scholarly journals Mitigation of Non-CO2 Aviation’s Climate Impact by Changing Cruise Altitudes

Aerospace ◽  
2021 ◽  
Vol 8 (2) ◽  
pp. 36
Author(s):  
Sigrun Matthes ◽  
Ling Lim ◽  
Ulrike Burkhardt ◽  
Katrin Dahlmann ◽  
Simone Dietmüller ◽  
...  
Keyword(s):  
Co2 Emissions ◽  
Temperature Change ◽  
Radiative Forcing ◽  
General Circulation ◽  
General Circulation Models ◽  
Sensitivity Study ◽  
Climate Impact ◽  
Flight Altitude ◽  
Co2 Effects ◽  
The Impact

Aviation is seeking for ways to reduce its climate impact caused by CO2 emissions and non-CO2 effects. Operational measures which change overall flight altitude have the potential to reduce climate impact of individual effects, comprising CO2 but in particular non-CO2 effects. We study the impact of changes of flight altitude, specifically aircraft flying 2000 feet higher and lower, with a set of global models comprising chemistry-transport, chemistry-climate and general circulation models integrating distinct aviation emission inventories representing such alternative flight altitudes, estimating changes in climate impact of aviation by quantifying radiative forcing and induced temperature change. We find in our sensitivity study that flying lower leads to a reduction of radiative forcing of non-CO2 effects together with slightly increased CO2 emissions and impacts, when cruise speed is not modified. Flying higher increases radiative forcing of non-CO2 effects by about 10%, together with a slight decrease of CO2 emissions and impacts. Overall, flying lower decreases aviation-induced temperature change by about 20%, as a decrease of non-CO2 impacts by about 30% dominates over slightly increasing CO2 impacts assuming a sustained emissions scenario. Those estimates are connected with a large but unquantified uncertainty. To improve the understanding of mechanisms controlling the aviation climate impact, we study the geographical distributions of aviation-induced modifications in the atmosphere, together with changes in global radiative forcing and suggest further efforts in order to reduce long standing uncertainties.

scholarly journals DMS atmospheric concentrations and sulphate aerosol indirect radiative forcing: a sensitivity study to the DMS source representation and oxidation

2003 ◽  
Vol 3 (1) ◽  
pp. 49-65 ◽  
Author(s):  
O. Boucher ◽  
C. Moulin ◽  
S. Belviso ◽  
O. Aumont ◽  
L. Bopp ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Marine Boundary Layer ◽  
Circulation Model ◽  
Sensitivity Study ◽  
Sulphate Aerosol ◽  
Sulphate Aerosols ◽  
The Impact ◽  
Atmospheric Concentrations ◽  
Indirect Radiative Forcing

Abstract. The global sulphur cycle has been simulated using a general circulation model with a focus on the source and oxidation of atmospheric dimethylsulphide (DMS). The sensitivity of atmospheric DMS to the oceanic DMS climatology, the parameterisation of the sea-air transfer and to the oxidant fields have been studied. The importance of additional oxidation pathways (by O3 in the gas- and aqueous-phases and by BrO in the gas phase) not incorporated in global models has also been evaluated. While three different climatologies of the oceanic DMS concentration produce rather similar global DMS fluxes to the atmosphere at 24-27 Tg S yr -1, there are large differences in the spatial and seasonal distribution. The relative contributions of OH and NO3 radicals to DMS oxidation depends critically on which oxidant fields are prescribed in the model. Oxidation by O3 appears to be significant at high latitudes in both hemispheres. Oxidation by BrO could be significant even for BrO concentrations at sub-pptv levels in the marine boundary layer. The impact of such refinements on the DMS chemistry onto the indirect radiative forcing by anthropogenic sulphate aerosols is also discussed.

scholarly journals A new method for evaluating the impact of vertical distribution on aerosol radiative forcing in general circulation models

2013 ◽  
Vol 13 (7) ◽  
pp. 18809-18853
Author(s):  
M. R. Vuolo ◽  
M. Schulz ◽  
Y. Balkanski ◽  
T. Takemura
Keyword(s):  
Vertical Distribution ◽  
Radiative Forcing ◽  
General Circulation ◽  
Cloud Amount ◽  
General Circulation Models ◽  
Individual Species ◽  
Clear Sky ◽  
Atmospheric Column ◽  
Aerosol Forcing ◽  
The Impact

