Slow feedbacks resulting from strongly enhanced atmospheric methane mixing ratios in a chemistry–climate model with mixed-layer ocean

Abstract. In a previous study the quasi-instantaneous chemical impacts (rapid adjustments) of strongly enhanced methane (CH4) mixing ratios have been analysed. However, to quantify the influence of the respective slow climate feedbacks on the chemical composition it is necessary to include the radiation-driven temperature feedback. Therefore, we perform sensitivity simulations with doubled and quintupled present-day (year 2010) CH4 mixing ratios with the chemistry–climate model EMAC (European Centre for Medium-Range Weather Forecasts, Hamburg version – Modular Earth Submodel System (ECHAM/MESSy) Atmospheric Chemistry) and include in a novel set-up a mixed-layer ocean model to account for tropospheric warming. Strong increases in CH4 lead to a reduction in the hydroxyl radical in the troposphere, thereby extending the CH4 lifetime. Slow climate feedbacks counteract this reduction in the hydroxyl radical through increases in tropospheric water vapour and ozone, thereby dampening the extension of CH4 lifetime in comparison with the quasi-instantaneous response. Changes in the stratospheric circulation evolve clearly with the warming of the troposphere. The Brewer–Dobson circulation strengthens, affecting the response of trace gases, such as ozone, water vapour and CH4 in the stratosphere, and also causing stratospheric temperature changes. In the middle and upper stratosphere, the increase in stratospheric water vapour is reduced with respect to the quasi-instantaneous response. We find that this difference cannot be explained by the response of the cold point and the associated water vapour entry values but by a weaker strengthening of the in situ source of water vapour through CH4 oxidation. However, in the lower stratosphere water vapour increases more strongly when tropospheric warming is accounted for, enlarging its overall radiative impact. The response of the stratosphere adjusted temperatures driven by slow climate feedbacks is dominated by these increases in stratospheric water vapour as well as strongly decreased ozone mixing ratios above the tropical tropopause, which result from enhanced tropical upwelling. While rapid radiative adjustments from ozone and stratospheric water vapour make an essential contribution to the effective CH4 radiative forcing, the radiative impact of the respective slow feedbacks is rather moderate. In line with this, the climate sensitivity from CH4 changes in this chemistry–climate model set-up is not significantly different from the climate sensitivity in carbon-dioxide-driven simulations, provided that the CH4 effective radiative forcing includes the rapid adjustments from ozone and stratospheric water vapour changes.

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Effects of Strongly Enhanced Atmospheric Methane Concentrations in a Fully Coupled Chemistry-Climate Model

10.5194/acp-2020-519 ◽

2020 ◽

Author(s):

Laura Stecher ◽

Franziska Winterstein ◽

Martin Dameris ◽

Patrick Jöckel ◽

Michael Ponater ◽

...

Keyword(s):

Hydroxyl Radical ◽

Water Vapour ◽

Climate Sensitivity ◽

Radiative Forcing ◽

Climate Model ◽

Atmospheric Methane ◽

Climate Feedbacks ◽

Mixing Ratios ◽

Radiative Impact ◽

Stratospheric Water Vapour

Abstract. In a previous study the quasi-instantaneous chemical impacts (rapid adjustments) of strongly enhanced methane (CH4) mixing ratios have been analyzed. However, to quantify the influence of the respective slow climate feedbacks on the chemical composition it is necessary to include the radiation driven temperature feedback. Therefore, we perform sensitivity simulations with doubled and fivefold present-day (year 2010) CH4 mixing ratios with the chemistry-climate model EMAC and include in a novel set-up a mixed layer ocean model to account for tropospheric warming. We find that the slow climate feedbacks counteract the reduction of the hydroxyl radical in the troposphere, which is caused by the strongly enhanced CH4 mixing ratios. Thereby also the resulting prolongation of the tropospheric CH4 lifetime is weakened compared to the quasi-instantaneous response considered previously. Changes in the stratospheric circulation evolve clearly with the warming of the troposphere. The Brewer-Dobson circulation strengthens, affecting the response of trace gases, such as ozone, water vapour and CH4 in the stratosphere, and also causing stratospheric temperature changes. In the middle and upper stratosphere, the increase of stratospheric water vapour is reduced with respect to the quasi-instantaneous response. Weaker increases of the hydroxyl radical cause the chemical depletion of CH4 to be less strongly enhanced and thus the in situ source of stratospheric water vapour as well. However, in the lower stratosphere water vapour increases more strongly when tropospheric warming is accounted for enlarging its overall radiative impact. The response of the stratospheric adjusted temperatures driven by slow climate feedbacks is dominated by these increases of stratospheric water vapour, as well as strongly decreased ozone mixing ratios above the tropical tropopause, which result from enhanced tropical upwelling. While rapid radiative adjustments from ozone and stratospheric water vapour make an essential contribution to the effective CH4 radiative forcing, the radiative impact of the respective slow feedbacks is rather moderate. In line with this, the climate sensitivity from CH4 changes in this chemistry-climate model setup is not significantly different from the climate sensitivity in carbon dioxide-driven simulations, provided that the CH4 effective radiative forcing includes the rapid adjustments from ozone and stratospheric water vapour changes.

