Understanding the influence of solar variability on the Earth's climate requires knowledge of solar variability, solar-terrestrial interactions, and the mechanisms determining the response of the Earth's climate system. We provide a summary of our current understanding in each of these three areas. Observations and mechanisms for the Sun's variability are described, including solar irradiance variations on both decadal and centennial time scales and their relation to galactic cosmic rays. Corresponding observations of variations of the Earth's climate on associated time scales are described, including variations in ozone, temperatures, winds, clouds, precipitation, and regional modes of variability such as the monsoons and the North Atlantic Oscillation. A discussion of the available solar and climate proxies is provided. Mechanisms proposed to explain these climate observations are described, including the effects of variations in solar irradiance and of charged particles. Finally, the contributions of solar variations to recent observations of global climate change are discussed.

<p> Yellow-cedar is a long-lived conifer of the North Pacific Coastal Temperate Rainforest region that is thought to be undergoing a continued natural range expansion in southeast Alaska. Yellow-cedar is locally rare in northeastern portions of the Alexander Archipelago, and the fairly homogenous climate and forest conditions across the region suggest that yellow-cedar&rsquo;s rarity could be due to its local migrational history rather than constraints on its growth. Yellow-cedar trees in northern range edge locations appear to be healthy, with few dead trees; additionally, yellow-cedar tend to be younger than co-dominant mountain and western hemlock trees, indicating recent establishment in existing forests.</p><p> To explore yellow-cedar&rsquo;s migration in the region, and determine if the range is expanding into unoccupied habitat, I located 11 leading edge yellow-cedar populations near Juneau, Alaska. I used the geographic context of these populations to determine the topographic, climatic, and disturbance factors associated with range edge population establishment. I used those same landscape variables to model suitable habitat for the species at the range edge. Based on habitat modeling, yellow-cedar is currently only occupying 0.8 percent of its potential landscape niche in the Juneau study area. Tree ages indicate that populations are relatively young for the species, indicating recent migration, and that most populations established during the Little Ice Age climate period (1100 &ndash; 1850).</p><p> To determine if yellow-cedar is continuing to colonize unoccupied habitat in the region, I located 29 plots at the edges of yellow-cedar stands to measure regeneration and expansion into existing forest communities. Despite abundant suitable habitat, yellow-cedar stand expansion appears stagnant in recent decades. On average, seedlings only dispersed 4.65 m beyond stand boundaries and few seedlings reached mature heights both inside and outside of existing yellow-cedar stands. Mature, 100 &ndash; 200-year-old trees were often observed abruptly at stand boundaries, indicating that most stand boundaries have not moved in the past ~150 years. When observed, seedlings were most common in high light understory plant communities and moderately wet portions of the soil drainage gradient, consistent with the species&rsquo; autecology in the region.</p><p> Despite an overall lack of regeneration via seed, yellow-cedar is reproducing via asexual layering in high densities across stands. Layering may be one strategy this species employs to slowly infill habitat and/or persist on the landscape until conditions are more favorable for sexual reproduction. This study leads to a picture of yellow-cedar migration as punctuated, and relatively slow, in southeast Alaska. Yellow-cedar&rsquo;s migration history and currently limited spread at the northeastern range edge should be considered when planning for the conservation and management of this high value tree under future climate scenarios.</p>

Using high-resolution topography, we link the stratigraphy of layered ice deposits at the north pole of Mars to astronomically driven climate variability. Observations of trough exposures within these deposits are used to construct virtual ice cores at 16 sites, to which we apply wavelet analysis to identify periodicities in layer properties. To confidently relate these periodicities to climatic forcing, we identify overlapping dominant stratigraphic wavelengths and compare their ratios to that of the two dominant modes of insolation variability. The average ratio of stratigraphic wavelengths in the profiles is 1.90.1, lower than the ratio of 2.3 between dominant insolation periodicities. A similar analysis of synthetic stratigraphic profiles created with a climate-driven model of ice and dust accumulation shows that this lower stratigraphic ratio is a natural consequence of time-variable ice accumulation rates.

