Future changes in the stratosphere-to-troposphere ozone mass flux and the contribution from climate change and ozone recovery

Using a state-of-the-art chemistry–climate model we investigate the future change in stratosphere–troposphere exchange (STE) of ozone, the drivers of this change, as well as the future distribution of stratospheric ozone in the troposphere. Supplementary to previous work, our focus is on changes on the monthly scale. The global mean annual influx of stratospheric ozone into the troposphere is projected to increase by 53 % between the years 2000 and 2100 under the RCP8.5 greenhouse gas scenario. The change in ozone mass flux (OMF) into the troposphere is positive throughout the year with maximal increase in the summer months of the respective hemispheres. In the Northern Hemisphere (NH) this summer maximum STE increase is a result of increasing greenhouse gas (GHG) concentrations, whilst in the Southern Hemisphere(SH) it is due to equal contributions from decreasing levels of ozone depleting substances (ODS) and increasing GHG concentrations. In the SH the GHG effect is dominating in the winter months. A large ODS-related ozone increase in the SH stratosphere leads to a change in the seasonal breathing term which results in a future decrease of the OMF into the troposphere in the SH in September and October. The resulting distributions of stratospheric ozone in the troposphere differ for the GHG and ODS changes due to the following: (a) ozone input occurs at different regions for GHG- (midlatitudes) and ODS-changes (high latitudes); and (b) stratospheric ozone is more efficiently mixed towards lower tropospheric levels in the case of ODS changes, whereas tropospheric ozone loss rates grow when GHG concentrations rise. The comparison between the moderate RCP6.0 and the extreme RCP8.5 emission scenarios reveals that the annual global OMF trend is smaller in the moderate scenario, but the resulting change in the contribution of ozone with stratospheric origin (O3s) to ozone in the troposphere is of comparable magnitude in both scenarios. This is due to the larger tropospheric ozone precursor emissions and hence ozone production in the RCP8.5 scenario

