scholarly journals The Key Role of Ozone-Depleting Substances in Weakening the Walker Circulation in the Second Half of the Twentieth Century

2019 ◽  
Vol 32 (5) ◽  
pp. 1411-1418 ◽  
Author(s):  
Lorenzo M. Polvani ◽  
Katinka Bellomo
Keyword(s):  
Twentieth Century ◽  
Pacific Ocean ◽  
Greenhouse Gases ◽  
Radiative Forcing ◽  
Climate Model ◽  
Walker Circulation ◽  
Surface Warming ◽  
Ozone Depleting Substances ◽  
The Antarctic ◽  
The Walker Circulation

It is widely appreciated that ozone-depleting substances (ODS), which have led to the formation of the Antarctic ozone hole, are also powerful greenhouse gases. In this study, we explore the consequence of the surface warming caused by ODS in the second half of the twentieth century over the Indo-Pacific Ocean, using the Whole Atmosphere Chemistry Climate Model (version 4). By contrasting two ensembles of chemistry–climate model integrations (with and without ODS forcing) over the period 1955–2005, we show that the additional greenhouse effect of ODS is crucial to producing a statistically significant weakening of the Walker circulation in our model over that period. When ODS concentrations are held fixed at 1955 levels, the forcing of the other well-mixed greenhouse gases alone leads to a strengthening—rather than weakening—of the Walker circulation because their warming effect is not sufficiently strong. Without increasing ODS, a surface warming delay in the eastern tropical Pacific Ocean leads to an increase in the sea surface temperature gradient between the eastern and western Pacific, with an associated strengthening of the Walker circulation. When increasing ODS are added, the considerably larger total radiative forcing produces a much faster warming in the eastern Pacific, causing the sign of the trend to reverse and the Walker circulation to weaken. Our modeling result suggests that ODS may have been key players in the observed weakening of the Walker circulation over the second half of the twentieth century.

scholarly journals Walker circulation response to extratropical radiative forcing

2020 ◽  
Vol 6 (47) ◽  
pp. eabd3021
Author(s):  
Sarah M. Kang ◽  
Shang-Ping Xie ◽  
Yechul Shin ◽  
Hanjun Kim ◽  
Yen-Ting Hwang ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Radiative Forcing ◽  
Climate Model ◽  
Walker Circulation ◽  
Coupled System ◽  
Subsurface Water ◽  
Eastern Equatorial Pacific ◽  
Global Impacts ◽  
Climate Model Simulations ◽  
The Walker Circulation

Walker circulation variability and associated zonal shifts in the heating of the tropical atmosphere have far-reaching global impacts well into high latitudes. Yet the reversed high latitude–to–Walker circulation teleconnection is not fully understood. Here, we reveal the dynamical pathways of this teleconnection across different components of the climate system using a hierarchy of climate model simulations. In the fully coupled system with ocean circulation adjustments, the Walker circulation strengthens in response to extratropical radiative cooling of either hemisphere, associated with the upwelling of colder subsurface water in the eastern equatorial Pacific. By contrast, in the absence of ocean circulation adjustments, the Walker circulation response is sensitive to the forcing hemisphere, due to the blocking effect of the northward-displaced climatological intertropical convergence zone and shortwave cloud radiative effects. Our study implies that energy biases in the extratropics can cause pronounced changes of tropical climate patterns.

scholarly journals Slowdown of the Walker circulation at solar cycle maximum

2019 ◽  
Vol 116 (15) ◽  
pp. 7186-7191 ◽  
Author(s):  
Stergios Misios ◽  
Lesley J. Gray ◽  
Mads F. Knudsen ◽  
Christoffer Karoff ◽  
Hauke Schmidt ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Radiative Forcing ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Walker Circulation ◽  
Internal Variability ◽  
Convective Precipitation ◽  
Solar Modulation ◽  
Central Pacific ◽  
Surface Warming

The Pacific Walker Circulation (PWC) fluctuates on interannual and multidecadal timescales under the influence of internal variability and external forcings. Here, we provide observational evidence that the 11-y solar cycle (SC) affects the PWC on decadal timescales. We observe a robust reduction of east–west sea-level pressure gradients over the Indo-Pacific Ocean during solar maxima and the following 1–2 y. This reduction is associated with westerly wind anomalies at the surface and throughout the equatorial troposphere in the western/central Pacific paired with an eastward shift of convective precipitation that brings more rainfall to the central Pacific. We show that this is initiated by a thermodynamical response of the global hydrological cycle to surface warming, further amplified by atmosphere–ocean coupling, leading to larger positive ocean temperature anomalies in the equatorial Pacific than expected from simple radiative forcing considerations. The observed solar modulation of the PWC is supported by a set of coupled ocean–atmosphere climate model simulations forced only by SC irradiance variations. We highlight the importance of a muted hydrology mechanism that acts to weaken the PWC. Demonstration of this mechanism acting on the 11-y SC timescale adds confidence in model predictions that the same mechanism also weakens the PWC under increasing greenhouse gas forcing.

