scholarly journals Equilibrium state and sensitivity of the simulated middle-to-late Eocene climate

2018 ◽  
Author(s):  
Michiel Baatsen ◽  
Anna S. von der Heydt ◽  
Matthew Huber ◽  
Michael A. Kliphuis ◽  
Peter K. Bijl ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Radiative Forcing ◽  
General Circulation ◽  
Middle Eocene ◽  
Late Eocene ◽  
Global Changes ◽  
The North ◽  
South Pacific Ocean ◽  
Polar Ice Sheets ◽  
Modelling Studies

Abstract. While the early Eocene has been considered in many modelling studies, detailed simulations of the middle and late Eocene climate are currently scarce. To understand Antarctic glaciation at the Eocene-Oligocene Transition (~ 34 Ma) as well as middle Eocene warmth, it is vital to have an adequate reconstruction of the middle-to-late Eocene climate. Here, we present a set of high resolution coupled climate simulations using the Community Earth System Model (CESM) version 1. Two middle-to-late Eocene cases are considered with new detailed 38 Ma geographical boundary conditions with a different radiative forcing. With 4 × pre-industrial concentrations of CO2 (i.e. 1120 ppm) and CH4 (~ 2700 ppb), the equilibrium sea surface temperatures correspond well to available late middle Eocene (42–38 Ma) proxies. Being generally cooler, the simulated climate with 2 × pre-industrial values is a good analog for that of the late Eocene (38–34 Ma). Deep water formation occurs in the South Pacific Ocean, while the North Atlantic is strongly stratified and virtually stagnant. A shallow and weak circumpolar current is present in the Southern Ocean with only minor effects on southward oceanic heat transport within wind-driven gyres. Terrestrial temperature proxies, although limited in coverage, also indicate that the results presented here are realistic. The reconstructed 38 Ma climate has a reduced equator-to-pole temperature gradient and a more symmetric meridional heat distribution compared to the pre-industrial reference. Climate sensitivity is similar (~ 0.7 °C/Wm2) to that of the present-day climate (~ 0.8 °C/Wm2; 3 °C per CO2 doubling), with significant polar amplification despite very limited sea ice and snow cover. High latitudes are mainly kept warm by albedo and cloud feedbacks in combination with global changes in geography and the absence of polar ice sheets. The integrated effect of geography, vegetation and ice accounts for a 6–7 °C offset between pre-industrial and 38 Ma Eocene boundary conditions. These 38 Ma simulations effectively show that a realistic middle-to-late Eocene climate can be reconstructed without the need for greenhouse gas concentrations much higher than proxy estimates. The general circulation and radiative budget allow for mild high-latitude regions and little to no snow and ice cover, without making equatorial regions extremely warm.

scholarly journals The middle-to-late Eocene greenhouse climate, modelled using the CESM 1.0.5

2020 ◽  
Author(s):  
Michiel Baatsen ◽  
Anna S. von der Heydt ◽  
Matthew Huber ◽  
Michael A. Kliphuis ◽  
Peter K. Bijl ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Greenhouse Gas ◽  
Radiative Forcing ◽  
Middle Eocene ◽  
Late Eocene ◽  
Collective Effects ◽  
Global Changes ◽  
Radiative Balance ◽  
Polar Ice Sheets ◽  
Modelling Studies

