scholarly journals Characterising the seasonal and geographical variability in tropospheric ozone, stratospheric influence and recent changes

2019 ◽  
Vol 19 (6) ◽  
pp. 3589-3620 ◽  
Author(s):  
Ryan S. Williams ◽  
Michaela I. Hegglin ◽  
Brian J. Kerridge ◽  
Patrick Jöckel ◽  
Barry G. Latter ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Data Availability ◽  
Ozone Production ◽  
Upper Troposphere ◽  
The World

Abstract. The stratospheric contribution to tropospheric ozone (O3) has been a subject of much debate in recent decades but is known to have an important influence. Recent improvements in diagnostic and modelling tools provide new evidence that the stratosphere has a much larger influence than previously thought. This study aims to characterise the seasonal and geographical distribution of tropospheric ozone, its variability, and its changes and provide quantification of the stratospheric influence on these measures. To this end, we evaluate hindcast specified-dynamics chemistry–climate model (CCM) simulations from the European Centre for Medium-Range Weather Forecasts – Hamburg (ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model and the Canadian Middle Atmosphere Model (CMAM), as contributed to the International Global Atmospheric Chemistry – Stratosphere-troposphere Processes And their Role in Climate (IGAC-SPARC) (IGAC–SPARC) Chemistry Climate Model Initiative (CCMI) activity, together with satellite observations from the Ozone Monitoring Instrument (OMI) and ozone-sonde profile measurements from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) over a period of concurrent data availability (2005–2010). An overall positive, seasonally dependent bias in 1000–450 hPa (∼0–5.5 km) sub-column ozone is found for EMAC, ranging from 2 to 8 Dobson units (DU), whereas CMAM is found to be in closer agreement with the observations, although with substantial seasonal and regional variation in the sign and magnitude of the bias (∼±4 DU). Although the application of OMI averaging kernels (AKs) improves agreement with model estimates from both EMAC and CMAM as expected, comparisons with ozone-sondes indicate a positive ozone bias in the lower stratosphere in CMAM, together with a negative bias in the troposphere resulting from a likely underestimation of photochemical ozone production. This has ramifications for diagnosing the level of model–measurement agreement. Model variability is found to be more similar in magnitude to that implied from ozone-sondes in comparison with OMI, which has significantly larger variability. Noting the overall consistency of the CCMs, the influence of the model chemistry schemes and internal dynamics is discussed in relation to the inter-model differences found. In particular, it is inferred that CMAM simulates a faster and shallower Brewer–Dobson circulation (BDC) compared to both EMAC and observational estimates, which has implications for the distribution and magnitude of the downward flux of stratospheric ozone over the most recent climatological period (1980–2010). Nonetheless, it is shown that the stratospheric influence on tropospheric ozone is significant and is estimated to exceed 50 % in the wintertime extratropics, even in the lower troposphere. Finally, long-term changes in the CCM ozone tracers are calculated for different seasons. An overall statistically significant increase in tropospheric ozone is found across much of the world but particularly in the Northern Hemisphere and in the middle to upper troposphere, where the increase is on the order of 4–6 ppbv (5 %–10 %) between 1980–1989 and 2001–2010. Our model study implies that attribution from stratosphere–troposphere exchange (STE) to such ozone changes ranges from 25 % to 30 % at the surface to as much as 50 %–80 % in the upper troposphere–lower stratosphere (UTLS) across some regions of the world, including western Eurasia, eastern North America, the South Pacific and the southern Indian Ocean. These findings highlight the importance of a well-resolved stratosphere in simulations of tropospheric ozone and its implications for the radiative forcing, air quality and oxidation capacity of the troposphere.

scholarly journals Characterising the Seasonal and Geographical Variability of Tropospheric Ozone, Stratospheric Influence and Recent Changes

