Earth's albedo is symmetric between the northern and southern hemispheres (NH and SH, respectively) because SH clouds compensate for higher NH clear-sky albedo, a feature that climate models have difficulty capturing. We assess how parameterized processes affect a model's cloud albedo and albedo symmetry using a perturbed parameter ensemble (PPE) of atmospheric simulations. Parameters most significant to simulated albedo symmetry impact precipitation, turbulent dissipation, and sea salt aerosol emissions. Constraining the PPE's shortwave cloud feedbacks using the observed albedo symmetry yields a range of +0.61 (Formula presented.) 0.24 W m−2 K−1 (66% confidence), which is stronger than that of the model's control simulation due to parameter settings that lead to greater loss of subtropical low clouds and weaker negative cloud phase feedback. Although these settings would reduce cloud albedo bias compared to the control simulation, we find that albedo symmetry has limited potential as a constraint for cloud feedbacks on its own.

Earth's Northern and Southern Hemispheres (NH and SH, respectively) have significantly different properties: the NH has a higher concentration of bright land surface area and aerosol emissions than the SH, making the Earth's clear-sky albedo hemispherically asymmetric. However, satellite observations have shown that higher cloud amount and reflectivity in the SH exactly compensate for this, making Earth's planetary albedo hemispherically symmetric. A physical explanation for this symmetry has not yet been found, but because it would give constraints for global cloud cover and its features, discovery of one may be a powerful tool in predicting the behavior of clouds in a changing climate.

The first chapter of this thesis investigates the hemispheric albedo symmetry in observations, and finds that its variability primarily stems from the tropics. General circulation models (GCMs) exhibit a large spread in albedo asymmetry biases; comparing these with observations reveals that the extratropics control mean-state modeled albedo asymmetry.

The second chapter compares the evolution of albedo asymmetries in GCMs when forced with increased CO₂ concentrations. Models agree on an initial asymmetry response due to Arctic warming and albedo reductions, but diverge thereafter, with some models recovering their pre-industrial asymmetry. Those that recover their asymmetry do so via SH extratropical cloud loss and thus have stronger positive cloud feedbacks, illustrating that an albedo symmetry-maintaining mechanism could have implications for climate sensitivity.

Sources of modeled albedo asymmetry biases are investigated in a single atmospheric GCM using a perturbed parameter ensemble in the third chapter. The most significant parameters to simulated albedo asymmetry are those controlling warm rain formation, turbulent dissipation, and sea salt aerosol emissions. Parameters controlling warm rain formation and turbulent dissipation primarily affect extratropical low cloud cover, and those affecting ice particle formation disproportionately affects SH midlatitude albedo. Parameter settings that reproduce the observed albedo symmetry tend towards more strongly positive shortwave cloud feedbacks.

The link between hemispheric asymmetries in clouds and large-scale circulation is investigated with idealized atmospheric GCM experiments in the fourth chapter. Introducing hemispheric asymmetry in ocean heat fluxes that emulate heat divergence (convergence) in the SH (NH) drives an atmospheric response that qualitatively reproduces the observed cloud distribution. We conclude that the hemispheric albedo symmetry is not possible without implicating surface forcing from ocean circulation and heat transport.

Contemporary general circulation models (GCMs) and Earth system models (ESMs) are developed by a large number of modeling groups globally. They use a wide range of representations of physical processes, allowing for structural (code) uncertainty to be partially quantified with multi-model ensembles (MMEs). Many models in the MMEs of the Coupled Model Intercomparison Project (CMIP) have a common development history due to sharing of code and schemes. This makes their projections statistically dependent and introduces biases in MME statistics. Previous research has focused on model output and code dependence, and model code genealogy of CMIP models has not been fully analyzed. We present a full reconstruction of CMIP3, CMIP5, and CMIP6 code genealogy of 167 atmospheric models, GCMs, and ESMs (of which 114 participated in CMIP) based on the available literature, with a focus on the atmospheric component and atmospheric physics. We identify 12 main model families. We propose family and ancestry weighting methods designed to reduce the effect of model structural dependence in MMEs. We analyze weighted effective climate sensitivity (ECS), climate feedbacks, forcing, and global mean near-surface air temperature, and how they differ by model family. Models in the same family often have similar climate properties. We show that weighting can partially reconcile differences in ECS and cloud feedbacks between CMIP5 and CMIP6. The results can help in understanding structural dependence between CMIP models, and the proposed ancestry and family weighting methods can be used in MME assessments to ameliorate model structural sampling biases.

The Earth's albedo is observed to be symmetric between the hemispheres on the annual mean timescale, despite the clear-sky albedo being asymmetrically higher in the Northern Hemisphere due to more land area and aerosol sources; this is because the mean cloud distribution currently compensates for the clear-sky asymmetry almost exactly. We investigate the evolution of the hemispheric difference in albedo in the Coupled Model Intercomparison Project Phase 6 (CMIP6) coupled model simulations following an abrupt quadrupling of CO₂ concentrations, to which all models respond with an initial decrease of albedo in the Northern Hemisphere (NH) due to loss of Arctic sea ice. Models disagree over whether the net effect of NH cloud responses is to reduce or amplify initial NH albedo reductions. After the initial response, the evolution of the hemispheric albedo difference diverges among models, with some models remaining stably at their new hemispheric albedo difference and others returning towards their pre-industrial difference primarily through a reduction in SH cloud cover. Whereas local increases in cloud cover contribute to negative shortwave cloud feedback, the cross-hemispheric communicating mechanism found to be primarily responsible for restoring hemispheric symmetry in the models studied implies positive shortwave cloud feedback.

