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Five distinct records of US tornado outbreak history are created by applying separate criteria from published definitions of 'outbreak' to the complete US tornado dataset covering 1975-2014. To identify statistical patterns in the resulting outbreak records, time trends were calculated using bivariate correlation against time (year), ANOVA was used to evaluate similarities and differences between the different records, and kernel density analysis was used to identify and map spatial patterns in outbreak variables in each record. The tornado record, and specifically the tornado outbreak record, shows a general increasing trend during the period of study for all five definitions, albeit only in the non-summer seasons. Results from ANOVA indicate statistically significant differences in outbreak records between definitions. According to our analyses, regardless of the definition, the total number of tornado outbreaks (TO), the total number of tornadoes that were part of an outbreak (Outbreak Tornadoes; OT), and outbreak tornadoes as a proportion of all tornadoes (OTP) exhibit their highest annual mean values in a tripole pattern including central Arkansas, central Mississippi, and northern Alabama. This is one of the few consistencies across outbreak records between the different definitions, and we propose that this region represents 'Tornado Outbreak Alley,' in contrastto the traditional 'Tornado Alley' of the southern Great Plains. KEYWORDS: Outbreak tornado, 'Tornado outbreak alley,' Multi-tornado events, HIGHLIGHTS: * Tornado outbreak histories based on different definitions of outbreak are statistically distinct from each other. * For all selected definitions of outbreak, positive trends were detected in all [...] more...

The climate of the past millennium provides a baseline for understanding the background of natural climate variability upon which current anthropogenic changes are superimposed. As this period also contains high [...] more...

There was a rise in the community of Neolithic people in the Gulf of Bothnia in modern-day Finland due to the 2,000-year-long warm climate phase about 4,000 years ago. The archaeological research into how these people survived during this period of climate change is discussed. more...

Development of continental aridity has been linked to late Cenozoic global cooling, but the evidence is indirect, based on terrestrial loess deposits and eolian silt in marine sediments, whereas direct dating of the inception of arid landforms has been frustrated by a lack of suitable methods. Here we report the first age determination of a major arid-zone dune field, based on cosmogenic [sup.10]Be and [sup.26]Al measurements of drill cores from dunes in the Simpson Desert, central Australia. Results show that the dune field began to form ca. 1 Ma, whereas dating using quartz optically stimulated luminescence indicates episodic dune building during late Quaternary ice ages. Less intense desertification began earlier; the previous cosmogenic exposure dating showed that neighboring stony deserts began to form at the onset of Quaternary ice ages 2-4 Ma. Aridity deepened and the dune field formed when ice age cycles increased their amplitude and switched their periods from 40 k.y. to 100 k.y. ca. 1 Ma. more...

