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

2015 ◽  
Vol 28 (6) ◽  
pp. 2512-2526 ◽  
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.

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

2012 ◽  
Vol 12 (1) ◽  
pp. 2057-2113 ◽  
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.

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

2012 ◽  
Vol 12 (10) ◽  
pp. 4699-4721 ◽  
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.

scholarly journals The SMHI Large Ensemble (SMHI-LENS) with EC-Earth3

2021 ◽  
Author(s):  
Klaus Wyser ◽  
Torben Koenigk ◽  
Uwe Fladrich ◽  
Ramon Fuentes-Franco ◽  
Mehdi Pasha Karami ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Large Ensemble ◽  
Sea Level Pressure ◽  
Near Surface ◽  
Surface Warming ◽  
Key Variables ◽  
Set Up

Abstract. The Swedish Meteorological and Hydrological Institute used the global climate model EC-Earth3 to perform a large ensemble of simulations (SMHI-LENS). It consists of 50 members, covers the period 1970 to 2100 and comprises the SSP1-1.9, SSP3-3.4, SSP5-3.4-OS and SSP5-8.5 scenarios. Thus, it is currently the only large ensemble that allows for analyzing the effect of delayed mitigation actions versus no mitigation efforts and versus earlier efforts leading to similar radiative forcing at year 2100. We describe the set-up of the SMHI-LENS in detail and provide first examples for its application. The ensemble mean future changes of key variables in atmosphere and ocean are analyzed and compared against the variability across the ensemble members. In agreement with other large ensemble simulations, we find that the future changes in the near surface temperature are more robust than those for precipitation or sea level pressure. As an example for a possible application of the SMHI-LENS, we analyse the probability of exceeding specific global surface warming levels in the different scenarios. None of the scenarios is able to keep global warming in the 21st century below 1.5 °C. In SSP1-1.9 there is a probability of approximately 70 % to stay below 2 °C warming while all other SSPs exceed this target in every single member of SMHI-LENS during the course of the century. We also investigate the point in time when the SSP5-8.5 and SSP5-3.4 ensembles separate, i.e. when their differences become significant, and likewise when the SSP5-3.4-OS and SSP4-3.4 ensembles become similar. Last, we show that the time of emergence of a separation between different scenarios can vary by several decades when reducing the ensemble size to 10 members.

scholarly journals The SMHI Large Ensemble (SMHI-LENS) with EC-Earth3.3.1

2021 ◽  
Vol 14 (7) ◽  
pp. 4781-4796
Author(s):  
Klaus Wyser ◽  
Torben Koenigk ◽  
Uwe Fladrich ◽  
Ramon Fuentes-Franco ◽  
Mehdi Pasha Karami ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Large Ensemble ◽  
Sea Level Pressure ◽  
Near Surface ◽  
Surface Warming ◽  
Key Variables ◽  
Set Up

Abstract. The Swedish Meteorological and Hydrological Institute used the global climate model EC-Earth3 to perform a large ensemble of simulations (SMHI-LENS). It consists of 50 members, covers the period 1970 to 2100, and comprises the SSP1-1.9, SSP3-3.4, SSP5-3.4-OS, and SSP5-8.5 scenarios. Thus, it is currently the only large ensemble that allows for analyzing the effect of delayed mitigation actions versus no mitigation efforts and versus earlier efforts leading to similar radiative forcing at the year 2100. We describe the set-up of the SMHI-LENS in detail and provide first examples of its application. The ensemble mean future changes in key variables in the atmosphere and ocean are analyzed and compared against the variability across the ensemble members. In agreement with other large-ensemble simulations, we find that the future changes in the near-surface temperature are more robust than those for precipitation or sea level pressure. As an example of a possible application of the SMHI-LENS, we analyze the probability of exceeding specific global surface warming levels in the different scenarios. None of the scenarios is able to keep global warming in the 21st century below 1.5 ∘C. In SSP1-1.9 there is a probability of approximately 70 % to stay below 2 ∘C warming, while all other SSPs exceed this target in every single member of SMHI-LENS during the course of the century. We also investigate the point in time when the SSP5-8.5 and SSP5-3.4 ensembles separate, i.e., when their differences become significant, and likewise when the SSP5-3.4-OS and SSP4-3.4 ensembles become similar. Last, we show that the time of emergence of a separation between different scenarios can vary by several decades when reducing the ensemble size to 10 members.

