publications

2024

1. Sci. Adv.

   Physical science research needed to evaluate the viability and risks of marine cloud brightening

   Graham Feingold , Virendra P. Ghate , Lynn M. Russell , and 28 more authors

   Science Advances, 2024

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   Marine cloud brightening (MCB) is the deliberate injection of aerosol particles into shallow marine clouds to increase their reflection of solar radiation and reduce the amount of energy absorbed by the climate system. From the physical science perspective, the consensus of a broad international group of scientists is that the viability of MCB will ultimately depend on whether observations and models can robustly assess the scale-up of local-to-global brightening in today’s climate and identify strategies that will ensure an equitable geographical distribution of the benefits and risks associated with projected regional changes in temperature and precipitation. To address the physical science knowledge gaps required to assess the societal implications of MCB, we propose a substantial and targeted program of research—field and laboratory experiments, monitoring, and numerical modeling across a range of scales.

2. Nat. Clim. Change

   Diminished efficacy of regional marine cloud brightening in a warmer world

   Jessica S. Wan , Chih-Chieh Jack Chen , Simone Tilmes , and 3 more authors

   Nature Climate Change, 2024

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   Marine cloud brightening (MCB) is a geoengineering proposal to cool atmospheric temperatures and reduce climate change impacts. As large-scale approaches to stabilize global mean temperatures pose governance challenges, regional interventions may be more attractive near term. Here we investigate the efficacy of regional MCB in the North Pacific to mitigate extreme heat in the Western United States. Under present-day conditions, we find MCB in the remote mid-latitudes or proximate subtropics reduces the relative risk of dangerous summer heat exposure by 55% and 16%, respectively. However, the same interventions under mid-century warming minimally reduce or even increase heat stress in the Western United States and across the world. This loss of efficacy may arise from a state-dependent response of the Atlantic Meridional Overturning Circulation to both anthropogenic warming and regional MCB. Our result demonstrates a risk in assuming that interventions effective under certain conditions will remain effective as the climate continues to change.

3. In review

   Targeted marine cloud brightening can dampen El Niño

   Jessica S. Wan , John T. Fasullo , Nan Rosenbloom , and 2 more authors

   In review, 2024

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   The most record-breaking climate extreme events are attributable to the compounding effects of greenhouse gas induced warming and natural climate variability1. Marine cloud brightening, a solar geoengineering strategy originally proposed to reduce long-term anthropogenic warming by making low marine clouds brighter2,3, could theoretically mitigate extreme events by instead targeting seasonal phenomena, such as El Niño-Southern Oscillation (ENSO). Yet the effectiveness of regional marine cloud brightening to deliberately modify ENSO has not been tested. By exploiting the opportunistic experiment provided by the 2019-2020 Australian wildfires4, we demonstrate that the observed cloud brightening and ensuing La Niña-like response can be reproduced by simulating marine cloud brightening in the southeast Pacific. We then explore how cloud brightening initiation time and duration modifies the impacts associated with the 1997-1998 and 2015-2016 El Niño events. We find that only the earliest and longest interventions effectively restore neutral ENSO conditions and dampen El Niño’s teleconnections during the event peak. Our results support the consideration of novel targets such as climate variability in solar geoengineering research and demonstrate how such proposals could complement existing tools such as ENSO forecasting for future climate risk mitigation policy.

2023

1. AREPS

   Hydrological Consequences of Solar Geoengineering

   Katharine Ricke , Jessica S. Wan , Marissa Saenger , and 1 more author

   Annual Review of Earth and Planetary Sciences, 2023

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   As atmospheric carbon dioxide concentrations rise and climate change becomes more destructive, geoengineering has become a subject of serious consideration. By reflecting a fraction of incoming sunlight, solar geoengineering could cool the planet quickly, but with uncertain effects on regional climatology, particularly hydrological patterns. Here, we review recent work on projected hydrologic outcomes of solar geoengineering, in the context of a robust literature on hydrological responses to climate change. While most approaches to solar geoengineering are expected to weaken the global hydrologic cycle, regional effects will vary based on implementation method and strategy. The literature on the hydrologic outcomes and impacts of geoengineering demonstrates that its implications for human welfare will depend on assumptions about underlying social conditions and objectives of intervention as well as the social lens through which projected effects are interpreted. We conclude with suggestions to reduce decision-relevant uncertainties in this novel field of Earth science inquiry. ▪The expected hydrological effects of reducing insolation are among the most uncertain and consequential impacts of solar geoengineering (SG). ▪Theoretical frameworks from broader climate science can help explain SG’s effects on global precipitation, relative humidity, and other aspects of hydroclimate. ▪The state of the knowledge on hydrological impacts of solar geoengineering is unevenly concentrated among regions. ▪Projected hydrological impacts from SG are scenario dependent and difficult to characterize as either harmful or beneficial. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 51 is May 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