Byline: Nicholas E. Graham (1,2), Malcolm K. Hughes (3), Caspar M. Ammann (4), Kim M. Cobb (5), Martin P. Hoerling (6), Douglas J. Kennett (7), James P. Kennett (8), Bert Rein (9), Lowell Stott (10), Peter E. Wigand (11,12), Taiyi Xu (6) Abstract: Terrestrial and marine late Holocene proxy records from the western and central US suggest that climate between approximately 500 and 1350 a.d. was marked by generally arid conditions with episodes of severe centennial-scale drought, elevated incidence of wild fire, cool sea surface temperatures (SSTs) along the California coast, and dune mobilization in the western plains. This Medieval Climate Anomaly (MCA) was followed by wetter conditions and warming coastal SSTs during the transition into the 'Little Ice Age' (LIA). Proxy records from the tropical Pacific Ocean show contemporaneous changes indicating cool central and eastern tropical Pacific SSTs during the MCA, with warmer than modern temperatures in the western equatorial Pacific. This pattern of mid-latitude and tropical climate conditions is consistent with the hypothesis that the dry MCA in the western US resulted (at least in part) from tropically forced changes in winter NH circulation patterns like those associated with modern La Nina episodes. We examine this hypothesis, and present other analyses showing that the imprint of MCA climate change appears in proxy records from widely distributed regions around the planet, and in many cases is consistent with a cool medieval tropical Pacific. One example, explored with numerical model results, is the suggestion of increased westerlies and warmer winter temperatures over northern Europe during medieval times. An analog technique for the combined use of proxy records and model results, Proxy Surrogate Reconstruction (PSR), is introduced. Author Affiliation: (1) Hydrologic Research Center, 12780 High Bluff Drive, Suite 250, San Diego, CA, 92130-2069, USA (2) Scripps Institution of Oceanography, La Jolla, CA, USA (3) University of Arizona, Tucson, AZ, USA (4) National Center for Atmospheric Research, Boulder, CO, USA (5) Georgia Technical Institute, Atlanta, GA, USA (6) NOAA Climate Diagnostics Center, Boulder, CO, USA (7) University of Oregon, Eugene, OR, USA (8) University of California Santa Barbara, Santa Barbara, CA, USA (9) Johannes Gutenberg-Universitat Mainz, Mainz, Germany (10) University of Southern California, Los Angeles, CA, USA (11) University of Nevada, Reno, NV, USA (12) California State University, Bakersfield, CA, USA Article History: Registration Date: 18/01/2007 Received Date: 16/02/2006 Accepted Date: 18/12/2006 Online Date: 03/04/2007 Article note: The online version of this article ( http://dx.doi.org/10.1007/s10584-007-9239-2) contains supplementary material, which is available to authorized users. more...

Byline: Georgina H. Endfield (1) Abstract: In this paper, unpublished archival documentary sources are used to explore the vulnerability to--and implications of--climatic variability and extreme weather events in colonial Mexico. Attention focuses on three regions covering a variety of environmental, social, economic, and political contexts and histories and located at key points along a north-south rainfall gradient: Chihuahua in the arid north, Oaxaca in the wetter south and Guanajuato located in the central Mexican highlands. A number of themes are considered. First, the significance of successive, prolonged, or combined climate events as triggers of agrarian crisis. Second, a case study demonstrating the national and regional impacts of a particularly devastating climate induced famine, culminating with the so-called 'Year of Hunger' between 1785 and 1786, is presented. The way in which social networks and community engagement were rallied as a means of fortifying social resilience to this and other crises will be highlighted. Third, the impacts of selected historical flood events are explored in order to highlight how the degree of impact of a flood was a function of public expectation, preparedness and also the particular socio-economic and environmental context in which the event took place. An overview of the spatial and temporal variations in vulnerability and resilience to climatic variability and extreme weather events in colonial Mexico is then provided, considering those recorded events that could potentially relate to broader scale, possibly global, climate changes. Author Affiliation: (1) School of Geography, University of Nottingham, University Park, Nottingham, NG 7 2RD, UK Article History: Registration Date: 18/04/2006 Received Date: 27/09/2005 Accepted Date: 03/04/2006 Online Date: 08/03/2007 more...

This study focuses on one of the most interesting times of the early instrumental period in northwest Europe (from 1730-1745) attempting to place the extremely cold year of 1740 and the unusual warmth of the 1730s decade in a longer context. The similarity of the features in the few long (and independent) instrumental records together with extensive documentary evidence clearly indicates that remarkable climatic changes occurred rapidly in this period. We use unpublished subjective circulation charts developed by the late Hubert Lamb, to assist in understanding the course of events, particularly during the extreme year of 1740 and the four subsequent years. We also compare these subjective charts with others recently developed using more objective modern reconstruction techniques. Apart from evidence of a reduction in the number of explosive volcanic eruptions following the 1690s, it is difficult to explain the changes in terms of our knowledge of the possible factors that have influenced this region during the 19th and 20th centuries. The study, therefore, highlights how estimates of natural climatic variability in this region based on more recent data may not fully encompass the possible known range. more...

