Large Methane Emissions From the Pantanal During Rising Water‐Levels Revealed by Regularly Measured Lower Troposphere CH₄ Profiles

The Pantanal region of Brazil is the largest seasonally flooded tropical grassland and, according to local chamber measurements, a substantial CH4 source. CH4 emissions from wetlands have recently become of heightened interest because global atmospheric 13CH4 data indicate they may contribute to the resumption of atmospheric CH4 growth since 2007. We have regularly measured vertical atmospheric profiles for 2 years in the center of the Pantanal with the objectives to obtain an estimate of CH4 emissions using an atmospheric approach, and provide information about flux seasonality and its relation to controlling factors. Boundary layer-free troposphere differences observed in the Pantanal are large compared to other wetlands. Total emissions based on a planetary boundary layer budgeting technique are 2.0–2.8 TgCH4 yr−1 (maximum flux ∼0.4 gCH4 m−2 d−1) while those based on a Bayesian inversion using an atmospheric transport model are ∼3.3 TgCH4 yr−1. Compared to recent estimates for Amazonia (∼41 ± 3 TgCH4 yr−1, maximum flux ∼0.3 gCH4 m−2 d−1) these emissions are not that large. Our Pantanal data suggest a clear flux seasonality with CH4 being released in large amounts just after water levels begin to rise again after minimum levels have been reached. CH4 emissions decline substantially once the maximum water level has been reached. While predictions with prognostic wetland CH4 emission models agree well with the magnitude of the fluxes, they disagree with the phasing. Our approach shows promise for detecting and understanding longer-term trends in CH4 emissions and the potential for future wetlands CH4 emissions climate feedbacks

Sixteen years of MOPITT satellite data strongly constrain Amazon CO fire emissions

Despite consensus on the overall downward trend in Amazon forest loss in the previous decade, estimates of yearly carbon emissions from deforestation still vary widely. Estimated carbon emissions are currently often based on data from local logging activity reports, changes in remotely sensed biomass as well as remote detection of fire hotspots, and burned area. Here, we use sixteen years of satellite-derived carbon monoxide (CO) columns to constrain fire CO emissions from the Amazon basin between 2003 and 2018. Through data assimilation, we produce 3-daily maps of fire CO emissions over the Amazon that we verified to be consistent with a long-term monitoring program of aircraft CO profiles over five sites in the Amazon. Our new product independently confirms a long-term decrease of 54 % in deforestation-related CO emissions over the study period. Interannual variability is large, with known anomalously dry years showing a more than fourfold increase in basin-wide fire emissions. At the level of individual Brazilian states, we find that both soil moisture anomalies and human ignitions determine fire activity, suggesting that future carbon release from fires depends on drought intensity as much as on continued forest protection. Our study shows that the atmospheric composition perspective on deforestation is a valuable additional monitoring instrument that complements existing bottom-up and remote sensing methods for land-use change. Extension of such a perspective to an operational framework is timely considering the observed increased fire intensity in the Amazon basin in 2019&ndash;2021.</p

Vegetation type is an important predictor of the arctic summer land surface energy budget

Despite the importance of high-latitude surface energy budgets (SEBs) for land-climate interactions in the rapidly changing Arctic, uncertainties in their prediction persist. Here, we harmonize SEB observations across a network of vegetated and glaciated sites at circumpolar scale (1994-2021). Our variance-partitioning analysis identifies vegetation type as an important predictor for SEB-components during Arctic summer (June-August), compared to other SEB-drivers including climate, latitude and permafrost characteristics. Differences among vegetation types can be of similar magnitude as between vegetation and glacier surfaces and are especially high for summer sensible and latent heat fluxes. The timing of SEB-flux summer-regimes (when daily mean values exceed 0 Wm(-2)) relative to snow-free and -onset dates varies substantially depending on vegetation type, implying vegetation controls on snow-cover and SEB-flux seasonality. Our results indicate complex shifts in surface energy fluxes with land-cover transitions and a lengthening summer season, and highlight the potential for improving future Earth system models via a refined representation of Arctic vegetation types.An international team of researchers finds high potential for improving climate projections by a more comprehensive treatment of largely ignored Arctic vegetation types, underscoring the importance of Arctic energy exchange measuring stations.Peer reviewe

The Community Land Model version 5 : description of new features, benchmarking, and impact of forcing uncertainty