2018 ◽  
Author(s):  
Ryan S. Williams ◽  
Michaela I. Hegglin ◽  
Brian J. Kerridge ◽  
Patrick Jöckel ◽  
Barry G. Latter ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Lower Troposphere ◽  
Data Availability ◽  
Ozone Production ◽  
Upper Troposphere ◽  
The World

Abstract. The stratospheric contribution to tropospheric ozone (O3) has been a subject of much debate in recent decades, but is known to have an important influence. Recent improvements in diagnostic and modelling tools provide new evidence that the stratosphere has a much larger influence than previously thought. This study aims to characterise the seasonal and geographical distribution of tropospheric ozone, its variability and changes, and provide quantification of the stratospheric influence on these measures. To this end, we evaluate hindcast specified dynamics chemistry-climate model (CCM) simulations from the ECHAM/MESSy Atmospheric Chemistry (EMAC) model and the Canadian Middle Atmosphere Model (CMAM), as contributed to the IGAC/SPARC Chemistry Climate Model Initiative (CCMI) activity, together with satellite observations from the Ozone Monitoring Instrument (OMI) and ozonesonde profile measurements from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) over a period of concurrent data availability (2005–2010). An overall positive, seasonally dependent bias in 1000–450 hPa (~ 0–5.5 km) subcolumn ozone is found for EMAC, ranging from 2–8 Dobson Units (DU), whereas CMAM is found to be in closer agreement with the observations, although with substantial seasonal and regional variation in the sign and magnitude of the bias (~ −4 to +4 DU). Although the application of OMI averaging kernels (AKs) improves agreement with model estimates from both EMAC and CMAM as expected, comparisons with ozonesondes indicate a positive ozone bias in the lower stratosphere in CMAM, together with an underestimation of photochemical ozone production (negative bias) in the troposphere. Model variability is found to be more similar in magnitude to that implied from ozonesondes, in comparison with OMI which has significantly larger variability. Noting the overall consistency of the CCMs, the influence of the model chemistry schemes and internal dynamics is discussed in relation to the inter-model differences found. In particular, it is shown that CMAM simulates a faster and shallower Brewer-Dobson Circulation (BDC) relative to both EMAC and observational estimates, which has implications for the distribution and magnitude of the downward flux of stratospheric ozone, over the most recent climatological period (1980–2010). Nonetheless, it is shown that the stratospheric influence on tropospheric ozone is larger than previously thought and is estimated to exceed 50 % in the wintertime extratropics, even in the lower troposphere. Finally, long term changes in the CCM ozone tracers are calculated for different seasons between 1980–89 and 2001–10. An overall statistically significant increase in tropospheric ozone is found across much of the world, but particularly in the Northern Hemisphere and in the middle to upper troposphere, where the increase is on the order of 4–6 ppbv (5–10 %). Our model study implies that attribution from stratosphere-troposphere exchange (STE) to such ozone changes ranges from 25–30 % at the surface to as much as 50–80 % in the upper troposphere-lower stratosphere (UTLS) across many regions of the world. These findings highlight the importance of a well-resolved stratosphere in simulations of tropospheric ozone and its implications for the radiative forcing, air quality and oxidation capacity of the troposphere.

scholarly journals Tropospheric ozone in CMIP6 simulations

2021 ◽  
Vol 21 (5) ◽  
pp. 4187-4218
Author(s):  
Paul T. Griffiths ◽  
Lee T. Murray ◽  
Guang Zeng ◽  
Youngsub Matthew Shin ◽  
N. Luke Abraham ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Tropospheric Ozone ◽  
Climate Models ◽  
Climate Model ◽  
Decadal Variability ◽  
Stratospheric Ozone ◽  
Ozone Production ◽  
Model Intercomparison ◽  
Chemical Production ◽  
Intercomparison Project