2. Environ. Res. Com.

   Connecting physical and social science datasets: challenges and pathways forward

   Sameer H. Shah , Cassandra R. O’Lenick , Jessica S. Wan , and 22 more authors

   Environmental Research Communications, 2023

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   The integration of physical and social science data can enable novel frameworks, methodologies, and innovative solutions important for addressing complex socio-environmental problems. Unfortunately, many technical, procedural, and institutional challenges hamper effective data integration—detracting from interdisciplinary socio-environmental research and broader public impact. This paper reports on the experiences and challenges of social and physical data integration, as experienced by diverse Early Career Researchers (ECRs), and offers strategies for coping with and addressing these challenges. Through a workshop convened by the National Center for Atmospheric Research (NCAR) Innovator Program, 33 participants from different disciplines, career stages, and institutions across the United States identified four thematic data integration challenges related to complexity and uncertainty, communication, scale, and institutional barriers. They further recommended individual, departmental, and institutional scale responses to cope with and address these integration challenges. These recommendations seek to inform faculty and department support for ECRs, who are often encouraged—and even expected—to engage in integrative, problem-focused, and solutions-oriented research.

2022

1. Geosci. Mod. Dev.

   Importance of different parameterization changes for the updated dust cycle modeling in the Community Atmosphere Model (version 6.1)

   Longlei Li , Natalie M. Mahowald , Jasper F. Kok , and 9 more authors

   Geoscientific Model Development, 2022

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   The Community Atmosphere Model (CAM6.1), the atmospheric component of the Community Earth System Model (CESM; version 2.1), simulates the life cycle (emission, transport, and deposition) of mineral dust and its interactions with physio-chemical components to quantify the impacts of dust on climate and the Earth system. The accuracy of such quantifications relies on how well dust-related processes are represented in the model. Here we update the parameterizations for the dust module, including those on the dust emission scheme, the aerosol dry deposition scheme, the size distribution of transported dust, and the treatment of dust particle shape. Multiple simulations were undertaken to evaluate the model performance against diverse observations, and to understand how each update alters the modeled dust cycle and the simulated dust direct radiative effect. The model–observation comparisons suggest that substantially improved model representations of the dust cycle are achieved primarily through the new more physically-based dust emission scheme. In comparison, the other modifications induced small changes to the modeled dust cycle and model–observation comparisons, except the size distribution of dust in the coarse mode, which can be even more influential than that of replacing the dust emission scheme. We highlight which changes introduced here are important for which regions, shedding light on further dust model developments required for more accurately estimating interactions between dust and climate.

2. DOE-NOAA

   DOE-NOAA Marine Cloud Brightening Workshop

   Graham Feingold , Virendra P. Ghate , Lynn M. Russell , and 28 more authors

   U.S. Department of Energy and U.S. Department of Commerce NOAA, 2022

2021

1. Atmo. Chem. Phys.

   Contribution of the world’s main dust source regions to the global cycle of desert dust

   Jasper F. Kok , Adeyemi A. Adebiyi , Samuel Albani , and 15 more authors

   Atmospheric Chemistry and Physics, 2021

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   Even though desert dust is the most abundant aerosol by mass in Earth s atmosphere, the relative contributions of the world s major source regions to the global dust cycle remain poorly constrained. This problem hinders accounting for the potentially large impact of regional differences in dust properties on clouds, the Earth s energy balance, and terrestrial and marine biogeochemical cycles. Here, we constrain the contribution of each of the world s main dust source regions to the global dust cycle. We use an analytical framework that integrates an ensemble of global aerosol model simulations with observationally informed constraints on the dust size distribution, extinction efficiency, and regional dust aerosol optical depth (DAOD). We obtain a dataset that constrains the relative contribution of nine major source regions to size-resolved dust emission, atmospheric loading, DAOD, concentration, and deposition flux. We find that the 22 29 Tg (1 standard error range) global loading of dust with a geometric diameter up to 20 um is partitioned as follows: North African source regions contribute 50% (11 15 Tg), Asian source regions contribute 40% (8 13 Tg), and North American and Southern Hemisphere regions contribute 10% (1.8 3.2 Tg). These results suggest that current models on average overestimate the contribution of North African sources to atmospheric dust loading at 65 %, while underestimating the contribution of Asian dust at 30 %. Our results further show that each source region s dust loading peaks in local spring and summer, which is partially driven by increased dust lifetime in those seasons. We also quantify the dust deposition flux to the Amazon rainforest to be 10 Tg yr1, which is a factor of 2 3 less than inferred from satellite data by previous work that likely overestimated dust deposition by underestimating the dust mass extinction efficiency. The data obtained in this paper can be used to obtain improved constraints on dust impacts on clouds, climate, biogeochemical cycles, and other parts of the Earth system.