Abstract. While the early Eocene has been considered in many modelling studies, detailed simulations of the middle and late Eocene climate are currently scarce. To get a better understanding of both Antarctic glaciation at the Eocene-Oligocene transition (~34 Ma) and late middle Eocene warmth, it is vital to have an adequate reconstruction of the middle-to-late Eocene climate. Results of higher (CMIP5-like) resolution coupled climate simulations are represented here using the Community Earth System Model (CESM) version 1. Two middle-to-late Eocene cases are considered with the same general boundary conditions but a different radiative forcing, using a new detailed 38 Ma geography reconstruction. Under 4× pre-industrial concentrations (PIC) of both CO2 (i.e. 1120 ppm) and CH4 (~2700 ppb), equilibrium sea surface temperatures correspond well to the available late middle Eocene (42–38 Ma; ~Bartonian) proxies. Being generally cooler, the simulated climate under 2× PIC forcing is a good analog for that of the late Eocene (38–34 Ma; ~Priabonian). Terrestrial temperature proxies, although their geographical coverage is sparse, also indicate that the results presented here are realistic. The reconstructed 38 Ma climate has a reduced equator-to-pole temperature gradient and a more symmetric meridional heat distribution compared to the pre-industrial reference. The collective effects of geography, vegetation and ice accounts for a global mean 5–7 °C difference between pre-industrial and 38 Ma Eocene boundary conditions, with important contributions from cloud and water vapour feedbacks. These simulations effectively show that a realistic middle-to-late Eocene climate can be reconstructed without the need for greenhouse gas concentrations much higher than proxy estimates (i.e. ~500–1200 ppm CO2). Equilibrium climate sensitivity is reduced (0.62 °C/W m2; 3.2 °C warming between 38 Ma 2× PIC and 4× PIC) compared to that of the present-day climate (0.79 °C/W m2; 3.1 °C per CO2 doubling). Despite very limited sea ice and snow cover in both 38Ma cases, the model still shows a factor ~2 polar amplification in response to a further increase of atmospheric greenhouse gas concentrations. High latitudes in the modelled Eocene climate are mainly kept warm by an altered radiative balance in combination with global changes in geography and the absence of polar ice sheets compared to the pre-industrial reference.

scholarly journals The middle to late Eocene greenhouse climate modelled using the CESM 1.0.5

2020 ◽  
Vol 16 (6) ◽  
pp. 2573-2597
Author(s):  
Michiel Baatsen ◽  
Anna S. von der Heydt ◽  
Matthew Huber ◽  
Michael A. Kliphuis ◽  
Peter K. Bijl ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Radiative Forcing ◽  
Middle Eocene ◽  
Late Eocene ◽  
Collective Effects ◽  
Polar Regions ◽  
Radiative Balance ◽  
Industrial Carbon ◽  
Greenhouse Climate ◽  
Modelling Studies

Abstract. The early and late Eocene have both been the subject of many modelling studies, but few have focused on the middle Eocene. The latter still holds many challenges for climate modellers but is also key to understanding the events leading towards the conditions needed for Antarctic glaciation at the Eocene–Oligocene transition. Here, we present the results of CMIP5-like coupled climate simulations using the Community Earth System Model (CESM) version 1. Using a new detailed 38 Ma geography reconstruction and higher model resolution compared to most previous modelling studies and sufficiently long equilibration times, these simulations will help to further understand the middle to late Eocene climate. At realistic levels of atmospheric greenhouse gases, the model is able to show overall good agreement with proxy records and capture the important aspects of a warm greenhouse climate during the Eocene. With a quadrupling of pre-industrial concentrations of both CO2 and CH4 (i.e. 1120 ppm and ∼2700 ppb, respectively, or 4 × PIC; pre-industrial carbon), sea surface temperatures correspond well to the available late middle Eocene (42–38 Ma; ∼ Bartonian) proxies. Being generally cooler, the simulated climate under 2 × PIC forcing is a good analogue for that of the late Eocene (38–34 Ma; ∼ Priabonian). Terrestrial temperature proxies, although their geographical coverage is sparse, also indicate that the results presented here are in agreement with the available information. Our simulated middle to late Eocene climate has a reduced Equator-to-pole temperature gradient and a more symmetric meridional heat distribution compared to the pre-industrial reference. The collective effects of geography, vegetation, and ice account for a global average 5–7 ∘C difference between pre-industrial and 38 Ma Eocene boundary conditions, with important contributions from cloud and water vapour feedbacks. This helps to explain Eocene warmth in general, without the need for greenhouse gas levels much higher than indicated by proxy estimates (i.e. ∼500–1200 ppm CO2) or low-latitude regions becoming unreasonably warm. High-latitude warmth supports the idea of mostly ice-free polar regions, even at 2 × PIC, with Antarctica experiencing particularly warm summers. An overall wet climate is seen in the simulated Eocene climate, which has a strongly monsoonal character. Equilibrium climate sensitivity is reduced (0.62 ∘C W−1 m2; 3.21 ∘C warming between 38 Ma 2 × PIC and 4 × PIC) compared to that of the present-day climate (0.80 ∘C W−1 m2; 3.17 ∘C per CO2 doubling). While the actual warming is similar, we see mainly a higher radiative forcing from the second PIC doubling. A more detailed analysis of energy fluxes shows that the regional radiative balance is mainly responsible for sustaining a low meridional temperature gradient in the Eocene climate, as well as the polar amplification seen towards even warmer conditions. These model results may be useful to reconsider the drivers of Eocene warmth and the Eocene–Oligocene transition (EOT) but can also be a base for more detailed comparisons to future proxy estimates.

