Climate Impacts of CALIPSO-Guided Corrections to Black Carbon Aerosol Vertical Distributions in a Global Climate Model

ABSTRACT El Niño–Southern Oscillation (ENSO) is the leading mode of Earth’s climate variability at interannual time scales with profound ecological and societal impacts, and it is projected to intensify in many climate models as the climate warms under the forcing of increasing CO2 concentration. Since the preindustrial era, black carbon (BC) emissions have substantially increased in the Northern Hemisphere. But how BC aerosol forcing may influence the occurrence of the extreme ENSO events has rarely been investigated. In this study, using simulations of a global climate model, we show that increases in BC emissions from both the midlatitudes and Arctic weaken latitudinal temperature gradients and northward heat transport, decrease tropical energy divergence, and increase sea surface temperature over the tropical oceans, with a surprising consequential increase in the frequency of extreme ENSO events. A corollary of this study is that reducing BC emissions might serve to mitigate the possible increasing frequency of extreme ENSO events under greenhouse warming, if the modeling result can be translated into the climate in reality.

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Simulation of black carbon in snow and its climate impact in the Canadian Global Climate Model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-18839-2015 ◽

2015 ◽

Vol 15 (13) ◽

pp. 18839-18882 ◽

Cited By ~ 1

Author(s):

M. Namazi ◽

K. von Salzen ◽

J. N. S. Cole

Keyword(s):

Black Carbon ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Surface Air Temperature ◽

Climate Impact ◽

Radiative Forcings ◽

Mixing Ratios ◽

Emission Changes ◽

The Impact

Abstract. A new physically-based parameterization of black carbon (BC) in snow was developed and implemented in the Canadian Atmospheric Global Climate Model (CanAM4.2). Simulated BC snow mixing ratios and BC snow radiative forcings are in good agreement with measurements and results from other models. Simulations with the improved model yield considerable trends in regional BC concentrations in snow and BC snow radiative forcings during the time period from 1950–1959 to 2000–2009. Increases in radiative forcings for Asia and decreases for Europe and North America are found to be associated with changes in BC emissions. Additional sensitivity simulations were performed in order to study the impact of BC emission changes between 1950–1959 and 2000–2009 on surface albedo, snow cover fraction, and surface air temperature. Results from these simulations indicate that impacts of BC emission changes on snow albedos between these two decades are small and not significant. Overall, changes in BC concentrations in snow have much smaller impacts on the cryosphere than the net warming surface air temperatures during the second half of the 20th century.

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Enhanced solar energy absorption by internally-mixed black carbon in snow grains

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-2057-2012 ◽

2012 ◽

Vol 12 (1) ◽

pp. 2057-2113 ◽

Cited By ~ 2

Author(s):

M. G. Flanner ◽

X. Liu ◽

C. Zhou ◽

J. E. Penner

Keyword(s):

