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2022 ◽  
Author(s):  
Ilaria Crotti ◽  
Aurelien Quiquet ◽  
Amaelle Landais ◽  
Barbara Stenni ◽  
David Wilson ◽  
...  

Abstract The response of the East Antarctic Ice Sheet to past intervals of oceanic and atmospheric warming is still not well constrained but critical for understanding both past and future sea-level change. Furthermore, the ice sheet in the Wilkes Subglacial Basin, which is characterized by a reverse-sloping bed, appears to have undergone thinning and ice discharge events during recent decades. By combining new glaciological evidence on ice sheet elevation from the TALDICE ice core with offshore sedimentological records and ice sheet modelling experiments, we reconstruct the ice dynamics in the Wilkes Subglacial Basin over the past 350,000 years. Our results indicate that the Wilkes Subglacial Basin experienced an extensive retreat 330,000 years ago and a more limited retreat 125,000 years ago. These changes coincided with warmer Southern Ocean temperatures and elevated global mean sea level during those interglacial periods, confirming the sensitivity of the Wilkes Subglacial Basin ice sheet to ocean warming and its potential role in sea-level change.


2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Sarah-Anne Nicholson ◽  
Daniel B. Whitt ◽  
Ilker Fer ◽  
Marcel D. du Plessis ◽  
Alice D. Lebéhot ◽  
...  

AbstractThe subpolar Southern Ocean is a critical region where CO2 outgassing influences the global mean air-sea CO2 flux (FCO2). However, the processes controlling the outgassing remain elusive. We show, using a multi-glider dataset combining FCO2 and ocean turbulence, that the air-sea gradient of CO2 (∆pCO2) is modulated by synoptic storm-driven ocean variability (20 µatm, 1–10 days) through two processes. Ekman transport explains 60% of the variability, and entrainment drives strong episodic CO2 outgassing events of 2–4 mol m−2 yr−1. Extrapolation across the subpolar Southern Ocean using a process model shows how ocean fronts spatially modulate synoptic variability in ∆pCO2 (6 µatm2 average) and how spatial variations in stratification influence synoptic entrainment of deeper carbon into the mixed layer (3.5 mol m−2 yr−1 average). These results not only constrain aliased-driven uncertainties in FCO2 but also the effects of synoptic variability on slower seasonal or longer ocean physics-carbon dynamics.


2022 ◽  
pp. 1-54

Abstract State-of-the-art climate models exhibit significant spread in the climatological value of atmospheric shortwave absorption (SWA). This study investigates both the possible causes and climatic impacts of this SWA inter-model spread. The inter-model spread of global-mean SWA largely originates from the inter-model difference in water vapor shortwave absorptivity. Hence, we alter the water vapor shortwave absorptivity in the Community Earth System Model, version 1, with Atmosphere Model, version 4 (CESM1-CAM4). Increasing the water vapor shortwave absorptivity leads to a reduction in global-mean precipitation and a La Niña-like cooling over the tropical Pacific. The global-mean atmospheric energy budget suggests that the precipitation is suppressed as a way to compensate for the increased SWA. The precipitation reduction is driven by the weakened surface winds, stabilized planetary boundary layer, and surface cooling. The La Niña-like cooling over the tropical Pacific is attributed to the zonal asymmetry of climatological evaporative damping efficiency and the low cloud enhancement over the eastern basin. Complementary fixed SSTs simulations suggest that the latter is more fundamental and that it primarily arises from atmospheric processes. Consistent with our experiments, the CMIP5/6 models with a higher global-mean SWA tend to exhibit the tropical Pacific toward a more La Niña-like mean state, highlighting the possible role of water vapor shortwave absorptivity for shaping the mean-state climate patterns.


2021 ◽  
Author(s):  
Jae-Seung Kim ◽  
Ki-Weon Seo ◽  
Jianli Chen ◽  
Clark Wilson

Abstract Global mean sea level has increased ~3.5 mm/yr over several decades due to increases in ocean mass and changes in sea water density. Ocean mass, accounting for about two-thirds of the increase, can be directly measured by the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GFO) satellites. An independent measure is obtained by combining satellite altimetry (measuring total sea level change) and Argo float data (measuring steric changes associated with sea water density). Many previous studies have reported that the two estimates of global mean ocean mass (GMOM) change are in good agreement within stated confidence intervals. Recently, particularly since 2016, estimates by the two methods have diverged. A partial explanation appears to be a spurious variation in steric sea level data. An additional contributor may be deficiencies in Glacial Isostatic Adjustment (GIA) corrections and degree-1 spherical harmonic (SH) coefficients. We found that erroneous corrections for GIA contaminate GRACE/GFO estimates as time goes forward. Errors in GIA corrections affect degree-1 SH coefficients, and degree-1 errors may also be associated with ocean dynamics. Poor estimates of degree-1 SH coefficients are likely an important source of discrepancies in the two methods of estimating GMOM change.