Ozone-Climate-Feedbacks in Simulations with the Chemistry-Climate Model EMAC

Die Entwicklung von stratosphärischem Ozon (O3) in der Zukunft ist von großem Interesse für Menschen, da die Intensität der solaren UV-Strahlung am Erdboden hauptsächlich von der Menge der O3-Moleküle in der Atmosphäre bestimmt wird. In der Vergangenheit führten die zunehmenden Emissionen von Ozon zerstörenden Substanzen (ODSs) zu einem globalem Ozonverlust in der Stratosphäre. Während die Emissionen von ODSs im Montrealer Protokoll erfolgreich reguliert wurden, steigen die anthropogenen Emissionen von Treibhausgasen (GHGs) jedoch stetig an. Die Prozesse, die O3 in der Stratosphäre kontrollieren, werden nicht nur von veränderten ODS-Konzentrationen modifiziert, sondern auch von der Zunahme der Treibhausgaskonzentrationen und dem damit einhergehenden Klimawandel. Mit dem Rückgang der ODS-Belastung in der Zukunft wird folglich der Einfluss des Klimawandels auf die Ozonentwicklung an Bedeutung gewinnen. In der vorliegenden Arbeit werden diese Ozon-Klima-Wechselwirkungen in Vergangenheit und Zukunft anhand von Simulationen mit dem Klima-Chemie-Modell EMAC untersucht. Durch die Trennung der Anteile von ODS- und GHG-Änderungen wird gezeigt, dass die O3-Änderungen in der Vergangenheit von der Chemie und insbesondere von der ODS-Zunahme dominiert sind. Zudem wird deutlich, dass die GHG-Zunahme ebenfalls einen Einfluss auf die Gasphasenchemie hat, jedoch kann keine Veränderung der polaren heterogenen Ozonchemie im Winter/Frühling identifiziert werden. In den Tropen tragen Änderungen im Transport wesentlich zur Ozonänderung bei. Hier führt ein verstärkter Export von lokal produziertem O3 zu einer Ozonabnahme. In der Südpolarregion wird der enorme chemische Ozonverlust durch einen verstärkten Import aus den mittleren Breiten im Frühjahr teilweise kompensiert. Am Ende des 21. Jahrhunderts wird ein beschleunigter Rückgang der Halogenbelastung in der Stratosphäre gefunden, der durch ein verstärktes, GHG bedingtes Aufsteigen in den Tropen und eine reduzierte Freisetzungsrate aus den Quellgasen verursacht wird. In der oberen Stratosphäre entsteht dadurch eine Abnahme der Effektivität im ClOx-Zyklus, die in derselben Größenordnung liegt wie die Abnahme der Effektivität im Chapman-Abbau durch die stratosphärische Abkühlung. Außerdem wird gezeigt, dass die GHG-Zunahme nicht zu einer erhöhten Effektivität des NOx-Zyklus im Vergleich zum Jahr 2000 führt. Hingegen wird durch Änderungen im HOx-Zyklus in der unteren Stratosphäre und unteren Mesosphäre ein negativer Beitrag zur relativen Ozonänderung gefunden. Die Signatur einer verstärkten stratosphärischen Zirkulation in der Zukunft ist in den Änderungen des Ozontransports enthalten. So bewirkt der Transport eine Ozonabnahme in den Tropen und eine Zunahme in der Nordpolarregion. Die GHG bedingten Änderungen in den chemischen und dynamischen Prozessen führt in den Extratropen zu einer beschleunigten Rückkehr von Ozon zu historischen Werten. In den Tropen verhindert der Transport eine Rückkehr bis zum Jahr 2100.The evolution of stratospheric ozone (O3) in the future is of major interest for human beings as the intensity of solar UV radiation on the surface is mainly determined by the amount of O3 molecules in the atmospheric column. In the past the increasing emissions of ozone depleting substances (ODSs) have led to a global destruction of stratospheric O3. While the emissions of ODSs have been successfully regulated in the Montreal Protocol and its amendments, the anthropogenic emissions of greenhouse gases (GHGs) are steadily increasing. For the prediction of future O3 it is essential to understand the different processes controlling the O3 abundance in the stratosphere, e.g. the chemistry and the transport of O3. As these processes can be modified by changing emissions of ODSs as well as by the increasing concentrations of GHGs in the atmosphere, the impact of climate change on the evolution of O3 will become more important in the future. In the present study the interactions between climate change and O3 in the recent past and the future are investigated by performing and anlaysing simulations with the chemistry- climate model EMAC. By separating the attributions from ODSs and GHGs as well as from chemistry and transport, it is found that in the past the O3 changes are dominated by the chemistry, especially by the changes in ODSs. The GHG increase also affects the catalytic O3 loss cycles due to temperature and compositions changes, but no impact on the heterogeneous chemistry in the polar winter/spring can be found. Ozone changes due to transport are important in the tropics as an increased export of locally produced O3 causes an additional O3 decrease. In the southern polar stratosphere the large chemical O3 loss is partially compensated by an increased import of O3 from the mid- latitudes. At the end of the 21st century an accelerated decrease of stratospheric chlorine and bromine concentrations is found due to a reduced release fraction from the source gases along with increasing GHGs. In the upper stratosphere this leads to a positive contribution from the ClOx cycle to O3 change in the same magnitude as stratospheric cooling leads to a positive contribution from the Chapman cycle. Furthermore, it is found that the increased emissions of GHGs will not lead to an O3 decrease due to the catalytic NOx cycle with respect to the year 2000. The effectivity of the HOx cycle is increased in the lower stratosphere and lower mesosphere, but decreased in-between. The signature of an intensified stratospheric circulation due to increased GHGs is found in the change of O3 transport with O3 decrease in the tropics and increase in the northern polar region. These GHG-induced processes lead to an earlier return of extratropical O3 to historical values than it is expected by the estimated decline in ODSs due to the restricted emissions. In the tropics the increased transport will avoid the return to previous levels until 2100

Chemical contribution to future tropical ozone change in the lower stratosphere

The future evolution of tropical ozone in a changing climate is investigated by analysing time slice simulations made with the chemistry–climate model EMAC. Between the present and the end of the 21st century a significant increase in ozone is found globally for the upper stratosphere and the extratropical lower stratosphere, while in the tropical lower stratosphere ozone decreases significantly by up to 30%. Previous studies have shown that this decrease is connected to changes in tropical upwelling. Here the dominant role of transport for the future ozone decrease is confirmed, but it is found that in addition changes in chemical ozone production and destruction do contribute to the ozone changes in the tropical lower stratosphere. Between 50 and 30 hPa the dynamically induced ozone decrease of up to 22% is amplified by 11–19% due to a reduced ozone production. This is counteracted by a decrease in the ozone loss causing an ozone increase by 15–28%. At 70 hPa the large ozone decrease due to transport (−52%) is reduced by an enhanced photochemical ozone production (+28%) but slightly increased (−5%) due to an enhanced ozone loss. It is found that the increase in the ozone production in the lowermost stratosphere is mainly due to a transport induced decrease in the overlying ozone column while at higher altitudes the ozone production decreases as a consequence of a chemically induced increase in the overlying ozone column. The ozone increase that is attributed to changes in ozone loss between 50 and 30 hPa is mainly caused by a slowing of the ClOx and NOx loss cycles. The enhanced ozone destruction below 70 hPa can be attributed to an increased efficiency of the HOx loss cycle. The role of ozone transport in determining the ozone trend in this region is found to depend on the changes in the net production as a reduced net production also reduces the amount of ozone that can be transported within an air parcel