Pre-Priabonian Palaeogene formations in southwestern Bulgaria and northern Greece: stratigraphy and tectonic implications

1998 ◽  
Vol 135 (1) ◽  
pp. 101-119 ◽  
Author(s):  
IVAN S. ZAGORCHEV
Keyword(s):  
Late Cretaceous ◽  
Middle Eocene ◽  
Regional Metamorphism ◽  
Late Eocene ◽  
Thin Layers ◽  
The South ◽  
Northern Greece ◽  
The North ◽  
Early Oligocene ◽  
Metamorphic Core

The Paril Formation (South Pirin and Slavyanka Mountains, southwestern Bulgaria) and the Prodromos Formation (Orvilos and Menikion Mountains, northern Greece) consist of breccia and olistostrome built up predominantly of marble fragments from the Precambrian Dobrostan Marble Formation (Bulgaria) and its equivalent Bos-Dag Marble Formation (Greece). The breccia and olistostrome are interbedded with thin layers of calcarenites (with occasional marble pebbles), siltstones, sandstones and limestones. The Paril and Prodromos formations unconformably cover the Precambrian marbles, and are themselves covered unconformably by Miocene and Pliocene sediments (Nevrokop Formation). The rocks of the Paril Formation are intruded by the Palaeogene (Late Eocene–Early Oligocene) Teshovo granitoid pluton, and are deformed and preserved in the two limbs of a Palaeogene anticline cored by the Teshovo pluton (Teshovo anticline). The Palaeocene–Middle Eocene age of the formations is based on these contact relations, and on occasional finds of Tertiary pollen, as well as on correlations with similar formations of the Laki (Kroumovgrad) Group throughout the Rhodope region.The presence of Palaeogene sediments within the pre-Palaeogene Pirin–Pangaion structural zone invalidates the concept of a ‘Rhodope metamorphic core complex’ that supposedly has undergone Palaeogene amphibolite-facies regional metamorphism, and afterwards has been exhumed by rapid crustal extension in Late Oligocene–Miocene times along a regional detachment surface. Other Palaeogene formations of pre-Priabonian (Middle Eocene and/or Bartonian) or earliest Priabonian age occur at the base of the Palaeogene sections in the Mesta graben complex (Dobrinishka Formation) and the Padesh basin (Souhostrel and Komatinitsa formations). The deposition of coarse continental sediments grading into marine formations (Laki or Kroumovgrad Group) in the Rhodope region at the beginning of the Palaeogene Period marks the first intense fragmentation of the mid- to late Cretaceous orogen, in particular, of the thickened body of the Morava-Rhodope structural zone situated to the south of the Srednogorie zone. The Srednogorie zone itself was folded and uplifted in Late Cretaceous time, thus dividing Palaeocene–Middle Eocene flysch of the Louda Kamchiya trough to the north, from the newly formed East Rhodope–West Thrace depression to the south.

scholarly journals Towards Direct Simulation of Future Tropical Cyclone Statistics in a High-Resolution Global Atmospheric Model

2010 ◽  
Vol 2010 ◽  
pp. 1-13 ◽  
Author(s):  
Michael F. Wehner ◽  
G. Bala ◽  
Phillip Duffy ◽  
Arthur A. Mirin ◽  
Raquel Romano
Keyword(s):  
High Resolution ◽  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
Atmospheric Model ◽  
Tropical Storm ◽  
Model Studies ◽  
The North ◽  
Resolution Model ◽  
High Resolution Model

We present a set of high-resolution global atmospheric general circulation model (AGCM) simulations focusing on the model's ability to represent tropical storms and their statistics. We find that the model produces storms of hurricane strength with realistic dynamical features. We also find that tropical storm statistics are reasonable, both globally and in the north Atlantic, when compared to recent observations. The sensitivity of simulated tropical storm statistics to increases in sea surface temperature (SST) is also investigated, revealing that a credible late 21st century SST increase produced increases in simulated tropical storm numbers and intensities in all ocean basins. While this paper supports previous high-resolution model and theoretical findings that the frequency of very intense storms will increase in a warmer climate, it differs notably from previous medium and high-resolution model studies that show a global reduction in total tropical storm frequency. However, we are quick to point out that this particular model finding remains speculative due to a lack of radiative forcing changes in our time-slice experiments as well as a focus on the Northern hemisphere tropical storm seasons.