Sea Ice ◽

Black Carbon ◽

Radiative Forcing ◽

Climate Model ◽

Volume Fraction ◽

Global Climate ◽

Global Climate Model ◽

Absorption Enhancement ◽

Liquid Droplets ◽

Vapor Transfer

Abstract. Here we explore light absorption by snowpack containing black carbon (BC) particles residing within ice grains. Basic considerations of particle volumes and BC/snow mass concentrations show that there are generally 0.05–109 BC particles for each ice grain. This suggests that internal BC is likely distributed as multiple inclusions within ice grains, and thus the dynamic effective medium approximation (DEMA) (Chýlek and Srivastava, 1983) is a more appropriate optical representation for BC/ice composites than coated-sphere or standard mixing approximations. DEMA calculations show that the 460 nm absorption cross-section of BC/ice composites, normalized to the mass of BC, is typically enhanced by factors of 1.8–2.1 relative to interstitial BC. BC effective radius is the dominant cause of variation in this enhancement, compared with ice grain size and BC volume fraction. We apply two atmospheric aerosol models that simulate interstitial and within-hydrometeor BC lifecycles. Although only ~2% of the atmospheric BC burden is cloud-borne, 71–83% of the BC deposited to global snow and sea-ice surfaces occurs within hydrometeors. Key processes responsible for within-snow BC deposition are development of hydrophilic coatings on BC, activation of liquid droplets, and subsequent snow formation through riming or ice nucleation by other species and aggregation/accretion of ice particles. Applying deposition fields from these aerosol models in offline snow and sea-ice simulations, we calculate that 32–73% of BC in global surface snow resides within ice grains. This fraction is smaller than the within-hydrometeor deposition fraction because meltwater flux preferentially removes internal BC, while sublimation and freezing within snowpack expose internal BC. Incorporating the DEMA into a global climate model, we simulate increases in BC/snow radiative forcing of 43–86%, relative to scenarios that apply external optical properties to all BC. We show that snow metamorphism driven by diffusive vapor transfer likely proceeds too slowly to alter the mass of internal BC while it is radiatively active, but neglected processes like wind pumping and convection may play much larger roles. These results suggest that a large portion of BC in surface snowpack may reside within ice grains and increase BC/snow radiative forcing, although measurements to evaluate this are lacking. Finally, previous studies of BC/snow forcing that neglected this absorption enhancement are not necessarily biased low, because of application of absorption-enhancing sulfate coatings to hydrophilic BC, neglect of coincident absorption by dust in snow, and implicit treatment of cloud-borne BC resulting in longer-range transport.

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Simulation of black carbon in snow and its climate impact in the Canadian Global Climate Model

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-10887-2015 ◽

2015 ◽

Vol 15 (18) ◽

pp. 10887-10904 ◽

Cited By ~ 11

Author(s):

M. Namazi ◽

K. von Salzen ◽

J. N. S. Cole

Keyword(s):

Black Carbon ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Surface Air Temperature ◽

Climate Impact ◽

Radiative Forcings ◽

Mixing Ratios ◽

Emission Changes ◽

The Impact

Abstract. A new physically based parameterisation of black carbon (BC) in snow was developed and implemented in the Canadian Atmospheric Global Climate Model (CanAM4.2). Simulated BC snow mixing ratios and BC snow radiative forcings are in good agreement with measurements and results from other models. Simulations with the improved model yield considerable trends in regional BC concentrations in snow and BC snow radiative forcings during the time period from 1950–1959 to 2000–2009. Increases in radiative forcings for Asia and decreases for Europe and North America are found to be associated with changes in BC emissions. Additional sensitivity simulations were performed in order to study the impact of BC emission changes between 1950–1959 and 2000–2009 on surface albedo, snow cover fraction, and surface air temperature. Results from these simulations indicate that impacts of BC emission changes on snow albedos between these 2 decades are small and not significant. Overall, changes in BC concentrations in snow have much smaller impacts on the cryosphere than the net warming surface air temperatures during the second half of the 20th century.

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Enhanced solar energy absorption by internally-mixed black carbon in snow grains

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-4699-2012 ◽

2012 ◽

Vol 12 (10) ◽

pp. 4699-4721 ◽

Cited By ~ 83

Author(s):

M. G. Flanner ◽

X. Liu ◽

C. Zhou ◽

J. E. Penner ◽

C. Jiao

Keyword(s):