Abstract. The quantification and understanding of direct aerosol forcing is essential in the study of climate. One of the main issues that makes its quantification difficult is the lack of a complete comprehension of the role of the aerosol and clouds vertical distribution. This work aims at reducing the incertitude of aerosol forcing due to the vertical superposition of several short-lived atmospheric components, in particular different aerosols species and clouds. We propose a method to quantify the contribution of different parts of the atmospheric column to the forcing, and to evaluate model differences by isolating the effect of radiative interactions only. Any microphysical or thermo-dynamical interactions between aerosols and clouds are deactivated in the model, to isolate the effects of radiative flux coupling. We investigate the contribution of aerosol above, below and in clouds, by using added diagnostics in the aerosol-climate model LMDz. We also compute the difference between the forcing of the ensemble of the aerosols and the sum of the forcings from individual species, in clear-sky. This difference is found to be moderate on global average (14%) but can reach high values regionally (up to 100%). The non-additivity of forcing already for clear-sky conditions shows, that in addition to represent well the amount of individual aerosol species, it is critical to capture the vertical distribution of all aerosols. Nonlinear effects are even more important when superposing aerosols and clouds. Four forcing computations are performed, one where the full aerosol 3-D distribution is used, and then three where aerosols are confined to regions above, inside and below clouds respectively. We find that the forcing of aerosols depends crucially on the presence of clouds and on their position relative to that of the aerosol, in particular for black carbon (BC). We observe a strong enhancement of the forcing of BC above clouds, attenuation for BC below clouds, and a moderate enhancement when BC is found within clouds. BC forcing efficiency amounts to 44, 171, 333 and 178 W m-2 per unit optical depth for BC below, within, above clouds and for the 3-D BC distribution, respectively. The different behaviour of forcing nonlinearities for these three components of the atmospheric column suggests that, an important reason for differences between cloudy-sky aerosol forcings from different models may come from different aerosol and clouds vertical distributions. Our method allows to evaluate the contribution to model differences due to aerosol and clouds radiative interactions only, by reading 3-D aerosol and cloud fields from different GCMs, into the same model. This method avoids differences in calculating optical aerosol properties and forcing to enter into the discussion of inter-model differences. It appears that the above and in-cloud amount of BC is larger for SPRINTARS (190 compared to 179), increasing its cloudy-sky forcing efficiency with respect to LMDz, being thus potentially an important factor for inter-model differences.

scholarly journals Fire emission heights in the climate system – Part 2: Impact on transport, Black Carbon concentrations and radiation

2015 ◽  
Vol 15 (5) ◽  
pp. 6695-6744 ◽  
Author(s):  
A. Veira ◽  
S. Kloster ◽  
N. A. J. Schutgens ◽  
J. W. Kaiser
Keyword(s):  
Black Carbon ◽  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
Climate Impact ◽  
Atmospheric Radiation ◽  
Plume Height ◽  
Near Surface ◽  
The Impact ◽  
Emission Height

Abstract. Wildfires represent a major source for aerosols impacting atmospheric radiation, atmospheric chemistry and cloud micro-physical properties. Although former studies indicated that the height of the aerosol–radiation interaction crucially affects the overall climate impact, the importance of fire emission heights in particular remains to be quantified. In this study we use the general circulation model ECHAM6 extended by the aerosol module HAM2 to investigate the impact of wildfire emission heights on atmospheric long-range transport, Black Carbon (BC) concentrations and atmospheric radiation. We simulate the wildfire aerosol release using either various versions of a semi-empirical plume height parametrization or prescribed standard emission heights in ECHAM6-HAM2. Extreme scenarios of near-surface or free-tropospheric only injections provide lower and upper constraints on the emission height climate impact. We find relative changes in mean global atmospheric BC burden of up to 7.9±4.4% caused by average changes in emission heights of 1.5–3.5 km. Regionally, changes in BC burden exceed 30–40% in the major biomass burning regions. The model evaluation of Aerosol Optical Thickness (AOT) against MODIS, AERONET and CALIOP observations indicates that the implementation of a plume height parametrization slightly reduces the ECHAM6-HAM2 biases regionally, but on the global scale these improvements in model performance are small. For prescribed emission release at the surface, wildfire emissions entail a total sky Top Of Atmosphere (TOA) Radiative Forcing (RF) of −0.16±0.06 W m−2. The application of a plume height parametrization which agrees reasonably well with observations introduces a slightly stronger negative TOA RF of −0.20±0.07 W m−2. The standard ECHAM6-HAM2 model in which 25% of the wildfire emissions are injected into the free troposphere and 75% into the planetary boundary layer, leads to a TOA RF of −0.24±0.06 W m−2. Overall, we conclude that simple plume height parametrizations provide sufficient representations of emission heights for global climate modeling. Significant improvements in aerosol wildfire modeling likely depend on better emission inventories and aerosol process modeling rather than on improved emission height parametrizations.

scholarly journals Do supersonic aircraft avoid contrails?

