Aerosol absorption in global models from AeroCom phase III

Abstract. Aerosol-induced absorption of shortwave radiation can modify the climate through local atmospheric heating, which affects lapse rates, precipitation, and cloud formation. Presently, the total amount of aerosol absorption is poorly constrained, and the main absorbing aerosol species (black carbon (BC), organic aerosols (OA), and mineral dust) are diversely quantified in global climate models. As part of the third phase of the Aerosol Comparisons between Observations and Models (AeroCom) intercomparison initiative (AeroCom phase III), we here document the distribution and magnitude of aerosol absorption in current global aerosol models and quantify the sources of intermodel spread, highlighting the difficulties of attributing absorption to different species. In total, 15 models have provided total present-day absorption at 550 nm (using year 2010 emissions), 11 of which have provided absorption per absorbing species. The multi-model global annual mean total absorption aerosol optical depth (AAOD) is 0.0054 (0.0020 to 0.0098; 550 nm), with the range given as the minimum and maximum model values. This is 28 % higher compared to the 0.0042 (0.0021 to 0.0076) multi-model mean in AeroCom phase II (using year 2000 emissions), but the difference is within 1 standard deviation, which, in this study, is 0.0023 (0.0019 in Phase II). Of the summed component AAOD, 60 % (range 36 %–84 %) is estimated to be due to BC, 31 % (12 %–49 %) is due to dust, and 11 % (0 %–24 %) is due to OA; however, the components are not independent in terms of their absorbing efficiency. In models with internal mixtures of absorbing aerosols, a major challenge is the lack of a common and simple method to attribute absorption to the different absorbing species. Therefore, when possible, the models with internally mixed aerosols in the present study have performed simulations using the same method for estimating absorption due to BC, OA, and dust, namely by removing it and comparing runs with and without the absorbing species. We discuss the challenges of attributing absorption to different species; we compare burden, refractive indices, and density; and we contrast models with internal mixing to models with external mixing. The model mean BC mass absorption coefficient (MAC) value is 10.1 (3.1 to 17.7) m2 g−1 (550 nm), and the model mean BC AAOD is 0.0030 (0.0007 to 0.0077). The difference in lifetime (and burden) in the models explains as much of the BC AAOD spread as the difference in BC MAC values. The difference in the spectral dependency between the models is striking. Several models have an absorption Ångstrøm exponent (AAE) close to 1, which likely is too low given current knowledge of spectral aerosol optical properties. Most models do not account for brown carbon and underestimate the spectral dependency for OA.

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Aerosol absorption in global models from AeroCom Phase III

10.5194/acp-2021-51 ◽

2021 ◽

Author(s):

Maria Sand ◽

Bjørn H. Samset ◽

Gunnar Myhre ◽

Jonas Gliß ◽

Susanne E. Bauer ◽

...

Keyword(s):