Abstract. The evolution of tropospheric ozone from 1850 to 2100 has been studied using data from Phase 6 of the Coupled Model Intercomparison Project (CMIP6). We evaluate long-term changes using coupled atmosphere–ocean chemistry–climate models, focusing on the CMIP Historical and ScenarioMIP ssp370 experiments, for which detailed tropospheric-ozone diagnostics were archived. The model ensemble has been evaluated against a suite of surface, sonde and satellite observations of the past several decades and found to reproduce well the salient spatial, seasonal and decadal variability and trends. The multi-model mean tropospheric-ozone burden increases from 247 ± 36 Tg in 1850 to a mean value of 356 ± 31 Tg for the period 2005–2014, an increase of 44 %. Modelled present-day values agree well with previous determinations (ACCENT: 336 ± 27 Tg; Atmospheric Chemistry and Climate Model Intercomparison Project, ACCMIP: 337 ± 23 Tg; Tropospheric Ozone Assessment Report, TOAR: 340 ± 34 Tg). In the ssp370 experiments, the ozone burden increases to 416 ± 35 Tg by 2100. The ozone budget has been examined over the same period using lumped ozone production (PO3) and loss (LO3) diagnostics. Both ozone production and chemical loss terms increase steadily over the period 1850 to 2100, with net chemical production (PO3-LO3) reaching a maximum around the year 2000. The residual term, which contains contributions from stratosphere–troposphere transport reaches a minimum around the same time before recovering in the 21st century, while dry deposition increases steadily over the period 1850–2100. Differences between the model residual terms are explained in terms of variation in tropopause height and stratospheric ozone burden.

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.

scholarly journals Ozone database in support of CMIP5 simulations: results and corresponding radiative forcing

2011 ◽  
Vol 11 (4) ◽  
pp. 10875-10933 ◽  
Author(s):  
I. Cionni ◽  
V. Eyring ◽  
J. F. Lamarque ◽  
W. J. Randel ◽  
D. S. Stevenson ◽  
...  
Keyword(s):  
Time Series ◽  
Ozone Depletion ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Satellite Observations ◽  
High Latitudes ◽  
The Future ◽  
Column Ozone

Abstract. A continuous tropospheric and stratospheric vertically resolved ozone time series, from 1850 to 2099, has been generated to be used as forcing in global climate models that do not include interactive chemistry. A multiple linear regression analysis of SAGE I+II satellite observations and polar ozonesonde measurements is used for the stratospheric zonal mean dataset during the well-observed period from 1979 to 2009. In addition to terms describing the mean annual cycle, the regression includes terms representing equivalent effective stratospheric chlorine (EESC) and the 11-yr solar cycle variability. The EESC regression fit coefficients, together with pre-1979 EESC values, are used to extrapolate the stratospheric ozone time series backward to 1850. While a similar procedure could be used to extrapolate into the future, coupled chemistry climate model (CCM) simulations indicate that future stratospheric ozone abundances are likely to be significantly affected by climate change, and capturing such effects through a regression model approach is not feasible. Therefore, the stratospheric ozone dataset is extended into the future (merged in 2009) with multi-model mean projections from 13 CCMs that performed a simulation until 2099 under the SRES (Special Report on Emission Scenarios) A1B greenhouse gas scenario and the A1 adjusted halogen scenario in the second round of the Chemistry-Climate Model Validation (CCMVal-2) Activity. The stratospheric zonal mean ozone time series is merged with a three-dimensional tropospheric data set extracted from simulations of the past by two CCMs (CAM3.5 and PUCCINI) and of the future by one CCM (CAM3.5). The future tropospheric ozone time series continues the historical CAM3.5 simulation until 2099 following the four different Representative Concentration Pathways (RCPs). Generally good agreement is found between the historical segment of the ozone database and satellite observations, although it should be noted that total column ozone is overestimated in the southern polar latitudes during spring and tropospheric column ozone is slightly underestimated. Vertical profiles of tropospheric ozone are broadly consistent with ozonesondes and in-situ measurements, with some deviations in regions of biomass burning. The tropospheric ozone radiative forcing (RF) from the 1850s to the 2000s is 0.23 W m−2, lower than previous results. The lower value is mainly due to (i) a smaller increase in biomass burning emissions; (ii) a larger influence of stratospheric ozone depletion on upper tropospheric ozone at high southern latitudes; and possibly (iii) a larger influence of clouds (which act to reduce the net forcing) compared to previous radiative forcing calculations. Over the same period, decreases in stratospheric ozone, mainly at high latitudes, produce a RF of −0.08 W m−2, which is more negative than the central Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) value of −0.05 W m−2, but which is within the stated range of −0.15 to +0.05 W m−2. The more negative value is explained by the fact that the regression model simulates significant ozone depletion prior to 1979, in line with the increase in EESC and as confirmed by CCMs, while the AR4 assumed no change in stratospheric RF prior to 1979. A negative RF of similar magnitude persists into the future, although its location shifts from high latitudes to the tropics. This shift is due to increases in polar stratospheric ozone, but decreases in tropical lower stratospheric ozone, related to a strengthening of the Brewer-Dobson circulation, particularly through the latter half of the 21st century. Differences in trends in tropospheric ozone among the four RCPs are mainly driven by different methane concentrations, resulting in a range of tropospheric ozone RFs between 0.4 and 0.1 W m−2 by 2100. The ozone dataset described here has been released for the Coupled Model Intercomparison Project (CMIP5) model simulations in netCDF Climate and Forecast (CF) Metadata Convention at the PCMDI website (http://cmip-pcmdi.llnl.gov/).