This study analyzes temporal trends and periodicity in seventy years of publicly available stream discharge and climate data for the Winooski River Basin of northern Vermont as well as lake level data for adjacent Lake Champlain. We also use random sampling and manual, point-based classification of recent and historical aerial imagery to quantify land use change over the past seventy years in the 2,704 km2 Winooski River Basin of northern Vermont. We find a general increase in annual precipitation, discharge, and mean lake level with time in the basin; discharge increases 18% over the period of record while precipitation increases by 14%. Over the last 70 years, mean annual temperature has increased at the Burlington Vermont station by 0.78 degrees Celsius (1.4 degrees Fahrenheit). Four sets of aerial photographs, taken at intervals of 12 to 29 years between 1937 and 2003 at thirty randomly selected sites, demonstrate that actively cleared land area has decreased by 14%, while forested land and impervious surfaces increased by 10% and 5%, respectively. Spectral analysis of precipitation, discharge and lake level data show a ~7.6 year periodicity, which is in phase with the North Atlantic Oscillation (NAO); higher than average precipitation and discharge are most likely when the NAO is in a positive mode. The NAO relationship demonstrates that discharge is largely controlled by precipitation; anthropogenic changing climate and changing land use over the past 70 years appear to have subtly changed the seasonality of discharge and caused an increase in base flow.

Scenario planning is a technique used to inform decision-making under uncertainty, and is increasingly applied in the field of climate change adaptation and policy. This paper describes applications that combine previously distinct scenario methods in new and innovative ways. It draws on numerous recent independent case studies to illustrate emerging practices, such as far stronger connections between researcher-driven and participatory approaches and cycling between exploratory and normative perspectives. The paper concludes with a call for greater support for, and collaboration among, practitioners with the argument that mixed methods are most effective for decision-making in the context of climate change challenges.

<p> Tropical precipitation is linked through the moist static energy (MSE) budget to the global distribution of sea surface temperatures (SSTs), and large deviations from the present-day SST distribution have been inferred for past climates and projected for global warming. We use idealized SST perturbation experiments in multiple atmospheric general circulation models (AGCMs) to examine the hydrologic and energetic responses in the zonal mean and in the African Sahel to SST perturbations. We also use observational data to assess the prospects for emergent constraints on future rainfall in the Sahel. </p><p> The tropical zonal mean anomalous MSE fluxes in the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) AM2.1 AGCM due to SST anomalies caused by either historical greenhouse gas or aerosol forcing primarily occur through the time-mean, zonal mean (Hadley) circulation. Away from the Intertropical Convergence Zone (ITCZ), this largely stems from altered efficiency of the Hadley circulation energy transport, i.e. the gross moist stability (GMS). A thermodynamic scaling-based estimate that relates GMS change to the local climatological moisture and temperature change relative to the ITCZ captures most of the qualitative GMS responses. It also yields a heuristic explanation for the well known correlation between low-latitude MSE fluxes and the ITCZ latitude. </p><p> Severe Sahelian drying with uniform SST warming in AM2.1 is eliminated when the default convective parameterization is replaced with an alternate. The drying is commensurate with MSE convergence due to suppressed ascent balanced by MSE divergence due to increased dry advection from the Sahara. These qualitative energetic responses to uniform warming are shared by five other GFDL models and ten CMIP5 models, although they do not translate into quantitative predictors of the Sahel rainfall response. Climatological values and interannual variability in observations and reanalyses suggest that drying in AM2.1 is exacerbated by an overly top-heavy ascent profile and positive feedbacks through cloud radiative properties. Simulations with patterned SST anomalies suggest a major role for mean SST variations in discrepancies among models and potentially in observed decadal variations of Sahelian precipitation.</p>

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2016. / The diaries of Jan van Riebeeck contains one of the oldest documentary records of weather phenomena for the southwestern Cape. They contain descriptions of daily wind direction and strength and daily rainfall events. The primary aim of this research is to reconstruct a comprehensive weather chronology for the southwestern Cape region from these diaries, spanning the period 1652-1665, and place this in context with the 20th-21st C climate for the region. The study further aims to examine the relationships between the 17th C society and natural environment. All climate and environmental information is extracted from the diaries and tabulated. Qualitative information on wind and rain was classified and transformed into quantitative data. Contemporary data retrieved from the Royal Observatory and the South African Weather Services are used to make comparisons between the historical study period and contemporary conditions. However, due to the qualitative nature of the historical data, statistical analysis demonstrated that such comparisons are limited. Within the historical period, analysis of the number of rain days demonstrated a distinct wet period in the first half followed by progressive drying. Wind data from the diaries reflected distinct seasonality linked to shifts in the position of the ITCZ. Additionally, unusual events including snow, hail, the Black south-easterly and ‘dirty rain’ are explored. Qualitative data revealed a heavy reliance on climate to support crops and livestock, and a range of environmental stresses to human health, infrastructure and food security. / LG2017