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The role of methane in projections of 21st century stratospheric water vapour

10.5194/acp-2016-545 ◽

2016 ◽

Author(s):

Laura Revell ◽

Andrea Stenke ◽

Eugene Rozanov ◽

William Ball ◽

Stefan Lossow ◽

...

Keyword(s):

Water Vapour ◽

Methane Oxidation ◽

21St Century ◽

Radiative Forcing ◽

Lower Stratosphere ◽

Climate Model ◽

Radiative Balance ◽

Canonical Representative ◽

Cold Point ◽

Stratospheric Water Vapour

Abstract. Stratospheric water vapour (SWV) is an important component of the Earth's atmosphere as it affects both radiative balance and the chemistry of the atmosphere. Key processes driving changes in SWV through the 21st century include dehydration of air masses transiting the cold-point tropopause (CPT) and methane oxidation. Increasing surface temperatures may strengthen the Brewer-Dobson circulation, such that more methane is transported into the stratosphere where it can be oxidised to SWV. We use a chemistry-climate model to simulate changes in SWV through the 21st century following the four canonical Representative Concentration Pathways (RCPs). Furthermore, we quantify the contribution that methane oxidation makes to SWV following each of the RCPs. The methane contribution to SWV maximises in the upper stratosphere, however modelled SWV trends are found to be driven predominantly by warming of the CPT and strengthening of the Brewer-Dobson circulation rather than by increasing methane oxidation. SWV changes by −5 % to 60 % (depending on the location in the atmosphere and emissions scenario) and increases in the lower stratosphere in all RCPs through the 21st century. Because the lower stratosphere is where water vapour radiative forcing maximises, SWV's influence on surface climate is also expected to increase through the 21st century.

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Long-term changes in stratospheric water vapour and its implications for climate

10.5194/egusphere-egu2020-8874 ◽

2020 ◽

Author(s):

Michaela I. Hegglin

Keyword(s):

Water Vapour ◽

Radiative Forcing ◽

Climate Model ◽

Climate Data ◽

Theoretical Understanding ◽

Radiative Balance ◽

Surface Climate ◽

Long Term Changes ◽

Stratospheric Water Vapour

Water vapour is the most important natural greenhouse gas in the atmosphere and provides a positive feedback to the climate forcing from carbon dioxide. Water vapour is also the source of hydroxyl (OH) which controls the lifetime of shorter-lived pollutants and long-lived greenhouse gases. Despite the importance of water vapour to chemistry and the radiative balance of the atmosphere, its observed long-term changes in the stratosphere are not well understood, and may even conflict with the theoretical understanding of its drivers.&#160;I here present a new climate data record of stratospheric water vapour developed within the ESA Water Vapour Climate Change Initiative and discuss recent changes in stratospheric water vapour concentrations in the light of earlier observational studies, modelling results from the SPARC Chemistry-Climate Model Initiative, and our theoretical understanding of its drivers. In addition, the radiative forcing of surface climate and inferred changes in the Brewer-Dobson Circulation will be highlighted.&#160;

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Investigation of strongly enhanced methane Part II: Slow climate feedbacks.