Phase Ii ◽

Climate Models ◽

Global Climate ◽

Global Climate Models ◽

Phase Iii ◽

Shortwave Radiation ◽

Cloud Formation ◽

Individual Species ◽

Aerosol Absorption ◽

The Difference

Abstract. Aerosol induced absorption of shortwave radiation can modify the climate through local atmospheric heating, which affects lapse rates, precipitation, and cloud formation. Presently, the total amount of such absorption is poorly constrained, and the main absorbing aerosol species (black carbon (BC), organic aerosols (OA) and mineral dust are diversely quantified in global climate models. As part of the third phase of the AeroCom model intercomparison initiative (AeroCom Phase III) we here document the distribution and magnitude of aerosol absorption in current global aerosols models and quantify the sources of intermodel spread. 15 models have provided total present-day absorption at 550 nm, and 11 of these models have provided absorption per absorbing species. The multi-model global annual mean total absorption aerosol optical depth (AAOD) is 0.0056 [0.0020 to 0.0097] (550 nm) with range given as the minimum and maximum model values. This is 31 % higher compared to 0.0042 [0.0021 to 0.0076] in AeroCom Phase II, but the difference/increase is within one standard deviation which in this study is 0.0024 (0.0019 in Phase II). The models show considerable diversity in absorption. Of the summed component AAOD, 57 % (range 34–84 %) is estimated to be due to BC, 30 % (12–49 %) is due to dust and 14 % (4–49 %) is due to OA, however the components are not entirely independent. Models with the lowest BC absorption tend to have the highest OA absorption, which illustrates the complexities in separating the species. The geographical distribution of AAOD between the models varies greatly and reflects the spread in global mean AAOD and in the relative contributions from individual species. The optical properties of BC are recognized as a large source of uncertainty. The model mean BC mass absorption coefficient (MACBC) value is 9.8 [3.1 to 16.6] m2 g−1 (550 nm). Observed MAC values from various locations range between 5.7–20.0 m2 g−1 (550 nm). Compared to retrievals of AAOD and absorption Ångstrøm exponent (AAE) from ground-based observations from the Aerosol Robotic Network (AERONET) stations, most models underestimate total AAOD and AAE. The difference in spectral dependency between the models is striking.

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Can a coupled meteorology–chemistry model reproduce the historical trend in aerosol direct radiative effects over the Northern Hemisphere?

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-9997-2015 ◽

2015 ◽

Vol 15 (17) ◽

pp. 9997-10018 ◽

Cited By ~ 24

Author(s):

J. Xing ◽

R. Mathur ◽

J. Pleim ◽

C. Hogrefe ◽

C.-M. Gan ◽

...

Keyword(s):

Northern Hemisphere ◽

Climate Models ◽

Global Climate ◽

Eastern China ◽

Global Climate Models ◽

Shortwave Radiation ◽

Historical Trend ◽

Clear Sky ◽

Northern Pacific ◽

Central Atlantic

Abstract. The ability of a coupled meteorology–chemistry model, i.e., Weather Research and Forecast and Community Multiscale Air Quality (WRF-CMAQ), to reproduce the historical trend in aerosol optical depth (AOD) and clear-sky shortwave radiation (SWR) over the Northern Hemisphere has been evaluated through a comparison of 21-year simulated results with observation-derived records from 1990 to 2010. Six satellite-retrieved AOD products including AVHRR, TOMS, SeaWiFS, MISR, MODIS-Terra and MODIS-Aqua as well as long-term historical records from 11 AERONET sites were used for the comparison of AOD trends. Clear-sky SWR products derived by CERES at both the top of atmosphere (TOA) and surface as well as surface SWR data derived from seven SURFRAD sites were used for the comparison of trends in SWR. The model successfully captured increasing AOD trends along with the corresponding increased TOA SWR (upwelling) and decreased surface SWR (downwelling) in both eastern China and the northern Pacific. The model also captured declining AOD trends along with the corresponding decreased TOA SWR (upwelling) and increased surface SWR (downwelling) in the eastern US, Europe and the northern Atlantic for the period of 2000–2010. However, the model underestimated the AOD over regions with substantial natural dust aerosol contributions, such as the Sahara Desert, Arabian Desert, central Atlantic and northern Indian Ocean. Estimates of the aerosol direct radiative effect (DRE) at TOA are comparable with those derived by measurements. Compared to global climate models (GCMs), the model exhibits better estimates of surface-aerosol direct radiative efficiency (Eτ). However, surface-DRE tends to be underestimated due to the underestimated AOD in land and dust regions. Further investigation of TOA-Eτ estimations as well as the dust module used for estimates of windblown-dust emissions is needed.

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Comparison of south Atlantic aerosol direct radiative effect overclouds from SCIAMACHY, POLDER and OMI/MODIS

10.5194/acp-2019-545 ◽

2019 ◽

Cited By ~ 2

Author(s):

Martin de Graaf ◽

Ruben Schulte ◽

Fanny Peers ◽

Fabien Waquet ◽

L. Gijsbert Tilstra ◽

...

