AMS radiocarbon dating and varve chronology of Lake Soppensee: 6000 to 12000 14C years BP

For the extension of the radiocarbon calibration curve beyond 10000 ¹⁴C y BP, laminated sediment from Lake Soppensee (central Switzerland) was dated. The radiocarbon time scale was obtained using accelerator mass spectrometry (AMS) dating of terrestrial macrofossils selected from the Soppensee sediment. Because of an unlaminated sediment section during the Younger Dryas (10000–11000 ¹⁴C y BP), the absolute time scale, based on counting annual layers (varves), had to be corrected for missing varves. The Soppensee radiocarbon-verve chronology covers the time period from 6000 to 12000 ¹⁴C y BP on the radiocarbon time scale and 7000 to 13000 calendar y BP on the absolute time scale. The good agreement with the tree ring curve in the interval from 7000 to 11450 cal y BP (cal y indicates calendar year) proves the annual character of the laminations. The ash layer of the Vasset/Killian Tephra (Massif Central, France) is dated at 8230±140 ¹⁴C y BP and 9407±44 cal y BP. The boundaries of the Younger Dryas biozone are placed at 10986±69 cal y BP (Younger Dryas/Preboreal) and 1212±86 cal y BP (Alleröd/Younger Dryas) on the absolute time scale. The absolute age of the Laacher See Tephra layer, dated with the radiocarbon method at 10 800 to 11200 ¹⁴C y BP, is estimated at 12350 ± 135 cal y BP. The oldest radiocarbon age of 14190±120 ¹⁴C y BP was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile. For the late Glacial, the offset between the radiocarbon (10000–12000 ^14C y BP) and the absolute time scale (11400–13000 cal y BP) in the Soppensee chronology is not greater than 1000 years, which differs from the trend of the U/Th-radiocarbon curve derived from corals.     

Fossil-pollen evidence for abrupt climate changes during the past 18 000 years in eastern North America

A quantitative measure of the rate at which fossil-pollen abundances changed over the last 18 000 years at 18 sites spread across eastern North America distinguishes local from regionally synchronous changes. Abrupt regional changes occurred at most sites in late-glacial time (at 13700, 12 300, and 10000 radiocarbon yr BP) and during the last 1000 years. The record of abrupt late-glacial vegetation changes in eastern North America correlates well with abrupt global changes in ice-sheet volume, mountain snow-lines, North Atlantic deep-water production, atmospheric CO₂, and atmospheric dust, although the palynological signal varies from site to site. Changes in vegetation during most of the Holocene, although locally significant, were not regionally synchronous. The analysis reveals non-alpine evidence for Neoglacial/Little Ice Age climate change during the last 1000 years, which was the only time during the Holocene when climate change was of sufficient magnitude to cause a synchronous vegetational response throughout the subcontinent. During the two millennia preceding this widespread synchronous change, the rate of change at all sites was low and the average rate of change was the lowest of the Holocene.Contribution to Clima Locarno Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Origin of the northern Atlantic's Heinrich events

As first noted by Heinrich, 1988, glacial age sediments in the eastern part of the northern Atlantic contain layers with unusually high ratios of ice-rafted lithic fragments to foraminifera shells. He estimated that these layers are spaced at intervals of roughly 10 000 years. In this paper we present detailed information documenting the existence of the upper five of these layers in ODP core 609 from 50° N and 24° W. Their ages are respectively 15 000 radiocarbon years, 20 000 radiocarbon years, 27 000 radiocarbon years, about 40 000 years, and about 50 000 years. We also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers. Although we are not of one mind regarding the origin of these layers, we lean toward an explanation that the Heinrich layers are debris released during the melting of massive influxes of icebergs into the northern Atlantic. These sudden inputs may be the result of surges along the eastern margin of the Laurentide ice sheet.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Climatic jumps in the flood/drought historical chronology of central China

Statistical series of flood/drought (F/D) grades and F/D variabilities were derived for the flood and drought chronology (2700 bc-1980 AD) of central China. Two types of climatic jumps were analyzed. The moving sign-test, T-test and F-test were applied to detect jump signals. A few wet-to-dry jumps for time-scales from decades to thousand years were compared with relevant climatic changes in other regions of the world. Changes in the annual rainfall due to jumps were estimated. Some F/D-deficient-to-F/D-frequent jumps were also found and their significance is discussed.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Rates of change in the European palynological record of the last 13 000 years and their climatic interpretation