2. Atmo. Chem. Phys.

   Improved representation of the global dust cycle using observational constraints on dust properties and abundance

   Jasper F. Kok , Adeyemi A. Adebiyi , Samuel Albani , and 17 more authors

   Atmospheric Chemistry and Physics, 2021

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   Even though desert dust is the most abundant aerosol by mass in Earth s atmosphere, atmospheric models struggle to accurately represent its spatial and temporal distribution. These model errors are partially caused by fundamental difficulties in simulating dust emission in coarseresolution models and in accurately representing dust microphysical properties. Here we mitigate these problems by developing a new methodology that yields an improved representation of the global dust cycle. We present an analytical framework that uses inverse modeling to integrate an ensemble of global model simulations with observational constraints on the dust size distribution, extinction efficiency, and regional dust aerosol optical depth.We then compare the inverse model results against independent measurements of dust surface concentration and deposition flux and find that errors are reduced by approximately a factor of 2 relative to current model simulations of the Northern Hemisphere dust cycle. The inverse model results show smaller improvements in the less dusty Southern Hemisphere, most likely because both the model simulations and the observational constraints used in the inverse model are less accurate. On a global basis, we find that the emission flux of dust with a geometric diameter up to 20 um (PM20) is approximately 5000 Tg yr1, which is greater than most models account for. This larger PM20 dust flux is needed to match observational constraints showing a large atmospheric loading of coarse dust. We obtain gridded datasets of dust emission, vertically integrated loading, dust aerosol optical depth, (surface) concentration, and wet and dry deposition fluxes that are resolved by season and particle size. As our results indicate that this dataset is more accurate than current model simulations and the MERRA-2 dust reanalysis product, it can be used to improve quantifications of dust impacts on the Earth system.

3. Geophys. Res. Let.

   Importance of Uncertainties in the Spatial Distribution of Preindustrial Wildfires for Estimating Aerosol Radiative Forcing

   J. S. Wan , D. S. Hamilton , and N. M. Mahowald

   Geophysical Research Letters, 2021

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   Uncertainty in preindustrial aerosol emissions, including fires, is one of the largest sources of uncertainty in estimating anthropogenic radiative forcing. Here, we quantify the range in aerosol forcing associated with uncertainty in the location and magnitude of preindustrial fire emissions in a climate model based on four emission estimates. With varied emission location and magnitude among the fire estimates, we find the change in aerosol forcing from present-day to preindustrial is between −0.4 and 0.3 W/m2 for direct radiative forcing and between −1.8 and 0.6 W/m2 for cloud albedo forcing. Altering only the spatial distribution of preindustrial fires for a fixed magnitude adds a previously unaccounted 25% uncertainty to the total aerosol radiative forcing range. Future studies must account for the uncertainty in the spatial distribution of fire and other aerosol emissions as regional differences contribute substantial additional uncertainty to anthropogenic radiative forcing estimates and the resultant climate sensitivity.

2019

1. Geosci. Mod. Dev.

   Improved methodologies for Earth system modelling of atmospheric soluble iron and observation comparisons using the Mechanism of Intermediate complexity for Modelling Iron (MIMI v.1.0)

   Douglas S. Hamilton , Rachel A. Scanza , Yan Feng , and 8 more authors

   Geoscientific Model Development, 2019

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   Herein, we present a description of the Mechanism of Intermediate complexity for Modelling Iron (MIMI v1.0). This iron processing module was developed for use within Earth system models and has been updated within a modal aerosol framework from the original implementation in a bulk aerosol model. MIMI simulates the emission and atmospheric processing of two main sources of iron in aerosol prior to deposition: mineral dust and combustion processes. Atmospheric dissolution of insoluble to soluble iron is parameterized by an acidic interstitial aerosol reaction and a separate in-cloud aerosol reaction scheme based on observations of enhanced aerosol iron solubility in the presence of oxalate. Updates include a more comprehensive treatment of combustion iron emissions, improvements to the iron dissolution scheme, and an improved physical dust mobilization scheme. An extensive dataset consisting predominantly of cruise-based observations was compiled to compare to the model. The annual mean modelled concentration of surface-level total iron compared well with observations but less so in the soluble fraction (iron solubility) for which observations are much more variable in space and time. Comparing model and observational data is sensitive to the definition of the average as well as the temporal and spatial range over which it is calculated. Through statistical analysis and examples, we show that a median or log-normal distribution is preferred when comparing with soluble iron observations. The iron solubility calculated at each model time step versus that calculated based on a ratio of the monthly mean values, which is routinely presented in aerosol studies and used in ocean biogeochemistry models, is on average globally one-third (34 %) higher. We redefined ocean deposition regions based on dominant iron emission sources and found that the daily variability in soluble iron simulated by MIMI was larger than that of previous model simulations. MIMI simulated a general increase in soluble iron deposition to Southern Hemisphere oceans by a factor of 2 to 4 compared with the previous version, which has implications for our understanding of the ocean biogeochemistry of these predominantly iron-limited ocean regions.