An official website of the United States government
Abstract Snow is the most reflective natural surface on Earth. Since fresh snow on bare sea ice increases the surface albedo, the impact of summer snow accumulation can have a negative radiative forcing effect, which would inhibit sea ice surface melt and potentially slow sea‐ice loss. However, it is not well known how often, where, and when summer snowfall events occur on Arctic sea ice. In this study, we used in situ and model snow depth data paired with surface albedo and atmospheric conditions from satellite retrievals to characterize summer snow accumulation on Arctic sea ice from 2003 to 2017. We found that, across the Arctic, ∼2 snow accumulation events occurred on initially snow‐free conditions each year. The average snow depth and albedo increases were ∼2 cm and 0.08, respectively. 16.5% of the snow accumulation events were optically thick (>3 cm deep) and lasted 2.9 days longer than the average snow accumulation event (3.4 days). Based on a simple, multiple scattering radiative transfer model, we estimated a −0.086 ± 0.020 W m−2change in the annual average top‐of‐the‐atmosphere radiative forcing for summer snowfall events in 2003–2017. The following work provides new information on the frequency, distribution, and duration of observed snow accumulation events over Arctic sea ice in summer. Such results may be particularly useful in understanding the impacts of ephemeral summer weather on surface albedo and their propagating effects on the radiative forcing over Arctic sea ice, as well as assessing climate model simulations of summer atmosphere‐ice processes.
more »
« less
Contribution of biomass burning to black carbon deposition on Andean glaciers: consequences for radiative forcing
Abstract Andean glaciers have melted rapidly since the 1960s. While some melting is likely due to anthropogenic climate change driven by increasing greenhouse gases, deposition of light-absorbing particles such as black carbon (BC) may also play a role. We hypothesize that BC from fires in the Amazon Basin and elsewhere may be deposited on Andean glaciers, reducing the surface albedo and inducing further melting. Here we investigate the role of BC deposition on albedo changes in the Andes for 2014–2019 by combining atmospheric chemistry modeling with observations of BC in snow or ice at four mountain sites in Peru (Quelccaya, Huascarán, Yanapaccha, and Shallap) and at one site in Bolivia (Illimani). We find that annual mean ice BC concentrations simulated by the chemical transport model GEOS-Chem for 2014–2019 are roughly consistent with those observed at the site with the longest record, Huascarán, with overestimates of 15%–40%. Smoke from fires account for 20%–70% of total wet and dry deposition fluxes, depending on the site. The rest of BC deposited comes from fossil fuel combustion. Using a snow albedo model, we find that the annual mean radiative forcing from the deposition of smoke BC alone on snow ranges from +0.1 to +3.2 W m−2under clear-sky conditions, with corresponding average albedo reductions of 0.04%–1.1%. These ranges are dependent on site and snow grain size. This result implies a potentially significant climate impact of biomass burning in the Amazon on radiative forcing in the Andes.
more »
« less
- Award ID(s):
- 1805819
- PAR ID:
- 10395190
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Environmental Research Letters
- Volume:
- 18
- Issue:
- 2
- ISSN:
- 1748-9326
- Page Range / eLocation ID:
- Article No. 024031
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract This study shows the impact of black carbon (BC) aerosol atmospheric rivers (AAR) on the Antarctic Sea ice retreat. We detect that a higher number of BC AARs arrived in the Antarctic region due to increased anthropogenic wildfire activities in 2019 in the Amazon compared to 2018. Our analyses suggest that the BC AARs led to a reduction in the sea ice albedo, increased the amount of sunlight absorbed at the surface, and a significant reduction of sea ice over the Weddell, Ross Sea (Ross), and Indian Ocean (IO) regions in 2019. The Weddell region experienced the largest amount of sea ice retreat ($$ \sim \mathrm{33,000} $$km2) during the presence of BC AARs as compared to$$ \sim \mathrm{13,000} $$ km2during non-BC days. We used a suite of data science techniques, including random forest, elastic net regression, matrix profile, canonical correlations, and causal discovery analyses, to discover the effects and validate them. Random forest, elastic net regression, and causal discovery analyses show that the shortwave upward radiative flux or the reflected sunlight, temperature, and longwave upward energy from the earth are the most important features that affect sea ice extent. Canonical correlation analysis confirms that aerosol optical depth is negatively correlated with albedo, positively correlated with shortwave energy absorbed at the surface, and negatively correlated with Sea Ice Extent. The relationship is stronger in 2019 than in 2018. This study also employs the matrix profile and convolution operation of the Convolution Neural Network (CNN) to detect anomalous events in sea ice loss. These methods show that a higher amount of anomalous melting events were detected over the Weddell and Ross regions.more » « less
