Research poster: Water source partitioning for shrubland transpiration using innovative field methods

Research poste

Initiation of a Stable Convective Hydroclimatic Regime in Central America Circa 9000 Years BP

Many Holocene hydroclimate records show rainfall changes that vary with local orbital insolation. However, some tropical regions display rainfall evolution that differs from gradual precessional pacing, suggesting that direct rainfall forcing effects were predominantly driven by sea-surface temperature thresholds or inter-ocean temperature gradients. Here we present a 12,000 yr continuous U/Th-dated precipitation record from a Guatemalan speleothem showing that Central American rainfall increased within a 2000 yr period from a persistently dry state to an active convective regime at 9000 yr BP and has remained strong thereafter. Our data suggest that the Holocene evolution of Central American rainfall was driven by exceeding a temperature threshold in the nearby tropical oceans. The sensitivity of this region to slow changes in radiative forcing is thus strongly mediated by internal dynamics acting on much faster time scales

Morning concurrent track 2: Creation and correction of myths about global warming

MORNING CONCURRENT TRACK 2: CREATION AND CORRECTION OF MYTHS ABOUT GLOBAL WARMING Moderator Robert Futrell Student Union Room 211 Matthew Lachniet – Global Warming Misconceptions and Myths: Barriers and Opportunities for Communicating Climate Change Science to a Non-scientific Audience Abstract: Opinions on an anthropogenic influence in global warming abound. Within the non-scientific public, the strength of one’s opinion commonly seems to be in inverse proportion to their knowledge of climate science. One reason for this disconnect between reality and opinion is the persistence of many climate change myths in popular knowledge of global warming. These myths are regularly propagated in popular media and internet blogs, some of which appear to be driven more by ideology than a quest for truth about Nature. In the past, the desire to provide balance in media coverage of global warming at the expense of scientific accuracy has handed the soapbox to many with minority viewpoints that are not supported by all of the available scientific evidence. However, many of these myths contain an element of but have been misunderstood (at best) by the general public and misappropriated (at worst) by interest groups on all sides of ideological spectrum. This presentation will outline some of the common myths on global warming and how they can be used as opportunities in a teaching environment to enhance students’ understanding of global warming and climate science. Gale Sinatra, CarolAnne Kardash, Gita Taasoobshirazi, Doug Lombardi – College Students’ Understanding of and Reactions to Global Warming Abstract: The principles underlying global climate change involve a complex interconnection between many scientific concepts that are difficult for students to understand. This study examined whether persuasive texts would impact readers’ willingness to take mitigative action to reduce the impacts of human-induced climate change. College students participating in the study were randomly assigned to read a persuasive text about global warming or the same text accompanied by a persuasive image. Both groups showed statistically significant increases in their knowledge about global warming and their willingness to take action to reduce its effects. This research demonstrates that persuasive text can produce not only change in students’ thinking about a controversial topic like global climate change, but may also promote a willingness to take action. This is significant because in the case of this topic, a change in students’ knowledge may not be a sufficient criterion for successful learning. It may be as important to promote willingness in future generations to take efforts to reduce their individual impact on the environment. E. Michael Nussbaum – Global Warming and Middle School: An Argument-Based Intervention Abstract: As part of a semester-long intervention to teach middle school students to critically evaluate arguments, 60 sixth- and seventh- graders from a Las Vegas charter school in the Clark County School District discussed issues surrounding global climate change. The presentation will first describe the argument-based intervention used with the students and its effect on attitude change. Most students became accepting of the existence of global climate change and the need to develop alternative modes of transportation. The intervention also provided students with some opportunity to learn about science, political, geography, and economics in an integrated way, as well as an opportunity to develop critical and creative thinking. Second, the overall findings of the research study will be presented, concluding that the skill of “weighing values” may be a productive one to teach to middle school students. Third, some misconceptions that students retained will be described so that future instructional efforts may address them. Doug Lombardi – Students’ Perceptions about the Plausibility of Human Induced Climate Change Abstract: Students can develop robust misconceptions when encountering complex phenomena such as global climate change. For example, students cite short0term and local weather events as evidence to support or refute long‐term changes, and thereby display a fundamental misunderstanding about the distinctions between weather and climate. This confusion may impact perceptions of plausibility about scientific statements that implicate humans in worldwide increases in global temperatures and widespread melting of snow and ice. Additionally, the confusion between weather and climate may be related to a fundamental lack of understanding about deep time, a concept that spans several scientific content areas. This presentation will describe an ongoing study involving undergraduate students enrolled in introductory geoscience and geography courses. Currently, students are completing three surveys examining the relationships between student understanding of deep time and their confusion about the distinctions between weather and climate, as well as how these levels of understanding influence perceptions about the plausibility of human‐induced global climate change. This presentation will highlight preliminary results