Keyword(s):

Biomass Burning ◽

Climate Models ◽

Global Climate ◽

Global Climate Models ◽

Radiation Budget ◽

Radiative Effect ◽

The South ◽

East Atlantic ◽

The Difference ◽

Aerosol Effects

Abstract. The Direct Radiative Effect (DRE) of aerosols above clouds has been found to be significant over the south-east Atlantic Ocean during the African biomass burning season due to elevated smoke layers absorbing radiation above the cloud deck. So far, global climate models have been unsuccessful in reproducing the high DRE values measured by various satellite instruments. Meanwhile, the radiative effects by aerosols have been identified as the largest source of uncertainty in global climate models. In this paper, three independent satellite datasets of DRE during the biomass burning season in 2006 are compared to constrain the south-east Atlantic radiation budget. The DRE of aerosols above clouds is derived from the spectrometer SCIAMACHY, the polarimeter POLDER, and from collocated measurements by the spectrometer OMI and imager MODIS. All three confirm the high DRE values during the biomass season, underlining the relevance of local aerosol effects. Differences between the instruments can be attributed mainly to sampling issues. When these are accounted for, the remaining differences can be completely explained by the higher cloud optical thickness derived from POLDER compared to the other instruments. Additionally, a neglect of AOT at SWIR wavelengths in the method used for SCIAMACHY and OMI/MODIS accounts for 26 % of the difference between POLDER and OMI/MODIS DRE.

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Cloud, precipitation and radiation responses to large perturbations in global dimethyl sulfide

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-10177-2018 ◽

2018 ◽

Vol 18 (14) ◽

pp. 10177-10198 ◽

Cited By ~ 8

Author(s):

Sonya L. Fiddes ◽

Matthew T. Woodhouse ◽

Zebedee Nicholls ◽

Todd P. Lane ◽

Robyn Schofield

Keyword(s):

Large Scale ◽

Climate Models ◽

Dimethyl Sulfide ◽

Cloud Fraction ◽

Global Climate Models ◽

Radiation Budget ◽

Shortwave Radiation ◽

Stratiform Cloud ◽

Aerosol Emission ◽

Low Cloud

Abstract. Natural aerosol emission represents one of the largest uncertainties in our understanding of the radiation budget. Sulfur emitted by marine organisms, as dimethyl sulfide (DMS), constitutes one-fifth of the global sulfur budget and yet the distribution, fluxes and fate of DMS remain poorly constrained. This study evaluates the Australian Community Climate and Earth System Simulator (ACCESS) United Kingdom Chemistry and Aerosol (UKCA) model in terms of cloud fraction, radiation and precipitation, and then quantifies the role of DMS in the chemistry–climate system. We find that ACCESS-UKCA has similar cloud and radiation biases to other global climate models. By removing all DMS, or alternatively significantly enhancing marine DMS, we find a top of the atmosphere radiative effect of 1.7 and −1.4 W m−2 respectively. The largest responses to these DMS perturbations (removal/enhancement) are in stratiform cloud decks in the Southern Hemisphere's eastern ocean basins. These regions show significant differences in low cloud (-9/+6 %), surface incoming shortwave radiation (+7/-5 W m−2) and large-scale rainfall (+15/-10 %). We demonstrate a precipitation suppression effect of DMS-derived aerosol in stratiform cloud deck regions due to DMS, coupled with an increase in low cloud fraction. The difference in low cloud fraction is an example of the aerosol lifetime effect. Globally, we find a sensitivity of temperature to annual DMS flux of 0.027 and 0.019 K per Tg yr−1 of sulfur, respectively. Other areas of low cloud formation, such as the Southern Ocean and stratiform cloud decks in the Northern Hemisphere, have a relatively weak response to DMS perturbations. We highlight the need for greater understanding of the DMS–climate cycle within the context of uncertainties and biases of climate models as well as those of DMS–climate observations.

