Search Results

This chapter briefly describes the current understanding of the recent geological history of climate and oceanography in the Indian Ocean and its implications for human-induced climate change. A series of dry and wet rainfall oscillations over the past few millenniums are associated with periods of prosperity and hardship for the people of the region. There is an emerging warming trajectory in the region reflected in a number of proxies and confirmed by various sources of environmental data. This is leading to more drought conditions in most of the region, extreme weather, and stressful temperature conditions for marine and other organisms. This trend and heterogeneity is expected to increase and the net effects will challenge the region’s ecology and human wellbeing.

This chapter frames our current state of knowledge about the physical climate in the period of the Roman Empire's expansion, flourishing, and final fragmentation, at roughly 200 BCE to 600 CE. The emphasis here is on the new evidence of paleoclimate proxy data. The chapter explores what it is starting to tell historians about the timing and nature of large-scale climate change in the centuries of interest. To conclude, the chapter draws together the disparate sources of evidence into a tentative narrative. It highlights the questions that can be asked about the relationship between climate change and historical change and underscores the need for more and better data to fill in such a narrative in the future.

This chapter presents an overview of the physical environment and the paleoclimate record of peninsular India during the latter half of the Holocene. It begins by describing the geographical and ecological situation in the present-day state of Maharashtra, and then focuses specifically on the impact of the monsoon system on agricultural production. After describing the contemporary environment and climate, the chapter outlines paleoclimate research from diverse data sources and describes the current synthetic view of the late Holocene climate, which challenges previously accepted models for understanding human–environment interactions in the Deccan Chalcolithic period.

This chapter discusses the modern climate of California and the paleoclimate and paleobiogeography of the California vegetation. California's Mediterranean climate of winter precipitation and protracted summer drought is an outcome of seasonal changes in global circulation. Climate variability in California is correlated with two-coupled ocean-atmospheric phenomena, the El Niño-Southern Oscillation and the Pacific Decadal Oscillation. The chapter also discusses global climate change, local plate tectonic history, and the development of the California flora since the late Cretaceous. Paleobiogeographic and climatic evidences are then compared to address how climate has influenced the paleobiota leading to modern vegetation. The chapter ends by considering areas for future research.

This chapter describes fossil deposits of mammals in the Badger Room of Porcupine Cave. The Badger Room is a small chamber in the Porcupine Cave system located approximately 25 m from the modern entrance to the cave. The Badger Room mammal fauna is very diverse; it contains abundant lagomorph, rodent, and carnivore remains. Some of the specimens were used to explore the paleoclimate of the region surrounding the cave. The climate spaces occupied by each species were assumed to encompass the physiological tolerance limits of each taxon with regard to temperature and moisture. The chapter also used autecological estimates for habitat reconstruction and analysis of the community structure of the mammal fauna.

Beneath the gently rolling, seemingly mundane topography that characterizes the shortgrass steppe is a complex mosaic of soils. Many of these soils are superimposed upon older, buried soils that formed in other millennia under different climatic regimes. The nature of this soil mosaic reveals much about the past and dictates much about the future of the shortgrass steppe. There is considerable heterogeneity among soils of the shortgrass steppe, yet they maintain a high degree of homogeneity when contrasted with soils of other ecosystems. The driving forces that make these soils alike are a semiarid climate and a resilient plant community ( P ielke and Doesken, chapter 2, this volume; and Lauenroth, chapter 5, this volume). The combined effects of vegetation and climate on soil development yield generally predictable results. Shortgrass steppe soils are characterized by the accumulation of organic matter in the surface (0–20 cm). Approximately 60% of the graminoid root mass resides in the - rst 10 cm of mineral soil (Schimel et al., 1986); 90% is contained in the surface 20 cm (Schimel et al., 1985). Surface horizons typically are darker hued than underlying horizons and have organic carbon contents that average 1% to 3% (Yonker et al., 1988). Shortgrass steppe soils maintain a high-percent base saturation (and high pH) because of low leaching and weathering potentials that result from semiarid conditions. Zones of secondary calcium carbonate accumulation are common in subsurface horizons and may appear as threads, seams, or nodules (Blecker et al., 1997). In addition, these soils are characterized by zones of secondary clay accumulation in subsurface horizons; clay accumulations are a result of either the in situ weathering of primary minerals or the translocation of clay minerals leached from the surface horizon. In either case, the maximum depth of accumulation gives some indication of the time-averaged depth of the wetting front in the soil pro- le (Blecker et al., 1997). The factors that produce considerable heterogeneity among the soils of the shortgrass steppe are related to parent material, the age of the soil, and the subtleties of topography. These factors vary at a - ner scale than either vegetation or climate.

