Modeling Obliquity and CO2 Effects on Southern Hemisphere Climate during the Past 408 ka*

2014 ◽  
Vol 27 (5) ◽  
pp. 1863-1875 ◽  
Author(s):  
Axel Timmermann ◽  
Tobias Friedrich ◽  
Oliver Elison Timm ◽  
Megumi O. Chikamoto ◽  
Ayako Abe-Ouchi ◽  
...  
Keyword(s):  
Greenhouse Gas ◽  
Heat Transport ◽  
Southern Hemisphere ◽  
Radiative Forcing ◽  
General Circulation ◽  
Storm Tracks ◽  
Transient Model ◽  
Middle Troposphere ◽  
The Past ◽  
Southern Hemisphere Westerlies

Abstract The effect of obliquity and CO2 changes on Southern Hemispheric climate is studied with a series of numerical modeling experiments. Using the Earth system model of intermediate complexity Loch–VECODE–ECBilt–CLIO–Agism Model (LOVECLIM) and a coupled general circulation model [Model for Interdisciplinary Research on Climate (MIROC)], it is shown in time-slice simulations that phases of low obliquity enhance the meridional extratropical temperature gradient, increase the atmospheric baroclinicity, and intensify the lower and middle troposphere Southern Hemisphere westerlies and storm tracks. Furthermore, a transient model simulation is conducted with LOVECLIM that covers the greenhouse gas, ice sheet, and orbital forcing history of the past 408 ka. This simulation reproduces reconstructed glacial–interglacial variations in temperature and sea ice qualitatively well and shows that the meridional heat transport associated with the orbitally paced modulation of middle troposphere westerlies and storm tracks partly offsets the effects of the direct shortwave obliquity forcing over Antarctica, thereby reinforcing the high correlation between CO2 radiative forcing and Antarctic temperature. The overall timing of temperature changes in Antarctica is hence determined by a balance of shortwave obliquity forcing, atmospheric heat transport changes, and greenhouse gas forcing. A shorter 130-ka transient model experiment with constant CO2 concentrations further demonstrates that surface Southern Hemisphere westerlies are primarily modulated by the obliquity cycle rather than by the CO2 radiative forcing.

scholarly journals Meridional Atmospheric Heat Transport Constrained by Energetics and Mediated by Large-Scale Diffusion

2019 ◽  
Vol 32 (12) ◽  
pp. 3655-3680 ◽  
Author(s):  
Kyle C. Armour ◽  
Nicholas Siler ◽  
Aaron Donohoe ◽  
Gerard H. Roe
Keyword(s):  
Greenhouse Gas ◽  
Heat Transport ◽  
Radiative Forcing ◽  
General Circulation ◽  
General Circulation Models ◽  
Balance Model ◽  
Ocean Heat Uptake ◽  
Atmospheric Heat Transport ◽  
Warming Pattern ◽  
Atmospheric Heat

Abstract Meridional atmospheric heat transport (AHT) has been investigated through three broad perspectives: a dynamic perspective, linking AHT to the poleward flux of moist static energy (MSE) by atmospheric motions; an energetic perspective, linking AHT to energy input to the atmosphere by top-of-atmosphere radiation and surface heat fluxes; and a diffusive perspective, representing AHT in terms downgradient energy transport. It is shown here that the three perspectives provide complementary diagnostics of meridional AHT and its changes under greenhouse gas forcing. When combined, the energetic and diffusive perspectives offer prognostic insights: anomalous AHT is constrained to satisfy the net energetic demands of radiative forcing, radiative feedbacks, and ocean heat uptake; in turn, the meridional pattern of warming must adjust to produce those AHT changes, and does so approximately according to diffusion of anomalous MSE. The relationship between temperature and MSE exerts strong constraints on the warming pattern, favoring polar amplification. These conclusions are supported by use of a diffusive moist energy balance model (EBM) that accurately predicts zonal-mean warming and AHT changes within comprehensive general circulation models (GCMs). A dry diffusive EBM predicts similar AHT changes in order to satisfy the same energetic constraints, but does so through tropically amplified warming—at odds with the GCMs’ polar-amplified warming pattern. The results suggest that polar-amplified warming is a near-inevitable consequence of a moist, diffusive atmosphere’s response to greenhouse gas forcing. In this view, atmospheric circulations must act to satisfy net AHT as constrained by energetics.