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Randomized Phase II Trial Comparing GA101 (Obinutuzumab) with Rituximab in Patients with Relapsed CD20 Indolent B-Cell Non-Hodgkin Lymphoma: Preliminary Analysis of the GAUSS Study

Blood ◽

10.1182/blood.v118.21.269.269 ◽

2011 ◽

Vol 118 (21) ◽

pp. 269-269 ◽

Cited By ~ 12

Author(s):

Laurie H. Sehn ◽

Andre Goy ◽

Fritz C. Offner ◽

Giovanni Martinelli ◽

Jonathan Friedberg ◽

...

Keyword(s):

Phase Ii ◽

Phase Ii Trial ◽

Early Time ◽

Response Rates ◽

Phase Iii ◽

Prognostic Features ◽

Efficacy Analysis ◽

Non Hodgkin Lymphoma ◽

Randomized Phase Ii ◽

The Difference

Abstract Abstract 269 Background: GA101 is the first type II glycoengineered CD20 monoclonal antibody in phase II/III clinical trials for CLL and NHL. In pre-clinical models GA101 mediated enhanced direct cell death and increased ADCC compared to other anti-CD20 antibodies. GA101 single-arm clinical studies have demonstrated responses in patients (pts) with relapsed/refractory NHL and CLL, but to date there have been no direct comparisons with rituximab. The aim of this randomized phase II trial was to compare efficacy and safety of monotherapy with GA101 versus rituximab in pts with relapsed indolent NHL. Study Design and Patients: Pts with relapsed indolent NHL requiring therapy who had demonstrated a prior response (CR/CRu or PR) to a rituximab-containing regimen lasting 6 months were eligible. A total of 175 pts (149 follicular (FL) and 26 non-follicular indolent NHL) stratified by histology were randomized 1:1 to receive 4 weekly infusions (Days 1, 8, 15, 22) of either GA101 (1000 mg, n87) or rituximab (375 mg/m2, n88). End of treatment response was assessed 2842 days after the last induction dose. Pts without evidence of progression following induction therapy received ongoing treatment with GA101 or rituximab every 2 months for up to 2 years at the same dose. The primary endpoint was overall response rate (ORR) in the FL population. Secondary endpoints included PFS, OS, and safety. Treatment arms were well balanced for standard prognostic features (age, ECOG PS, Ann Arbor stage, FLIPI risk score at initial diagnosis, LDH) and prior treatment characteristics. Pts in both arms had received a median of 2 prior lines of therapy (range: 17 GA101 arm; 16 rituximab arm) and 99 had received prior rituximab. At baseline, pts in the GA101 cohort had a larger volume of disease based on the median sum of product diameters; SPD GA101 cohort 2397 mm2(range 19229326 mm2) v SPD rituximab cohort 1934 mm2(range 25211255 mm2). Results: The primary efficacy analysis was conducted in the FL population at the end of induction. Based on investigator assessment, ORR for GA101 was 43.2 (32/74) v 38.7 (29/75) for rituximab. The difference in response rates was 4.6 (95 CI -12.0, 21.1). The CR/CRu rate in the GA101 arm was 10.8 v 6.7 for rituximab. At the time of analysis 28/149 pts had progressed, 15/74 on GA101 and 13/75 on rituximab. A central blinded radiology review (IRF) was performed to independently assess response. The difference in response rates by the IRF was 15.2 (95 CI -0.7, 31.2; ORR, GA101 v rituximab: 43.2 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} ${\scriptstyle \raisebox{1ex}{32$}\!\left/ \!\raisebox{-1ex}{$74$}\right.}\]$ \end{document}v 28.0 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} ${\scriptstyle \raisebox{1ex}{21$}\!\left/ \!\raisebox{-1ex}{$75$}\right.}\]$ \end{document}). In the overall population (FL non-follicular indolent NHL), the ORR as assessed by investigators was 43.2 (38/88) v 35.6 (31/87) and by the IRF was 42.0 (37/88) v 24.1 (21/87) for GA101 and rituximab, respectively. Safety was analyzed in the overall population. No new safety signals were observed in either arm. One patient in the rituximab arm died from cardio-pulmonary arrest and 1 patient in the GA101 arm died from pulmonary aspergillosis. More pts discontinued therapy during induction in the rituximab arm (7 pts v 4 GA101 pts). Discontinuations with GA101 occurred as a result of infusion related reactions (IRR, 3 pts) and orthostatic hypotension (1 pt). A greater number of pts in the rituximab arm experienced an SAE during the induction period (9 pts v 5 GA101 pts). SAEs in the GA101 arm occurred as a result of IRR (2 pts), febrile neutropenia (1 pt), pleural effusion (1 pt) and nephrolithiasis (1 pt). More pts in the GA101 arm reported IRRs (GA101 v rituximab: any grade, 72 v 49; grade 3/4, 11 v 5). IRRs were primarily seen during the first infusion and decreased in both frequency and severity with subsequent infusions. Other AEs (any grade) that occurred at a 5 higher incidence with GA101 included fatigue (23 v 17), cough (10 v 1), back pain (7 v 2), decreased appetite (7 v 2) and insomnia (5 v 0). Conclusions: Treatment with GA101 in pts with relapsed NHL resulted in higher response rates compared to rituximab as assessed by both investigators and the IRF at an early time point. GA101 was well tolerated, although a higher rate of IRRs was noted, the majority were grade 1/2 in severity and did not result in significant differences in treatment discontinuation. This is the first head to head trial of GA101 against rituximab and has demonstrated higher response rates without appreciable differences in safety. GA101 is under study in phase III trials in combination with chemotherapy. Disclosures: Sehn: Roche/Genentech: Consultancy, Honoraria, Research Funding. Goy:Roche/Genentech: Consultancy, Honoraria. Friedberg:Roche/Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees. Lasserre:Roche: Employment. Fine:Roche: Employment. Press:Roche/Genentech: Consultancy, Honoraria.