2007 ◽  
Vol 7 (5) ◽  
pp. 12927-12958 ◽  
Author(s):  
A. Stenke ◽  
V. Grewe ◽  
S. Pechtl
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
Climate Impact ◽  
Air Traffic ◽  
Partial Substitution ◽  
Tropical Regions ◽  
Model Simulations ◽  
Supersonic Aircraft ◽  
The Impact

Abstract. The impact of a potential future fleet of supersonic aircraft on contrail coverage and contrail radiative forcing is investigated by means of simulations with the general circulation model ECHAM4.L39(DLR) including a contrail parameterization. The model simulations consider air traffic inventories of a subsonic fleet and of a combined fleet of sub- and supersonic aircraft for the years 2025 and 2050, respectively. In case of the combined fleet, part of the subsonic fleet is replaced by supersonic aircraft. Supersonic aircraft fly at higher cruise levels (18 to 20 km) than subsonic aircraft (10 to 12 km). The different ambient meteorological conditions in terms of temperature and humidity affect the formation of contrails. At subsonic cruise levels, the combined air traffic scenario reveals a reduction in contrail cover in northern extratropics, especially over the North Atlantic and Pacific. At supersonic flight levels, contrail formation is mainly restricted to tropical regions. The northern extratropical stratosphere is only in winter cold enough for the formation of contrails. Total contrail coverage is only marginally affected by the shift in flight altitude. The model simulations indicate a global annual mean contrail cover of 0.372% for the subsonic and 0.366% for the combined fleet in 2050, respectively. The simulated contrail radiative forcing is most closely correlated to the total contrail cover, although contrails in the tropical lower stratosphere are found to be optically thinner than contrails in the extratropical upper troposphere. The global annual mean contrail radiative forcing in 2050 (2025) amounts to 24.7 mW m−2 (9.4 mW m−2) for the subsonic fleet and 24.2 mW m−2 (9.3 mW m−2) for the combined fleet. A reduced supersonic cruise speed (Mach 1.6 instead of Mach 2.0) leads to a downward shift in contrail cover, but does not affect global mean total contrail cover and contrail radiative forcing. Hence the partial substitution of subsonic air traffic leads to a shift of contrail occurrence from mid to low latitudes, but the resulting change in contrail-induced climate impact is almost negligible.

scholarly journals A new method for evaluating the impact of vertical distribution on aerosol radiative forcing in general circulation models

2014 ◽  
Vol 14 (2) ◽  
pp. 877-897 ◽  
Author(s):  
M. R. Vuolo ◽  
M. Schulz ◽  
Y. Balkanski ◽  
T. Takemura
Keyword(s):  
Vertical Distribution ◽  
Radiative Forcing ◽  
General Circulation ◽  
Climate Model ◽  
Nonlinear Effects ◽  
General Circulation Models ◽  
Individual Species ◽  
Aerosol Radiative Forcing ◽  
Atmospheric Column ◽  
The Impact