A short history of the series with daily observations of barometric pressure in Padova (since 1725) is made, with special reference to the types of barometers used, their locations, the types of corrections (which were only partial in the early period), the calibrations and the comparison with primary instruments. The paper also describes the homogenisation of the series and the procedures used to fill the small gaps. The Padova series was compared with previously well investigated series from the ADVICE and IMPROVE projects and especially with the nearby Milan series in order to check its reliability. Trend analysis shows an increase in pressure (some 1 hPa) during the last a hundred year. This trend is a common feature for Northem Italy. An effect of the increased air pressure is a local lowering of the Northern Mediterranean Sea level by 1 cm. The part of the year mostly affected by this increase is from late spring to August and corresponds to an extension of the hot season, characterised by an earlier start, and longer duration of the Azores Anticyclone. This reduces the penetration of the Atlantic disturbances in the Northern Mediterranean and the precipitation associated with the passage of fronts. This change is associated with an increase in thermoconvective activity with thunderstorms and heavy precipitation. This explains why, in the last decades, the annual total amount of precipitation is slightly decreased and at the same time the frequency of intense rainfall is increased. Moreover, a comparison of the day-to-day pressure variability with the Western Mediterranean Oscillation (WeMO) indicates a significant positive correlation during the late autumn-early winter period. An increase of the WeMO index means a strengthening of the baric dipole from Azores to Northern Italy, that could be explained by a deepening of the cyclonic circulation over northern Italy from November to January. more...

Vickers focus people are believed to have practiced a lifeway based upon foraging and gardening in the Tiger Hills, a glacial-moraine upland, in southwestern Manitoba. It has also been argued that Vickers focus society was more socially complex than earlier hunter-gatherer groups in the region relying almost exclusively on bison hunting. There is evidence to suggest limited stratification in Vickers focus culture and clear evidence of a widespread exchange network that brought a variety of exotic materials and finely made ceramic vessels into the Lowton site. Other smaller seasonal sites have been identified nearby. These have been interpreted as satellites of the Lowton site. These people appeared as immigrants in the area circa A.D. 1400. Sometime around A.D. 1450 they left the Tiger Hills and have been identified further west in the Lauder Sandhills around 100 years later, following an intensive foraging lifeway. There is evidence they had begun to exploit bison more intensively and this trend is further intensified in the Sanderson site in southeastern Saskatchewan, where a full-fledged bison hunting economy was followed. The cause for their relocation and altered subsistence strategy is believed to have resulted from a sudden, drastic cold spike during the Little Ice-Age. Keywords: horticulture, climate change, settlement patterns, environmental biodiversity, subsistence change more...

Three lines of evidence for abrupt tropical climate change, both past and present, are presented. First, annually and decadally averaged [delta][sup.18]O and net mass-balance histories for the last 400 and 2,000 yr, respectively, demonstrate that the current warming at high elevations in the mid-to low latitudes is unprecedented for at least the last 2 millennia. Second, the continuing retreat of most mid-to low-latitude glaciers, many having persisted for thousands of years, signals a recent and abrupt change in the Earth's climate system. Finally, rooted, soft-bodied wetland plants, now exposed along the margins as the Quelccaya ice cap (Peru) retreats, have been radiocarbon dated and, when coupled with other widespread proxy evidence, provide strong evidence for an abrupt mid-Holocene climate event that marked the transition from early Holocene (pre-5,000-yr-B.P.) conditions to cooler, late Holocene (post-5,000-yr-B.P.) conditions. This abrupt event, [approximately equal to] 5,200 yr ago, was widespread and spatially coherent through much of the tropics and was coincident with structural changes in several civilizations. These three lines of evidence argue that the present warming and associated glacier retreat are unprecedented in some areas for at least 5,200 yr. The ongoing global-scale, rapid retreat of mountain glaciers is not only contributing to global sea-level rise but also threatening freshwater supplies in many of the world's most populous regions. icecore | isotopes | paleoclimate | precipitation | Holocene more...

