Brian H. Luckman

The unusual nature of recent snowpack declines in the North American cordillera.

The snowpack covering the mountains of western North America has decreased dramatically during the past 50 years. In western North America, snowpack has declined in recent decades, and further losses are projected through the 21st century. Here, we evaluate the uniqueness of recent declines using snowpack reconstructions from 66 tree-ring chronologies in key runoff-generating areas of the Colorado, Columbia, and Missouri River drainages. Over the past millennium, late 20th century snowpack reductions are almost unprecedented in magnitude across the northern Rocky Mountains and in their north-south synchrony across the cordillera. Both the snowpack declines and their synchrony result from unparalleled springtime warming that is due to positive reinforcement of the anthropogenic warming by decadal variability. The increasing role of warming on large-scale snowpack variability and trends foreshadows fundamental impacts on streamflow and water supplies across the western United States.

The Mt Logan Holocene—late Wisconsinan isotope record: tropical Pacific—Yukon connections

The ice core recovered from Prospector Russell Col on Mt Logan (5.4 km a.s.l.), in the Yukon spans over 20 000 years. This unique record offers a Pacific view of the stable isotope and chemical record from the Lateglacial to the present. The timescale is based on seasonal counted years, the largest known volcanic acid signatures and the major shift in stable isotopes and chemistry at the end of the Younger Dryas. There are large and sustained changes in the stable isotopic record that are anti-correlated with marine and continental chemistry series. The oxygen-18 in this area is not a proxy for palaeotemperature but rather for source region. The last major isotope shift in AD 1840 in δ(18O) and chemistry is compared with the Quinns ENSO record. During periods of more frequent La Niña (stronger tropical easterlies) there is more zonal flow of water vapour transport to the Pacific Northwest, δ(18O) values are larger and the deuterium excess d smaller. These periods coincide with periods of lower accumulation/precipitation in southern Yukon. The Holocene δ(18O) record indicates many large shifts between the meridional (strong El Niño) and zonal (La Niña). Comparison of the Logan isotopic record and the moisture/temperature-sensitive time series of peat bog inception dates for the Northwest shows a strong correlation (0.36) that points to high accumulation rates coincident with low δ(18O) and enhanced meridional flow. Major changes in the core at 4200 BP and 7000—8000 BP point to enhanced meridional flow, which coincide with big changes in the Pacific palaeorecords of the balance between El Niño and La Niña. 4200 BP seems to have inaugurated the `modern ENSO world.

Holocene timberline fluctuations in jasper national park, alberta.

Pollen, fossil logs, and macrofossils from three high-elevation sites in the Maligne Range, Jasper National Park, Alberta, provide the first detailed record of timberline fluctuations in the Canadian Rockies during the last 8700 years. Timberlines were much higher than at present between 8700 to 5200 years ago but oscillated significantly in elevation, with a major episode of timberline recession punctuating two periods of high timberline between about 6700 to 5900 and about 8700 to 7000 years ago. Since 5200 years ago, regional timberlines have generally receded with perhaps brief reversals, reaching their lowest recorded positions sometime after 500 years ago.

Annual push moraines as climate proxy

[1]xa0We reconstruct the terminus position of a mountain glacier in British Columbia, Canada from annual push moraines formed between 1959 and 2007. Our reconstruction represents the longest, annually-resolved record of length change for a North American glacier. Comparison of annual recession with climate records indicates that glacier recession is controlled by air temperatures during the ablation season and accumulation season precipitation during the previous decade. Analysis among records of glacier frontal variation and mass balance in western North America similarly reveals an immediate terminus reaction to summer and net balance and a delayed reaction to winter and net balance. Other mountain ranges may contain long series of push moraines that could be exploited as climate proxies, and to improve understanding of glacier response to climate.

Snowpack variations since AD 1150 in the Andes of Chile and Argentina (30°–37°S) inferred from rainfall, tree‐ring and documentary records

[1]xa0The Andean snowpack is the main source of freshwater and arguably the single most important natural resource for the populated, semi-arid regions of central Chile and central-western Argentina. However, apart from recent analyses of instrumental snowpack data, very little is known about the long term variability of this key natural resource. Here we present two complementary, annually-resolved reconstructions of winter snow accumulation in the southern Andes between 30°–37°S. The reconstructions cover the past 850xa0years and were developed using simple regression models based on snowpack proxies with different inherent limitations. Rainfall data from central Chile (very strongly correlated with snow accumulation values in the adjacent mountains) were used to extend a regional 1951–2010 snowpack record back to AD 1866. Subsequently, snow accumulation variations since AD 1150 were inferred from precipitation-sensitive tree-ring width series. The reconstructed snowpack values were validated with independent historical and instrumental information. An innovative time series analysis approach allowed the identification of the onset, duration and statistical significance of the main intra- to multi-decadal patterns in the reconstructions and indicates that variations observed in the last 60xa0years are not particularly anomalous when assessed in a multi-century context. In addition to providing new information on past variations for a highly relevant hydroclimatic variable in the southern Andes, the snowpack reconstructions can also be used to improve the understanding and modeling of related, larger-scale atmospheric features such as ENSO and the PDO.