The Community Land Model (CLM) is the land component of the Community Earth System Model (CESM) and is used in several global and regional modeling systems. In this paper, we introduce model developments included in CLM version 5 (CLM5), which is the default land component for CESM2. We assess an ensemble of simulations, including prescribed and prognostic vegetation state, multiple forcing data sets, and CLM4, CLM4.5, and CLM5, against a range of metrics including from the International Land Model Benchmarking (ILAMBv2) package. CLM5 includes new and updated processes and parameterizations: (1) dynamic land units, (2) updated parameterizations and structure for hydrology and snow (spatially explicit soil depth, dry surface layer, revised groundwater scheme, revised canopy interception and canopy snow processes, updated fresh snow density, simple firn model, and Model for Scale Adaptive River Transport), (3) plant hydraulics and hydraulic redistribution, (4) revised nitrogen cycling (flexible leaf stoichiometry, leaf N optimization for photosynthesis, and carbon costs for plant nitrogen uptake), (5) global crop model with six crop types and time‐evolving irrigated areas and fertilization rates, (6) updated urban building energy, (7) carbon isotopes, and (8) updated stomatal physiology. New optional features include demographically structured dynamic vegetation model (Functionally Assembled Terrestrial Ecosystem Simulator), ozone damage to plants, and fire trace gas emissions coupling to the atmosphere. Conclusive establishment of improvement or degradation of individual variables or metrics is challenged by forcing uncertainty, parametric uncertainty, and model structural complexity, but the multivariate metrics presented here suggest a general broad improvement from CLM4 to CLM5

Detection, attribution and quantification of methane emissions using mobile measurement techniques in European cities

Global actions are required to reduce Greenhouse Gas (GHG) emissions, and thus mitigate global warming. On the 4th of November 2016 the Paris agreement between 196 countries entered into force which aims to limit global warming to less than 2 °C. Methane (CH4) has a relatively short atmospheric lifetime (≈10 years) which makes it an effective mitigation target to slow down global warming on the short to medium term. The CH4 mitigations can be implemented faster and have less severe economic effects than reduction of carbon dioxide (CO2) emissions because CO2 emission is directly proportional to energy consumption. Despite the attractiveness of CH4 reduction, on the longer term also CO2 emission will need to be reduced to zero around the middle of this century to reach the goals of the Paris agreement. Among all the CH4 sources, emission mitigation in the energy sectors seems to be the most time efficient and cost effective compared to emission reduction from other sectors. CH4 emissions from the energy sector, particularly from production, storage, transportation, distribution and end-use of fossil fuels (oil, gas and coal) contribute 19% to total anthropogenic CH4 emissions in Europe. This contribution can increase to more than 60% in fossil fuel producing countries. Fossil fuel related emission have been identified as an interesting target within the CH4 reduction strategy of the EU. The emissions from these activities are mainly estimated using Emission Factors (EFs) and Activity Data (AD) in inventories. The EFs are the ratio of emission rate per activity unit, e.g. kg of CH4 emitted per amount of gas produced. The EFs are tabulated in reports from national or international agencies, and standard EFs for emission reporting have been tabulated by the Intergovernmental Panel on Climate Change (IPCC). However, the EFs can vary temporally and spatially which increases the uncertainty in the estimated emissions. To reduce the uncertainty, independent measurement campaigns are required to update or verify these EFs, some of which are outdated or are possibly affected by sampling and / or emission rate biases. Detailed information is required on where and how large the emissions are, for effective mitigation policies. This thesis was carried out within the MEMO2 (MEthane goes MObile, MEasurements and MOdelling) project, with the objective to use mobile measurement techniques to improve our understanding of CH4 emissions. The main focus was on emissions in the energy sector. In this thesis, we provide detailed results from detection, quantification and attribution of CH4 emissions from extensive measurement campaigns focusing on emissions from the gas distribution networks in cities. These measurements showed that the contribution of CH4 emissions from natural gas leaks, microbial or combustion sources are different from one city to another, thus dedicated emission mitigation policies are required for different cities

Hydrodynamics and suspended sediment dynamics in estuarine channel networks: an idealised modelling approach

Estuaries are bodies of water that connect river to sea. Many of them are composed of multiple interconnected channels and thus constitute a so-called estuarine channel network. They are important for both ecology and economy. Freshwater and fluvial sediments are continuously discharged into the system by the river flow. Additionally, the tidal flow causes water and sediments being periodically imported from and exported into the open sea. Water and sediments are exchanged at the junctions of the channels. Therefore, estuarine channel networks feature complex hydrodynamics and sediment dynamics. The latter gives rise to the estuarine turbidity maximum (ETM), where the suspended sediment concentration attains a local maximum. The aim of this thesis is to understand more about the response of the hydrodynamics and the ETM dynamics in estuarine channel networks to natural environmental conditions, as well as due to changes in these conditions due to e.g. climate change or anthropogenic measures. To understand the dependence of their along-channel and vertical structure on forcings, geometry characteristics and sea level changes, an idealised process based model that resolves the flow vertical structure is developed and applied to the Yangtze Estuary. Increasing river discharge enhances the friction for tides by increasing both internal and bottom stresses. Changes in tidal forcing are correlated with the friction for both tide and river. A shortcut channel reduces the water level difference in adjacent channels. SLR results in larger friction parameters, faster propagation of tides, and more even distribution of river water transport. To disentangle the various contributions of physical drivers to net water transport (NWT) in estuarine networks and to investigate the sensitivities of net water transport to above-mentioned change, the model is further developed to resolve density-gradients. NWT due to tidal rectifications and density-driven flow can be comparable to river discharge. Varying river discharge mainly affects NWT due to river as tide-river interaction is weak and density-driven flow is shown to be insensitive to salt intrusion. Conversely, variations in tidal amplitude strongly affect NWT related to tidal rectification and density-driven flow. The deepening (narrowing) of one channel affected the NWT mostly through the density-driven flow (momentum advection). Furthermore, NWT distribution in the Yangtze is insensitive to SLR up to 2 m because the effects of SLR on transport due to different drivers compensate each other. ETM locations in an idealised three-channel network on fluvial sediment input and the local deepening and narrowing of a seaward channel is investigated. Sensitivity results show that, keeping river discharge fixed, a larger fluvial sediment input leads to the upstream shift of ETMs and an increase in the overall sediment concentration. Both deepening or narrowing of a seaward channel may influence the ETMs in the entire network. Furthermore, the effect of either deepening or narrowing of a seaward channel on the ETM locations in the network depends on the system geometry and the dominant hydrodynamic conditions. Therefore, the response of the ETM location to local geometric changes can only be understood by analysing the dominant sediment transport mechanisms