A high-resolution proxy record of precipitation and evaporation variability through the past 1700 yr from [delta][sup.18]O analysis of a varved lake sequence from central Turkey shows rapid shifts between dry periods (A.D. 300-500 and A.D. 1400-1950) and wetter intervals (A.D. 560-750 and A.D. 1000-1350). Changes are consistent with changes in instrumental and proxy records of the Indian monsoon, dry summers in the Eastern Mediterranean being associated with periods of enhanced monsoon rainfall. In addition, major shifts in the record are coherent with changes in North Atlantic winter climate, with cold, wet periods in the Alps occurring at times of dry Turkish climate. Keywords: Turkey, paleoclimate, monsoon, isotopes, lake sediments, North Sea--Caspian pattern. more...

Bill Ruddiman (Climatic Change, 61, 261-293, 2003) recently suggested that early civilisations could have saved us from an ice age because land management over substantial areas caused an increase in atmospheric C[O.sub.2] concentration. Ruddiman suggests a decreasing 'natural course' of the Holocene greenhouse gases concentrations and sea-level by referring to analogous situations in the past, namely the last three interglacials. An examination of marine isotopic stage 11 would perhaps make Ruddiman's argument even more thought-challenging. Yet, the hypothesis of a natural lowering of C[O.sub.2] during the Holocene contradicts recent numerical simulations of the Earth carbon cycle during this period. We think that the only way to resolve this conflict is to properly assimilate the palaeoclimate information in numerical climate models. As a general rule, models are insufficiently tested with respect to the wide range of climate situations that succeeded during the Pleistocene. In this comment, we present three definitions of paleoclimate information assimilation with relevant examples. We also present original results with the Louvain-la-Neuve climate-ice sheet model suggesting that if, indeed, the Holocene atmospheric C[O.sub.2] increase is anthropogenic, a late Holocene glacial inception is plausible, but not certain, depending on the exact time evolution of the atmospheric C[O.sub.2] concentration during this period. more...

120,000-11,700 years ago--During the Last Glacial Period, a series of sudden climate changes occurred simultaneously in many parts of the world, according to a study published recently in Science. A [...] more...

Early Holocene lacustrine, tree-ring, ice-core, and marine records reveal that the Northern Hemisphere underwent a short cooling event at 10 300 calendar yr B.P. (9100 [sup.14]C yr B.P.). The records were compared on a common high-resolution time scale and show that the event lasted less than 200 yr, with a cooling peak of 50 yr, and the event coincides with a distinct Holocene thermohaline disturbance recognized in the North Atlantic Ocean. In spite of well-known freshwater forcings at the time of the event, the negligible difference between the modeled [DELTA][sup.14]C record, based on the GISP2 (Greenland Ice Sheet Project 2) [sup.10]Be data, and the measured values, does not allow for detectable [DELTA][sup.14]C changes related to global ocean ventilation. We can, however, show that the onset of the cooling coincides with the onset of one of the largest Holocene [sup.10]Be flux peaks. This finding may imply that the climate system is more sensitive to solar-related changes than previously thought and that such changes may be an important underlying mechanism for sub-Milankovitch climate variability. Keywords: Holocene, sub-Milankovitch cooling event, lake sediments, marine records, ice-core proxies, tree rings, [DELTA][sup.14]C, [sup.10]Be, [sup.14]C modeling, solar forcing. more...

Julie Cruikshank (1) ABSTRACT. In northwestern North America, glaciers figure prominently in both indigenous oral traditions and narratives of geophysical sciences. These perspectives intersect in discussions about global warming, predicted [...] more...

This article provides evidence of prehistoric climatic change on the Polynesian island of Motutapu, by investigating prehistoric shellfish for anomalies in molluscan representations. The author suggests that such evidence can be used to explain changes in archaeological records such as the abandonment of sites, voyaging patterns and migrations, and prehistoric environmental impact. more...

