Ravikiran Hegde

Understanding climate-relevant radiative processes requires radiation-transfer tools that balance physical fidelity, computational efficiency, and interpretability. Existing approaches span a broad but sparse hierarchy: idealized models miss key radiative processes, operational schemes trade physical tractability for accuracy and efficiency, and although line-by-line models are physically accurate, their computational cost prohibits direct coupling to Earth system models. This leaves a critical gap for models that are physically tractable, asymptotically convergent, and efficient.We investigate alternative representations of gas absorption, a key component for clear-sky radiation transfer. Using simple functional forms per frequency, we represent the pressure–temperature scaling of absorption. Absorption cross sections, radiative fluxes, and heating rates are evaluated for representative atmospheric profiles and compared against a benchmark line-by-line reference model. We show that these functional forms can reproduce the pressure–temperature dependence of gas absorption, thus replacing large multidimensional lookup tables. Combined with monochromatic spectral quadrature points (Czarnecki et al., 2023), this approach will enable highly efficient, physically tractable gas absorption calculations in climate models.

Stratospheric sulfate aerosols, produced by explosive volcanic eruptions or through artificial stratospheric aerosol injection for solar radiation management, can perturb Earth’s radiative budget for several years. However, the understanding of the state dependence of aerosol forcing and its effect on radiative feedback remains incomplete.We use a one-dimensional radiative–convective equilibrium model of the tropical atmosphere to quantify the clear-sky forcing and feedback contributions from aerosol absorbing and re-emitting longwave radiation, stratospheric heating, and enhanced stratospheric water vapor.We show that aerosol forcing exhibits a stronger surface temperature dependence than CO2 forcing. Between 280 and 300 K, aerosol forcing becomes less negative with increasing surface temperature because its longwave component becomes increasingly positive. Additionally, the radiative feedback is less negative in the presence of the aerosol. Both the feedback’s dependence on aerosol concentration and the forcing’s dependence on temperature arise from aerosol absorption in optically thin spectral regions, which masks temperature-dependent surface emission.This highlights the critical role of the spectral nature of aerosol longwave absorption in determining the surface temperature dependence of stratospheric sulfate forcing and in weakening radiative feedbacks compared to an atmosphere without stratospheric aerosol.

Stratospheric sulfate aerosol originating from explosive volcanic eruptions can perturb the radiative budget for several years. However, the understanding of the state dependence of aerosol forcing and its effect on the radiative feedback is still incomplete. Using a one-dimensional radiative–convective equilibrium model of the tropical atmosphere, we quantify the contributions to clear-sky forcing and feedback from absorbing and re-emitting longwave radiation, stratospheric heating, and enhanced stratospheric water vapour. We show that aerosol forcing has a stronger surface temperature dependence than CO₂ forcing. At surface temperatures from 280 to 300 K, the aerosol forcing becomes less negative (weaker) with increasing surface temperature because its longwave component becomes more positive. Additionally, the radiative feedback is less negative in the presence of the aerosol. The dependence of the feedback parameter on the aerosol concentration and of the forcing magnitude on temperature arises from the same process: aerosol absorbs in the spectral range in which the atmosphere is optically thin and thus spectrally masks the temperature-dependent surface emissions. The study highlights the critical role played by the spectral nature of aerosol longwave absorption in determining the surface temperature dependence of the forcing and in reducing the feedback in comparison to an atmosphere without stratospheric aerosol.

Stratospheric sulfate aerosol originating from explosive volcanic eruptions can perturb the radiative budget for several years following the eruption. However, the understanding of the state dependence of aerosol forcing and its effect on the radiative feedback is still incomplete. We quantify the contributions to clear-sky forcing and feedback from absorbing and re-emitting longwave radiation, stratospheric heating, and enhanced stratospheric water vapour. We show that, at surface temperatures from 280 K to 300 K, the aerosol forcing becomes less negative (weaker) with increasing surface temperature because its longwave component becomes more positive. Aerosol forcing has a stronger surface temperature dependence than CO₂ forcing. This stronger dependence arises because, unlike CO_2, the aerosol predominantly absorbs in the spectral range in which the atmosphere is optically thin and thus spectrally masks the surface-temperature dependence of emissions. Additionally, the radiative feedback to surface temperature change is less negative in the presence of the aerosol. This is mainly due to the fact that the temperature of the aerosol layer is largely independent of the surface temperature, leading to a masking of emission changes through the aerosol layer. The study highlights the critical role played by the spectral nature of aerosol longwave absorption in determining the surface temperature dependence of the forcing and in reducing the feedback in comparison to an atmosphere without stratospheric aerosol.

Stratospheric sulfate aerosol originating from explosive volcanic eruptions can perturb the radiative budget for several years following the eruption. However, the understanding of the state dependence of aerosol forcing and its effect on the radiative feedback is still incomplete. We quantify the contributions to clear-sky forcing and feedback from absorbing and re-emitting longwave radiation, stratospheric heating, and enhanced stratospheric water vapour. We show that, at surface temperatures from 280 K to 300 K, the aerosol forcing becomes less negative (weaker) with increasing surface temperature because its longwave component becomes more positive. Aerosol forcing has a stronger surface temperature dependence than CO₂ forcing. This stronger dependence arises because, unlike CO_2, the aerosol predominantly absorbs in the spectral range in which the atmosphere is optically thin and thus spectrally masks the surface-temperature dependence of emissions. Additionally, the radiative feedback to surface temperature change is less negative in the presence of the aerosol. This is mainly due to the fact that the temperature of the aerosol layer is largely independent of the surface temperature, leading to a masking of emission changes through the aerosol layer. The study highlights the critical role played by the spectral nature of aerosol longwave absorption in determining the surface temperature dependence of the forcing and in reducing the feedback in comparison to an atmosphere without stratospheric aerosol.