scholarly journals Evaluation of ACCMIP outgoing longwave radiation from tropospheric ozone using TES satellite observations

2013 ◽  
Vol 13 (8) ◽  
pp. 4057-4072 ◽  
Author(s):  
K. W. Bowman ◽  
D. T. Shindell ◽  
H. M. Worden ◽  
J.F. Lamarque ◽  
P. J. Young ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Tropospheric Ozone ◽  
Outgoing Longwave Radiation ◽  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Longwave Radiation ◽  
Satellite Observations ◽  
Ensemble Mean ◽  
High Bias

Abstract. We use simultaneous observations of tropospheric ozone and outgoing longwave radiation (OLR) sensitivity to tropospheric ozone from the Tropospheric Emission Spectrometer (TES) to evaluate model tropospheric ozone and its effect on OLR simulated by a suite of chemistry-climate models that participated in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP). The ensemble mean of ACCMIP models show a persistent but modest tropospheric ozone low bias (5–20 ppb) in the Southern Hemisphere (SH) and modest high bias (5–10 ppb) in the Northern Hemisphere (NH) relative to TES ozone for 2005–2010. These ozone biases have a significant impact on the OLR. Using TES instantaneous radiative kernels (IRK), we show that the ACCMIP ensemble mean tropospheric ozone low bias leads up to 120 mW m−2 OLR high bias locally but zonally compensating errors reduce the global OLR high bias to 39 ± 41 m Wm−2 relative to TES data. We show that there is a correlation (R2 = 0.59) between the magnitude of the ACCMIP OLR bias and the deviation of the ACCMIP preindustrial to present day (1750–2010) ozone radiative forcing (RF) from the ensemble ozone RF mean. However, this correlation is driven primarily by models whose absolute OLR bias from tropospheric ozone exceeds 100 m Wm−2. Removing these models leads to a mean ozone radiative forcing of 394 ± 42 m Wm−2. The mean is about the same and the standard deviation is about 30% lower than an ensemble ozone RF of 384 ± 60 m Wm−2 derived from 14 of the 16 ACCMIP models reported in a companion ACCMIP study. These results point towards a profitable direction of combining satellite observations and chemistry-climate model simulations to reduce uncertainty in ozone radiative forcing.