Impacts of stratospheric ozone and greenhouse gas changes on the Southern Hemisphere circulation in the CCMI models

2020 ◽  
Author(s):  
Bo-Reum Han ◽  
Jung Choi ◽  
Seok-Woo Son
Keyword(s):  
Greenhouse Gas ◽  
Southern Hemisphere ◽  
General Circulation ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Southern Annular Mode ◽  
Hadley Cell ◽  
The Past ◽  
The Future ◽  
Circulation Changes

<p> The impacts of stratospheric ozone and greenhouse gas changes on the Southern Hemisphere (SH) climate are re-visited by examining the single forcing experiments from the Chemistry-Climate Model Initiative (CCMI) project. In particular, the fixed ozone-depleting substance (ODS) runs and the fixed greenhouse gas (GHG) concentration runs are directly compared with the reference runs for both the past and future. Consistent with the previous studies, the SH-summer general circulation changes, such as changes in the jet location, Hadley cell edge, and Southern Annular Mode (SAM), show the opposite trends from the past to the future in response to the Antarctic ozone depletion and recovery. The GHG-induced circulation changes largely enhance the ozone-induced circulation changes in the past, but partly cancel them in the future. The ozone recovery-related tropospheric circulation return dates are also estimated in this study. We will further discuss the inter-model diversity among the CCMI models.</p>

scholarly journals Improved estimates of preindustrial biomass burning reduce the magnitude of aerosol climate forcing in the Southern Hemisphere

2021 ◽  
Vol 7 (22) ◽  
pp. eabc1379
Author(s):  
Pengfei Liu ◽  
Jed O. Kaplan ◽  
Loretta J. Mickley ◽  
Yang Li ◽  
Nathan J. Chellman ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Radiative Forcing ◽  
Ice Core ◽  
Ice Cores ◽  
Terrestrial Ecosystems ◽  
Rapid Expansion ◽  
Past Century ◽  
Fire Emissions ◽  
The Past ◽  
Fire Activity

Fire plays a pivotal role in shaping terrestrial ecosystems and the chemical composition of the atmosphere and thus influences Earth’s climate. The trend and magnitude of fire activity over the past few centuries are controversial, which hinders understanding of preindustrial to present-day aerosol radiative forcing. Here, we present evidence from records of 14 Antarctic ice cores and 1 central Andean ice core, suggesting that historical fire activity in the Southern Hemisphere (SH) exceeded present-day levels. To understand this observation, we use a global fire model to show that overall SH fire emissions could have declined by 30% over the 20th century, possibly because of the rapid expansion of land use for agriculture and animal production in middle to high latitudes. Radiative forcing calculations suggest that the decreasing trend in SH fire emissions over the past century largely compensates for the cooling effect of increasing aerosols from fossil fuel and biofuel sources.

scholarly journals Two hundred fifty years of aerosols and climate: the end of the age of aerosols

2014 ◽  
Vol 14 (2) ◽  
pp. 537-549 ◽  
Author(s):  
S. J. Smith ◽  
T. C. Bond
Keyword(s):  
Greenhouse Gas ◽  
Radiative Forcing ◽  
Pollutant Emissions ◽  
Past Century ◽  
Successful Implementation ◽  
Reference Scenario ◽  
Low Carbon ◽  
Substantial Impact ◽  
The Past ◽  
A Minor

Abstract. Carbonaceous and sulfur aerosols have a substantial global and regional influence on climate, resulting in a net cooling to date, in addition to their impact on health and ecosystems. The magnitude of this influence has changed substantially over the past and is expected to continue to change into the future. An integrated picture of the changing climatic influence of black carbon, organic carbon and sulfate over the period 1850 through 2100, focusing on uncertainty, is presented using updated historical inventories and a coordinated set of emission projections. We describe, in detail, the aerosol emissions from the RCP4.5 scenario and its associated reference scenario. While aerosols have had a substantial impact on climate over the past century, we show that, by the end of the 21st century, aerosols will likely be only a minor contributor to radiative forcing due to increases in greenhouse gas forcing and a net global decrease in pollutant emissions. This outcome is even more certain under a successful implementation of a policy to limit greenhouse gas emissions as low-carbon energy technologies that do not emit appreciable aerosol or SO2 are deployed.