Interpretation of structures in the southeastern Nechako Basin, British Columbia, from seismic reflection, well log, and potential field data1This article is one of a series of papers published in this Special Issue on the theme of New insights in Cordilleran Intermontane geoscience: reducing exploration risk in the mountain pine beetle-affected area, British Columbia.2Geological Survey of Canada Contribution 20100002.

2011 ◽  
Vol 48 (6) ◽  
pp. 1000-1020 ◽  
Author(s):  
Nathan Hayward ◽  
Andrew J. Calvert
Keyword(s):  
British Columbia ◽  
Potential Field ◽  
Seismic Reflection ◽  
Middle Eocene ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Late Eocene ◽  
Strike Slip ◽  
Potential Field Data ◽  
The North

The structure and stratigraphy of the southeast Nechako Basin, which are poorly understood primarily because of substantial volcanic cover, are investigated in an analysis of seismic reflection, well, and potential field data. Formation and development of the SE Nechako Basin resulted in sub-basins containing Cretaceous and Eocene rocks. Interpretation reveals that dextral transtension in the Early to Middle Eocene created NNW-trending, en echelon, strike-slip faults linked by pull-apart basins, which locally contain a thickness of Eocene volcaniclastic rocks of >3 km. This structural pattern is consistent with regional observations that suggest the transfer of slip from the Yalakom fault to the north via a series of en echelon strike-slip faults. In the Middle to Late Eocene, faults associated with a change in the direction of stress, echoed by the north-trending right-lateral Fraser fault, reactivated and cut earlier structures. A simple model agrees with local observations, that northeast-directed compression was subparallel to the relic Cretaceous grain. Cretaceous rocks are discontinuous throughout the basin and may be remnants of a broader basin, or a number of contemporaneous basins, formed in a regional transpressional tectonic setting that caused northeast-directed thrusting along the eastern side of the Coast Plutonic Complex. Results suggest that thrusting affected most of the SE Nechako Basin, as observed across the Intermontane Belt to the northwest and southeast. The pattern of deposition of Neogene volcanic rocks of the Chilcotin Group was in part controlled by the Eocene structural grain, but we find no evidence of Neogene deformation.

The climate in Antarctica during the Middle Eocene: a modelling perspective

2020 ◽  
Author(s):  
Frederic Fluteau ◽  
Delphine Tardif ◽  
Guillaume Le Hir ◽  
Yannick Donnadieu ◽  
Pierre Sepulchre ◽  
...  
Keyword(s):  
General Circulation ◽  
Middle Eocene ◽  
Circulation Model ◽  
Late Eocene ◽  
Proxy Data ◽  
Polar Climate ◽  
Sedimentary Sequences ◽  
Orbital Configuration ◽  
Wet Climate ◽  
End Members

<p>The Middle Eocene represents the last ice-free period of the Cenozoic. Vegetation proxy data (wood, leaves, palynomorphs) discovered in the Antarctica peninsula and neighbouring islands or hosted in sedimentary sequences deposited on the continental margin reveal the presence of paratropical rain forests which thrived along the Antarctica coast during the Early Eocene. During the Middle and Late Eocene these flora have been progressively replaced by temperate <em>Nothofagus</em>-dominated rainforests (Contreras et al., 2013). Jacques et al. (2012) proposed, using a physiognomic approach (CLAMP), that a warm temperate and wet climate (with a marked summer rainy season) prevails until the middle Eocene (43±2 Ma) on the tip of the Antarctica Peninsula.</p><p>            To better constrain the climate in Antarctica and understand processes governing the polar climate during the Middle Eocene, we performed a set of experiments using the IPCC-like Earth System Model (IPSL-CM5A2-VLR) forced with a Middle Eocene (~40 Ma) paleogeography reconstruction and a 4 times pre-industrial atmospheric CO<sub>2</sub> level (1120ppm). To highlight the importance of the seasonality, we launched 6 orbital configurations exploring end-members situations. To complete the procedure, simulated sea surface temperatures and sea ice extents were then employed as boundary conditions to force the Atmospheric General circulation model LMDz6 (run at higher spatial resolution) coupled with a soil and vegetation model ORCHIDEE to simulate the corresponding vegetation over Antarctica. The 6 end-members Earth's orbital configuration allows exploring the full climatic spectrum which would have been recorded by proxy data. Simulated changes in atmospheric circulation will be discussed and the simulated climate and vegetation will be confronted to paleoclimatic indicators and vegetation data.</p>

scholarly journals High sensitivity of Bering Sea winter sea ice to winter insolation and carbon dioxide over the last 5500 years