Abstract. The quantification and understanding of direct aerosol forcing is essential in the study of climate. One of the main issues that makes its quantification difficult is the lack of a complete understanding of the role of the vertical distribution of aerosols and clouds. This work aims at reducing the uncertainty of aerosol top-of-the-atmosphere (TOA) forcing due to the vertical superposition of several short-lived atmospheric components, in particular different aerosol species and clouds. We propose a method to quantify the contribution of different parts of the atmospheric column to the TOA forcing as well as to evaluate the contribution to model differences that is exclusively due to different spatial distributions of aerosols and clouds. We investigate the contribution of aerosol above, below and in clouds by using added diagnostics in the aerosol–climate model LMDz. We also compute the difference between the TOA forcing of the ensemble of the aerosols and the sum of the forcings from individual species in clear sky. This difference is found to be moderate for the global average (14%) but can reach high values regionally (up to 100%). Nonlinear effects are even more important when superposing aerosols and clouds. Four forcing computations are performed: one where the full aerosol 3-D distribution is used, and then three where aerosols are confined to regions above, inside and below clouds, respectively. We find that the TOA forcing of aerosols depends crucially on the presence of clouds and on their position relative to that of the aerosol, in particular for black carbon (BC). We observe a strong enhancement of the TOA forcing of BC above clouds, attenuation for BC below clouds, and a moderate enhancement when BC is found within clouds. BC above clouds accounts for only about 30% of the total BC optical depth but for 55% of the forcing, while forcing efficiency increases by a factor of 7.5 when passing from below to above clouds. The different behaviour of forcing nonlinearities for these three components of the atmospheric column encouraged us to develop the method for application to inter-model variability studies by reading 3-D aerosol and cloud fields from different general circulation models (GCMs) into the same model. We apply the method to the comparison of forcing due to the aerosols and clouds distributions of the general circulation models LMDz and SPRINTARS. The different amount of BC above but also within clouds is revealed to play a major role on the differences of cloudy-sky forcings between the two models, which can exceed 100% regionally.

scholarly journals Do supersonic aircraft avoid contrails?

2008 ◽  
Vol 8 (4) ◽  
pp. 955-967 ◽  
Author(s):  
A. Stenke ◽  
V. Grewe ◽  
S. Pechtl
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
Climate Impact ◽  
Air Traffic ◽  
Partial Substitution ◽  
Tropical Regions ◽  
Model Simulations ◽  
Supersonic Aircraft ◽  
The Impact

Abstract. The impact of a potential future fleet of supersonic aircraft on contrail coverage and contrail radiative forcing is investigated by means of simulations with the general circulation model ECHAM4.L39(DLR) including a contrail parameterization. The model simulations consider air traffic inventories of a subsonic fleet and of a combined fleet of sub- and supersonic aircraft for the years 2025 and 2050, respectively. In case of the combined fleet, part of the subsonic fleet is replaced by supersonic aircraft. The combined air traffic scenario reveals a reduction in contrail cover at subsonic cruise levels (10 to 12 km) in the northern extratropics, especially over the North Atlantic and North Pacific. At supersonic flight levels (18 to 20 km), contrail formation is mainly restricted to tropical regions. Only in winter is the northern extratropical stratosphere above the 100 hPa level cold enough for the formation of contrails. Total contrail coverage is only marginally affected by the shift in flight altitude. The model simulations indicate a global annual mean contrail cover of 0.372% for the subsonic and 0.366% for the combined fleet in 2050. The simulated contrail radiative forcing is most closely correlated to the total contrail cover, although contrails in the tropical lower stratosphere are found to be optically thinner than contrails in the extratropical upper troposphere. The global annual mean contrail radiative forcing in 2050 (2025) amounts to 24.7 mW m−2 (9.4 mW m−2) for the subsonic fleet and 24.2 mW m−2 (9.3 mW m−2) for the combined fleet. A reduction of the supersonic cruise speed from Mach 2.0 to Mach 1.6 leads to a downward shift in contrail cover, but does not affect global mean total contrail cover and contrail radiative forcing. Hence the partial substitution of subsonic air traffic leads to a shift of contrail occurrence from mid to low latitudes, but the resulting change in contrail-induced climate impact is almost negligible.

scholarly journals Climate hypersensitivity to solar forcing?

2000 ◽  
Vol 18 (5) ◽  
pp. 583-588 ◽  
Author(s):  
W. Soon ◽  
E. Posmentier ◽  
S. Baliunas
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Solar Physics ◽  
Stratospheric Ozone ◽  
General Circulation Models ◽  
Static Stability ◽  
Radiative Properties ◽  
Balance Model ◽  
Solar Forcing ◽  
Solar Uv