Water vapour in the Upper Troposphere and Lower Stratosphere (UTLS): A new vertically resolved dataset from limb and nadir satellite observations

2020 ◽  
Author(s):  
Hao Ye ◽  
Michaela Hegglin ◽  
Martina Krämer ◽  
Christian Rolf ◽  
Alexandra Laeng ◽  
...  
Keyword(s):  
Climate Change ◽  
Water Vapour ◽  
Radiative Forcing ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Chemical Properties ◽  
Upper Troposphere ◽  
Data Record ◽  
Tropopause Region ◽  
Quality Water

&lt;p&gt;Water vapour in the upper troposphere and lower stratosphere (UTLS) has a significant impact both on the radiative and chemical properties of the atmosphere. Reliable water vapour observations are essential for the evaluation of the accuracy of UTLS water vapour from model simulations, and thereafter of the contribution to the global radiative forcing and climate change. Limb-viewing and nadir satellites provide high quality water vapour observations above the lower stratosphere and below the upper troposphere, respectively, but show large uncertainties in the tropopause region.&lt;span&gt;&amp;#160; &lt;/span&gt;Within the ESA Water Vapour Climate Change Initiative, we have developed a new scheme to optimally estimate water vapour profiles in the UTLS and in particular across the tropopause, by merging observations from a set of limb and nadir satellites from 2010 to 2014. The new data record of vertically resolved water vapour is validated against the aircraft in-situ water vapour observations from the JULIA database and frostpoint hydrometer records from WAVAS. Furthermore, the new data record is used to evaluate the UTLS water vapour distribution and interannual variations from chemistry-climate model (CCM) simulations and the ERA-5 reanalysis.&lt;/p&gt;

Investigation of strongly enhanced methane Part I: Chemical feedbacks and rapid adjustments.

2020 ◽  
Author(s):  
Franziska Winterstein ◽  
Patrick Jöckel ◽  
Martin Dameris ◽  
Michael Ponater ◽  
Fabian Tanalski ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
Climate Model ◽  
Numerical Study ◽  
Stratospheric Ozone ◽  
Lower Boundary ◽  
Tropospheric Chemistry ◽  
Substantial Part ◽  
Mixing Ratios ◽  
The Impact

&lt;p&gt;Methane (CH&lt;sub&gt;4&lt;/sub&gt;) is the second most important greenhouse gas, which atmospheric concentration is influenced by human activities and currently on a sharp rise. We present a study with numerical simulations using a Chemistry-Climate-Model (CCM), which are performed to assess possible consequences of strongly enhanced CH&lt;sub&gt;4&lt;/sub&gt; concentrations in the Earth's atmosphere for the climate.&lt;/p&gt;&lt;p&gt;Our analysis includes experiments with 2xCH&lt;sub&gt;4&lt;/sub&gt; and 5xCH&lt;sub&gt;4&lt;/sub&gt; present day (2010) lower boundary mixing ratios using the CCM EMAC. The simulations are conducted with prescribed oceanic conditions, mimicking present day tropospheric temperatures as its changes are largely suppressed. By doing so we are able to investigate the quasi-instantaneous chemical impact on the atmosphere. We find that the massive increase in CH&lt;sub&gt;4&lt;/sub&gt; strongly influences the tropospheric chemistry by reducing the OH abundance and thereby extending the tropospheric CH&lt;sub&gt;4&lt;/sub&gt; lifetime as well as the residence time of other chemical pollutants. The region above the tropopause is impacted by a substantial rise in stratospheric water vapor (SWV). The stratospheric ozone (O&lt;sub&gt;3&lt;/sub&gt;) column increases overall, but SWV induced stratospheric cooling also leads to enhanced ozone depletion in the Antarctic lower stratosphere. Regional&amp;#160; patterns of ozone change are affected by modification of stratospheric dynamics, i.e. increased tropical up-welling and stronger meridional transport&amp;#160; towards the polar regions. We calculate the net radiative impact (RI) of the 2xCH&lt;sub&gt;4&lt;/sub&gt; experiment to be 0.69 W m&lt;sup&gt;-2&lt;/sup&gt; and for the 5xCH&lt;sub&gt;4&lt;/sub&gt; experiment to be 1.79 W m&lt;sup&gt;-2&lt;/sup&gt;. A substantial part of the RI is contributed by chemically induced O&lt;sub&gt;3&lt;/sub&gt; and SWV changes, in line with previous radiative forcing estimates and is for the first time splitted and spatially asigned to its chemical contributors.&lt;/p&gt;&lt;p&gt;This numerical study using a CCM with prescibed oceanic conditions shows the rapid responses to significantly enhanced CH&lt;sub&gt;4&lt;/sub&gt; mixing ratios, which is the first step towards investigating the impact of possible strong future CH&lt;sub&gt;4&lt;/sub&gt; emissions on atmospheric chemistry and its feedback on climate.&lt;/p&gt;