Sea Ice ◽

Black Carbon ◽

Radiative Forcing ◽

Climate Model ◽

Volume Fraction ◽

Global Climate ◽

Global Climate Model ◽

Absorption Enhancement ◽

Liquid Droplets ◽

Vapor Transfer

Abstract. Here we explore light absorption by snowpack containing black carbon (BC) particles residing within ice grains. Basic considerations of particle volumes and BC/snow mass concentrations show that there are generally 0.05–109 BC particles for each ice grain. This suggests that internal BC is likely distributed as multiple inclusions within ice grains, and thus the dynamic effective medium approximation (DEMA) (Chýlek and Srivastava, 1983) is a more appropriate optical representation for BC/ice composites than coated-sphere or standard mixing approximations. DEMA calculations show that the 460 nm absorption cross-section of BC/ice composites, normalized to the mass of BC, is typically enhanced by factors of 1.8–2.1 relative to interstitial BC. BC effective radius is the dominant cause of variation in this enhancement, compared with ice grain size and BC volume fraction. We apply two atmospheric aerosol models that simulate interstitial and within-hydrometeor BC lifecycles. Although only ~2% of the atmospheric BC burden is cloud-borne, 71–83% of the BC deposited to global snow and sea-ice surfaces occurs within hydrometeors. Key processes responsible for within-snow BC deposition are development of hydrophilic coatings on BC, activation of liquid droplets, and subsequent snow formation through riming or ice nucleation by other species and aggregation/accretion of ice particles. Applying deposition fields from these aerosol models in offline snow and sea-ice simulations, we calculate that 32–73% of BC in global surface snow resides within ice grains. This fraction is smaller than the within-hydrometeor deposition fraction because meltwater flux preferentially removes internal BC, while sublimation and freezing within snowpack expose internal BC. Incorporating the DEMA into a global climate model, we simulate increases in BC/snow radiative forcing of 43–86%, relative to scenarios that apply external optical properties to all BC. We show that snow metamorphism driven by diffusive vapor transfer likely proceeds too slowly to alter the mass of internal BC while it is radiatively active, but neglected processes like wind pumping and convection may play much larger roles. These results suggest that a large portion of BC in surface snowpack may reside within ice grains and increase BC/snow radiative forcing, although measurements to evaluate this are lacking. Finally, previous studies of BC/snow forcing that neglected this absorption enhancement are not necessarily biased low, because of application of absorption-enhancing sulfate coatings to hydrophilic BC, neglect of coincident absorption by dust in snow, and implicit treatment of cloud-borne BC resulting in longer-range transport.

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The G4Foam Experiment: global climate impacts of regional ocean albedo modification

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-595-2017 ◽

2017 ◽

Vol 17 (1) ◽

pp. 595-613 ◽

Cited By ~ 8

Author(s):

Corey J. Gabriel ◽

Alan Robock ◽

Lili Xia ◽

Brian Zambri ◽

Ben Kravitz

Keyword(s):

Southern Hemisphere ◽

Radiative Forcing ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Ocean Surface ◽

Climate Impacts ◽

Hadley Cell ◽

Ocean Gyres ◽

The Tropics

Abstract. Reducing insolation has been proposed as a geoengineering response to global warming. Here we present the results of climate model simulations of a unique Geoengineering Model Intercomparison Project Testbed experiment to investigate the benefits and risks of a scheme that would brighten certain oceanic regions. The National Center for Atmospheric Research CESM CAM4-Chem global climate model was modified to simulate a scheme in which the albedo of the ocean surface is increased over the subtropical ocean gyres in the Southern Hemisphere. In theory, this could be accomplished using a stable, nondispersive foam, comprised of tiny, highly reflective microbubbles. Such a foam has been developed under idealized conditions, although deployment at a large scale is presently infeasible. We conducted three ensemble members of a simulation (G4Foam) from 2020 through to 2069 in which the albedo of the ocean surface is set to 0.15 (an increase of 150 %) over the three subtropical ocean gyres in the Southern Hemisphere, against a background of the RCP6.0 (representative concentration pathway resulting in +6 W m−2 radiative forcing by 2100) scenario. After 2069, geoengineering is ceased, and the simulation is run for an additional 20 years. Global mean surface temperature in G4Foam is 0.6 K lower than RCP6.0, with statistically significant cooling relative to RCP6.0 south of 30° N. There is an increase in rainfall over land, most pronouncedly in the tropics during the June–July–August season, relative to both G4SSA (specified stratospheric aerosols) and RCP6.0. Heavily populated and highly cultivated regions throughout the tropics, including the Sahel, southern Asia, the Maritime Continent, Central America, and much of the Amazon experience a statistically significant increase in precipitation minus evaporation. The temperature response to the relatively modest global average forcing of −1.5 W m−2 is amplified through a series of positive cloud feedbacks, in which more shortwave radiation is reflected. The precipitation response is primarily the result of the intensification of the southern Hadley cell, as its mean position migrates northward and away from the Equator in response to the asymmetric cooling.