Shedding new light on the radiative impacts of ozone-depleting substances

2020 ◽  
Author(s):  
Gabriel Chiodo ◽  
Lorenzo M. Polvani
Keyword(s):  
Twentieth Century ◽  
Ozone Depletion ◽  
Stratospheric Ozone ◽  
Walker Circulation ◽  
Climate Impacts ◽  
The Arctic ◽  
Temperature Structure ◽  
Stratospheric Ozone Depletion ◽  
Ozone Depleting Substances ◽  
The Walker Circulation

<p>It is well established that ozone-depleting substances (ODS) have been the primary cause of stratospheric ozone depletion. It is also widely accepted that stratospheric ozone depletion has been the primary driver of summertime circulation trends in the Austral Hemisphere in the second half of the twentieth century. However, the climate impacts of ODS that are independent of ozone depletion have received little attention. It has long been known that, while much less abundant than carbon dioxide, ODS have a much higher global warming potential (GWP) ecent studies have indicated that ODS may have played a key-role in the observed weakening trends of the Walker circulation (Polvani and Bellomo, 2019), and in the warming of the Arctic and the associated sea ice loss (Polvani et al., 2020). <span>that the climate efficacy of ODS may be much larger than previously thought, but </span><span>.</span></p><p>Here, we seek to better understand the radiative effect of ODS in the global atmosphere. Instead of confining our attention on a single metric, e.g. globally averaged radiative forcing (RF) or GWP which are typically reported in the IPCC Assessment Reports, we seek to understand how ODS alter the temperature structure of the entire atmosphere. Focusing on the half-century 1950-2000, which saw the largest growth of ODS concentrations in the atmosphere, we start by performing careful computations of the RF of individual ODS, including the effects of rapid temperature adjustments. We then explore how the vertical and latitudinal distribution of ODS (which are not well mixed in the stratosphere) affects their RF, and what temperature responses are associated with those changes. These calculations are repeated individually for each of the other well-mixed GHG, as well as for other composition changes arising from ODS (ozone depletion). It is shown that ODS, in contrast to other GHG, warm the lower stratosphere, implying a different fingerprint from CO2. Furthermore, the RF of ODS exhibits the largest meridional gradient of any other well-mixed GHG. Implications for the climate efficacy of ODS, and more generally for climate sensitivity, will be discussed.</p><p>References</p><p>Polvani, L.M and K. Bellomo: The key role of ozone depleting substances in weakening the Walker circulation in the second half of the 20th century, <em>J. Climate</em>, <strong>32</strong>, 1411-1418 (2019).</p><p>Polvani et al.,: Substantial twentieth-century Arctic warmng caused by ozone depleting substances, <em>Nature Climate Change, </em>in press (2019)</p>

Substantial twentieth-century Arctic warming caused by ozone-depleting substances

2020 ◽  
Author(s):  
Lorenzo Polvani ◽  
Michael Previdi ◽  
Mark England ◽  
Gabriel Chiodo ◽  
Karen Smith
Keyword(s):  
Climate Change ◽  
Twentieth Century ◽  
Greenhouse Gases ◽  
Climate Model ◽  
Dominant Role ◽  
Montreal Protocol ◽  
The Arctic ◽  
Atmospheric Concentration ◽  
Arctic Warming ◽  
Ozone Depleting Substances