2020 ◽  
Vol 6 (36) ◽  
pp. eaaz9588
Author(s):  
Miriam C. Jones ◽  
Max Berkelhammer ◽  
Katherine J. Keller ◽  
Kei Yoshimura ◽  
Matthew J. Wooller
Keyword(s):  
Sea Ice ◽  
Bering Sea ◽  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
High Sensitivity ◽  
Sea Ice Extent ◽  
The North ◽  
Winter Insolation ◽  
The Bering Sea

Anomalously low winter sea ice extent and early retreat in CE 2018 and 2019 challenge previous notions that winter sea ice in the Bering Sea has been stable over the instrumental record, although long-term records remain limited. Here, we use a record of peat cellulose oxygen isotopes from St. Matthew Island along with isotope-enabled general circulation model (IsoGSM) simulations to generate a 5500-year record of Bering Sea winter sea ice extent. Results show that over the last 5500 years, sea ice in the Bering Sea decreased in response to increasing winter insolation and atmospheric CO2, suggesting that the North Pacific is highly sensitive to small changes in radiative forcing. We find that CE 2018 sea ice conditions were the lowest of the last 5500 years, and results suggest that sea ice loss may lag changes in CO2 concentrations by several decades.

scholarly journals North Atlantic marine biogenic silica accumulation through the early to middle Paleogene: implications for ocean circulation and silicate weathering feedback

2021 ◽  
Vol 17 (5) ◽  
pp. 1937-1954
Author(s):  
Jakub Witkowski ◽  
Karolina Bryłka ◽  
Steven M. Bohaty ◽  
Elżbieta Mydłowska ◽  
Donald E. Penman ◽  
...  
Keyword(s):  
North Atlantic ◽  
Biogenic Silica ◽  
Middle Eocene ◽  
Nutrient Supply ◽  
Late Eocene ◽  
Silicate Weathering ◽  
Early Eocene ◽  
The North ◽  
History Of ◽  
The North Atlantic

Abstract. The Paleogene history of biogenic opal accumulation in the North Atlantic provides insight into both the evolution of deepwater circulation in the Atlantic basin and weathering responses to major climate shifts. However, existing records are compromised by low temporal resolution and/or stratigraphic discontinuities. In order to address this problem, we present a multi-site, high-resolution record of biogenic silica (bioSiO2) accumulation from Blake Nose (ODP Leg 171B, western North Atlantic) spanning the early Paleocene to late Eocene time interval (∼65–34 Ma). This record represents the longest single-locality history of marine bioSiO2 burial compiled to date and offers a unique perspective into changes in bioSiO2 fluxes through the early to middle Paleogene extreme greenhouse interval and the subsequent period of long-term cooling. Blake Nose bioSiO2 fluxes display prominent fluctuations that we attribute to variations in sub-thermocline nutrient supply via cyclonic eddies associated with the Gulf Stream. Following elevated and pulsed bioSiO2 accumulation through the Paleocene to early Eocene greenhouse interval, a prolonged interval of markedly elevated bioSiO2 flux in the middle Eocene between ∼46 and 42 Ma is proposed to reflect nutrient enrichment at Blake Nose due to invigorated overturning circulation following an early onset of Northern Component Water export from the Norwegian–Greenland Sea at ∼49 Ma. Reduced bioSiO2 flux in the North Atlantic, in combination with increased bioSiO2 flux documented in existing records from the equatorial Pacific between ∼42 and 38 Ma, is interpreted to indicate diminished nutrient supply and reduced biosiliceous productivity at Blake Nose in response to weakening of the overturning circulation. Subsequently, in the late Eocene, a deepwater circulation regime favoring limited bioSiO2 burial in the Atlantic and enhanced bioSiO2 burial in the Pacific was established after ∼38 Ma, likely in conjunction with re-invigoration of deepwater export from the North Atlantic. We also observe that Blake Nose bioSiO2 fluxes through the middle Eocene cooling interval (∼48 to 34 Ma) are similar to or higher than background fluxes throughout the late Paleocene–early Eocene interval (∼65 to 48 Ma) of intense greenhouse warmth. This observation is consistent with a temporally variable rather than constant silicate weathering feedback strength model for the Paleogene, which would instead predict that marine bioSiO2 burial should peak during periods of extreme warming.