Abstract. We compare the equilibrium climate responses of a quasi-dynamical energy balance model to radiative forcing by equivalent changes in CO2, solar total irradiance (Stot) and solar UV (SUV). The response is largest in the SUV case, in which the imposed UV radiative forcing is preferentially absorbed in the layer above 250 mb, in contrast to the weak response from global-columnar radiative loading by increases in CO2 or Stot. The hypersensitive response of the climate system to solar UV forcing is caused by strongly coupled feedback involving vertical static stability, tropical thick cirrus ice clouds and stratospheric ozone. This mechanism offers a plausible explanation of the apparent hypersensitivity of climate to solar forcing, as suggested by analyses of recent climatic records. The model hypersensitivity strongly depends on climate parameters, especially cloud radiative properties, but is effective for arguably realistic values of these parameters. The proposed solar forcing mechanism should be further confirmed using other models (e.g., general circulation models) that may better capture radiative and dynamical couplings of the troposphere and stratosphere.Key words: Meteorology and atmospheric dynamics (climatology · general or miscellaneous) · Solar physics · astrophysics · and astronomy (ultraviolet emissions)

scholarly journals The faint young Sun problem revisited with a 3-D climate–carbon model – Part 1

2014 ◽  
Vol 10 (2) ◽  
pp. 697-713 ◽  
Author(s):  
G. Le Hir ◽  
Y. Teitler ◽  
F. Fluteau ◽  
Y. Donnadieu ◽  
P. Philippot
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Freezing Point ◽  
Climatic Factors ◽  
General Circulation Models ◽  
Companion Paper ◽  
One Dimensional ◽  
Carbon Dioxide Concentrations ◽  
Wide Range ◽  
High Concentrations

Abstract. During the Archaean, the Sun's luminosity was 18 to 25% lower than the present day. One-dimensional radiative convective models (RCM) generally infer that high concentrations of greenhouse gases (CO2, CH4) are required to prevent the early Earth's surface temperature from dropping below the freezing point of liquid water and satisfying the faint young Sun paradox (FYSP, an Earth temperature at least as warm as today). Using a one-dimensional (1-D) model, it was proposed in 2010 that the association of a reduced albedo and less reflective clouds may have been responsible for the maintenance of a warm climate during the Archaean without requiring high concentrations of atmospheric CO2 (pCO2). More recently, 3-D climate simulations have been performed using atmospheric general circulation models (AGCM) and Earth system models of intermediate complexity (EMIC). These studies were able to solve the FYSP through a large range of carbon dioxide concentrations, from 0.6 bar with an EMIC to several millibars with AGCMs. To better understand this wide range in pCO2, we investigated the early Earth climate using an atmospheric GCM coupled to a slab ocean. Our simulations include the ice-albedo feedback and specific Archaean climatic factors such as a faster Earth rotation rate, high atmospheric concentrations of CO2 and/or CH4, a reduced continental surface, a saltier ocean, and different cloudiness. We estimated full glaciation thresholds for the early Archaean and quantified positive radiative forcing required to solve the FYSP. We also demonstrated why RCM and EMIC tend to overestimate greenhouse gas concentrations required to avoid full glaciations or solve the FYSP. Carbon cycle–climate interplays and conditions for sustaining pCO2 will be discussed in a companion paper.

scholarly journals Large methane releases lead to strong aerosol forcing and reduced cloudiness

2011 ◽  
Vol 11 (3) ◽  
pp. 9057-9081
Author(s):  
T. Kurtén ◽  
L. Zhou ◽  
R. Makkonen ◽  
J. Merikanto ◽  
P. Räisänen ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Cloud Droplet ◽  
Fold Increase ◽  
General Circulation Models ◽  
Large Temperature ◽  
Atmospheric Lifetime ◽  
Temperature Changes ◽  
Aerosol Forcing ◽  
Rapid Amplification

Abstract. The release of vast quantities of methane into the atmosphere as a result of clathrate destabilization is a potential mechanism for rapid amplification of global warming. Previous studies have calculated the enhanced warming based mainly on the radiative effect of the methane itself, with smaller contributions from the associated carbon dioxide or ozone increases. Here, we study the effect of strongly elevated methane (CH4) levels on oxidant and aerosol particle concentrations using a combination of chemistry-transport and general circulation models. A 10-fold increase in methane concentrations is predicted to significantly decrease hydroxyl radical (OH) concentrations, while moderately increasing ozone (O3). These changes lead to a 70% increase in the atmospheric lifetime of methane, and an 18% decrease in global mean cloud droplet number concentrations (CDNC). The CDNC change causes a radiative forcing that is comparable in magnitude to the longwave radiative forcing ("enhanced greenhouse effect") of the added methane. Together, the indirect CH4-O3 and CH4-OH-aerosol forcings could more than double the warming effect of large methane increases. Our findings may help explain the anomalously large temperature changes associated with historic methane releases.

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