scholarly journals Impacts of multi-layer overlap on contrail radiative forcing

2021 ◽  
Vol 21 (3) ◽  
pp. 1649-1681
Author(s):  
Inés Sanz-Morère ◽  
Sebastian D. Eastham ◽  
Florian Allroggen ◽  
Raymond L. Speth ◽  
Steven R. H. Barrett
Keyword(s):  
North Atlantic ◽  
Airline Industry ◽  
Radiative Forcing ◽  
Geographic Location ◽  
Longwave Radiation ◽  
Climate Impacts ◽  
Climate Forcing ◽  
The North ◽  
The North Atlantic ◽  
Total Impact

Abstract. Condensation trails (“contrails”) which form behind aircraft are estimated to cause on the order of 50 % of the total climate forcing of aviation, matching the total impact of all accumulated aviation-attributable CO2. The climate impacts of these contrails are highly uncertain, in part due to the effect of overlap between contrails and other cloud layers. Although literature estimates suggest that overlap could change even the sign of contrail radiative forcing (RF), the impacts of cloud–contrail overlaps are not well understood, and the effect of contrail–contrail overlap has never been quantified. In this study we develop and apply a new model of contrail radiative forcing which explicitly accounts for overlap between cloud layers. Assuming maximum possible overlap to provide an upper bound on impacts, cloud–contrail overlap is found to reduce the shortwave-cooling effect attributable to aviation by 66 % while reducing the longwave-warming effect by only 37 %. Therefore, on average in 2015, cloud–contrail overlap increased the net radiative forcing from contrails. We also quantify the sensitivity of contrail radiative forcing to cloud cover with respect to geographic location. Clouds significantly increase warming at high latitudes and over sea, transforming cooling contrails into warming ones in the North Atlantic corridor. Based on the same data, our results indicate that disregarding overlap between a given pair of contrail layers can result in longwave and shortwave radiative forcing being overestimated by up to 16 % and 25 %, respectively, with the highest bias observed at high optical depths (> 0.4) and high solar zenith angles (> 75∘). When applied to estimated global contrail coverage data for 2015, contrail–contrail overlap reduces both the longwave and shortwave forcing by ∼ 2 % relative to calculations which ignore overlap. The effect is greater for longwave radiation, resulting in a 3 % net reduction in the estimated RF when overlap is correctly accounted for. This suggests that contrail–contrail overlap radiative effects can likely be neglected in estimates of the current-day environmental impacts of aviation. However, the effect of contrail–contrail overlap may increase in the future as the airline industry grows into new regions.

scholarly journals Effect of contrail overlap on radiative impact attributable to aviation contrails

2020 ◽  
Author(s):  
Inés Sanz-Morère ◽  
Sebastian D. Eastham ◽  
Florian Allroggen ◽  
Raymond L. Speth ◽  
Steven R. H. Barrett
Keyword(s):  
North Atlantic ◽  
Airline Industry ◽  
Radiative Forcing ◽  
Geographic Location ◽  
Longwave Radiation ◽  
Climate Impact ◽  
Climate Impacts ◽  
The North ◽  
Radiative Impact ◽  
Total Impact

Abstract. Condensation trails (“contrails”) which form behind aircraft are estimated to cause on the order of 50 % of the total climate impact of aviation, matching the total impact of all accumulated aviation-attributable CO2. The climate impacts of these contrails are highly uncertain, in part due to the poorly-understood effect of overlap between contrails and other cloud layers. With the airline industry projected to grow by approximately 4.5 % each year over the next 20 years, instances of contrail overlap are expected to increase, including any potential mitigating or amplifying effects on contrail-attributable radiative forcing. However, the impacts of cloud-contrail overlaps are not well understood, and the effect of contrail-contrail overlap has never been quantified. In this study we develop and apply a new model of contrail radiative forcing which explicitly accounts for overlap between cloud layers. Cloud-contrail overlap is found to be responsible for 93 % of net radiative forcing attributable to 2015 contrails. We also find significant variation in the sensitivity of contrail radiative forcing to cloud cover with respect to geographic location. Clouds significantly increase warming at high latitudes and over sea, transforming cooling contrails into warming ones in the North-Atlantic corridor. Based on the same data, our results indicate that disregarding overlap between a given pair of contrail layers can result in longwave and shortwave radiative forcing being overestimated by up to 16 % and 25 % respectively, with the highest bias observed at high optical depths (> 0.4) and high solar zenith angles (> 75°). When applied to estimated global contrail coverage data for 2015, contrail-contrail overlap reduces both the longwave and shortwave forcing by ~ 2 % relative to calculations which ignore overlap. The effect is greater for longwave radiation, resulting in a 3 % net reduction in the estimated RF when overlap is correctly accounted for. This suggests that contrail-contrail overlap effects can likely be neglected in estimates of the current-day environmental impacts of aviation. However, the effect of contrail-contrail overlap is likely to increase in the future as the airline industry extends into new regions, intensifies in existing regions, and invests in higher-efficiency engines which are thought to promote contrail formation.

