Trace gases can have a significant impact on the Earth's climate, and the analysis of changes in these gases and an understanding of how much of these changes are a result of human activity is important for understanding global climate change. Methane (CH4) is the second only to CO2 in radiative forcing over the last 200 years, and its concentration in the atmosphere has more than doubled since 1750. Sources and sinks of CH4 have characteristic isotopic effects, which shift the relative concentration of the methane isotopologues. Spectroscopic techniques for of analysis the isotopic composition of methane have been evolving since the early 1990's, and promise real-time, in-situ measurements that would provide unprecedented information on the methane atmospheric cycle. Here we present our development and results of a new optical spectroscopic isotope ratio instrument using cavity ringdown spectroscopy in the near IR region using the ν2+2ν3 overtone band. This region has limited interference from other molecules, and an advantageous juxtaposition of a 13CH4 triplet, and a single 12CH4 peak, allowing near-simultaneous measurement of both isotopologues. We present the results of two datasets showing high linearity over a wide range of isotope ratios, which achieved a precision of ±4 /. We present analysis of the data and consider the effects of temperature and molecular interference.

Regions that have experienced recent successive cold winters such as the Northeast of North America and Siberia have endured critical social and economic impacts from anomalous low temperatures in recent years, despite warming global temperatures. It is well known that the Tropospheric Polar Vortex (TPV), or jet stream, is a primary influence on many mid-latitude winter weather patterns. However, the strong circumpolar westerlies that maximize at around 60° latitude just above the tropopause, known as the Stratospheric Polar Vortex (SPV), can affect tropospheric circulation and thus winter weather in the Northern Hemisphere. Strong upward propagating waves can affect the geographic extent and strength of the SPV resulting in a weakened polar vortex state, which can in turn bring persistent weather events to the mid-latitudes. Here, an index of SPV spatiotemporal variability is presented using observation based analysis of zonal wind and geopotential height to show changes in SPV behavior at a seasonal scale from 1950-2018. Utilizing the CMIP5 suite of global climate models, historical and projected simulations of the SPV's climatological extent and strength are analyzed from 1915 to the end of this century, taking into account models with enhanced stratospheric representation. Simulated results are largely consistent with trends in the observational data, which suggest continued increases in average SPV size throughout this century. If future SPV disturbances increase in frequency, there could be negative impacts in ecosystem and agricultural health, infrastructure damage, and to human safety. A more advanced understanding of SPV trends and anomalous events could improve forecasts of cold air outbreaks (CAOs) and severe or persistent winter weather.

Glaciers in the North Cascades store winter snowfall as ice and release it in late summer as melt, providing an important regional source of water and hydroelectric energy. The future of glaciers in the North Cascades, Washington, were evaluated using a regional glaciation model driven by the Community Climate System Model 4 global climate model. The climate model was coupled with three Representative Concentration Pathways (RCPs), 2.6, 4.5, and 8.5. These RCPs provide a business-as-usual scenario (RCP 8.5), which assumes society makes little to no efforts to reduce greenhouse gas emissions, a best-case scenario (RCP 2.6) with strong attempts to mitigate greenhouse gas emissions, and a moderate scenario (RCP 4.5). Spun up from 850 C.E., modeled glacier area for 1970 was 96-102% of observed. By 2100 the predicted area relative to the total observed area in 1900 was 42% for RCP 2.6, 16% for RCP 45, and 5% for RCP 8.5. By 2100 only glaciers on high peaks, such as Mt. Baker and Glacier Peak, will remain (145.98 km2, RCP 2.6; 70.49 km2, RCP 4.5; 16.82 km2, RCP 8.5) and entirely gone by 2200 in any of the three climate scenarios.