-
Abstract Black carbon emitted by incomplete combustion of fossil fuels and biomass has a net warming effect in the atmosphere and reduces the albedo when deposited on ice and snow; accurate knowledge of past emissions is essential to quantify and model associated global climate forcing. Although bottom-up inventories provide historical Black Carbon emission estimates that are widely used in Earth System Models, they are poorly constrained by observations prior to the late 20th century. Here we use an objective inversion technique based on detailed atmospheric transport and deposition modeling to reconstruct 1850 to 2000 emissions from thirteen Northern Hemisphere ice-core records. We find substantial discrepancies between reconstructed Black Carbon emissions and existing bottom-up inventories which do not fully capture the complex spatial-temporal emission patterns. Our findings imply changes to existing historical Black Carbon radiative forcing estimates are necessary, with potential implications for observation-constrained climate sensitivity.more » « less
-
Abstract. Parameterizations that impact wet removal of black carbon (BC)remain uncertain in global climate models. In this study, we enhance thedefault wet deposition scheme for BC in the Community Earth System Model (CESM)to (a) add relevant physical processes that were not resolved in thedefault model and (b) facilitate understanding of the relative importanceof various cloud processes on BC distributions. We find that the enhancedscheme greatly improves model performance against HIPPO observationsrelative to the default scheme. We find that convection scavenging, aerosolactivation, ice nucleation, evaporation of rain or snow, and below-cloudscavenging dominate wet deposition of BC. BC conversion rates for processesrelated to in-cloud water–ice conversion (i.e., riming, the Bergeronprocess, and evaporation of cloud water sedimentation) are relativelysmaller, but have large seasonal variations. We also conduct sensitivitysimulations that turn off each cloud process one at a time to quantify theinfluence of cloud processes on BC distributions and radiative forcing.Convective scavenging is found to have the largest impact onBC concentrations at mid-altitudes over the tropics and even globally. Inaddition, BC is sensitive to all cloud processes over the NorthernHemisphere at high latitudes. As for BC vertical distributions, convectivescavenging greatly influences BC fractions at different altitudes.Suppressing BC droplet activation in clouds mainly decreases the fraction ofcolumn BC below 5 km, whereas suppressing BC ice nucleation increases thatabove 10 km. During wintertime, the Bergeron process also significantlyincreases BC concentrations at lower altitudes over the Arctic. Oursimulation yields a global BC burden of 85 Gg; corresponding directradiative forcing (DRF) of BC estimated using the Parallel Offline RadiativeTransfer (PORT) is 0.13 W m−2, much lower than previous studies. Therange of DRF derived from sensitivity simulations is large, 0.09–0.33 W m−2,corresponding to BC burdens varying from 73 to 151 Gg. Due todifferences in BC vertical distributions among each sensitivity simulation,fractional changes in DRF (relative to the baseline simulation) are alwayshigher than fractional changes in BC burdens; this occurs because relocating BCin the vertical influences the radiative forcing per BC mass. Our resultshighlight the influences of cloud microphysical processes on BC concentrationsand radiative forcing.more » « less
-
Refractory black carbon (rBC) aerosols in air and precipitation result from incomplete combustion. Prior to 18th century industrialization, the primary emission sources were wildfires and agricultural fires. After industrialization, fossil fuel burning has become an important emission source as well. Because these aerosols are import contributors to Earth’s radiative forcing both in the air and when deposited to bright surfaces such as fresh snow, quantifying past rBC emissions is critical to accurate Earth System Modeling. This data set contains 1750 to 2010 annual rBC depositional fluxes measured in a global array of 31, mostly polar ice cores. They were used (Zhang et al., Nature Communications, 2024) to reconstruct atmospheric rBC emissions using the atmospheric chemical transport GEOS-Chem. Details on the rBC measurement methods and chronology development are provided in the associated references for the individual ice core records.more » « less