Stratospheric sulfate aerosol originating from explosive volcanic eruptions can perturb the radiative budget for several years following the eruption. However, the understanding of the state dependence of aerosol forcing and its effect on the radiative feedback is still incomplete. We quantify the contributions to clear-sky forcing and feedback from absorbing and re-emitting longwave radiation, stratospheric heating, and enhanced stratospheric water vapour. We show that, at surface temperatures from 280 K to 300 K, the aerosol forcing becomes less negative (weaker) with increasing surface temperature because its longwave component becomes more positive. Aerosol forcing has a stronger surface temperature dependence than CO₂ forcing. This stronger dependence arises because, unlike CO_2, the aerosol predominantly absorbs in the spectral range in which the atmosphere is optically thin and thus spectrally masks the surface-temperature dependence of emissions. Additionally, the radiative feedback to surface temperature change is less negative in the presence of the aerosol. This is mainly due to the fact that the temperature of the aerosol layer is largely independent of the surface temperature, leading to a masking of emission changes through the aerosol layer. The study highlights the critical role played by the spectral nature of aerosol longwave absorption in determining the surface temperature dependence of the forcing and in reducing the feedback in comparison to an atmosphere without stratospheric aerosol.

Stratospheric sulfate aerosol originating from explosive volcanic eruptions can perturb the radiative budget for several years following the eruption. However, the understanding of the state dependence of aerosol forcing and its effect on the radiative feedback is still incomplete. We quantify the contributions to clear-sky forcing and feedback from absorbing and re-emitting longwave radiation, stratospheric heating, and enhanced stratospheric water vapour. We show that, at surface temperatures from 280 K to 300 K, the aerosol forcing becomes less negative (weaker) with increasing surface temperature because its longwave component becomes more positive. Aerosol forcing has a stronger surface temperature dependence than CO₂ forcing. This stronger dependence arises because, unlike CO_2, the aerosol predominantly absorbs in the spectral range in which the atmosphere is optically thin and thus spectrally masks the surface-temperature dependence of emissions. Additionally, the radiative feedback to surface temperature change is less negative in the presence of the aerosol. This is mainly due to the fact that the temperature of the aerosol layer is largely independent of the surface temperature, leading to a masking of emission changes through the aerosol layer. The study highlights the critical role played by the spectral nature of aerosol longwave absorption in determining the surface temperature dependence of the forcing and in reducing the feedback in comparison to an atmosphere without stratospheric aerosol.

Stratospheric sulfate aerosol originating from explosive volcanic eruptions can perturb the radiative budget for several years following the eruption. However, the understanding of the state dependence of aerosol forcing and its effect on the radiative feedback is still incomplete. We quantify the contributions to clear-sky forcing and feedback from absorbing and re-emitting longwave radiation, stratospheric heating, and enhanced stratospheric water vapour. We show that, at surface temperatures from 280 K to 300 K, the aerosol forcing becomes less negative (weaker) with increasing surface temperature because its longwave component becomes more positive. Aerosol forcing has a stronger surface temperature dependence than CO₂ forcing. This stronger dependence arises because, unlike CO_2, the aerosol predominantly absorbs in the spectral range in which the atmosphere is optically thin and thus spectrally masks the surface-temperature dependence of emissions. Additionally, the radiative feedback to surface temperature change is less negative in the presence of the aerosol. This is mainly due to the fact that the temperature of the aerosol layer is largely independent of the surface temperature, leading to a masking of emission changes through the aerosol layer. The study highlights the critical role played by the spectral nature of aerosol longwave absorption in determining the surface temperature dependence of the forcing and in reducing the feedback in comparison to an atmosphere without stratospheric aerosol.

Stratospheric sulfate aerosol originating from explosive volcanic eruptions can perturb the radiative budget for several years following the eruption. However, the understanding of the state dependence of aerosol forcing and its effect on the radiative feedback is still incomplete. We quantify the contributions to clear-sky forcing and feedback from absorbing and re-emitting longwave radiation, stratospheric heating, and enhanced stratospheric water vapour. We show that, at surface temperatures from 280 K to 300 K, the aerosol forcing becomes less negative (weaker) with increasing surface temperature because its longwave component becomes more positive. Aerosol forcing has a stronger surface temperature dependence than CO₂ forcing. This stronger dependence arises because, unlike CO_2, the aerosol predominantly absorbs in the spectral range in which the atmosphere is optically thin and thus spectrally masks the surface-temperature dependence of emissions. Additionally, the radiative feedback to surface temperature change is less negative in the presence of the aerosol. This is mainly due to the fact that the temperature of the aerosol layer is largely independent of the surface temperature, leading to a masking of emission changes through the aerosol layer. The study highlights the critical role played by the spectral nature of aerosol longwave absorption in determining the surface temperature dependence of the forcing and in reducing the feedback in comparison to an atmosphere without stratospheric aerosol.