Mineral dust both influences and is influenced by climate on many timescales, from seconds to epochs. Its complex interactions with the climate system are still being unraveled. For example, dust fluxes change in tandem with other records of past changes in climate, and dust source is often presumed to change as well, in response to shifts in climate conditions in source regions; changes in wind regimes; or changes in atmospheric transport pathways. In this work, I investigate dust records from the Southern Hemisphere from ice core and marine sediment core climate archives, looking at both flux and provenance in order elucidate the conditions that allowed for those particles to travel from source to sink. Using multiple radiogenic isotope systems as tracers (87Sr/86Sr, εNd(0), 206Pb/207Pb, and 208Pb/207Pb), I geochemically “fingerprint” of dust particles from Southern Hemisphere climate archives over the last glacial cycle. I compare the dust fingerprints to potential source areas (PSA’s) from across the Southern Hemisphere in order to identify the sources of dust found in the WAIS Divide and Taylor Glacier ice cores from West Antarctica, as well as from marine sediment core ELT39.75 in the Tasman Sea. I use endmember mixing theory to determine the relative contribution of different sources to the climate archives over time. In West Antarctica, I geochemically identify specific local volcanoes from Marie Byrd Land as significant particle contributors to the WAIS Divide ice core during the previous glacial period. In the Tasman Sea, I identify a specific region of southeastern Australia as primary the dust source over the past glacial cycle, with the source remaining constant across glacial-interglacial climate transitions. This clarifies that the “fingerprint” of Australian dust is relatively invariant over time and allows a single Australian signature to be used as an endmember for identifying dust provenance in climate archives downwind. I also identify the dust sources in the WAIS Divide during the Last Glacial Maximum and through the early deglacial, identifying southern South America as the predominant source during cold stages. WAIS Divide and Taylor Glacier dust records do not record dust source changes across millennial-scale climate events, suggesting that a) the source regions did not change, b) the transport pathways remained pinned, or c) the proxy is not sensitive to changes in these variables. Contributions from local volcanoes are also inferred from the WAIS dust record using mixing theory. In summary, I find that the radiogenic isotope fingerprint of dust samples from the archives analyzed show subtle or no changes in source over climate transitions, and therefore the strategy of dust particles as a tracer of past atmospheric circulation pathways should be approached cautiously.

Abstract not available

In this study the natural variability of Southern Ocean water masses on interannual to centennial time scales is investigated using a long-term integration of the Commonwealth Scientic and Industrial Research Organisation (CSIRO) coupled climate model. We focus our attention on analysing the variability of Antarctic IntermediateWater (AAIW), Circumpolar DeepWater (CDW), and Antarctic Bottom Water (AABW). We present an analysis of the dominant modes of temperature and salinity (T - S) variability within these water masses. Climate signals are detected and analysed as they get transmitted into the interior from the water mass formation regions. Eastward propagating wavenumber-1, -2, and -3 signals are identied using a complex empirical orthogonal function (CEOF) analysis along the core of the AAIW layer. Variability in air-sea heat uxes and ice meltwater rates are shown by heat and salt budget analyses to control variability of Antarctic Surface Water where density surfaces associated with AAIW outcrop. The dominant mode in the CDW layer is found to exhibit an interbasin-scale of variability originating from the North Atlantic, and propagating southward into the Southern Ocean. Salinity dipole anomalies appear to propagate around the Atlantic meridional overturning circulation with the strengthening and weakening of North Atlantic Deep Water formation. In the AABW layer, T - S anomalies are shown to originate from the southwestern Weddell Sea, driven by salinity variations and convective overturning in the region. It is also demonstrated that the model exhibits spatial patterns of T - S variability for the most part consistent with limited observational record in the Southern Hemisphere. However, some observations of decadal T - S changes are found to be beyond that seen in the model in its unperturbed state. We further assess sea surface temperature (SST) variability modes in the Indian Ocean on interannual time scales in the CSIRO model and in reanalysis data. The emergence of a meridional SST dipole during years of southwest Western Australian rainfall extremes is shown to be connected to a large-scale mode of Indian Ocean climate variability. The evolution of the dipole is controlled by variations in atmospheric circulation driving anomalous latent heat uxes with wind-driven ocean transport moderating the impact of evaporation and setting the conditions favourable for the next generation phase of an opposite dipole.

