Volume 61, Issue 2 e2022RG000796
Commissioned Manuscript

Reducing Aerosol Forcing Uncertainty by Combining Models With Satellite and Within-The-Atmosphere Observations: A Three-Way Street

Ralph A. Kahn

Corresponding Author

Ralph A. Kahn

Earth Sciences Division, NASA Goddard Space Flight Center, MD, Greenbelt, USA

Correspondence to:

R. A. Kahn,

[email protected]

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Elisabeth Andrews

Elisabeth Andrews

Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Boulder, CO, USA

Colorado and Global Monitoring Laboratory, NOAA, Boulder, CO, USA

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Charles A. Brock

Charles A. Brock

Chemical Sciences Laboratory, NOAA, Boulder, CO, USA

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Mian Chin

Mian Chin

Earth Sciences Division, NASA Goddard Space Flight Center, MD, Greenbelt, USA

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Graham Feingold

Graham Feingold

Chemical Sciences Laboratory, NOAA, Boulder, CO, USA

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Andrew Gettelman

Andrew Gettelman

National Center for Atmospheric Research, Boulder, CO, USA

Now at Pacific Northwest National Laboratory, Richland, WA, USA

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Robert C. Levy

Robert C. Levy

Earth Sciences Division, NASA Goddard Space Flight Center, MD, Greenbelt, USA

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Daniel M. Murphy

Daniel M. Murphy

Chemical Sciences Laboratory, NOAA, Boulder, CO, USA

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Athanasios Nenes

Athanasios Nenes

Laboratory of Atmospheric Processes and Their Impacts, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

Center for the Study of Air Quality and Climate Change, Foundation for Research and Technology Hellas (FORTH), Thessaloniki, Greece

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Jeffrey R. Pierce

Jeffrey R. Pierce

Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA

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Thomas Popp

Thomas Popp

German Aerospace Center (DLR), German Remote Sensing Data Center (DFD), Oberpfaffenhofen, Germany

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Jens Redemann

Jens Redemann

School of Meteorology, University of Oklahoma, Norman, OK, USA

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Andrew M. Sayer

Andrew M. Sayer

Earth Sciences Division, NASA Goddard Space Flight Center, MD, Greenbelt, USA

University of Maryland, Baltimore County, Baltimore, MD, USA

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Arlindo M. da Silva

Arlindo M. da Silva

Earth Sciences Division, NASA Goddard Space Flight Center, MD, Greenbelt, USA

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Larisa Sogacheva

Larisa Sogacheva

Finnish Meteorological Institute, Climate Research Programme, Helsinki, Finland

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Philip Stier

Philip Stier

Department of Physics, University of Oxford, Oxford, UK

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First published: 03 May 2023
Citations: 1

Abstract

Aerosol forcing uncertainty represents the largest climate forcing uncertainty overall. Its magnitude has remained virtually undiminished over the past 20 years despite considerable advances in understanding most of the key contributing elements. Recent work has produced modest increases only in the confidence of the uncertainty estimate itself. This review summarizes the contributions toward reducing the uncertainty in the aerosol forcing of climate made by satellite observations, measurements taken within the atmosphere, as well as modeling and data assimilation. We adopt a more measurement-oriented perspective than most reviews of the subject in assessing the strengths and limitations of each; gaps and possible ways to fill them are considered. Currently planned programs supporting advanced, global-scale satellite and surface-based aerosol, cloud, and precursor gas observations, climate modeling, and intensive field campaigns aimed at characterizing the underlying physical and chemical processes involved, are all essential. But in addition, new efforts are needed: (a) to obtain systematic aircraft in situ measurements capturing the multi-variate probability distribution functions of particle optical, microphysical, and chemical properties (and associated uncertainty estimates), as well as co-variability with meteorology, for the major aerosol airmass types; (b) to conceive, develop, and implement a suborbital (aircraft plus surface-based) program aimed at systematically quantifying the cloud-scale microphysics, cloud optical properties, and cloud-related vertical velocities associated with aerosol-cloud interactions; and (c) to focus much more research on integrating the unique contributions of satellite observations, suborbital measurements, and modeling, to reduce the persistent uncertainty in aerosol climate forcing.

Key Points

  • Aerosol climate forcing uncertainty is virtually undiminished despite two decades of advances in many aspects of aerosol-climate science

  • This review concludes that current and planned aerosol modeling, satellite and ground-based observation programs remain essential

  • New, systematic aircraft aerosol-particle and cloud-process measurements are also needed, along with better model-measurement integration

Plain Language Summary

Aerosols, such as airborne wildfire smoke, desert dust, volcanic and pollution particles, affect Earth's climate by reflecting (some also absorb) sunlight. These aerosol particles also play key roles in cloud formation and evolution, further affecting the planet's energy balance. The magnitudes of these effects, and even the underlying mechanisms, represent the largest uncertainty in climate modeling. Despite two decades of advances in many aspects of aerosol-climate science, aerosol climate forcing uncertainty is virtually undiminished. Yet, reducing this uncertainty is critical for any effort to attribute, mitigate, or predict climate changes. We adopt a measurement-oriented perspective to assess the strengths and limitations of measurement and modeling programs, and conclude that current and planned efforts need to continue. However, in addition, new efforts are needed: (a) to obtain aircraft in situ measurements that capture systematically aerosol particle properties for the major aerosol airmass types, globally, (b) to conceive, develop, and implement an aircraft and surface-based program aimed at filling gaps in our understanding of the interactions between aerosol particles and clouds, along with (c) much more research focused on integrating the unique contributions of satellite observations, suborbital measurements, and modeling, to reduce the uncertainty in our understanding of Earth's changing climate.

Conflict of Interest

The authors declare no conflicts of interest relevant to this study.

Data Availability Statement

This paper represents a review and analysis of previously published work. As such, the underlying data are made available from the original sources through the cited literature.