Greenhouse Gas and Ozone Radiative Forcing for the RCP8.5 Scenario with the EMAC Chemistry-Climate Model

One metric to show the impact of changes in the human and natural emissions of climate active agents on the earth's climate system is the concept of radiative forcing (RF). It quantifies the energy imbalance that occurs when an imposed perturbation, for instance by a change in the mixing ratio of a greenhouse gas (GHG), takes place. There are several ways to calculate the radiative forcing, which differ in the included feedback processes. The instantaneous RF is calculated with fixed atmospheric background conditions to get the net change in the radiative flux ”instantaneously”, while the adjusted RF allows the temperature profile to adjust to a new equilibrium in the stratosphere, with the tropospheric temperature profile remaining unchanged. The goal of this study is to derive the RF of the troposphere due to projected future changes of ozone and GHGs by applying the new sub-model RAD in the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. The instantaneous and adjusted RFs for the GHGs as well as for ozone (tropospheric and stratospheric changes separated) have been calculated. The analyses are based on the reference period 1865 (10 years from a time slice simulation) and the RF is derived for every decade from 1965 (1960–1969) until 2095 (2090–2099). The ozone and GHG concentrations, needed as input for the RF calculations, are taken from a transient simulations of the EMAC chemistry-climate model. The simulations extend from 1960 to 2100, and include forcings by GHGs following the specifications of the RCP8.5 scenario, and by ozone depleting substances following the specification of the adjusted A1 scenario. Sea- surface temperatures and sea-ice concentrations were prescribed from the Max Planck Institute ocean model (MPIOM)

Impact of rising greenhouse gas concentrations on future tropical ozone and UV exposure

Future projections of tropical total column ozone (TCO) are challenging, as its evolution is affected not only by the expected decline of ozone depleting substances but also by the uncertain increase of greenhouse gas (GHG) emissions. To assess the range of tropical TCO projections, we analyze simulations with a chemistry-climate model forced by three different GHG scenarios (Representative Concentration Pathway (RCP) 4.5, RCP6.0, and RCP8.5). We find that tropical TCO will be lower by the end of the 21st century compared to the 1960s in all scenarios with the largest decrease in the medium RCP6.0 scenario. Uncertainties of the projected TCO changes arise from the magnitude of stratospheric column decrease and tropospheric ozone increase which both strongly vary between the scenarios. In the three scenario simulations the stratospheric column decrease is not compensated by the increase in tropospheric ozone. The concomitant increase in harmful ultraviolet irradiance reaches up to 15% in specific regions in the RCP6.0 scenario

Earth System Chemistry integrated Modelling (ESCiMo) with the Modular Earth Submodel System (MESSy) version 2.51

Three types of reference simulations, as recommended by the Chemistry–Climate Model Initiative (CCMI), have been performed with version 2.51 of the European Centre for Medium-Range Weather Forecasts – Hamburg (ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model: hindcast simulations (1950–2011), hindcast simulations with specified dynamics (1979–2013), i.e. nudged towards ERA-Interim reanalysis data, and combined hindcast and projection simulations (1950–2100). The manuscript summarizes the updates of the model system and details the different model set-ups used, including the on-line calculated diagnostics. Simulations have been performed with two different nudging set-ups, with and without interactive tropospheric aerosol, and with and without a coupled ocean model. Two different vertical resolutions have been applied. The on-line calculated sources and sinks of reactive species are quantified and a first evaluation of the simulation results from a global perspective is provided as a quality check of the data. The focus is on the intercomparison of the different model set-ups. The simulation data will become publicly available via CCMI and the Climate and Environmental Retrieval and Archive (CERA) database of the German Climate Computing Centre (DKRZ). This manuscript is intended to serve as an extensive reference for further analyses of the Earth System Chemistry integrated Modelling (ESCiMo) simulations

Mitochondria! Regulation of the 26S Proteasome

The proteasome is the main proteolytic system for targeted protein degradation in the cell and is fine-tuned according to cellular needs. Here, we demonstrate that mitochondrial dysfunction and concomitant metabolic reprogramming of the tricarboxylic acid (TCA) cycle reduce the assembly and activity of the 26S proteasome. Both mitochondrial mutations in respiratory complex I and treatment with the anti-diabetic drug metformin impair 26S proteasome activity. Defective 26S assembly is reversible and can be overcome by supplementation of aspartate or pyruvate. This metabolic regulation of 26S activity involves specific regulation of proteasome assembly factors via the mTORC1 pathway. Of note, reducing 26S activity by metformin confers increased resistance toward the proteasome inhibitor bortezomib, which is reversible upon pyruvate supplementation. Our study uncovers unexpected consequences of defective mitochondrial metabolism for proteasomal protein degradation in the cell, which has important pathophysiological and therapeutic implications