Interpretation of discrete and continuum modes in a two-layer Eady model

The upper rigid lid of the conventional Eady model for baroclinic instability is replaced by a more realistic stratosphere with an increased buoyancy frequency and a different shear of the zonal wind. Previously reported results of a normal-mode stability analysis are re-interpreted using the concept of interacting surface and tropopause PV anomalies, called PV building blocks (PVBs). In this perspective, which directly relates to the counter-propagating Rossby wave formalism, the appearance of both the short-wave and the long-wave cut-off becomes physically transparent. New results include a discussion of the continuum modes in terms of interacting PVBs. Continuum modes are modal solutions to the inviscid linearised equations, specified by non-zero PV at one interior level (as well as non-zero PV at the surface and the tropopause). If the stratospheric zonal wind decreases with height, the continuum modes cause resonances at multiple (even stratospheric) levels. These resonant continuum modes may play an important role in the explanation of disturbance growth from initial conditions in which the discrete normal modes are neutral

Dynamics of calving glaciers: comparison of three models

A minimal model of a tidewater glacier based solely on mass conservation is compared with two one-dimensional numerical flowline models, one with the calving rate proportional to water depth, and the other with the flotation criterion as a boundary condition at the glacier terminus. The models were run with two simplified bed geometries and two mass-balance formulations. The models simulate the full cycle of length variations and the equilibrium states for a tidewater glacier. This study shows that the branching of the equilibrium states depends significantly on the bed geometry. The similarity between the results of the three models indicates that if there is a submarine undulation at the terminus of a tidewater glacier, any model in which the frontal ice loss is related to the water depth yields qualitatively the same non-linear behaviour. For large glaciers extending into deep water, the flotation model causes unrealistic behaviour

On the direction of Rossby wave breaking in blocking

The direction of Rossby wave breaking at the onset of large-scale atmospheric blocking events is shown to relate closely to its position relative to the location of the climatological storm tracks. Using ERA-Interim reanalysis data from October 1989 to March 2009 and a dynamicallybased blocking index, Rossby wave breaking is shown to occur preferentially cyclonically to the north, and anticyclonically to the south of the average storm tracks location. Therefore the results support existing theory on the relation between Rossby wave breaking direction and barotropic shear of the background wind. The further away from the storm tracks the breaking occurs, the stronger this preference in breaking direction. Regional differences can also be explained. For the European region on average 70 % of the detected blocking took place after anticyclonic Rossby wave breaking event that occurred on average 6" south of the climatological storm tracks position. Over Western Pacific wave breaking prior to blocking occurs predominantly cyclonically and on average 6" north of the storm tracks. Differences in blocking duration and intensity are found to be within estimated error margins at most longitudes, except for the Atlantic-Europe sector where the blocking events following anticyclonic blocking are also the strongest

Design and bifurcation analysis of implicit Earth System Models

The research presented in this thesis seeks to advance the exploration of feedbacks and transitions in the climate system. This aim motivates the development of fully implicit climate models that support a thorough exploration of equilibria through computational techniques that combine dynamical systems theory and numerical linear algebra. The core goal of this research is the development of a fully implicit Earth system model of intermediate complexity: the I-EMIC. With the I-EMIC, the construction of bifurcation diagrams for large-scale climate problems comes within reach. The model supports high dimensional fixed-point iterations that are fundamental to the numerical continuation techniques that construct branches of equilibria for complex problems. Moreover, stability properties, 'tipping points' and possible oscillatory behavior can be investigated through the solution of large-scale eigenvalue problems. We present the design and analysis of several implicit geophysical models, which are subjected to reformulations and eventually combined into a working implicit Earth system model. This demonstrates that it is possible to formulate climate models implicitly, combine them while maintaining differentiability, and that it is possible to solve the resulting linear systems and eigenvalue problems