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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 [...]

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.

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.

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

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.

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.

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.

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.

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 [...]

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.

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 [...]

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.

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.

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.

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.

During the Messinian, ~6 m.y. ago, massive sea-level fall and widespread deposition of evaporites occurred in the Mediterranean Sea when it became isolated from the world oceans. Here we present the first hydrogen isotope data from individual sedimentary biomarkers, n-alkanes and isoprenoids, that tracked climatically driven hydrographic changes in response to extreme evaporation during the Messinian salinity crisis. The stable hydrogen and carbon isotope compositions of these biomarkers show a range of 160[salinity] in [Delta]D values and 14[salinity] in [Delta][sup.13]C values, and roughly covary. This indicates that the source waters of the biomarkers were therefore in some cases extremely enriched in deuterium, having average [Delta]D as great as +66[salinity] VSMOW (Vienna standard mean ocean water). Such values are only known from desert climates today. Because the offset between the [Delta]D values of n-alkanes and isoprenoids preserved in the Miocene sedimentary rocks is similar to the offset found in modern biological samples, we conclude that diagenesis did not significantly affect the primary deuterium concentrations. Keywords: D/H, stable isotopes, biomarkers, Messinian, climate change, evaporation.

The periods from 1675-1715 (Late Maunder Minimum; LMM) and 1780-1830 (Early Instrumental Period; EIP) delineate important parts of the so-called `Little Ice Age' (LIA), in which Europe experienced predominant cooling. Documentary data, assembled from a number of sources, in the course of the EU funded research project ADVICE (Annual to Decadal Variability of Climate in Europe), has been used to locate and describe events in the southern Balkans and eastern Mediterranean. The resulting data has been used firstly to investigate the incidence of phenomena such as crops sterility, famine and epidemics and their relationships with climate, and secondly to analyse the extent of variability, particularly the occurrence of extreme events, such as severe winters (cold, wet or snowy), long periods of drought and wet periods. During the LMM and EIP, more such extreme situations were apparent compared with the last 50 years of the twentieth century. From the scattered data found for 1675-1715 and 1780-1830, the winter and spring climate in southern Balkans and the eastern Mediterranean, especially during the LMM, can be characterised as cooler and relatively rainier with a higher variability compared with the recent decades.

This paper presents a review of the time period A.D. 1400-1980 based on Greenland ice cores from the central west Greenland averaged record, and from winter and summer seasonal isotopic records from the Greenland Ice Sheet Project 2 (GISP2). This time period includes the so-called 'Little Ice Age'. The concept of the 'Little Ice Age' has evolved from the idea of a simple, centuries-long period of lower temperatures to a more complex view of temporal and spatial climatic variability. In the central Greenland ice core isotopic signals, the fifteenth and early sixteenth centuries show multi-decadal excursions above and below the mean reference. The sixteenth and mid-eighteenth to mid-nineteenth centuries are notable for decade-to-decade swings (high-low) in the isotopic signal, while multi-decadal low excursions dominate the seventeenth century. The 'subdued' nature of the 'Little Ice Age' isotopic signal in central Greenland is probably influenced by the North Atlantic Oscillation (NAO), which presents opposing temperature excursions between west Greenland and northern Europe. Changes in the prevailing atmospheric circulation (Iceland Low) can explain some of the spatial and temporal variability between the central Greenland isotopic records and Iceland temperature. Key Words: Greenland; ice cores; isotopes; 'Little Ice Age'

Zonal circulation indices with monthly and seasonal resolutions are calculated based on gridded monthly mean sea-level pressure (SLP) reconstructed back to 1780 by Jones et al. (1999): an overall zonal index for the whole European area between 30 [degrees] W and 40 [degrees] E, a normalized index for the North Atlantic Oscillation (NAO), and a similar index for Central Europe. For most of the early time up to the mid-nineteenth century we get preferred negative anomalies in the NAO index for winter and preferred positive ones for summer. The turning points in cumulative anomalies - during the 1850s for winter and during the 1870s for summer - indicate a transition period in circulation modes from the 'Little Ice Age' to the recent climate in Europe. Running correlations (time windows of 21 years with time steps of one year) between zonal indices and regional temperature time series from Central England, Stockholm and two Central European regions are all indicating major instationarities in these relationships with a particular decline in winter correlations around the turn from the nineteenth to the twentieth centuries. Aspects of different circulation patterns linked with these variabilites are discussed. Key Words: zonal indices; running correlations; temperature; Europe

Environmental proxies of soil erosion on Iceland, and oceanographic conditions on the adjacent shelf, were measured on a 50 cm box core taken from the southwest Iceland shelf in 1993 during cruise 93030 of the Canadian ship, CSS Hudson. These data, covering the last' several centuries, are compared with the documentary record of sea-ice changes around Iceland since A.D. 1600. The site is under the influence of the Irminger Current, which carries warm, saline, Atlantic water northward along the shelf. Because of the relative warmth of this current, sea ice rarely occurs off southwest Iceland, even during the most severe sea-ice intervals of the historical record. In severe sea-ice years, however, the ice drifts clockwise around Iceland from the northeast and east and, in rare cases, reaches the southern coasts (Ogilvie, 1992). The chronology of the core was established by converting the basal radiocarbon date to calendar years and assuming a linear sedimentation rate from the base of the core to the year of collection, 1993. Organic carbon, stable C and O istotope ratios, planktonic foraminiferal assemblages, and sediment magnetic parameters were measured on samples from the core, plotted against calendar years and compared to the Icelandic sea-ice index. The environmental proxies suggest that increased soil erosion, reduced salinity, and, possibly, decreased marine productivity prevailed during the severe sea-ice interval lasting from the last quarter of the eighteenth century to around 1920. Such a situation could develop with climatic cooling, increased storminess, and loss of vegetation cover to stabilise the soil. Although the core site generally lies outside the sea-ice limits, the evidence clearly shows the influence of sea ice and fresh water, and is sensitive to the overall climatic deterioration manifested by the sea-ice record. Key Words: 'Little Ice Age'; Soil erosion; Foraminifera; Palaeoceanography; Sea Ice

Byline: Claudia Tebaldi (1), Katharine Hayhoe (2,3), Julie M. Arblaster (4,5), Gerald A. Meehl (4) Author Affiliation: (1) Institute for the Study of Society and Environment, National Center for Atmospheric Research (NCAR), PO BOX 3000, Boulder, CO, 80301, USA (2) Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA (3) Department of Geosciences, Texas Tech University, Lubbock, TX, USA (4) Climate and Global Dynamics Division, NCAR, Boulder, CO, USA (5) Bureau of Meteorology Research Centre, Melbourne, Australia Article History: Registration Date: 19/02/2007 Online Date: 15/03/2007 Article note: The online version of the original article can be found at: doi: 10.1007/s10584-006-9051-4.

Research evidence suggests that earlier, humans were the victims of significant and sudden climate change when variations in rainfall over thousands of years severely disrupted human settlements. Some of these climate changes occurred in the Holocene, when humans were expanding their presence across the planet, creating societies, and learning to adapt to the conditions around them.

Research supports the theory that volcanism is behind the mass extinction that occurred on Earth about 250 mil years ago. The research suggests that the Siberian Traps, the planet's largest known volcanic region, are much larger than previously believed, and were able to cause the climate perturbation necessary for mass extinction.

The article examines the geological record for evidence of past climatic changes and their environmental impact. While the article allows that atmospheric carbon has a significant effect on the environment, drastic changes have occurred, or can occur, for other reasons, such as a nuclear winter.