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Climate change threatens Chinook salmon throughout their life cycle

Communications Biology ◽

10.1038/s42003-021-01734-w ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Lisa G. Crozier ◽

Brian J. Burke ◽

Brandon E. Chasco ◽

Daniel L. Widener ◽

Richard W. Zabel

Keyword(s):

Climate Change ◽

Chinook Salmon ◽

Climate Model ◽

Pacific Salmon ◽

Global Climate ◽

Global Climate Model ◽

Climate Impacts ◽

Future Climate Change ◽

Life Stages ◽

Recent Climate

AbstractWidespread declines in Atlantic and Pacific salmon (Salmo salar and Oncorhynchus spp.) have tracked recent climate changes, but managers still lack quantitative projections of the viability of any individual population in response to future climate change. To address this gap, we assembled a vast database of survival and other data for eight wild populations of threatened Chinook salmon (O. tshawytscha). For each population, we evaluated climate impacts at all life stages and modeled future trajectories forced by global climate model projections. Populations rapidly declined in response to increasing sea surface temperatures and other factors across diverse model assumptions and climate scenarios. Strong density dependence limited the number of salmon that survived early life stages, suggesting a potentially efficacious target for conservation effort. Other solutions require a better understanding of the factors that limit survival at sea. We conclude that dramatic increases in smolt survival are needed to overcome the negative impacts of climate change for this threatened species.

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Climate Impacts of Large-Scale Wind Farms as Parameterized in a Global Climate Model

Journal of Climate ◽

10.1175/jcli-d-14-00245.1 ◽

2015 ◽

Vol 28 (15) ◽

pp. 6160-6180 ◽

Cited By ~ 20

Author(s):

Anna C. Fitch

Keyword(s):

Large Scale ◽

Wind Farm ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Wind Farms ◽

Electricity Demand ◽

Climate Impacts ◽

Maximum Temperature ◽

Installed Capacity

Abstract The local, regional, and global climate impacts of a large-scale global deployment of wind power in regionally high densities over land are investigated for a 60-yr period. Wind farms are represented as elevated momentum sinks as well as enhanced turbulence to represent turbine blade mixing in the Community Atmosphere Model, version 5 (CAM5), a global climate model. For a total installed capacity of 2.5 TW, to provide 16% of the world’s projected electricity demand in 2050, minimal impacts are found both regionally and globally on temperature, sensible and latent heat fluxes, cloud, and precipitation. A mean near-surface warming of 0.12 ± 0.07 K is seen within the wind farms, with a global-mean temperature change of −0.013 ± 0.015 K. Impacts on wind speed and turbulence are more pronounced but largely confined within the wind farm areas. Increasing the wind farm areas to provide an installed capacity of 10 TW, or 65% of the 2050 electricity demand, causes further impacts; however, they remain slight overall. Maximum temperature changes are less than 0.5 K in the wind farm areas. To provide 20 TW of installed capacity, or 130% of the 2050 electricity demand, impacts both within the wind farms and beyond become more pronounced, with a doubling in turbine density. However, maximum temperature changes remain less than 0.7 K. Representing wind farms instead as an increase in surface roughness generally produces similar mean results; however, maximum changes increase, and influences on wind and turbulence are exaggerated. Overall, wind farm impacts are much weaker than those expected from greenhouse gas emissions, with very slight global-mean climate impacts.

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A Standardized Global Climate Model Study Showing Unique Properties for the Climate Response to Black Carbon Aerosols

Journal of Climate ◽

10.1175/jcli-d-14-00050.1 ◽

2015 ◽

Vol 28 (6) ◽

pp. 2512-2526 ◽

Cited By ~ 18

Author(s):

M. Sand ◽

T. Iversen ◽

P. Bohlinger ◽

A. Kirkevåg ◽

I. Seierstad ◽

...