scholarly journals Radiative forcing since preindustrial times due to ozone change in the troposphere and the lower stratosphere

2006 ◽  
Vol 6 (3) ◽  
pp. 575-599 ◽  
Author(s):  
M. Gauss ◽  
G. Myhre ◽  
I. S. A. Isaksen ◽  
V. Grewe ◽  
G. Pitari ◽  
...  
Keyword(s):  
Climate Change ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Climate Models ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Transport Models ◽  
Stratospheric Chemistry ◽  
Ozone Column ◽  
Global Mean

Abstract. Changes in atmospheric ozone have occurred since the preindustrial era as a result of increasing anthropogenic emissions. Within ACCENT, a European Network of Excellence, ozone changes between 1850 and 2000 are assessed for the troposphere and the lower stratosphere (up to 30 km) by a variety of seven chemistry-climate models and three chemical transport models. The modeled ozone changes are taken as input for detailed calculations of radiative forcing. When only changes in chemistry are considered (constant climate) the modeled global-mean tropospheric ozone column increase since preindustrial times ranges from 7.9 DU to 13.8 DU among the ten participating models, while the stratospheric column reduction lies between 14.1 DU and 28.6 DU in the models considering stratospheric chemistry. The resulting radiative forcing is strongly dependent on the location and altitude of the modeled ozone change and varies between 0.25 Wm−2 and 0.45 Wm−2 due to ozone change in the troposphere and −0.123 Wm−2 and +0.066 Wm−2 due to the stratospheric ozone change. Changes in ozone and other greenhouse gases since preindustrial times have altered climate. Six out of the ten participating models have performed an additional calculation taking into account both chemical and climate change. In most models the isolated effect of climate change is an enhancement of the tropospheric ozone column increase, while the stratospheric reduction becomes slightly less severe. In the three climate-chemistry models with detailed tropospheric and stratospheric chemistry the inclusion of climate change increases the resulting radiative forcing due to tropospheric ozone change by up to 0.10 Wm−2, while the radiative forcing due to stratospheric ozone change is reduced by up to 0.034 Wm−2. Considering tropospheric and stratospheric change combined, the total ozone column change is negative while the resulting net radiative forcing is positive.

scholarly journals Sulfate geoengineering impact on methane transport and lifetime: results from the Geoengineering Model Intercomparison Project (GeoMIP)

2017 ◽  
Vol 17 (18) ◽  
pp. 11209-11226 ◽  
Author(s):  
Daniele Visioni ◽  
Giovanni Pitari ◽  
Valentina Aquila ◽  
Simone Tilmes ◽  
Irene Cionni ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Radiation Absorption ◽  
Coupled Models ◽  
Upper Troposphere ◽  
Aerosol Scattering ◽  
Intercomparison Project ◽  
Planetary Albedo ◽  
The Tropics