Numerous supraglacial and proglacial lakes have developed on debris-covered glaciers in conjunction with 20th-century retreat associated with global warming. When a glacier holds a substantial debris cover on its lower reach and/or is calving into a proglacial water body, the behaviour of its terminus can be modified to varying degrees compared to that of land-terminating or debris-free glaciers. The terminus is not just retreating from its frontal position but it is disintegrating through several processes that are linked. An improved understanding of these glacier margins is needed for the prediction and management of hazards associated with these types of lakes for hydroelectric power generation, recreational purposes and areas threatened by potential glacier outburst floods as well as for the interpretation of glacio-geological records and reconstruction of former glacial environments and palaeoclimate. The principal research question of this study is how processes of ice loss contribute to the terminus disintegration of a debris-covered, lake-calving glacier. This is addressed by an application of a field-based strategy which includes extensive field observations of variables, processes and their controls, and subsequent analysis of the data in the light of previous models and concepts. The study attempts to combine and integrate different aspects of glaciological research that have previously been examined mostly separately. It investigates the prevalent processes at the glacier terminus and their controls over different time periods ranging from days to years at Mueller, Hooker and Tasman Glaciers in Mount Cook National Park, New Zealand. The data form the basis for models of calving and pond development and future retreat scenarios. This study has demonstrated that this glacial environment is characterised by ice-frontal processes with complex inter-relationships that vary between glaciers and in particular between stages of terminus development. While surface ice melt in the terminus area is substantially reduced by supraglacial debris, sub-debris melt contributes the largest fraction of ice loss. Other important effects of debris are restraining thermal undercutting, reducing subaqueous melt and decreasing buoyancy. Data from supraglacial ponds and proglacial lakes show that limnological factors become increasingly important with increasing pond/lake size. Changes in water currents and temperature lead to changes in significance and rates of ice loss processes, the most important being the change from melting to predominantly calving. This study has confirmed the hypothesis that thermal undercutting is the rate-controlling process for calving. This process is controlled by the cliff geometry, debris supply, subaqueous geometry and water temperatures, currents and level variations. The results from the examination of calving processes suggest that the process of regular, progressive calving through the stages suggested previously may not be widely applicable to slow-moving, lake-calving glaciers. The several forms of subaerial calving identified in this study can present themselves as largely independent events, a combination of events or as a progression. At the central submerged part of the ice face, subaqueous ice melt is likely to be the dominant form of ice loss, leading to horizontal ice loss. Subaqueous calving is prevalent in gently-sloping lateral areas, leading to vertical ice loss. This process is controlled by buoyancy forces which are affected by sedimentation and lake and glacier geometry. The onset of subaqueous calving in the earlier stages of lake development is a crucial process for the transition to faster disintegration and ice loss, accelerating subaqueous melt. Due to the complex inter-relationships attempts to formulate general relationships between calving or retreat rates and other glaciological parameters may not be feasible.

No description available.

With climate change arising as an important issue in the 21th century, many states have been working diligently to develop climate action plans with the hopes of reducing greenhouse gas emissions and stop climate change from occurring. According to scientists' theories, however, many places across the globe are already feeling the effects of a changing climate and must therefore switch their focus from mitigation to adaptation. In the United States, there has been a focus on how climate change will impact one of the most vulnerable parts of the country, the transportation infrastructure. Many countries have already begun adapting their transportation infrastructure to climate change including the United States. This thesis focuses on how states are adapting to climate change by analyzing strategies, frameworks, and reports released by these states in order to document where they stand in regards to adaptation of the transportation network. The states that are adapting their transportation infrastructure are Washington, Oregon, California, Hawaii, Alaska, Florida, North Carolina, Maryland, Delaware, Pennsylvania, Michigan, Connecticut, Massachusetts, Vermont, and Maine. There is also a brief summary of how Canada and the United Kingdom are preparing for climate change with an analysis of frameworks and strategies used to adapt their transportation infrastructure. The ultimate goal of this thesis is to provide engineers and policymakers with evidence that several states are implementing adaptation into transportation projects and provide a variety of strategies for them to use in their own state. Specifically, this report provides applications of adaptation for Georgia to use, so that they can begin the lengthy process of adapting their transportation infrastructure to climate change.

Thesis (Ph. D.)--University of Arizona, 2000. / Includes bibliographical references. Also available online.