scholarly journals Climate impacts on multidecadal <i>p</i>CO<sub>2</sub> variability in the North Atlantic: 1948–2009

2015 ◽  
Vol 12 (17) ◽  
pp. 15223-15244
Author(s):  
M. L. Breeden ◽  
G. A. McKinley
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Dissolved Inorganic Carbon ◽  
Atlantic Multidecadal Oscillation ◽  
Climate Impacts ◽  
Co2 Uptake ◽  
Subpolar Gyre ◽  
The North ◽  
The North Atlantic

Abstract. The North Atlantic is the most intense region of ocean CO2 uptake. Here, we investigate multidecadal timescale variability of the partial pressure CO2 (pCO2) that is due to the natural carbon cycle using a regional model forced with realistic climate and pre-industrial atmospheric pCO2 for 1948–2009. Large-scale patterns of natural pCO2 variability are primarily associated with basin-averaged sea surface temperature (SST) that, in turn, is composed of two parts: the Atlantic Multidecadal Oscillation (AMO) and a long-term positive SST trend. The North Atlantic Oscillation (NAO) drives a secondary mode of variability. For the primary mode, positive AMO and the SST trend modify pCO2 with different mechanisms and spatial patterns. Warming with the positive AMO increases subpolar gyre pCO2, but there is also a significant reduction of dissolved inorganic carbon (DIC) due primarily to reduced vertical mixing. The net impact of positive AMO is to reduce pCO2 in the subpolar gyre. Through direct impacts on SST, the net impacts of positive AMO is to increase pCO2 in the subtropical gyre. From 1980 to present, long-term SST warming has amplified AMO impacts on pCO2.

Evolving Relative Importance of the Southern Ocean and North Atlantic in Anthropogenic Ocean Heat Uptake

2018 ◽  
Vol 31 (18) ◽  
pp. 7459-7479 ◽  
Author(s):  
Jia-Rui Shi ◽  
Shang-Ping Xie ◽  
Lynne D. Talley
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Radiative Forcing ◽  
Meridional Overturning Circulation ◽  
Anthropogenic Heat ◽  
Anthropogenic Aerosols ◽  
Ocean Heat Uptake ◽  
The North ◽  
Heat Uptake ◽  
The North Atlantic

Ocean uptake of anthropogenic heat over the past 15 years has mostly occurred in the Southern Ocean, based on Argo float observations. This agrees with historical simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5), where the Southern Ocean (south of 30°S) accounts for 72% ± 28% of global heat uptake, while the contribution from the North Atlantic north of 30°N is only 6%. Aerosols preferentially cool the Northern Hemisphere, and the effect on surface heat flux over the subpolar North Atlantic opposes the greenhouse gas (GHG) effect in nearly equal magnitude. This heat uptake compensation is associated with weakening (strengthening) of the Atlantic meridional overturning circulation (AMOC) in response to GHG (aerosol) radiative forcing. Aerosols are projected to decline in the near future, reinforcing the greenhouse effect on the North Atlantic heat uptake. As a result, the Southern Ocean, which will continue to take up anthropogenic heat largely through the mean upwelling of water from depth, will be joined by increased relative contribution from the North Atlantic because of substantial AMOC slowdown in the twenty-first century. In the RCP8.5 scenario, the percentage contribution to global uptake is projected to decrease to 48% ± 8% in the Southern Ocean and increase to 26% ± 6% in the northern North Atlantic. Despite the large uncertainty in the magnitude of projected aerosol forcing, our results suggest that anthropogenic aerosols, given their geographic distributions and temporal trajectories, strongly influence the high-latitude ocean heat uptake and interhemispheric asymmetry through AMOC change.