Abstract. Sulfate geoengineering (SG), made by sustained injection of SO2 in the tropical lower stratosphere, may impact the CH4 abundance through several photochemical mechanisms affecting tropospheric OH and hence the methane lifetime. (a) The reflection of incoming solar radiation increases the planetary albedo and cools the surface, with a tropospheric H2O decrease. (b) The tropospheric UV budget is upset by the additional aerosol scattering and stratospheric ozone changes: the net effect is meridionally not uniform, with a net decrease in the tropics, thus producing less tropospheric O(1D). (c) The extratropical downwelling motion from the lower stratosphere tends to increase the sulfate aerosol surface area density available for heterogeneous chemical reactions in the mid-to-upper troposphere, thus reducing the amount of NOx and O3 production. (d) The tropical lower stratosphere is warmed by solar and planetary radiation absorption by the aerosols. The heating rate perturbation is highly latitude dependent, producing a stronger meridional component of the Brewer–Dobson circulation. The net effect on tropospheric OH due to the enhanced stratosphere–troposphere exchange may be positive or negative depending on the net result of different superimposed species perturbations (CH4, NOy, O3, SO4) in the extratropical upper troposphere and lower stratosphere (UTLS). In addition, the atmospheric stabilization resulting from the tropospheric cooling and lower stratospheric warming favors an additional decrease of the UTLS extratropical CH4 by lowering the horizontal eddy mixing. Two climate–chemistry coupled models are used to explore the above radiative, chemical and dynamical mechanisms affecting CH4 transport and lifetime (ULAQ-CCM and GEOSCCM). The CH4 lifetime may become significantly longer (by approximately 16 %) with a sustained injection of 8 Tg-SO2 yr−1 starting in the year 2020, which implies an increase of tropospheric CH4 (200 ppbv) and a positive indirect radiative forcing of sulfate geoengineering due to CH4 changes (+0.10 W m−2 in the 2040–2049 decade and +0.15 W m−2 in the 2060–2069 decade).

scholarly journals Implication of extreme atmospheric methane concentrations for chemistry-climate connections

2019 ◽  
Author(s):  
Franziska Winterstein ◽  
Fabian Tanalski ◽  
Patrick Jöckel ◽  
Martin Dameris ◽  
Michael Ponater
Keyword(s):  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
Climate Model ◽  
Numerical Study ◽  
Stratospheric Ozone ◽  
Tropospheric Chemistry ◽  
Substantial Part ◽  
Atmospheric Concentration ◽  
Regional Patterns ◽  
The Impact

Abstract. Methane (CH4) is the second most important greenhouse gas, which atmospheric concentration is influenced by human activities. In this study, numerical simulations with a chemistry-climate model (CCM) are performed aiming to assess possible consequences of significantly enhanced CH4 concentrations in the Earth's atmosphere for the climate. We analyze experiments with 2xCH4 and 5xCH4 present day (2010) mixing ratio and its quasi-instantaneous chemical impact on the atmosphere. The massive increase in CH4 strongly influences the tropospheric chemistry by reducing the hydroxyl radical (OH) abundance and thereby extending the CH4 lifetime as well as the residence time of other chemical pollutants. The region above the tropopause is impacted by a substantial rise in stratospheric water vapor (SWV). The stratospheric ozone (O3) column increases overall, but SWV induced stratospheric cooling also leads to a enhanced ozone depletion in the Antarctic lower stratosphere. Regional patterns of ozone change are affected by modification of stratospheric dynamics, i.e. increased tropical up-welling and stronger meridional transport towards the polar regions. We calculate the net radiative impact (RI) of the 2xCH4 experiment to be 0.69 W/m2 and for the 5xCH4 experiment to be 1.79 W/m2. A substantial part of the RI is contributed by chemically induced O3 and SWV changes, in line with previous radiative forcing estimates. To our knowledge this is the first numerical study using a CCM with respect to two/fivefold CH4 concentrations and it is therefore an overdue analysis as it emphasizes the impact of possible strong future CH4 emissions on atmospheric chemistry and its feedback on climate.

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