<p>The rapid warming of the Arctic, perhaps the most striking evidence of climate change, is believed to arise from increases in atmospheric concentration of greenhouse gases since the industrial revolution.  While the dominant role of carbon dioxide is undisputed, another important set of anthropogenic greenhouse gases was also being emitted over the second half of the twentieth century: ozone-depleting substances (ODS).  These compounds, in addition to causing the ozone hole over Antarctica, have long been recognized as powerful greenhouse gases.  However, their contribution to Arctic warming has not been quantified to date.  We do so here by analyzing ensembles of climate model integrations specifically designed for this purpose, spanning the period 1955-2005 when atmospheric concentrations of ODS increased rapidly.  We show that when ODS are kept fixed the forced Arctic surface warming, and the forced sea ice loss, are only half as large as when ODS are allowed to increase.  We also demonstrate that the large Arctic impact of ODS occurs primarily via direct radiative warming, not via ozone depletion.  Our findings reveal a substantial, and hitherto unrecognized, contribution of ODS to recent Arctic warming and highlight the importance of the Montreal Protocol as a major climate change mitigation treaty.</p>

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 Chemical and climatic drivers of radiative forcing due to changes in stratospheric and tropospheric ozone over the 21<sup>st</sup> century

2017 ◽  
Author(s):  
Antara Banerjee ◽  
Amanda C. Maycock ◽  
John A. Pyle
Keyword(s):  
Greenhouse Gas ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Radiative Forcings ◽  
Climatic Drivers ◽  
Ozone Precursor ◽  
Ozone Depleting Substances ◽  
Projected Changes

Abstract. The ozone radiative forcings (RFs) resulting from projected changes in climate, ozone-depleting substances (ODSs), non-methane ozone precursor emissions and methane between the years 2000 and 2100 are calculated using simulations from the UM-UKCA chemistry-climate model. Projected measures to improve air-quality through reductions in tropospheric ozone precursor emissions present a co-benefit for climate, with a net global mean ozone RF of −0.09 Wm−2. This is opposed by a positive ozone RF of 0.07 Wm−2 due to future decreases in ODSs, which is mainly driven by an increase in tropospheric ozone through stratosphere-to-troposphere exchange. An increase in methane abundance by more than a factor of two (as projected by the RCP8.5 scenario) is found to drive an ozone RF of 0.19 Wm−2, which would greatly outweigh the climate benefits of tropospheric non-methane ozone precursor reductions. A third of the ozone RF due to the projected increase in methane results from increases in stratospheric ozone. The sign of the ozone RF due to future changes in climate (including the radiative effects of greenhouse gas concentrations, sea surface temperatures and sea ice changes) is shown to be dependent on the greenhouse gas emissions pathway, with a positive RF (0.06 Wm−2) for RCP4.5 and a negative RF (−0.07 Wm−2) for the RCP8.5 scenario. This dependence arises from differences in the contribution to RF from stratospheric ozone changes.

Some future projections from coupling the U.K. Earth System Model to the Antarctic ice sheets

2021 ◽  
Author(s):  
Anthony Siahaan
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Ice Sheet ◽  
Mass Gain ◽  
Ice Shelves ◽  
Positive Effects ◽  
Basal Melting ◽  
The Antarctic ◽  
The Impact ◽  
Increasing Precipitation

&lt;p&gt;A UKESM climate model which is coupled annually to the BISICLES ice sheet model to enable a two way interactions in Antarctica has been developed&amp;#160;&lt;br&gt;and run through a small ensemble of four SSP1-1.9 &amp; SSP5-8.5 scenario members. Under the extreme anthropogenic forcing, all the initial condition&amp;#160;&lt;br&gt;ensemble members develop strong melting under the cold &amp; large Ross and Filchner-Ronne ice-shelves, where it starts after the first half of simulation&amp;#160;&lt;br&gt;period for the former and in the last decade of the run for the latter. Despite that, during the 85 years timescale of these scenario runs, the stronger radiative forcing has positive effects on the ice-sheet mass gain through increasing precipitation on grounded ice regions which offsets the impact of basal melting in ice discharge across the grounding lines.&lt;/p&gt;

scholarly journals Ozone sensitivity to varying greenhouse gases and ozone-depleting substances in CCMI simulations

2017 ◽  
Author(s):  
Olaf Morgenstern ◽  
Hideharu Akiyoshi ◽  
Yousuke Yamashita ◽  
Douglas E. Kinnison ◽  
Rolando R. Garcia ◽  
...  
Keyword(s):  
Greenhouse Gases ◽  
Climate Model ◽  
Phase 1 ◽  
Coupled Model ◽  
Total Column Ozone ◽  
Ozone Sensitivity ◽  
Intercomparison Project ◽  
Ozone Depleting Substances ◽  
Column Ozone ◽  
Total Column