Why Is There an Early Spring Cooling Shift Downstream of the Tibetan Plateau?

2005 ◽  
Vol 18 (22) ◽  
pp. 4660-4668 ◽  
Author(s):  
Jian Li ◽  
Rucong Yu ◽  
Tianjun Zhou ◽  
Bin Wang
Keyword(s):  
Tibetan Plateau ◽  
North Africa ◽  
North Atlantic ◽  
Radiative Forcing ◽  
Temperature Shift ◽  
Early Spring ◽  
Climate Feedback ◽  
The Tibetan Plateau ◽  
The North ◽  
The North Atlantic

Abstract The temperature shift over the eastern flank of the Tibetan Plateau is examined using the last 50 yr of Chinese surface station observations. It was found that a strong cooling shift occurs in early spring (March and April) and late summer (July, August, and September) in contrast to the warming shift in other seasons. The cause of the March–April (MA) cooling is investigated in this study. The MA cooling shift on the lee side of the Tibetan Plateau is found to be not a local phenomenon, but rather it is associated with an eastward extension of a cooling signal originating from North Africa that is related to the North Atlantic Oscillation (NAO) in the previous winter. The midtropospheric westerlies over the North Atlantic and North Africa tend to intensify during positive NAO phases. The enhanced westerlies, after passing over the Tibetan Plateau, result in strengthened ascending motion against the lee side of the plateau, which favors the formation of midlevel stratiform clouds. The increased amount of stratus clouds induces a negative net cloud–radiative forcing, which thereby cools the surface air and triggers a positive cloud–temperature feedback. In this way, the cooling signal from the upstream could “jump” over the Tibetan Plateau and leave a footprint on its lee side. The continental stratiform cloud–climate feedback plays a significant role in the amplification of the cooling shift downstream of the Tibetan Plateau.

Infrared radiative forcing of a Saharan dust plume in the North Atlantic

1998 ◽  
Vol 29 ◽  
pp. S1301-S1302 ◽  
Author(s):  
P. Chazette ◽  
J. Pelon ◽  
I. Carrasco ◽  
V. Trouillet ◽  
F. Dulac
Keyword(s):  
North Atlantic ◽  
Radiative Forcing ◽  
Saharan Dust ◽  
The North ◽  
The North Atlantic

Transient climate response to Arctic sea-ice loss with two ice-constraining methods

2021 ◽  
pp. 1-50
Author(s):  
Amélie Simon ◽  
Guillaume Gastineau ◽  
Claude Frankignoul ◽  
Clément Rousset ◽  
Francis Codron
Keyword(s):  
Thermal Conductivity ◽  
Sea Ice ◽  
North Atlantic ◽  
Arctic Sea Ice ◽  
Climate Impacts ◽  
The Arctic ◽  
The North ◽  
Arctic Sea ◽  
The North Atlantic ◽  
Arctic Sea Ice Loss

AbstractThe impact of Arctic sea-ice loss on the ocean and atmosphere is investigated focusing on a gradual reduction of Arctic sea-ice by 20% on annual mean, occurring within 30 years, starting from present-day conditions. Two ice-constraining methods are explored to melt Arctic sea-ice in a coupled climate model, while keeping present-day conditions for external forcing. The first method uses a reduction of sea-ice albedo, which modifies the incoming surface shortwave radiation. The second method uses a reduction of thermal conductivity, which changes the heat conduction flux inside ice. Reduced thermal conductivity inhibits oceanic cooling in winter and sea-ice basal growth, reducing seasonality of sea-ice thickness. For similar Arctic sea-ice area loss, decreasing the albedo induces larger Arctic warming than reducing the conductivity, especially in spring. Both ice-constraining methods produce similar climate impacts, but with smaller anomalies when reducing the conductivity. In the Arctic, the sea-ice loss leads to an increase of the North Atlantic water inflow in the Barents Sea and Eastern Arctic, while the salinity decreases and the gyre intensifies in the Beaufort Sea. In the North Atlantic, the subtropical gyre shifts southward and the Atlantic meridional overturning circulation weakens. A dipole of sea-level pressure anomalies sets up in winter over Northern Siberia and the North Atlantic, which resembles the negative phase of the North Atlantic Oscillation. In the tropics, the Atlantic Intertropical Convergence Zone shifts southward as the South Atlantic Ocean warms. In addition, Walker circulation reorganizes and the Southeastern Pacific Ocean cools.