The instrumental record shows steadily rising global surface temperatures as the atmospheric concentration of carbon dioxide and other greenhouse gases increased during the industrial age. Numerous complementary scientific techniques have shown clearly that these increases are due to human activity, notably burning fossil fuels. The instrumental record is complemented by proxy measurements that reliably document the earth’s temperature and the atmospheric concentration of carbon dioxide for hundreds of thousands, and in some cases, millions of years. Present conditions are unprecedented in those time frames. Without drastic reductions in the emission of carbon dioxide the worst is yet to come.

Exciting days lie ahead for paleolimnology. As we embark on a new millennium, the opportunities and challenges in this field are extremely bright. As an epilogue to this book, it seems appropriate to conclude with a few of the developments that seem to me particularly promising for the near future. 1. Increasing application of paleolimnological data to address problems in global climate change. Paleolimnologists need to make governments and societies aware of the importance of high-resolution paleorecords from lakes for providing information about baseline variability of the biosphere, consequences and histories of past climate change events, and past responses of our precious aquatic resources to such changes. Paleolimnology should and will increasingly play a role in providing decision-makers with critical information about earth system history as they formulate policies to cope with these changes. Few, if any, paleoenvironmental records provide earth history records in environments as intimately associated with human activity as lake deposits. Lakes and wetlands are increasingly recognized as potentially important components of the global carbon cycle, especially as environments for sequestering large volumes of carbon, and future research will undoubtedly quantify the magnitude and dynamics of this role. Paleolimnologists will need to work even more closely with climate modelers, hydrologists, and atmospheric scientists in years to come, to insure that the paleorecords we study will help resolve important questions about the earth’s climate system. 2. Advances in geobiology. The rapid developments of new and automated tools in molecular biology and organic geochemistry for analyzing small sample volumes and extracting compound-specific isotopic information from organic compounds have important implications for paleolimnology. In years to come we will increasingly rely on organic geochemistry and microbial geobiology to help decipher the organic record of algal primary producers, decomposers, and other elements of the microbial food web. These are components of a lake’s ecosystem that ecologists recognize as immensely important in biogeochemical cycles and as being on the front line of lake responses to changes in climate and watershed processes, but which have heretofore been largely intractable to any detailed interpretation by paleolimnologists.

This concluding chapter summarizes the contributions of earlier chapters in this book and discusses the relevance of the Daka Member to broader questions of paleoclimate and evolution. It outlines the impacts that Daka fossils have had on the different taxonomic groups and also considers some recent attempts to relate biotic evolution to paleoclimate.

A description of my personal journey from climate scientist to becoming a Jungian psychologist. An exploration of how Earth’s climate of the deep past relates to where the climate system is headed over this century.

In this chapter, the author explains how the hockey stick arose as a logical consequence of decades of work by paleoclimate researchers that led to increasingly rich networks of climate proxy data and the introduction of new ways to use such data to reconstruct past climates. He first considers early efforts to build year-by-year chronologies of climate change at many locations around the globe, reaching back centuries and in some cases millennia, using proxy records such as tree rings and ice cores. He then discusses his postdoctoral research aimed at developing and applying a new statistical approach to the problem of proxy climate reconstruction by focusing on the underlying spatial patterns of variation in the surface temperatures of the Northern Hemisphere. He also describes the reaction generated by his study, carried out in collaboration with Raymond Bradley and Malcolm Hughes, from the media and those who perceived that the findings undermined one of their primary arguments against human-caused climate change. Finally, the author reviews the history behind the IPCC Third Assessment Report published in 2001.

This chapter explains how the hockey stick emerged as a fundamental icon in the assault against the scientific case for human-caused climate change after it was displayed in the IPCC Third Assessment Report's Summary for Policy Makers in 2001. Thrust into the limelight, the hockey stick would be displayed in public lectures by IPCC chairman Sir John Houghton of the UK and appear in books written about climate change. Vice President Al Gore cited the findings of the hockey stick study, known as MBH99, in a number of his speeches on climate change during 1999. In the years following publication of the hockey stick, a healthy scientific debate developed within the paleoclimate research community over the details, such as how cold the Northern Hemisphere was on the whole during the Little Ice Age, or how warm it was at the height of the medieval climate anomaly/medieval warm period. The chapter also discusses the campaign launched by climate change deniers to discredit the author's hockey stick paper.