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Could the cloud cover in future climate models be improved by incorporating the role of sea spray in surface heat fluxes?

10.5194/egusphere-egu2020-6316 ◽

2020 ◽

Author(s):

Yajuan Song ◽

Fangli Qiao ◽

Qi Shu ◽

Jiping Liu ◽

Ying Bao ◽

...

Keyword(s):

Latent Heat ◽

Cloud Cover ◽

Climate Models ◽

Climate Model ◽

Global Climate ◽

Heat Fluxes ◽

Global Climate Models ◽

Shortwave Radiation ◽

Sea Spray ◽

Low Level

Accurate cloud cover and radiative effect simulation remains a long-standing challenge for global climate models (GCMs). The Southern Ocean (SO) cloud cover is substantially underestimated by most GCMs. Therefore, too much shortwave radiation is absorbed by oceans, which causes an overly warm sea surface temperature (SST) bias over the SO. For the first time, sea spray effects on latent and sensible heat fluxes are considered in a climate model. The most notable sea spray impacts on heat fluxes occur over the SO, with anomalous latent heat fluxes up to -7.74 W m-2. Enhanced latent heat release lead to SST cooling. In addition, more clouds are formed over the SO to reflect excessive downward shortwave radiation, especially low-level clouds at 1.51% increments. Our results provide a feasible solution to mitigate the lack of low-level clouds and overly warm SST biases over the SO in GCMs.