scholarly journals Atlantic Multidecadal Variability and the U.K. ACSIS Program

2018 ◽  
Vol 99 (2) ◽  
pp. 415-425 ◽  
Author(s):  
R. T. Sutton ◽  
G. D. McCarthy ◽  
J. Robson ◽  
B. Sinha ◽  
A. T. Archibald ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Heat Content ◽  
Climate Impacts ◽  
Environmental Research ◽  
Atlantic Multidecadal Variability ◽  
Multidecadal Variability ◽  
The North ◽  
Holistic Understanding ◽  
The North Atlantic

Abstract Atlantic multidecadal variability (AMV) is the term used to describe the pattern of variability in North Atlantic sea surface temperatures (SSTs) that is characterized by decades of basinwide warm or cool anomalies, relative to the global mean. AMV has been associated with numerous climate impacts in many regions of the world including decadal variations in temperature and rainfall patterns, hurricane activity, and sea level changes. Given its importance, understanding the physical processes that drive AMV and the extent to which its evolution is predictable is a key challenge in climate science. A leading hypothesis is that natural variations in ocean circulation control changes in ocean heat content and consequently AMV phases. However, this view has been challenged recently by claims that changing natural and anthropogenic radiative forcings are critical drivers of AMV. Others have argued that changes in ocean circulation are not required. Here, we review the leading hypotheses and mechanisms for AMV and discuss the key debates. In particular, we highlight the need for a holistic understanding of AMV. This perspective is a key motivation for a major new U.K. research program: the North Atlantic Climate System Integrated Study (ACSIS), which brings together seven of the United Kingdom’s leading environmental research institutes to enable a broad spectrum approach to the challenges of AMV. ACSIS will deliver the first fully integrated assessment of recent decadal changes in the North Atlantic, will investigate the attribution of these changes to their proximal and ultimate causes, and will assess the potential to predict future changes.

Atmospheric composition changes in CMIP6 experiments over the North Atlantic region

2020 ◽  
Author(s):  
Paul Griffiths ◽  
James Keeble ◽  
Fiona O'Connor ◽  
Alexander Archibald ◽  
John Pyle ◽  
...  
Keyword(s):  
North Atlantic ◽  
Radiative Forcing ◽  
Climate Model ◽  
Climate System ◽  
Atmospheric Composition ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
The North ◽  
North Atlantic Climate ◽  
The North Atlantic

&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;p&gt;A grand challenge in the field of chemistry-climate modelling is understanding the connection between anthropogenic emissions, atmospheric composition and the radiative forcing of trace gases and aerosols.&lt;/p&gt; &lt;p&gt;The 6th phase of the Coupled Model Intercomparison Project (CMIP6) includes a number of climate model experiments that can be used for this purpose.&amp;#160; AerChemMIP [Collins et al.2017] focuses on calculating the radiative forcing of gases and aerosol particles over the period 1850 to 2100, and comprises several tiers of experiments designed to attribute the effect of changes in emissions.&amp;#160;&lt;/p&gt; &lt;p&gt;The UK Earth System Model, UKESM-1, is a novel climate model developed for CMIP6&amp;#160; [Sellar et al., 2019] and is a community research tool for studying past and future climate.&amp;#160; It includes a detailed treatment of tropospheric chemistry, interactive BVOC emissions and extensive stratospheric chemistry.&lt;/p&gt; &lt;p&gt;The North Atlantic Climate System is an area of current interest [Robson et al., 2020] and is the focus of the UKRI 'ACSIS' project.&amp;#160; ACSIS brings together scientists from a range of different specialisms to understand complex changes in the North Atlantic climate system.&amp;#160;&amp;#160;&amp;#160; By understanding how these changes relate to external drivers of climate, such as human activity, or natural variability, ACSIS aims to improve our capability to detect, explain and predict changes in the North Atlantic climate system.&lt;/p&gt; &lt;p&gt;We present an analysis of the evolution of atmospheric composition over the period 1950-2015. The work is based on a recent global multi-model evaluation of tropospheric ozone for CMIP6 [Griffiths et al., 2020] , but focuses on changes over the North Atlantic region in UKESM-1.&amp;#160; We draw on CMIP and AerChemMIP simulations to provide an initial survey of the response of this region to changing emissions , focusing on atmospheric composition and attempting attribution from a series of targeted experiments involving perturbed emissions .&lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt;

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