Archaeological site investigations on the South Atlantic Coastal Plain have revealed stratified cultural remains in sand deposits of mixed aeolian and fluvial origins, aeolian sand sheets and dunes, alluvial terraces, and Carolina Bay rims. These sites are typically shallow but have yielded discernible archaeostratigraphy within sand dominated deposits by using luminescence dating (OSL), AMS radiocarbon dating, and close interval sediment sampling. Periods of site burial are linked to regional and global paleoclimate records, including Bond events, and provide broader reconstructions for human ecology and periods of site burial.

This chapter begins by reviewing the geologic development of present-day California, including the roles of plate tectonics and mountain uplift. It next reviews the history of the climate from around 50 million years ago (coincident with the origins of the modern land area), through progressive drying and cooling, to the origin of the modern Mediterranean-type climatic regime in the last 2 million years. It finally summarizes the broad outlines of California's floristic history from 50 million years ago to the present.

We analyze a 2400-year rainfall reconstruction from an ultra-high-resolution absolutely-dated stalagmite (JX-6) from southwestern Mexico (Lachniet et al., 2012). Oxygen isotope variations correlate strongly to rainfall amount in the Mexico City area since 1870 CE, and for the wider southwestern Mexico region since 1948, allowing us to quantitatively reconstruct rainfall variability for the Basin of Mexico and Sierra Madre del Sur for the past 2400 years. Because oxygen isotopes integrate rainfall variations over broad geographic regions, our data suggest substantial variations in Mesoamerican monsoon strength over the past two millennia. As a result of low age uncertainties (≤ 11 yr), our stalagmite paleoclimate reconstruction allows us to place robust ages on past rainfall variations with a resolution an order of magnitude more precise than archeological dates associated with societal change. We relate our new rainfall reconstruction to the sequence of events at Teotihuacan (Millon, 1967; Cowgill, 2015a) and to other pre-Colombian civilizations in Mesoamerica. We observe a centuries long drying trend that culminated in peak drought conditions in ca. 750 CE related to a weakening monsoon, which may have been a stressor on Mesoamerican societies. Teotihuacan is an ideal location to test for links between climate change and society, because it was located in a semi-arid highland valley with limited permanent water sources, which relied upon spring fed irrigation to ensure a reliable maize harvest (Sanders, 1977). The city of Teotihuacan was one of the largest Mesoamerican cities, which apparently reached population sizes of 80,000 to 100,000 inhabitants by AD 300 (Cowgill, 1997; 2015a). Following the “Great Fire”, which dates approximately to AD 550, population decreased to lower levels and many buildings were abandoned (Cowgill, 2015). Because of the apparent reliance on rainwater capture (Linn é, 2003) and spring-fed agriculture in the Teotihuacan valley to ensure food security and drinking water, food production and domestic water supplies should have been sensitive to rainfall variations that recharge the surficial aquifer that sustained spring discharge prior recent groundwater extraction.

Multiple palaeoclimatic reconstructions point to a succession of major droughts in the Maya Lowlands between AD 750 and 1100 superimposed on a regional drying trend that itself was marked by considerable spatial and temporal variability. The longest and most severe regional droughts occurred between AD 800 and 900 and again between AD 1000 and 1100. Well-dated historical records carved on stone monuments from forty Classic Period civic-ceremonial centers reflect a dynamic sociopolitical landscape between AD 250 and 800 marked by a complex of antagonistic, diplomatic, lineage-based, and subordinate networks. Warfare between Maya polities increased between AD 600 and 800 within the context of population expansion and long-term environmental degradation exacerbated by increasing drought. Nevertheless, in spite of the clear effects of drought on network collapse during the Classic Period, one lingering question is why polities in the northern lowlands persisted and even flourished between AD 800 and 1000 (Puuc Maya and Chichén Itzá) before they too fragmented during an extended and severe regional drought between AD 1000 and 1100. Here we review available regional climate records during this critical transition and consider the different sociopolitical trajectories in the South/Central versus Northern Maya lowlands.