Keyword(s):

Black Carbon ◽

Radiative Forcing ◽

Climate Model ◽

Kernel Method ◽

Global Climate ◽

Global Climate Model ◽

Climate Response ◽

Air Concentration ◽

Surface Warming ◽

The Difference

Abstract The climate response to an abrupt increase of black carbon (BC) aerosols is compared to the standard CMIP5 experiment of quadrupling CO2 concentrations in air. The global climate model NorESM with interactive aerosols is used. One experiment employs prescribed BC emissions with calculated concentrations coupled to atmospheric processes (emission-driven) while a second prescribes BC concentrations in air (concentration-driven) from a precalculation with the same model and emissions, but where the calculated BC does not force the climate dynamics. The difference quantifies effects of feedbacks between airborne BC and other climate processes. BC emissions are multiplied with 25, yielding an instantaneous top-of-atmosphere (TOA) radiative forcing (RF) comparable to the quadrupling of atmospheric CO2. A radiative kernel method is applied to estimate the different feedbacks. In both BC runs, BC leads to a much smaller surface warming than CO2. Rapid atmospheric feedbacks reduce the BC-induced TOA forcing by approximately 75% over the first year (10% for CO2). For BC, equilibrium is quickly re-established, whereas for CO2 equilibration requires a much longer time than 150 years. Emission-driven BC responses in the atmosphere are much larger than the concentration-driven. The northward displacement of the intertropical convergence zone (ITCZ) in the BC emission-driven experiment enhances both the vertical transport and deposition of BC from Southeast Asia. The study shows that prescribing BC concentrations may lead to seriously inaccurate conclusions, but other models with less efficient transport may produce results with smaller differences.

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The G4Foam Experiment: Global Climate Impacts of Regional Ocean Albedo Modification

10.5194/acp-2016-849 ◽

2016 ◽

Author(s):

Corey J. Gabriel ◽

Alan Robock ◽

Lili Xia ◽

Brian Zambri

Keyword(s):

Southern Hemisphere ◽

Radiative Forcing ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Ocean Surface ◽

Climate Impacts ◽

Hadley Cell ◽

Ocean Gyres ◽

The Tropics

Abstract. Reducing insolation has been proposed as a geoengineering response to global warming. Here we present the results of climate model simulations of a unique Geoengineering Model Intercomparison Project Testbed experiment to investigate the benefits and risks of a scheme that would brighten certain oceanic regions. The National Center for Atmospheric Research CESM-CAM4-CHEM global climate model was modified to simulate a scheme in which the albedo of the ocean surface is raised over the subtropical ocean gyres in the Southern Hemisphere. Like the commonly studied stratospheric geoengineering and marine cloud brightening proposals, this ocean albedo modification scheme is not currently possible. However, a stable, nondispersive foam, comprised of tiny, highly reflective microbubbles has been developed under idealized conditions, and, hence, a geoengineering scheme which simulates the effects of large-scale deployment of these microbubbles is appropriate to study at this time. One goal of this scheme is to cool Earth without reducing monsoon rainfall. We conducted three ensemble members of a simulation (G4Foam) from 2020 through 2069 in which the albedo of the ocean surface is raised to 0.15 over the three subtropical ocean gyres in the Southern Hemisphere, at the same time as increasing the radiative forcing with the RCP6.0 (representative concentration pathway resulting in +6 W m−2 radiative forcing by 2100) scenario, and then continuing the simulation for 20 more years with RCP6.0. Global mean surface temperature in G4Foam is 0.6 K lower than RCP6.0, with statistically significant cooling relative to RCP6.0 south of 30 °N and an increase in rainfall over land, most pronouncedly in the tropics during the June–July–August season, relative to both G4SSA (specified stratospheric aerosols) and RCP6.0. Heavily populated and highly cultivated regions throughout the tropics, including the Sahel, Southern Asia, the Maritime Continent, Central America and much of the Amazon experience a statistically significant increase in precipitation minus evaporation. The temperature response to the relatively modest global average forcing of −1.5 W m−2 is amplified through a series of positive cloud feedbacks, in which more shortwave radiation is reflected. The precipitation response is primarily the result of the intensification of the southern Hadley cell, as its mean position migrates northward and away from the Equator in response to the asymmetric cooling.

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