Reasons for the extinction of the Neandertals, including climatic changes and competition from modern humans, are discussed. Study of Palaeolithic human DNA remains shows the Neandertals to be a distinct sub-species of Home sapiens. The replacement of Neandertals by modern invaders some 40,000 years ago Changes in stone-artifact production were evidence of the replacement of Neanderals by modern invaders some 40,000 years ago. more...

The 'Medieval Warm Period' is studied to determine its actual warmth and the possible implications it may have to 20th century warming. There is evidence of brief warming periods between 1010-1190, but any implications are inconclusive. more...

Historical documentation describing events on the Mediterranean coast of the Iberian Peninsula allows us to reconstruct the record of catastrophic floods. Through this information, it is possible to identify and to date three climatic oscillations within the so-called 'Little Ice Age': 1570-1630, 1760-1800 and 1830-1870, which coincide with advances in some Alps glaciers. more...

Two sets of paraclimatic data, obtained from direct description rather than measurements of weather conditions, are available for the region between June 1753 and September 1756. These are described and their use as an integrated data set for providing comparisons with the modern climatic regime based on probability analyses is discussed. Comparisons are made in the frequency and timing of frosts, wet days, dry spells and wind direction. These show that, compared with the present, the region experienced earlier and more intense winter cold, fewer wet days and longer dry spells, more frequent westerlies and seasonally more frequent northerlies and easterlies. Further investigation indicates that the record of conditions in the Cork region was compatible with other European data, although some differences of detail are apparent. more...

Studies of the past climate are generally justified through the need to place past, present, and future extremes of climate in a longer historical context. It is important to know how much climate has varied in the past in order to quantify the size and significance of natural fluctuations of the climate system. The underlying premise of such studies is that the past is the key to the future. more...

Author(s): Nele Meckler [sup.1] Author Affiliations: (1) Nele Meckler is in the Department of Earth Science and Bjerknes Centre for Climate Research, University of Bergen, 5007 Bergen, Norway., Cave stalagmites [...], Decoded and precisely dated information encrypted in stalagmites from a cave in China reveal past climatic changes and provide insight into the complex interactions in today's climate system. See Letter p.640 A 640,000-year record of the Asian monsoon Prior records of the Asian monsoon have revealed cyclic variations over hundreds of thousands of years, probably driven by variations in insolation caused by the precession of Earth's orbit. Hai Cheng and colleagues now provide a speleothem record from Chinese cave samples that extends earlier records to 640,000 years ago, close to the maximum age possible with uranium/thorium dating. This spectacular record confirms that the characteristic '100,000-year' ice age cycle corresponds to an integral number (four or five) of precession cycles, and that insolation influences millennial-scale variations in monsoon strength. more...

Lake salinity fluctuations indicate that intense droughts occurred frequently before AD 1200 in the Northern Great Plain (NGP) region of central North America. The intensities and frequencies of drought in the last 2300 years in the NGP is reconstructed using the Moon Lake salinity fluctuations as inferred from fossil diatom assemblages. These droughts continued for centuries and those during AD 200-370, AD 700-850 and AD 1000-1200 were the extreme ones. The low salinity after AD 1200 indicates that this period had been wetter and cooler than the preceding years. more...

Drilling of ice samples in Greenland under the European Greenland Ice Core Project and the Greenland Ice Sheet Project have furnished climatic change history from as far back as 250,000 years. Core sampling reveals distinct epochs of moderate conditions followed by sudden warming and gradual cooling. The ice cores also reveal evidence of changes in the atmospheric concentration of carbon dioxide and methane. The current significant levels of these greenhouse gases forebode further shifts in global climatic conditions in the near future. more...