In the craft brewing industry, kegging solutions have changed dramatically in recent years. While steel kegs once dominated the draught beer market, single-use plastic kegs have increased in popularity due to their convenience, especially in the craft brewing sector. With the increasing importance of the circular economy and the introduction of policies in Europe to move away from single-use plastic systems, this study aims to assess and compare the sustainability of conventional steel and single-use plastic kegs. The environmental and economic performance are assessed through life cycle assessment and life cycle costing approaches. The results suggest that steel kegs have better environmental performance and life cycle costs. However, these are limited to the local markets, and with larger distances, plastic kegs may become the better option due to their lower weight, suggesting that both kegs are useful in certain situations. This is especially important in countries that have long distances between breweries and their markets. The importance of extending the lifetime of the keg fleet is also highlighted to improve the environmental performance as the results are influenced by the assumption on the lifetime of the steel kegs. To improve the environmental performance of plastic kegs, efficient closed-loop recycling systems should be developed. Careful decision-making is needed to ensure that more sustainable packaging options are chosen for draught beer and that sustainability aspects be taken into account beyond convenience.

Despite the unequal partitioning of land and aerosol sources between the hemispheres, Earth’s albedo is observed to be persistently symmetric about the equator. This symmetry is determined by the compensation of clouds to the clear-sky albedo. Here, the variability of this interhemispheric albedo symmetry is explored by decomposing observed radiative fluxes in the CERES EBAF satellite data record into components reflected by the atmosphere, clouds, and the surface. We find that the degree of interhemispheric albedo symmetry has not changed significantly throughout the observational record. The variability of the interhemispheric difference in reflected solar radiation (asymmetry) is strongly determined by tropical and subtropical cloud cover, particularly those related to nonneutral phases of El Niño–Southern Oscillation (ENSO). As ENSO is the most significant source of interannual variability in reflected radiation on a global scale, this underscores the interhemispheric albedo symmetry as a robust feature of Earth’s current annual mean climate. Comparing this feature in observations with simulations from coupled models reveals that the degree of modeled albedo symmetry is mostly dependent on biases in reflected radiation in the midlatitudes, and that models that overestimate its variability the most have larger biases in reflected radiation in the tropics. The degree of model albedo symmetry is improved when driven with historical sea surface temperatures, indicating that the degree of symmetry in Earth’s albedo is dependent on the representation of cloud responses to coupled ocean–atmosphere processes.

As the climate changes, human livelihoods will increasingly be threatened by extreme weather events. To provide adequate disaster relief, states extensively rely on multilateral institutions, in particular the United Nations (UN). However, the determinants of this multilateral disaster aid channeled through the UN are poorly understood. To fill this gap, we examine the determinants of UN disaster aid using a dataset on UN aid covering almost 2,000 climate-related disasters occurring between 2006 and 2017. We make two principal contributions. First, we add to research on disaster impacts by linking existing disaster data from the Emergency Events Database (EM-DAT) to a meteorological reanalysis. We generate a uniquely global hazard severity measure that is comparable across different climate-related disaster types, and assess and bolster measurement validity of EM-DAT climate-related disasters. Second, by combining these data with social data on aid and its correlates, we contribute to the literature on aid disbursements. We show that UN disaster aid is primarily shaped by humanitarian considerations, rather than by strategic donor interests. These results are supported by a series of regression and out-of-sample prediction analyses and appear consistent with the view that multilateral institutions are able to shield aid allocation decisions from particular state interests to ensure that aid is motivated by need.

Earth’s albedo has remained symmetric between the northern and southern hemispheres over the satellite record, a feature that climate models have difficulty capturing. We investigate causes of these biases using a perturbed parameter ensemble of atmospheric simulations to probe the sensitivity of the albedo symmetry to cloud properties and the processes that control them. We find that the most significant parameters to simulated albedo symmetry impact precipitation, turbulent dissipation, and sea salt aerosol emissions. Constraining shortwave cloud feedbacks using the observed albedo symmetry leads to a range of +0.61±0.24 W m^-2 K^-1 (66% confidence). These are stronger than the model’s control settings due to greater loss of subtropical low clouds and weaker negative cloud phase feedback. Comparing the constrained and control parameter settings shows a preference towards settings that would reduce the control simulation’s biases, indicating that the constraint can select for representations that capture the observed cloud cover.

Clouds in the Southern Hemisphere (SH) extratropics make up for the Northern Hemisphere (NH)’s greater tropical cloud cover and clear-sky albedo, making Earth’s planetary albedo hemispherically symmetric over the satellite record. Knowledge of a mechanism for maintaining hemispheric albedo symmetry would prove valuable for understanding cloud responses to external forcings. Using simulations of an Earth-like aquaplanet, we investigate the role of ocean heat transport (OHT) in determining hemispheric differences in cloud cover. With increasing northward cross-equatorial OHT, the SH becomes dominant in low cloud cover at all latitudes, while NH increases in high clouds are negated by reductions in low clouds. We describe a dynamical link between the increasing SH extratropical cloud cover and increasing NH tropical cloud cover with more northward cross-equatorial OHT. We investigate the effects of clouds and condensation on AHT responses, which increase southward AHT through latent heating in the extratropics and radiative effects in lower latitudes, aiding in reducing the hemispheric energy contrast. Because SH cloud increases are greater than NH cloud reductions, increasing cloud asymmetry with more northward cross-equatorial OHT leads to net increases in global cloud cover and cooling.