Abstract. Ozone fields simulated for the Chemistry-Climate Model Initiative (CCMI) will be used as forcing data in the 6th Coupled Model Intercomparison Project (CMIP6). Here we assess, using reference and sensitivity simulations produced for phase 1 of CCMI, the suitability of CCMI-1 model results for this process, investigating the degree of consistency amongst models regarding their responses to variations in individual forcings. We consider the influences of methane, nitrous oxide, a combination of chlorinated or brominated ozone-depleting substances (ODSs), and a combination of carbon dioxide and other greenhouse gases (GHGs). We find varying degrees of consistency in the models' responses in ozone to these individual forcings, including some considerable disagreement. In particular, the response of total-column ozone to these forcings is less consistent across the multi-model ensemble than profile comparisons. The likely cause of this is lower-stratospheric transport and dynamical responses exhibiting substantial inter-model differences. The findings imply that the ozone fields derived from CCMI-1 are subject to considerable uncertainties regarding the impacts of these anthropogenic forcings.

Numerical modeling of the natural and anthropogenic factors influence on the past and future changes in polar, mid-latitude and tropical ozone

2020 ◽  
Author(s):  
Sergei Smyshlyaev ◽  
Polina Blakitnaya ◽  
Maxim Motsakov ◽  
Vener Galin
Keyword(s):  
Solar Activity ◽  
Greenhouse Gases ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Stratospheric Ozone ◽  
Stratospheric Aerosol ◽  
Anthropogenic Factors ◽  
The Past ◽  
Ozone Depleting Substances ◽  
Natural And Anthropogenic Factors

&lt;p&gt;The INM RAS &amp;#8211; RSHU chemistry-climate model of the lower and middle atmosphere is used to compare the role of natural and anthropogenic factors in the observed and expected variability of stratospheric ozone. Numerical experiments have been carried out on several scenarios of separate and combined effects of solar activity, stratospheric aerosol, sea surface temperature, greenhouse gases, and ozone-depleting substances emissions on ozone for the period from 1979 to 2050. Simulations for the past and present periods are compared to the results of ground-based and satellite observations, as well as MERRA and ERA-Interim re-analysis. Estimation of future ozone changes are based on different scenarios of changes in solar activity and emissions of ozone-depleting substances and greenhouse gases, as well as the possibility of large volcanic aerosol emissions at different periods of time.&lt;/p&gt;

scholarly journals Antarctic ozone depletion between 1960 and 1980 in observations and chemistry–climate model simulations

2016 ◽  
Vol 16 (24) ◽  
pp. 15619-15627 ◽  
Author(s):  
Ulrike Langematz ◽  
Franziska Schmidt ◽  
Markus Kunze ◽  
Gregory E. Bodeker ◽  
Peter Braesicke
Keyword(s):  
Ozone Depletion ◽  
Climate Model ◽  
Total Column Ozone ◽  
Antarctic Ozone ◽  
Climate Model Simulations ◽  
Ozone Depleting Substances ◽  
Column Ozone ◽  
The Antarctic ◽  
Total Column

Abstract. The year 1980 has often been used as a benchmark for the return of Antarctic ozone to conditions assumed to be unaffected by emissions of ozone-depleting substances (ODSs), implying that anthropogenic ozone depletion in Antarctica started around 1980. Here, the extent of anthropogenically driven Antarctic ozone depletion prior to 1980 is examined using output from transient chemistry–climate model (CCM) simulations from 1960 to 2000 with prescribed changes of ozone-depleting substance concentrations in conjunction with observations. A regression model is used to attribute CCM modelled and observed changes in Antarctic total column ozone to halogen-driven chemistry prior to 1980. Wintertime Antarctic ozone is strongly affected by dynamical processes that vary in amplitude from year to year and from model to model. However, when the dynamical and chemical impacts on ozone are separated, all models consistently show a long-term, halogen-induced negative trend in Antarctic ozone from 1960 to 1980. The anthropogenically driven ozone loss from 1960 to 1980 ranges between 26.4 ± 3.4 and 49.8 ± 6.2 % of the total anthropogenic ozone depletion from 1960 to 2000. An even stronger ozone decline of 56.4 ± 6.8 % was estimated from ozone observations. This analysis of the observations and simulations from 17 CCMs clarifies that while the return of Antarctic ozone to 1980 values remains a valid milestone, achieving that milestone is not indicative of full recovery of the Antarctic ozone layer from the effects of ODSs.

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