Large ensemble assessment of how the global surface warming response to cumulative carbon differs for negative and positive carbon emissions  

2021 ◽  
Author(s):  
Negar Vakilifard ◽  
Katherine Turner ◽  
Ric Williams ◽  
Philip Holden ◽  
Neil Edwards ◽  
...  
Keyword(s):  
Carbon Emissions ◽  
Radiative Forcing ◽  
Climate Model ◽  
Climate Feedback ◽  
Climate Response ◽  
Ocean Heat Uptake ◽  
Transient Climate Response ◽  
Surface Warming ◽  
Radiative Processes ◽  
Negative Emission

<p>The controls of the effective transient climate response (TCRE), defined in terms of the dependence of surface warming since the pre-industrial to the cumulative carbon emission, is explained in terms of climate model experiments for a scenario including positive emissions and then negative emission over a period of 400 years. We employ a pre-calibrated ensemble of GENIE, grid-enabled integrated Earth system model, consisting of 86 members to determine the process of controlling TCRE in both CO<sub>2</sub> emissions and drawdown phases. Our results are based on the GENIE simulations with historical forcing from AD 850 including land use change, and the future forcing defined by CO<sub>2</sub> emissions and a non-CO<sub>2</sub> radiative forcing timeseries. We present the results for the point-source carbon capture and storage (CCS) scenario as a negative emission scenario, following the medium representative concentration pathway (RCP4.5), assuming that the rate of emission drawdown is 2 PgC/yr CO<sub>2</sub> for the duration of 100 years. The climate response differs between the periods of positive and negative carbon emissions with a greater ensemble spread during the negative carbon emissions. The controls of the spread in ensemble responses are explained in terms of a combination of thermal processes (involving ocean heat uptake and physical climate feedback), radiative processes (saturation in radiative forcing from CO<sub>2</sub> and non-CO<sub>2</sub> contributions) and carbon dependences (involving terrestrial and ocean carbon uptake).  </p>

scholarly journals Comparison of ice particle characteristics simulated by the Community Atmosphere Model (CAM5) with in-situ observations

2014 ◽  
Vol 14 (6) ◽  
pp. 7637-7681 ◽  
Author(s):  
T. Eidhammer ◽  
H. Morrison ◽  
A. Bansemer ◽  
A. Gettelman ◽  
A. J. Heymsfield
Keyword(s):  
Size Distribution ◽  
Radiative Forcing ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Atmospheric Model ◽  
Slope Parameter ◽  
Cloud Radiative Forcing ◽  
Threshold Size ◽  
Cloud Ice

Abstract. Detailed measurements of ice crystals in cirrus clouds were used to compare with results from the Community Atmospheric Model Version 5 (CAM5) global climate model. The observations are from two different field campaigns with contrasting conditions: Atmospheric Radiation Measurements Spring Cloud Intensive Operational Period in 2000 (ARM-IOP), which was characterized primarily by midlatitude frontal clouds and cirrus, and Tropical Composition, Cloud and Climate Coupling (TC4), which was dominated by anvil cirrus. Results show that the model typically overestimates the slope parameter of the exponential size distributions of cloud ice and snow, while the variation with temperature (height) is comparable. The model also overestimates the ice/snow number concentration (0th moment of the size distribution) and underestimates higher moments (2nd through 5th), but compares well with observations for the 1st moment. Overall the model shows better agreement with observations for TC4 than for ARM-IOP in regards to the moments. The mass-weighted terminal fallspeed is lower in the model compared to observations for both ARM-IOP and TC4, which is partly due to the overestimation of the size distribution slope parameter. Sensitivity tests with modification of the threshold size for cloud ice to snow autoconversion (Dcs) do not show noticeable improvement in modeled moments, slope parameter and mass weighed fallspeed compared to observations. Further, there is considerable sensitivity of the cloud radiative forcing to Dcs, consistent with previous studies, but no value of Dcs improves modeled cloud radiative forcing compared to measurements. Since the autoconversion of cloud ice to snow using the threshold size Dcs has little physical basis, future improvement to combine cloud ice and snow into a single category, eliminating the need for autoconversion, is suggested.

How detailed do cloud microphysics need to be in climate models?