Water Source Partitioning for Shrubland Transpiration Using Innovative Field Methods

37 PowerPoint slides Convener: Franco Biondi, UNR & Michael Young, DRI Session 4: Ecological Change and Water Resources Abstract: -Climate change models predict a decline in precipitation over the next few decades throughout much of the southwest. -Such change has the potential to shift water uptake dynamics of phreatophytes -If groundwater pumping also occurs, the impact of climate change could be exacerbated. -A better understanding of the forces that drive the coupling and decoupling of phreatophytes to groundwater is needed

Extreme rainfall activity in the Australian tropics reflects changes in the El Niño/Southern Oscillation over the last two millennia

Assessing temporal variability in extreme rainfall events before the historical era is complicated by the sparsity of long-term “direct” storm proxies. Here we present a 2,200-y-long, accurate, and precisely dated record of cave flooding events from the northwest Australian tropics that we interpret, based on an integrated analysis of meteorological data and sediment layers within stalagmites, as representing a proxy for extreme rainfall events derived primarily from tropical cyclones (TCs) and secondarily from the regional summer monsoon. This time series reveals substantial multicentennial variability in extreme rainfall, with elevated occurrence rates characterizing the twentieth century, 850–1450 CE (Common Era), and 50–400 CE; reduced activity marks 1450–1650 CE and 500–850 CE. These trends are similar to reconstructed numbers of TCs in the North Atlantic and Caribbean basins, and they form temporal and spatial patterns best explained by secular changes in the dominant mode of the El Niño/Southern Oscillation (ENSO), the primary driver of modern TC variability. We thus attribute long-term shifts in cyclogenesis in both the central Australian and North Atlantic sectors over the past two millennia to entrenched El Niño or La Niña states of the tropical Pacific. The influence of ENSO on monsoon precipitation in this region of northwest Australia is muted, but ENSO-driven changes to the monsoon may have complemented changes to TC activity

Interhemispheric antiphasing of neotropical precipitation during the past millennium

Uncertainty about the influence of anthropogenic radiative forcing on the position and strength of convective rainfall in the Intertropical Convergence Zone (ITCZ) inhibits our ability to project future tropical hydroclimate change in a warmer world. Paleoclimatic and modeling data inform on the timescales and mechanisms of ITCZ variability; yet a comprehensive, long-term perspective remains elusive. Here, we quantify the evolution of neotropical hydroclimate over the preindustrial past millennium (850 to 1850 CE) using a synthesis of 48 paleo-records, accounting for uncertainties in paleo-archive age models. We show that an interhemispheric pattern of precipitation antiphasing occurred on multicentury timescales in response to changes in natural radiative forcing. The conventionally defined “Little Ice Age” (1450 to 1850 CE) was marked by a clear shift toward wetter conditions in the southern neotropics and a less distinct and spatiotemporally complex transition toward drier conditions in the northern neotropics. This pattern of hydroclimatic change is consistent with results from climate model simulations indicating that a relative cooling of the Northern Hemisphere caused a southward shift in the thermal equator across the Atlantic basin and a southerly displacement of the ITCZ in the tropical Americas, with volcanic forcing as the principal driver. These findings are at odds with proxy-based reconstructions of ITCZ behavior in the western Pacific basin, where changes in ITCZ width and intensity, rather than mean position, appear to have driven hydroclimate transitions over the last millennium. This reinforces the idea that ITCZ responses to external forcing are region specific, complicating projections of the tropical precipitation response to global warming