10.5194/egusphere-egu2020-9852 ◽

2020 ◽

Author(s):

Laura Stecher ◽

Franziska Winterstein ◽

Martin Dameris ◽

Patrick Jöckel ◽

Michael Ponater

Keyword(s):

Climate Model ◽

Lower Boundary ◽

Tropospheric Temperature ◽

Climate Feedbacks ◽

Climatic Impact ◽

Stratospheric Water Vapor ◽

Boundary Mixing ◽

Mixing Ratios ◽

Show Evidence ◽

Set Up

Methane (CH4) is the second most important anthropogenic greenhouse gas and its atmospheric abundance is rising rapidly at the moment (e.g. Nisbet et al., 2019).&#160;We assess the effects of doubled and fivefold present-day (2010) CH4 lower boundary mixing ratios on the basis of sensitivity simulations with the chemistry-climate model EMAC. As a follow-up on Winterstein et al. (2019) we investigate slow adjustments by applying a mixed layer ocean (MLO) model instead of prescribed oceanic conditions. In the simulations with prescribed oceanic conditions, tropospheric temperature changes are largely suppressed, while with MLO tropospheric temperatures adjust to the forcing. In the present study we compare the changes in the MLO sensitivity simulations to the sensitivity simulations with prescribed oceanic conditions (Winterstein et al., 2019). Comparing the responses of these two sets of sensitivity simulations separates rapid adjustments and the effects of slow climate feedbacks associated with tropospheric warming.The chemical interactions in the stratosphere in the MLO set-up (slow adjustments) compare in general well with the results of Winterstein et al. (2019) (rapid adjustments). The increase of stratospheric water vapor is albeit 5 % (15 %) points weaker in the MLO doubling (fivefolding) experiment compared to the doubling (fivefolding) experiment with prescribed oceanic conditions in line with a weaker increase of stratospheric OH. Stronger O3 decrease and CH4 increase in the lowermost tropical stratosphere in the MLO sensitivity simulations compared to the sensitivity simulations with prescribed oceanic conditions indicate a more distinct strengthening of tropical up-welling due to tropospheric warming in the MLO set-up. The MLO simulations also show evidence of a strengthening of the Brewer-Dobson Circulation. When separating the quasi-instantaneous chemically induced O3 response from the O3 response pattern in the MLO set-up, the O3 response to slow climate feedbacks remains. This pattern is consistent with the O3 response to slow climate feedbacks induced by increases of CO2.This first of its kind study shows the climatic impact of strongly enhanced CH4 mixing ratios and how the slow climate response of tropospheric warming potentially damp instantaneous chemical feedbacks.

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Stratospheric water vapour and high climate sensitivity in a version of the HadSM3 climate model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-6241-2010 ◽

2010 ◽

Vol 10 (3) ◽

pp. 6241-6255 ◽

Cited By ~ 1

Author(s):

M. M. Joshi ◽

M. J. Webb ◽

A. C. Maycock ◽

M. Collins

Keyword(s):

Water Vapour ◽

Climate Sensitivity ◽

Climate Model ◽

Temperature Response ◽

Ensemble Member ◽

Intergovernmental Panel ◽

Individual Parameter ◽

Humidity Change ◽

Hadley Centre ◽

Stratospheric Water Vapour

Abstract. It has been shown previously that one member of the Met Office Hadley Centre single-parameter perturbed physics ensemble – the so-called "low entrainment parameter" member – has a much higher climate sensitivity than other individual parameter perturbations. Here we show that the concentration of stratospheric water vapour in this member is over three times higher than observations, and, more importantly for climate sensitivity, increases significantly when climate warms. The large surface temperature response of this ensemble member is more consistent with a feedback associated with the stratospheric humidity change, rather than high clouds as has been previously suggested. The direct relationship between the bias in the control state (elevated stratospheric humidity) and the cause of the high climate sensitivity (a further increase in stratospheric humidity) lends further doubt as to the realism of this particular integration. This, together with other evidence, lowers the likelihood that the climate system's physical sensitivity might be significantly higher than the likely upper range quoted in the Intergovernmental Panel on Climate Change's fourth assessment report.

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The role of methane in projections of 21st century stratospheric water vapour

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-13067-2016 ◽

2016 ◽

Vol 16 (20) ◽

pp. 13067-13080 ◽

Cited By ~ 12

Author(s):

Laura E. Revell ◽

Andrea Stenke ◽

Eugene Rozanov ◽

William Ball ◽

Stefan Lossow ◽

...