2021 ◽  
Author(s):  
SHEN Zhou ◽  
Ligia Barna ◽  
Shivesh Kishore Karan ◽  
Lorie Hamelin

The removal of additional carbon dioxide from the atmosphere is indispensable for controlling global warming. This study proposed the concept of ‘biopump’, as plants capable of significantly transferring carbon into the soil. The Carbon Storage in Arable land and Anthropogenic Products (CSAAP) relates to the cultivation of ‘biopumps’ on marginal arable lands poor in soil organic carbon (SOC) and their conversion into long-lived anthropogenic products. Based on a list of twenty-seven biopumps assembled from a literature review, this study proposed a method for the regional prioritization of biopumps, considering among others their ability to increase SOC and adaptation. A list with eight woody and eight herbaceous biopumps was recommended for France. To illustrate the potential of the CSAAP strategy for products encompassing a variety of lifetimes, carbon flows, from biopump cultivation to biomaterial manufacturing and end-of-life, were tracked in time to calculate their influence on global mean temperature change. An illustration was performed on the basis of a French case study, where Miscanthus is grown on spatially identified marginal lands quantified as 11,187- 24,007 km2. Planting biopumps on these lands could increase by 0.23 to 0.49 Mt carbon stocked as SOC annually, which represents 0.19%- 0.41% of the annual French carbon budget during 2015-2018. If the carbon contained in the biomass is indefinitely kept in anthropogenic products, it could represent 13.07% of the same carbon budget. We concluded that biopumps could induce negative emission by 2100, with efficiency strongly depending upon carbon’ residence time in the anthroposphere.


2021 ◽  
Author(s):  
Antony Siahaan ◽  
Robin Smith ◽  
Paul Holland ◽  
Adrian Jenkins ◽  
Jonathan M. Gregory ◽  
...  

Abstract. The Antarctic Ice Sheet will play a crucial role in the evolution of global mean sea-level as the climate warms. An interactively coupled climate and ice sheet model is needed to understand the impacts of ice—climate feedbacks during this evolution. Here we use a two-way coupling between the U.K. Earth System Model and the BISICLES dynamic ice sheet model to investigate Antarctic ice—climate interactions under two climate change scenarios. We perform ensembles of SSP1-1.9 and SSP5-8.5 scenario simulations to 2100, which we believe are the first such simulations with a climate model with two-way coupling between both atmosphere and ocean models to dynamic models of the Greenland and Antarctic ice sheets. In SSP1-1.9 simulations, ice shelf basal melting and grounded ice mass loss are generally lower than present rates during the entire simulation period. In contrast, the responses to SSP5-8.5 forcing are strong. By the end of 21st century, these simulations feature order-of-magnitude increases in basal melting of the Ross and Filchner-Ronne ice shelves, caused by intrusions of warm ocean water masses. Due to the slow response of ice sheet drawdown, this strong melting does not cause a substantial increase in ice discharge during the simulations. The surface mass balance in SSP5-8.5 simulations shows a pattern of strong decrease on ice shelves, caused by increased melting, and strong increase on grounded ice, caused by increased snowfall. Despite strong surface and basal melting of the ice shelves, increased snowfall dominates the mass budget of the grounded ice, leading to an ensemble-mean Antarctic contribution to global mean sea level of a fall of 22 mm by 2100 in the SSP5-8.5 scenario. We hypothesise that this signal would revert to sea-level rise on longer timescales, caused by the ice sheet dynamic response to ice shelf thinning. These results demonstrate the need for fully coupled ice—climate models in reducing the substantial uncertainty in sea-level rise from the Antarctic Ice Sheet.