scholarly journals The Atmospheric Response to Surface Heating under Maximum Entropy Production

2014 ◽  
Vol 71 (6) ◽  
pp. 2204-2220
Author(s):  
A. Gjermundsen ◽  
J. H. LaCasce ◽  
L. S. Graff
Keyword(s):  
Entropy Production ◽  
Maximum Entropy ◽  
Heat Transport ◽  
General Circulation ◽  
Heat Fluxes ◽  
Storm Tracks ◽  
Atmospheric Response ◽  
Maximum Entropy Production ◽  
Surface Temperatures ◽  
Low Latitudes

Abstract In numerous studies, midlatitude storm tracks have been shown to shift poleward under global warming scenarios. Among the possible causes, changes in sea surface temperature (SST) have been shown to affect both the intensity and the position of the tracks. Increased SSTs can increase both the lateral heating occurring in the tropics and the midlatitude temperature gradients, both of which increase tropospheric baroclinicity. To better understand the response to altered SST, a simplified energy balance model (EBM) is used. This employs the principal of maximum entropy production (MEP) to determine the meridional heat fluxes in the atmosphere. The model is similar to one proposed by Paltridge (1975) but represents only the atmospheric response (the surface temperatures are fixed). The model is then compared with a full atmospheric general circulation model [Community Atmosphere Model, version 3 (CAM3)]. In response to perturbed surface temperatures, EBM exhibits similar changes in (vertically integrated) air temperature, convective heat fluxes, and meridional heat transport. However, the changes in CAM3 are often more localized, particularly at low latitudes. This, in turn, results in a shift of the storm tracks in CAM3, which is largely absent in EBM. EBM is more successful, however, at representing the response to changes in high-latitude heating or cooling. Therefore, MEP is evidently a plausible representation for heat transport in the midlatitudes, but not necessarily at low latitudes.

scholarly journals Climate Sensitivity to Changes in Ocean Heat Transport

2011 ◽  
Vol 24 (19) ◽  
pp. 5015-5030 ◽  
Author(s):  
Marcelo Barreiro ◽  
Annalisa Cherchi ◽  
Simona Masina
Keyword(s):  
Heat Transport ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Circulation Model ◽  
Ocean Heat Transport ◽  
Sea Ice Extent ◽  
The Past ◽  
Low Clouds ◽  
Marine Stratus ◽  
Low Cloud

Using an atmospheric general circulation model coupled to a slab ocean, the effects of ocean heat transport (OHT) on climate are studied by prescribing OHT from 0 to 2 times the present-day values. In agreement with previous studies, an increase in OHT from zero to present-day conditions warms the climate by decreasing the albedo due to reduced sea ice extent and marine stratus cloud cover and by increasing the greenhouse effect through a moistening of the atmosphere. However, when the OHT is further increased, the solution becomes highly dependent on a positive radiative feedback between tropical low clouds and sea surface temperature. The strength of the low cloud–SST feedback combined with the model design may produce solutions that are globally colder than in the control run, mainly due to an unrealistically strong equatorial cooling. Excluding those cases, results indicate that the climate warms only if the OHT increase does not exceed more than 10% of the present-day value in the case of a strong cloud–SST feedback and more than 25% when this feedback is weak. Larger OHT increases lead to a cold state where low clouds cover most of the deep tropics, increasing the tropical albedo and drying the atmosphere. This suggests that the present-day climate is close to a state where the OHT maximizes its warming effects on climate and raises doubts about the possibility that greater OHT in the past may have induced significantly warmer climates than that of today.

scholarly journals The Effects of the Spatial Distribution of Direct Anthropogenic Aerosols Radiative Forcing on Atmospheric Circulation