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Long-term variability of shortwave absorption under abrupt-4xCO2 climate forcing and its visible and near-IR contributions

10.5194/egusphere-egu2020-12529 ◽

2020 ◽

Author(s):

Maria Z. Hakuba ◽

Alejandro Bodas-Salcedo ◽

Graeme Stephens

Keyword(s):

Global Warming ◽

Near Infrared ◽

Climate Models ◽

Global Climate ◽

Global Climate Models ◽

Climate Forcing ◽

Shortwave Radiation ◽

Hemispheric Differences ◽

Climate Feedbacks

While ongoing global warming is largely the result of reduced outgoing longwave radiation (OLR), climate feedbacks associated with changes in atmospheric water vapor and surface albedo are expected to enhance the absorption of shortwave radiation (ASR) and to sustain global warming on centennial time scales beyond the OLR modulations. These feedbacks as well as positive cloud feedbacks reduce the reflected shortwave (SW) flux at the top-of-atmosphere (TOA) and are a result of scattering and absorbing processes that differ by their near-infrared (NIR) and visible (VIS) contributions. Since direct measurements of broadband NIR (~0.7-5 mm) and VIS (~0.2-0.7 mm) radiation flux do not exist, we utilize UKESM1 simulations to study SW, NIR, and VIS climate feedbacks under preindustrial and abrupt-4xCO2 climate forcing.Besides its global long-term behavior, the spatial variability and key physical controls of ASR are not well characterized either. A prominent example is the unexplained hemispheric symmetry in planetary albedo that is consistently missed by current global climate models yielding unrealistic precipitation and circulation patterns. Although energetically equivalent, the observed hemispheric albedos differ spectrally, reflecting the uneven distribution of clouds and land masses. We use the same UKESM1 simulations to contrast inter-hemispheric differences in SW, NIR and VIS, and their relation to changes in clouds, the gaseous atmosphere and surface properties to shed light on processes relevant to the present-day symmetry, model biases, and potential future changes.

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Uncertainty in Forced and Natural Arctic Solar Absorption Variations in CMIP6 Models

Journal of Climate ◽

10.1175/jcli-d-20-0244.1 ◽

2021 ◽

Vol 34 (3) ◽

pp. 931-948

Author(s):

Anne Sledd ◽

Tristan L’Ecuyer

Keyword(s):

Sea Ice ◽

Climate Models ◽

Global Climate ◽

Coupled Model ◽

Internal Variability ◽

Global Climate Models ◽

Shortwave Radiation ◽

The Arctic ◽

Solar Absorption ◽

Clear Sky

AbstractThe Arctic is rapidly changing, with increasingly dramatic sea ice loss and surface warming in recent decades. Shortwave radiation plays a key role in Arctic warming during summer months, and absorbed shortwave radiation has been increasing largely because of greater sea ice loss. Clouds can influence this ice–albedo feedback by modulating the amount of shortwave radiation incident on the Arctic Ocean. In turn, clouds impact the amount of time that must elapse before forced trends in Arctic shortwave absorption emerge from internal variability. This study determines whether the forced climate response of absorbed shortwave radiation in the Arctic has emerged in the modern satellite record and global climate models. From 18 years of satellite observations from CERES-EBAF, we find that recent declines in sea ice are large enough to produce a statistically significant trend (1.7 × 106 PJ or 3.9% per decade) in observed clear-sky absorbed shortwave radiation. However, clouds preclude any forced trends in all-sky absorption from emerging within the existing satellite record. Across 18 models from phase 6 of the Coupled Model Intercomparison Project (CMIP6), the predicted time to emergence of absorbed shortwave radiation trends varies from 8 to 39 and from 8 to 35 years for all-sky and clear-sky conditions, respectively, across two future scenarios. Furthermore, most models fail to reproduce the observed cloud delaying effect because of differences in internal variability. Contrary to observations, one-third of models suggest that clouds may reduce the time to emergence of absorbed shortwave trends relative to clear skies, an artifact that may be the result of inaccurate representations of cloud feedbacks.

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A Hybrid Cloud Regime Methodology Used to Evaluate Southern Ocean Cloud and Shortwave Radiation Errors in ACCESS

Journal of Climate ◽

10.1175/jcli-d-14-00846.1 ◽

2015 ◽

Vol 28 (15) ◽

pp. 6001-6018 ◽

Cited By ~ 15

Author(s):

Shannon Mason ◽

Jennifer K. Fletcher ◽

John M. Haynes ◽

Charmaine Franklin ◽

Alain Protat ◽

...