scholarly journals The impact of different glacial boundary conditions on atmospheric dynamics and precipitation in the North Atlantic region

2012 ◽  
Vol 8 (1) ◽  
pp. 63-101
Author(s):  
D. Hofer ◽  
C. C. Raible ◽  
A. Dehnert ◽  
J. Kuhlemann
Keyword(s):  
Boundary Conditions ◽  
North Atlantic ◽  
General Circulation ◽  
Ice Sheet ◽  
Atmospheric Dynamics ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
The North ◽  
The North Atlantic ◽  
The Impact

Abstract. Using a highly resolved atmospheric general circulation model the impact of different glacial boundary conditions on precipitation and atmospheric dynamics in the North Atlantic region is investigated. Seven 30-yr time slice experiments of the Last Glacial Maximum (21 ka ago) and of a less pronounced glacial state – the Middle Weichselian (65 ka ago) – are compared to analyse the sensitivity to changes in the ice sheet distribution, in the radiative forcing, and in the prescribed time-varying lower boundary conditions, which are taken from a lower-resolved but fully-coupled atmosphere-ocean general circulation model. The strongest differences are found for simulations with different heights of the Laurentide ice sheet. A large altitude of this ice sheet leads to a southward displacement of the jet stream and the storm track in the North Atlantic region. These changes in the atmospheric dynamics generate a band of increased precipitation in the mid-latitudes across the Atlantic to southern Europe in winter, while the precipitation pattern in summer is only marginally affected. The impact of the radiative forcing differences between the two glacial periods and of the prescribed time-varying lower boundary conditions – evaluated using two simulations of the Last Glacial Maximum with a global mean temperature difference of 1.1 °C – are of second order compared to the one of the Laurentide ice sheet. They affect the atmospheric dynamics and precipitation in a similar but less pronounced manner as the topographic changes.

scholarly journals Sensitivity of the radiative forcing by stratospheric sulfur geoengineering to the amount and strategy of the SO<sub>2</sub>injection studied with the LMDZ-S3A model

2018 ◽  
Vol 18 (4) ◽  
pp. 2769-2786 ◽  
Author(s):  
Christoph Kleinschmitt ◽  
Olivier Boucher ◽  
Ulrich Platt
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Quasi Biennial Oscillation ◽  
Detailed Model ◽  
Mass Unit ◽  
Modelling Studies ◽  
Injection Rates

Abstract. The enhancement of the stratospheric sulfate aerosol layer has been proposed as a method of geoengineering to abate global warming. Previous modelling studies found that stratospheric aerosol geoengineering (SAG) could effectively compensate for the warming by greenhouse gases on the global scale, but also that the achievable cooling effect per sulfur mass unit, i.e. the forcing efficiency, decreases with increasing injection rate. In this study we use the atmospheric general circulation model LMDZ with the sectional aerosol module S3A to determine how the forcing efficiency depends on the injected amount of SO2, the injection height, and the spatio-temporal pattern of injection. We find that the forcing efficiency may decrease more drastically for larger SO2 injections than previously estimated. As a result, the net instantaneous radiative forcing does not exceed the limit of –2 W m−2 for continuous equatorial SO2 injections and it decreases (in absolute value) for injection rates larger than 20 Tg S yr−1. In contrast to other studies, the net radiative forcing in our experiments is fairly constant with injection height (in a range 17 to 23 km) for a given amount of SO2 injected. Also, spreading the SO2 injections between 30∘ S and 30∘ N or injecting only seasonally from varying latitudes does not result in a significantly larger (i.e. more negative) radiative forcing. Other key characteristics of our simulations include a consequent stratospheric heating, caused by the absorption of solar and infrared radiation by the aerosol, and changes in stratospheric dynamics, with a collapse of the quasi-biennial oscillation at larger injection rates, which has impacts on the resulting spatial aerosol distribution, size, and optical properties. But it has to be noted that the complexity and uncertainty of stratospheric processes cause considerable disagreement among different modelling studies of stratospheric aerosol geoengineering. This may be addressed through detailed model intercomparison activities, as observations to constrain the simulations of stratospheric aerosol geoengineering are not available and analogues (such as volcanic eruptions) are imperfect.

Sign in / Sign up

Export Citation Format

Share Document