2018 ◽  
Vol 31 (17) ◽  
pp. 7129-7145 ◽  
Author(s):  
Rei Chemke ◽  
Guy Dagan
Keyword(s):  
Spatial Distribution ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
Hadley Cell ◽  
Global Circulation Model ◽  
Anthropogenic Aerosols

The large uncertainty in estimating the global aerosol radiative forcing (ARF) is one of the major challenges the climate community faces for climate projection. While the global-mean ARF may affect global quantities such as surface temperature, its spatial distribution may result in local thermodynamical and, thus, dynamical changes. Future changes in aerosol emissions distribution could further modulate the atmospheric circulation. Here, the effects of the spatial distribution of the direct anthropogenic ARF are studied using an idealized global circulation model, forced by a range of estimated-ARF amplitudes, based on the Copernicus Atmosphere Monitoring Service data. The spatial distribution of the estimated-ARF is globally decomposed, and the effects of the different modes on the circulation are studied. The most dominant spatial distribution feature is the cooling of the Northern Hemisphere in comparison to the Southern Hemisphere. This induces a negative meridional temperature gradient around the equator, which modulates the mean fields in the tropics. The ITCZ weakens and shifts southward, and the Northern (Southern) Hemisphere Hadley cell strengthens (weakens). The localization of the ARF in the Northern Hemisphere midlatitudes shifts the subtropical jet poleward and strengthens both the eddy-driven jet and Ferrel cell, because of the weakening of high-latitude eddy fluxes. Finally, the larger aerosol concentration in Asia compared to North America results in an equatorial superrotating jet. Understanding the effects of the different modes on the general circulation may help elucidate the circulation’s future response to the projected changes in ARF distribution.

The sensitivity of chemical loss of Arctic ozone to future levels of GHGs

2021 ◽  
Author(s):  
Peter von der Gathen ◽  
Rigel Kivi ◽  
Ingo Wohltmann ◽  
Ross Salawitch ◽  
Markus Rex
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Polar Vortex ◽  
General Circulation Models ◽  
Significant Rise ◽  
Meteorological Conditions ◽  
Local Maxima ◽  
The Past ◽  
Rcp 8.5 ◽  
Stratospheric Clouds

<p>The chemical loss of ozone during Arctic winter and spring due to anthropogenic halogens is driven by temperature at high latitudes, with more loss occurring during cold years with meteorological conditions that are favourable for formation of polar stratospheric clouds (PSCs). We show that a positive, statistically significant rise in the local maxima of PSC formation potential (PFP<sup>LM</sup>), i.e. seasonal integrals of the fraction of the vortex volume below the formation temperature of PSCs, within the Northern Hemisphere polar vortex over the past four decades is apparent in data from four meteorological centres. Output from numerous General Circulation Models (GCMs) that submitted results to the CMIP5 and CMIP6 archives also exhibits positive trends in PFP<sup>LM</sup> over 1950 to 2100, with the highest values occurring at end of century for model runs driven by increasing radiative forcing of climate due to greenhouse gases (GHGs) (i.e., the RCP 8.5 scenario for CMIP5 and the SSP5-8.5 scenario for CMIP6). We combine projections of the future decline in stratospheric halogen loading and possible future increases in stratospheric humidity with GCM-based forecasts of PFP to suggest that conditions favourable for large, seasonal loss of Arctic column O<sub>3</sub> could persist until the end of this century, especially for GCM simulations constrained by either the RCP 8.5 or SSP5-8.5 GHG scenario. Conversely, if future GHG loading follow the SSP1-2.6 scenario, conditions favourable for chemical loss of Arctic O3 are projected to decline throughout the rest of this century.</p>

Aerosol versus greenhouse gas impacts on Southern Hemisphere general circulation changes

2018 ◽  
Vol 52 (7-8) ◽  
pp. 4127-4142 ◽  
Author(s):  
Jung Choi ◽  
Seok-Woo Son ◽  
Rokjin J. Park
Keyword(s):  
Greenhouse Gas ◽  
Southern Hemisphere ◽  
General Circulation ◽  
Circulation Changes
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