2021 ◽  
Author(s):  
Ulrike Proske ◽  
Sylvaine Ferrachat ◽  
David Neubauer ◽  
Ulrike Lohmann
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Computing Time ◽  
Cloud Microphysics ◽  
Model Response ◽  
Microphysical Processes ◽  
Improved Accuracy

<p>Clouds are of major importance for the climate system, but the radiative forcing resulting from their interaction with aerosols remains uncertain. To improve the representation of clouds in climate models, the parameterisations of cloud microphysical processes (CMPs) have become increasingly detailed. However, more detailed climate models do not necessarily result in improved accuracy for estimates of radiative forcing (Knutti and Sedláček, 2013; Carslaw et al., 2018). On the contrary, simpler formulations are cheaper, sufficient for some applications, and allow for an easier understanding of the respective process' effect in the model.</p><p>This study aims to gain an understanding which CMP parameterisation complexity is sufficient through simplification. We gradually phase out processes such as riming or aggregation from the global climate model ECHAM-HAM, meaning that the processes are only allowed to exhibit a fraction of their effect on the model state. The shape of the model response as a function of the artificially scaled effect of a given process helps to understand the importance of this process for the model response and its potential for simplification. For example, if partially removing a process induces only minor alterations in the present day climate, this process presents as a good candidate for simplification. This may be then further investigated, for example in terms of computing time.<br>The resulting sensitivities to CMP complexity are envisioned to guide CMP model simplifications as well as steer research towards those processes where a more accurate representation proves to be necessary.</p><p> </p><p><br>Carslaw, Kenneth, Lindsay Lee, Leighton Regayre, and Jill Johnson (Feb. 2018). “Climate Models Are Uncertain, but We Can Do Something About It”. In: Eos 99. doi: 10.1029/2018EO093757</p><p>Knutti, Reto and Jan Sedláček (Apr. 2013). “Robustness and Uncertainties in the New CMIP5 Climate Model Projections”. In: Nature Climate Change 3.4, pp. 369–373. doi: 10.1038/nclimate1716</p>

Aerosol Radiative Forcing and Forcing Efficiency in the UVB for Regions Affected by Saharan and Asian Mineral Dust

2009 ◽  
Vol 66 (4) ◽  
pp. 1033-1040 ◽  
Author(s):  
O. E. García ◽  
A. M. Díaz ◽  
F. J. Expósito ◽  
J. P. Díaz ◽  
A. Redondas ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Radiative Forcing ◽  
Climate Model ◽  
Mineral Dust ◽  
Global Climate ◽  
Global Climate Model ◽  
Aerosol Radiative Forcing ◽  
Benchmark Database ◽  
Aerosol Radiative

Abstract The influence of mineral dust on ultraviolet energy transfer is studied for two different mineralogical origins. The aerosol radiative forcing ΔF and the forcing efficiency at the surface ΔFeff in the range 290–325 nm were estimated in ground-based stations affected by the Saharan and Asian deserts during the dusty seasons. UVB solar measurements were taken from the World Ozone and Ultraviolet Data Center (WOUDC) for four Asian stations (2000–04) and from the Santa Cruz Observatory, Canary Islands (2002–03), under Gobi and Sahara Desert influences, respectively. The Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth at 550 nm was used to characterize the aerosol load τ, whereas the aerosol index provided by the Total Ozone Mapping Spectrometer (TOMS) sensor was employed to identify the mineral dust events. The ΔF is strongly affected by the aerosol load, the values found being comparable in both regions during the dusty seasons. Under those conditions, ΔF values as large as −1.29 ± 0.53 W m−2 (τ550 = 0.48 ± 0.24) and −1.43 ± 0.38 W m−2 (τ550 = 0.54 ± 0.26) were reached under Saharan and Asian dust conditions, respectively. Nevertheless, significant differences have been observed in the aerosol radiative forcing per unit of aerosol optical depth in the slant path, τS. The maximum ΔFeff values associated with dust influences were −1.55 ± 0.20 W m−2 τS550−1 for the Saharan region and −0.95 ± 0.11 W m−2 τS550−1 in the Asian area. These results may be used as a benchmark database for establishing aerosol corrections in UV satellite products or in global climate model estimations.

scholarly journals Black Carbon Increases Frequency of Extreme ENSO Events

2019 ◽  
Vol 32 (23) ◽  
pp. 8323-8333 ◽  
Author(s):  
Sijia Lou ◽  
Yang Yang ◽  
Hailong Wang ◽  
Jian Lu ◽  
Steven J. Smith ◽  
...  
Keyword(s):  
Black Carbon ◽  
Climate Models ◽  
Climate Model ◽  
Southern Oscillation ◽  
Global Climate ◽  
Global Climate Model ◽  
Co2 Concentration ◽  
Enso Events ◽  
Aerosol Forcing ◽  
Earth’S Climate

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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