Keyword(s):

Southern Ocean ◽

Climate Models ◽

Global Climate ◽

Evaluation Studies ◽

Global Climate Models ◽

Shortwave Radiation ◽

Extratropical Cyclones ◽

Hybrid Cloud ◽

Cloud Parameterization ◽

Cloud Regimes

AbstractA deficit of shortwave cloud forcing over the Southern Ocean is persistent in many global climate models. Cloud regimes have been widely used in model evaluation studies to make a process-oriented diagnosis of cloud parameterization errors, but cloud regimes have some limitations in resolving both observed and simulated cloud behavior. A hybrid methodology is developed for identifying cloud regimes from observed and simulated cloud simultaneously.Through this methodology, 11 hybrid cloud regimes are identified in the ACCESS1.3 model for the high-latitude Southern Ocean. The hybrid cloud regimes resolve the features of observed cloud and characterize cloud errors in the model. The simulated properties of the hybrid cloud regimes, and their occurrence over the Southern Ocean and in the context of extratropical cyclones, are evaluated, and their contributions to the shortwave radiation errors are quantified.Three errors are identified: an overall deficit of cloud fraction, a tendency toward optically thin low and midtopped cloud, and an absence of a shallow frontal-type cloud at high latitudes and in the warm fronts of extratropical cyclones.To demonstrate the utility of the hybrid cloud regimes for the evaluation of changes to the model, the effects of selected changes to the model microphysics are investigated.

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LGM permafrost distribution: how well can the latest PMIP multi-model ensembles reconstruct?

Climate of the Past Discussions ◽

10.5194/cpd-9-1565-2013 ◽

2013 ◽

Vol 9 (2) ◽

pp. 1565-1597 ◽

Cited By ~ 1

Author(s):

K. Saito ◽

T. Sueyoshi ◽

S. Marchenko ◽

V. Romanovsky ◽

B. Otto-Bliesner ◽

...

Keyword(s):

Climate Models ◽

Global Climate ◽

Direct Method ◽

Surface Air Temperature ◽

Global Scale ◽

Global Climate Models ◽

Phase Iii ◽

Frozen Ground ◽

Soil Temperatures ◽

Model Ensembles

Abstract. Global-scale frozen ground distribution during the Last Glacial Maximum (LGM) was reconstructed using multi-model ensembles of global climate models, and then compared with evidence-based knowledge and earlier numerical results. Modeled soil temperatures, taken from Paleoclimate Modelling Intercomparison Project Phase III (PMIP3) simulations, were used to diagnose the subsurface thermal regime and determine underlying frozen ground types for the present-day (pre-industrial; 0 k) and the LGM (21 k). This direct method was then compared to the earlier indirect method, which categorizes the underlying frozen ground type from surface air temperature, applied to both the PMIP2 (phase II) and PMIP3 products. Both direct and indirect diagnoses for 0 k showed strong agreement with the present-day observation-based map, although the soil temperature ensemble showed a higher diversity among the models partly due to varying complexity of the implemented subsurface processes. The area of continuous permafrost estimated by the multi-model analysis was 25.6 million km2 for LGM, in contrast to 12.7 million km2 for the pre-industrial control, whereas seasonally, frozen ground increased from 22.5 million km2 to 32.6 million km2. These changes in area resulted mainly from a cooler climate at LGM, but other factors as well, such as the presence of huge land ice sheets and the consequent expansion of total land area due to sea-level change. LGM permafrost boundaries modeled by the PMIP3 ensemble-improved over those of the PMIP2 due to higher spatial resolutions and improved climatology-also compared better to previous knowledge derived from the geomorphological and geocryological evidences. Combinatorial applications of coupled climate models and detailed stand-alone physical-ecological models for the cold-region terrestrial, paleo-, and modern climates will advance our understanding of the functionality and variability of the frozen ground subsystem in the global eco-climate system.

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