Science-Policy Dialogues for Water Security: Addressing Vulnerability and Adaptation to Global Change in the Arid Americas

www.EnvironmEntmagazinE.org voLUmE 54 nUmBEr 3 Climate change and watersupply uncertainty coupled with mounting human demands for water are straining the availability and quality of freshwater in much of the world. These twin forces cause a palpable rise in societal vulnerability, here considered as susceptibility to adverse effects of global environmental change.1 The vulnerability of water supplies (or, water vulnerability) places human communities at risk for exposure,2 or change,3 and thereby creates huge adaptation challenges. The actions being taken to reduce risks and capitalize on opportunities are considered adaptation or adaptive strategies.4 The most sensitive and vulnerable communities are those that face the greatest exposure and are most limited in their capacity to adapt. Rapidly growing and ever wealthier urban populations, expanding agribusinesses, diverse industries, extensive mining, power generation, and tourism often deprive water from or degrade its quality for use by marginalized populations of smallholder farmers and the urban poor, as well as for ecosystems along streams, lakes, and coasts recognized as biodiversity hotspots in the arid landscape. The arid5 Americas—as characterized by the southwestern United States, northwestern Mexico, north-central Chile and Argentina, and northeastern Brazil—manifest the just-described challenges especially well.6 This article focuses on two areas where our research team has been developing science-policy adaptation strategies: (1) the Sonora-Arizona drylands shared by Mexico and the United States (See map at right), and (2) the drylands east and west of the Central Andes in Chile and Argentina (see map, page 32). In these areas water remains acutely limited even as drought and flood extremes increase, ecosystems are under growing pressure, and economic globalization drives water demand. These global-change conditions threaten the security of access to water. Yet the foregoing conditions prevail—with little regard for constraints to supply, insufficient understanding of vulnerability, and inadequate attention to adaptive measures.7 To the extent that such problems are attributable to human agency,8 there is evidence that effective policies and actions can alleviate some of the harm.9 Our article describes two interactive Science-Policy Dialogues for Water Security:

Dendroclimatology from Regional to Continental Scales: Understanding Regional Processes to Reconstruct Large-Scale Climatic Variations Across the Western Americas

Common patterns of climatic variability across the Western Americas are modulated by tropical and extra-tropical oscillatory modes operating at different temporal scales. Interannual climatic variations in the tropics and subtropics of the Western Americas are largely regulated by El Nino-Southern Oscillation (ENSO), whereas decadal-scale variations are induced by long-term Pacific modes of climate variability such as the Pacific Decadal Oscillation (PDO). At higher latitudes, climate variations are dominated by oscillations in the Annular Modes (the Arctic and Antarctic Oscillations) which show both interannual and longer-scale temporal oscillations. Here we use a recently-developed network of tree-ring chronologies to document past climatic variations along the length of the Western Cordilleras. The local and regional characterization of the relationships between climate and tree-growth provide the basis to compare climatic variations in temperature- and precipitation-sensitive records in the Western Americas over the past 3–4 centuries. Upper-elevation records from tree-ring sites in the Gulf of Alaska and Patagonia reveal the occurrence of concurrent decade-scale oscillations in temperature during the last 400 years modulated by PDO. The most recent fluctuation from the cold- to the warm-phase of the PDO in the mid 1970s induced marked changes in tree growth in most extratropical temperature-sensitive chronologies in the Western Cordilleras of both Hemispheres. Common patterns of interannual variations in tree-ring chronologies from the relatively-dry subtropics in western North and South America are largely modulated by ENSO. We used an independent reconstruction of Nino-3 sea surface temperature (SST) to document relationships to tree growth in the southwestern US, the Bolivian Altiplano and Central Chile and also to show strong correlations between these regions. These results further document the strong influence of SSTs in the tropical Pacific as a common forcing of precipitation variations in the subtropical Western America during the past 3–4 centuries. Common patterns of interdecadal or longer-scale variability in tree-ring chronologies from the subarctic and subantarctic regions also suggest common forcings for the annular modes of high-latitude climate variability. A clear separation of the relative influence of tropical versus high-latitude modes of variability is currently difficult to establish: discriminating between tropical and extra-tropical influences on tree growth still remains elusive, particularly in subtropical and temperate regions along our transect. We still need independent reconstructions of tropical and polar modes of climate variability to gain insight into past forcing interactions and the combined effect on climates of the Western Americas. Finally, we also include a series of brief examples (as ‘boxes’) illustrating some of the major regional developments in dendrochronology over this global transect in the last 10 years.

Tree Rings and Natural Hazards: An Introduction

Each year, natural disasters claim thousands of lives and lead to economic losses of several billion US dollars worldwide. In 2008, natural disasters caused 240,500 fatalities and losses of more than US

Glacially mediated impacts of climate warming on alpine lakes of the Canadian Rocky Mountains

250 billion (SwissRe 2009), making it one of the largest annual amounts ever recorded. More than 90% of people killed by catastrophic events in 2008 were during two tropical cyclones (Myanmar and Philippines) and the 7.9 moment-magnitude earthquake hitting China’s Sichuan region in May 2008 (Rodriguez et al. 2009). In February 2009, severe bush fires destroyed several villages in Victoria (Australia), killing more than 90 people and leaving 700 houses in ashes (Shaban 2009).

Tree rings and natural hazards - A state-of-the-art

Climate warming is having a more pronounced impact ontemperature change in alpine and polar regions than on aglobal scale (Beniston 2006, Lemke et al. 2007). For theCordillera region of North America, climate models predictthat warming will increase with elevation, reaching its maxi-mum at mid-northern latitudes (Bradley et al. 2004). Den-drochronological models have already shown that summertemperatures in the Canadian Rockies were anomalouslywarm during the 20