The global mean surface air temperature (SAT) or the Northern Hemisphere mean SAT has increased since the late nineteenth century, but the mean precipitation around the world has not formed a definite tendency to increase. A lot of studies showed that different climate and environmental changes during the past 100 years over various regions in the world were experienced. The climate change in China over the past 100 years and its impact on China's environmental conditions needs to be investigated in more detail. Data sets of surface air temperature and atmospheric precipitation over China since 1880 up to the present are now available. In this paper, a drought index has been formulated corresponding to both the temperature and precipitation. Based on three series of temperature, precipitation, and drought index, interdecadal changes in all 7 regions of China and temperature differences among individual regions are analyzed. Some interesting facts are revealed using the wavelet transform method. In Northeast China, the aridification trend has become more serious since 1970s. Drought index in North China has also reached a high value during 1990s, which seems similar to that period 1920s-1940s. In Northwest China, the highest temperature appeared over the period 1930s-1940s. Along the Yangtze River valley in central eastern China and Southwest China, interdecadal high temperature occurred from 1920s to 1940s and in 1990s, but the drought climate mainly appeared from 1920s to early 1940s. In South China, temperature remained at a high value over the period 1910s-1940s, but the smaller-scale variation of drought index was remarkable from 1880 to 1998. Consequently, the quasi-20-year oscillation (smaller-scale variation) and the quasi-70-year oscillation (secular variation) obviously exist in temperature and precipitation series in different regions over China. Climate change and intensified human activity in China have induced certain environmental evolutions, such as the frequency change of dust-storm event in northern China, no-flow in the lower reaches of the Yellow River and the runoff variation in Northwest China. On the other hand, frequent floods along the Yangtze River and high frequency of drought disaster have resulted in tremendous economic losses in the last decade in China. The primary reason for these happenings may be attributed to the evolution of the monsoon system in East Asian. more...

Thunder-day occurrences during a 100-year period based on data from carefully screened records of 86 first-order stations distributed across the United States were assessed for temporal fluctuations and trends during 1896-1995. Short-term ([is less than] 10-year) fluctuations of adjacent stations were often dissimilar reflecting localized differences in storm activity in a few years, making spatial interpretations difficult. But, temporal fluctuations based on 20-year and longer periods exhibited regional coherence reflecting the control of large, synoptic-scale weather systems on the distribution of thunderstorms over broad areas. Classification of station fluctuations based on 20-year periods revealed six types of distributions existed and they formed 12 discrete areas across the nation. One type present in the lower Midwest and the South had a peak in storm activity in 1916-1935 followed by a general decline to 1976-1995. A second type maximizing at the same time had its minimum earlier, in 1956-1975. Another distribution found at stations in the upper Midwest and Northeast had a mid-century peak (1936-1955) with a recent minimum in 1976-1995. A fourth distribution also peaked in 1936-1955 but had an early minimum in 1896-1915, and it mainly occurred in the northern plains and Rocky Mountains. A fifth distribution peaked during 1956-1975 and was found at stations in four areas including the central High Plains, Southwest, northern Great Lakes, and Southeast. The sixth temporal distribution showed a steady increase in storm activity during the 100-year period, peaking in 1976-1995, and covered a large area extending from the Pacific Northwest across the central Rockies and into the southern High Plains. The national average distribution based on all station values peaked in mid century. The national distribution differs markedly from several regional distributions illustrating the importance of using regional analysis to assess temporal fluctuations in severe weather conditions in the nation. The 100-year linear trends of the 86 stations defined six regions across the U.S. Significant upward trends existed over most of the western two-thirds of the nation, unchanging trends existed in the northern plains and Midwest, and downward trends were found in most of the nation's east. The up trends in storm-day frequencies in the southern plains occurred where storm damage is greatest and where demographic changes have added to storm losses over time. The national patterns of trends and storm distributions were similar to those found for hail. The temporal distributions of storm activity helped explain recent increases in major storms and their losses, conditions which have increased in the west and south. more...