Keyword(s):

Water Vapour ◽

Methane Oxidation ◽

21St Century ◽

Radiative Forcing ◽

Lower Stratosphere ◽

Climate Model ◽

Radiative Balance ◽

Canonical Representative ◽

Cold Point ◽

Stratospheric Water Vapour

Abstract. Stratospheric water vapour (SWV) is an important component of the Earth's atmosphere as it affects both radiative balance and the chemistry of the atmosphere. Key processes driving changes in SWV include dehydration of air masses transiting the cold-point tropopause (CPT) and methane oxidation. We use a chemistry–climate model to simulate changes in SWV through the 21st century following the four canonical representative concentration pathways (RCPs). Furthermore, we quantify the contribution that methane oxidation makes to SWV following each of the RCPs. Although the methane contribution to SWV maximizes in the upper stratosphere, modelled SWV trends are found to be driven predominantly by warming of the CPT rather than by increasing methane oxidation. SWV changes by −5 to 60 % (depending on the location in the atmosphere and emissions scenario) and increases in the lower stratosphere in all RCPs through the 21st century. Because the lower stratosphere is where water vapour radiative forcing maximizes, SWV's influence on surface climate is also expected to increase through the 21st century.

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Stratospheric water vapour and high climate sensitivity in a version of the HadSM3 climate model

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-7161-2010 ◽

2010 ◽

Vol 10 (15) ◽

pp. 7161-7167 ◽

Cited By ~ 15

Author(s):

M. M. Joshi ◽

M. J. Webb ◽

A. C. Maycock ◽

M. Collins

Keyword(s):

Water Vapour ◽

Climate Sensitivity ◽

Climate Model ◽

Temperature Response ◽

Ensemble Member ◽

Intergovernmental Panel ◽

Individual Parameter ◽

Humidity Change ◽

Hadley Centre ◽

Stratospheric Water Vapour

Abstract. It has been shown previously that one member of the Met Office Hadley Centre single-parameter perturbed physics ensemble – the so-called "low entrainment parameter" member – has a much higher climate sensitivity than other individual parameter perturbations. Here we show that the concentration of stratospheric water vapour in this member is over three times higher than observations, and, more importantly for climate sensitivity, increases significantly when climate warms. The large surface temperature response of this ensemble member is more consistent with stratospheric humidity change, rather than upper tropospheric clouds as has been previously suggested. The direct relationship between the bias in the control state (elevated stratospheric humidity) and the cause of the high climate sensitivity (a further increase in stratospheric humidity) lends further doubt as to the realism of this particular integration. This, together with other evidence, lowers the likelihood that the climate system's physical sensitivity is significantly higher than the likely upper range quoted in the Intergovernmental Panel on Climate Change's Fourth Assessment Report.

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Simulation of the isotopic composition of stratospheric water vapour – Part 1: Description and evaluation of the EMAC model

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-5537-2015 ◽

2015 ◽

Vol 15 (10) ◽

pp. 5537-5555 ◽

Cited By ~ 8

Author(s):

R. Eichinger ◽

P. Jöckel ◽

S. Brinkop ◽

M. Werner ◽

S. Lossow

Keyword(s):

Isotopic Composition ◽

Water Vapour ◽

General Circulation ◽

Climate Model ◽

Hydrological Cycle ◽

Circulation Model ◽

Isotope Ratios ◽

Physical Fractionation ◽

Water Isotopologues ◽

Stratospheric Water Vapour

Abstract. This modelling study aims at an improved understanding of the processes that determine the water vapour budget in the stratosphere by means of the investigation of water isotope ratios. An additional (and separate from the actual) hydrological cycle has been introduced into the chemistry–climate model EMAC, including the water isotopologues HDO and H218O and their physical fractionation processes. Additionally an explicit computation of the contribution of methane oxidation to H2O and HDO has been incorporated. The model expansions allow detailed analyses of water vapour and its isotope ratio with respect to deuterium throughout the stratosphere and in the transition region to the troposphere. In order to assure the correct representation of the water isotopologues in the model's hydrological cycle, the expanded system has been evaluated in several steps. The physical fractionation effects have been evaluated by comparison of the simulated isotopic composition of precipitation with measurements from a ground-based network (GNIP) and with the results from the isotopologue-enabled general circulation model ECHAM5-wiso. The model's representation of the chemical HDO precursor CH3D in the stratosphere has been confirmed by a comparison with chemical transport models (1-D, CHEM2D) and measurements from radiosonde flights. Finally, the simulated stratospheric HDO and the isotopic composition of water vapour have been evaluated, with respect to retrievals from three different satellite instruments (MIPAS, ACE-FTS, SMR). Discrepancies in stratospheric water vapour isotope ratios between two of the three satellite retrievals can now partly be explained.

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Historical greenhouse gas concentrations

10.5194/gmd-2016-169 ◽

2016 ◽

Cited By ~ 6

Author(s):

Malte Meinshausen ◽

Elisabeth Vogel ◽

Alexander Nauels ◽

Katja Lorbacher ◽

Nicolai Meinshausen ◽

...