2021 ◽  
Vol 13 (24) ◽  
pp. 5150
Author(s):  
Faisal S. Boudala ◽  
Jason A. Milbrandt

In this study, the climatologies of three different satellite cloud products, all based on passive sensors (CERES Edition 4.1 [EBAF4.1 and SYN4.1] and ISCCP–H), were evaluated against the CALIPSO-GOCCP (GOCCP) data, which are based on active sensors and, hence, were treated as the reference. Based on monthly averaged data (ocean + land), the passive sensors underestimated the total cloud cover (TCC) at lower (TCC < 50%), but, overall, they correlated well with the GOCCP data (r = 0.97). Over land, the passive sensors underestimated the TCC, with a mean difference (MD) of −2.6%, followed by the EBAF4.1 and ISCCP-H data with a MD of −2.0%. Over the ocean, the CERES-based products overestimated the TCC, but the SYN4.1 agreed better with the GOCCP data. The ISCCP-H data on average underestimated the TCC both over oceanic and continental regions. The annual mean TCC distribution over the globe revealed that the passive sensors generally underestimated the TCC over continental dry regions in northern Africa and southeastern South America as compared to the GOCCP, particularly over the summer hemisphere. The CERES datasets overestimated the TCC over the Pacific Islands between the Indian and eastern Pacific Oceans, particularly during the winter hemisphere. The ISCCP-H data also underestimated the TCC, particularly over the southern hemisphere near 60° S where the other datasets showed a significantly enhanced TCC. The ISCCP data also showed less TCC when compared against the GOCCP data over the tropical regions, particularly over the southern Pacific and Atlantic Oceans near the equator and also over the polar regions where the satellite retrieval using the passive sensors was generally much more challenging. The calculated global mean root meant square deviation value for the ISCCP-H data was 6%, a factor of 2 higher than the CERES datasets. Based on these results, overall, the EBAF4.1 agreed better with the GOCCP data.


Abstract A globally consistent ground validation method for remotely sensed precipitation products is crucial for building confidence in these products. This study develops a new methodology to validate the IMERG precipitation products through the use of SMAP soil moisture changes as a proxy for precipitation occurrence. Using a standard 2x2 contingency table method, preliminary results provide confidence in SMAP’s ability to be utilized as a validation tool for IMERG as results are comparable to previous validation studies. However, the method allows for an overestimate of false alarm frequency due to light precipitation events that can evaporate before the subsequent SMAP overpass and changes in overpass-to-overpass SMAP soil moisture that are within the range of SMAP uncertainty. To counter these issues, a 3x3 contingency table is used to reduce noise and extract more signal from the detection method. Through the use of this novel approach, the validation method produces a global mean POD of 0.64 and global mean FAR of 0.40, the first global-scale ground validation skill scores for the IMERG products. Advancing the method to validate precipitation quantity and the development of a real-time validation for the IMERG Early product are the crucial next developments.


2021 ◽  
pp. 1-61

Abstract The latest Sixth Coupled Model Intercomparison Project (CMIP6) multi-model ensemble shows a broader range of projected warming than the previous-generation CMIP5 ensemble. We show that the projected warming is well-correlated with tropical and subtropical low-level cloud properties. These physically-meaningful relations enable us to use observed cloud properties to constrain future climate warming. We develop multivariate-linear-regression models with metrics selected from a set of potential constraints based on a step-wise selection approach. The resulting linear regression model using two low-cloud metrics shows better cross-validated results than regression models which use single metrics as constraints. Application of a regression model using the low-cloud metrics to climate projections results in similar estimates of the mean, but substantially-narrower ranges, of projected 21st century warming when compared with unconstrained simulations. The resulting projected global-mean warming in 2081-2100 relative to 1995-2014 is 2.84-5.12 K (5-95% range) for Shared Socioeconomic Pathway (SSP) 5-8.5, compared with a range of 2.34-5.81 K for unconstrained projections, and 0.60-1.70 K for SSP1-2.6, compared to an unconstrained range of 0.38-2.04 K. We provide evidence for a higher lower-bound of the projected warming range than that obtained from constrained projections based on the past global-mean temperature trend. Consideration of the impact of the sea surface temperature pattern effect on the recent observed warming trend, which is not well-captured in the CMIP6 ensemble, indicates that the relatively-low projected warming resulting from the global-mean temperature trend constraint may not be reliable and provides further justification for the use of climatologically-based cloud metrics to constrain projections.


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