Sensitivity of northwest Australian tropical cyclone activity to ITCZ migration since 500 CE

Tropical cyclones (TCs) regularly form in association with the intertropical convergence zone (ITCZ), and thus, its positioning has implications for global TC activity. While the poleward extent of the ITCZ has varied markedly over past centuries, the sensitivity with which TCs responded remains poorly understood from the proxy record, particularly in the Southern Hemisphere. Here, we present a high-resolution, composite stalagmite record of ITCZ migrations over tropical Australia for the past 1500 years. When integrated with a TC reconstruction from the Australian subtropics, this time series, along with downscaled climate model simulations, provides an unprecedented examination of the dependence of subtropical TC activity on meridional shifts in the ITCZ. TCs tracked the ITCZ at multidecadal to centennial scales, with a more southward position enhancing TC-derived rainfall in the subtropics. TCs may play an increasingly important role in Western Australia’s moisture budgets as subtropical aridity increases due to anthropogenic warming

Variability of trace-elements and δ18O in drip water from Gruta del Rey Marcos, Guatemala; seasonal and environmental effects, and its implications for paleoclimate reconstructions

Guatemala is located at the core of one of the largest warming pools in the planet, the Western Hemisphere Warm Pool, an important source of tropical moisture to middle and high latitudes and, thus, a key area for paleoclimatic studies. This, along the karst pervasiveness in the area provides the opportunity to obtain high-resolution records of past hydroclimatic conditions using stalagmites. Despite this, the atmospheric and geochemical processes that might affect the variability of geochemical proxies in stalagmites are yet to be constrained, as no cave-monitoring in the area has been carried out previously. Here, we present a 2.5-year cave-monitoring study from Gruta del Rey Marcos, Guatemala, which allows to understand the effect of external atmospheric and environmental conditions upon the variability of δ18O, Mg/Ca, Sr/Ca, and Ba/Ca in drip water. By incorporating cave ventilation dynamics, isotopic information of local rainfall and cave-river water, we are able to understand the most relevant processes that affect the variability of the geochemical proxies in drip water, hence stalagmites. Our results suggest that two-isotopically distinct rainfall regimes, as well as tropical cyclones affecting the area contribute to the composition of the drip-water, hence the resulting stalagmites, with low δ18O (∼-6‰ VSMOW) values indicative of strong convective activity, whilst high δ18O values (−4.5 and −5‰ VSMOW), are indicative of poor convection and proportionally more significant winter-frontal rainfall. We also demonstrate that the trace-element composition of drip water is largely modulated by PCP, and thus, the variability in underlying stalagmites can be interpreted to reflect changes in karst humidity, with low E/Ca ratios (E = Mg, Sr, Ba), indicative of a wet epikarst and high E/Ca ratios indicative of a dry epikarst. Our results provide essential information for the interpretation of the δ18O and trace element variability in stalagmites, which can result in robust paleoclimatic reconstructions from Gruta del Rey Marcos and elsewhere in central America and southern Mexico

A Multiproxy Database of Western North American Holocene Paleoclimate Records

Holocene climate reconstructions are useful for understanding the diverse features and spatial heterogeneity of past and future climate change. Here we present a database of western North American Holocene paleoclimate records. The database gathers paleoclimate time series from 184 terrestrial and marine sites, including 381 individual proxy records. The records span at least 4000 of the last 12 000 years (median duration of 10 725 years) and have been screened for resolution, chronologic control, and climate sensitivity. Records were included that reflect temperature, hydroclimate, or circulation features. The database is shared in the machine readable Linked Paleo Data (LiPD) format and includes geochronologic data for generating site-level time-uncertain ensembles. This publicly accessible and curated collection of proxy paleoclimate records will have wide research applications, including, for example, investigations of the primary features of ocean-atmospheric circulation along the eastern margin of the North Pacific and the latitudinal response of climate to orbital changes. The database is available for download at https://doi.org/10.6084/m9.figshare.12863843.v1 (Routson and McKay, 2020)