The summer rainfall region of South Africa is dominated by convective thunderstorm development from October to March. The result is that lightning is a common event over most of the country during this time. The South African Weather Service (SAWS) installed a stateof- the-art Lightning Detection Network (LDN) in late 2005 in order to accurately monitor lightning across South Africa. Data from this network for 2006 was utilised in order to develop an initial climatology of lightning in South Africa. Analyses were performed of lightning ground flash density, flash median peak current and flash multiplicity on a 0.2° grid across South Africa. The highest ground flash density values were found along the eastern escarpment of the country, extending onto the high interior plateau. There is a general decrease in flash density from east to west, with almost no lightning recorded on the west coast of the country. The regions of highest flash density recorded the highest percentages of negative polarity lightning. The percentage of positive lightning was higher in the winter months, as was the median peak current of lightning of both polarities. The median peak current distribution displayed distinct bands of current values oriented in northwest to southeast bands across the country. The bands of higher median peak current correspond to the regions to the rear of the interior trough axis in areas dominated by stratiform cloud development and were more dominant in the mid summer months. The highest flash multiplicity was recorded in the regions of highest flash density. Along the southern escarpment, on the eastern side of South Africa, flash multiplicity values exceeded 3 flashes per square kilometer. The highest flash multiplicity of negative polarity lightning was recorded in the spring and early summer. Throughout the year, the percentage of single stroke flashes for positive lightning is high. Topography and the position of the surface trough have a very strong influence on the ground flash density and median peak current distributions, but not on the flash multiplicity distribution. The results from the analyses of the three lightning variables were then combined to determine risk indexes of high intensity lightning and of positive polarity lightning. The eastern part of South Africa is at extreme risk from both large amounts of lightning and from positive polarity lightning, whereas the regions in the northwest of the country that are dominated by mining are at extreme risk from mainly positive polarity lightning.

Thesis advisor: Corinne I. Wong / The South American Monsoon System is the dominant convective system over tropical South America during austral summer that is critical to a region heavily dependent on agricultural and hydroelectric production. An understanding of the controls on moisture conditions throughout Brazil is critical to assessing recurrent droughts and global climate change responses. An increasing number of monsoon reconstructions from δ¹⁸O records provide insight into last millennium variation of regional monsoon intensity. However, the relationship between past variations in monsoon intensity and local moisture conditions has yet to be investigated. In this study, we develop speleothem ⁸⁷Sr/⁸⁶Sr values as a paleo-moisture proxy from a cave site located in central Brazil. Increasing speleothem ⁸⁷Sr/⁸⁶Sr values and decreasing δ²³⁴U values over the last millennium indicate progressively wetter conditions. A similar trend in monsoon intensity is not evident in δ¹⁸O records from the region, suggesting that monsoon intensity is decoupled from the local moisture conditions through the late Holocene. The potential decoupling between the monsoon and local moisture conditions suggests that processes independent from those governing monsoon intensity may play a critical role in dictating moisture variability in the region. / Thesis (MS) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

<p> Climate change has the potential to expose sea turtle nests to higher temperatures, which may negatively impact sea turtle hatchling vigor. In this study, loggerhead and green hatchlings were sampled from the Boca Raton, Florida beach and via lab incubation, and hatchling vigor was determined. Elevated nest temperatures decreased loggerhead and green turtle hatchling performance and corticosterone levels, with the most significant effects found in hatchlings exposed to maximum incubation temperatures above 35 &deg;C during late development. Lab-incubated loggerhead post-hatchling corticosterone levels and growth rates were also determined. The differences seen in corticosterone levels with overall nest incubation temperatures, mean temperatures during early, middle or late stages of development, and its negative correlation with hatchling performance improves our understanding of the underlying physiological mechanisms linking elevated incubation temperatures and sub-lethal physiological effects that may significantly impact hatchling survival, a critical step for sea turtle conservation in south Florida and elsewhere.</p><p>