Keyword(s):

Climate Change ◽

Greenhouse Gas ◽

Radiative Forcing ◽

Sulfur Hexafluoride ◽

Climate Model ◽

Future Climate Change ◽

Large Set ◽

Mixing Ratios ◽

Surface Mixing ◽

Cooling Effects

Abstract. Atmospheric greenhouse gas concentrations are at unprecedented, record-high levels compared to pre-industrial reconstructions over the last 800,000 years. Those elevated greenhouse gas concentrations warm the planet and together with net cooling effects by aerosols, they are the reason of observed climate change over the past 150 years. An accurate representation of those concentrations is hence important to understand and model recent and future climate change. So far, community efforts to create composite datasets with seasonal and latitudinal information have focused on marine boundary layer conditions and recent trends since 1980s. Here, we provide consolidated data sets of historical atmospheric (volume) mixing ratios of 43 greenhouse gases specifically for the purpose of climate model runs. The presented datasets are based on AGAGE and NOAA networks and a large set of literature studies. In contrast to previous intercomparisons, the new datasets are latitudinally resolved, and include seasonality over the period between year 0 to 2014. We assimilate data for CO2, methane (CH4) and nitrous oxide (N2O), 5 chlorofluorocarbons (CFCs), 3 hydrochlorofluorocarbons (HCFCs), 16 hydrofluorocarbons (HFCs), 3 halons, methyl bromide (CH3Br), 3 perfluorocarbons (PFCs), sulfur hexafluoride (SF6), nitrogen triflouride (NF3) and sulfuryl fluoride (SO2F2). We estimate 1850 annual and global mean surface mixing ratios of CO2 at 284.3 ppmv, CH4 at 808.2 ppbv and N2O at 273.0 ppbv and quantify the seasonal and hemispheric gradients of surface mixing ratios. Compared to earlier intercomparisons, the stronger implied radiative forcing in the northern hemisphere winter (due to the latitudinal gradient and seasonality) may help to improve the skill of climate models to reproduce past climate and thereby reduce uncertainty in future projections.

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Instantaneous longwave radiative impact of ozone: an application on IASI/MetOp observations

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-21177-2015 ◽

2015 ◽

Vol 15 (15) ◽

pp. 21177-21218

Author(s):

S. Doniki ◽

D. Hurtmans ◽

L. Clarisse ◽

C. Clerbaux ◽

H. M. Worden ◽

...

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Longwave Radiation ◽

Polar Regions ◽

Direct Integration ◽

Direct Integration Method ◽

Radiative Impact ◽

Ozone Variation ◽

Atmospheric Sounding ◽

Stratospheric Intrusions

Abstract. Ozone is an important greenhouse gas in terms of anthropogenic radiative forcing (RF). RF calculations for ozone were until recently entirely model based and significant discrepancies were reported due to different model characteristics. However, new instantaneous radiative kernels (IRKs) calculated from hyperspectral thermal IR satellites have been able to help adjudicate between different climate model RF calculations. IRKs are defined as the sensitivity of the outgoing longwave radiation (OLR) flux with respect to the ozone vertical distribution in the full 9.6 μm band. Previous methods applied to measurements from the Tropospheric Emission Spectrometer (TES) on Aura, rely on an anisotropy approximation for the angular integration. In this paper, we present a more accurate but more computationally expensive method to calculate these kernels. The method of direct integration is based on similar principles with the anisotropy approximation, but deals more precisely with the integration of the Jacobians. We describe both methods and highlight their differences with respect to the IRKs and the ozone longwave radiative effect (LWRE), i.e. the radiative impact in OLR due to absorption by ozone, for both tropospheric and total columns, from measurements of the Infrared Atmospheric Sounding Interferometer (IASI) onboard MetOp-A. Biases between the two methods vary from −25 to +20 % for the LWRE, depending on the viewing angle. These biases point to the inadequacy of the anisotropy method, especially at nadir, suggesting that the TES derived LWRE are biased low by around 25 % and that chemistry-climate model OLR biases with respect to TES are underestimated. In this paper we also exploit the sampling performance of IASI to obtain first daily global distributions of the LWRE, for 12 days (the 15th of each month) in 2011, calculated with the direct integration method. We show that the temporal variation of global and latitudinal averages of the LWRE shows patterns which are controlled by changes in the surface temperature and ozone variation due to specific processes, such as the ozone hole in the Polar regions and stratospheric intrusions into the troposphere.

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