂across Strahler orders in high alkalinity systems. In contrast, alkalinity dramatically increases isotope equilibration timescales, which acts to decouple CO₂and DIC variations from the isotopic composition even under low alkalinity. This significantly complicates a common method for carbon source identification. Based on similar impacts on atmospheric equilibration for stable and radio‐ carbon isotopologues, we develop a quantitative method for partitioning groundwater and stream corridor carbon sources in carbonate‐dominated watersheds. Together, these results provide a framework to guide fieldwork and interpretations of stream network CO₂patterns across variable alkalinities. 

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5. Variability and Controls of p CO ₂ and Air‐Water CO ₂ Fluxes in a Temperate River

   https://doi.org/10.1029/2024JG008434  

   Young, Fischer L; Colman, Benjamin P; Carter, Alice M; Fiejó_de_Lima, Rafael; Shangguan, Qipei; Payn, Robert A; DeGrandpre, Michael D (February 2025, Journal of Geophysical Research: Biogeosciences)

   Abstract Measurements of riverine dissolved inorganic carbon, total alkalinity (A_T), pH, and the partial pressure of carbon dioxide (pCO₂) can provide insights into the biogeochemical function of rivers, including the processes that control biological production, chemical speciation, and air‐water CO₂fluxes. The complexity created by these combined processes dictates that studies of inorganic carbon be made over broad spatial and temporal scales. Time‐series data like these are relatively rare, however, because sampling and measurements are labor intensive and, for some variables, good measurement quality is difficult to achieve (e.g., pH). In this study, spectrophotometric pH and A_Twere quantified with high precision and accuracy at biweekly to monthly intervals over a four‐year period (2018–2021) along 216 km of the Upper Clark Fork River (UCFR) in the northern Rocky Mountains, USA. We use these and other time‐series data to provide insights into the processes that control river inorganic carbon, with a focus onpCO₂and air‐water CO₂fluxes. We found that seasonal snowmelt runoff increasedpCO₂and that expected increase and decrease ofpCO₂due to seasonal heating and cooling were likely offset by an increase and loss of algal biomass, respectively. Overall, the UCFR was a small net source (0.08 ± 0.14 mol m⁻² d⁻¹) of CO₂to the atmosphere over the four‐year study period with highly variable annual averages (0.0–0.10 mol m⁻² d⁻¹). The seasonally correlated, offsetting mechanisms highlight the challenges in predictingpCO₂and air‐water CO₂fluxes in rivers. 

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