Rates of change of pollen spectra throughout Europe during the last 13 000 years have been calculated. The overall mean rate of change curve shows peaks corresponding to known times of rapid palaeoenvironmental change between 13 000 and 12000y BP, and between 10 000 and 9000 y BP. These peaks are strongest in the north and west of Europe. As in eastern North America (Jacobson et al. 1987), highest rates of change are recorded during the last millennium. At this time the changes of greatest magnitude are in areas of Europe with winter climate conditions strongly influenced by the North Atlantic. It is hypothesized that the overall pattern of Holocene climate change in Europe, and especially the changes of the last millennium, result from changes in the North Atlantic that have most strongly influenced winter conditions in western Europe.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Recent hydroclimatic fluctuations and their effects on water resources in Illinois

Two contrasting 18 yr periods (1950–1967 and 1968–1985) were compared to illustrate the hydrologic and water resources effects of a change to a wetter climatic regime over Illinois. For the nine State Climate Divisions, precipitation increases and fluctuations in wetness measured by Palmer Drought Indices revealed a marked shift between the periods. The seasonal variability and spatial coherence of this precipitation climate fluctuation and its impacts are examined in detail and quantitative relationships are derived between Drought Indices and measured soil moisture and streamflow at several sites. Riverflow and well level changes are consistent with this climate change on the 20–40 yr time-scale which has had some significance for water management in the area.     

Radioisotopic evidence of perturbations of recent sedimentary record in lakes: a word of caution for climate studies

The rate of climatic change estimated from the gradient of signals recorded in lake sediments may be erroneous if post-depositional perturbations are overlooked. A smear out of a pulse signal, over a variable thickness of core section, due to physical or biological mixing, is a well known phenomena. Much less attention is paid to a possible overestimation of the rate of change when a part of record is missing due to an erosion event. In this paper we show a few examples of recent lake sediment perturbations and the resulting distortions in the time scale, as documented by short-lived radionuclides.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Stable isotope (O and C) and pollen trends in eastern Lake Erie,evidence for a locally-induced climatic reversal of Younger Dryas age in the Great Lakes basin

A cool period from about 11000 to 10 500 BP (11 to 10.5 ka) is recognized in pollen records from the southern Great Lakes area by the return of Picea and Abies dominance and by the persistence of herbs. The area of cooling appears centred on the Upper Great Lakes. A high-resolution record (ca. 9 mm/y) from a borehole in eastern Lake Erie reveals, in the same time interval, this pollen anomaly, isotope evidence of meltwater presence (a — 3 per mil shift in ¹⁸O and a +1.1 per mil shift in ¹³C), increased sand, and reduced detrital calcite content, all suggesting concurrent cooling of Lake Erie. The onset of cooling is mainly attributed to the effect of enhanced meltwater inflow on the relatively large upstream Main Lake Algonquin during the first eastward discharge of glacial Lake Agassiz. Termination of the cooling coincides with drainage of Lake Algonquin, and is attributed to loss of its cooling effectiveness associated with a substantial reduction in its surface area. It is hypothesized that the cold extra inflow effectively prolonged the seasonal presence of lake ice and the period of spring overturn in Lake Algonquin. The deep mixing would have greatly increased the thermal conductive capacity of this extensive lake, causing suppression of summer surface lakewater temperatures and reduction of onshore growing-degree days. Alternatively, a rapid flow of meltwater, buoyed on sediment-charged (denser) lakewater, may have kept the lake surface cold in summer. Other factors such as wind-shifted pollen deposition and possible effects from the Younger Dryas North Atlantic cooling could have contributed to the Great Lakes climatic reversal, but further studies are needed to resolve their relative significance.Contribution to Climo Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate ProgramGeological Survey of Canada Contribution 58 890     

Estimates of monoterpene and isoprene emissions from the forests in Switzerland

Emission rates of biogenic volatile organic compounds emitted by the forests were estimated for five geographical regions as well as for all Switzerland. Monoterpene and isoprene emissions rates were calculated for each main tree species separately using the relevant parameters such as temperature, light intensity and leaf biomass density. Biogenic emissions from the forests were found to be about 23% of the total annual VOC emissions (anthropogenic and biogenic) in Switzerland. The highest emissions are in July and lowest in January. Calculations showed that the coniferous trees are the main sources of the biogenic emissions. The major contribution comes from the Norway spruce (picea abies) forests due to their abundance and high leaf biomass density. Although broad-leaved forests cover 27% of all the forests in Switzerland, their contribution to the biogenic emissions is only 3%. Monoterpenes are the main species emitted, whereas only 3% is released as isoprene. The highest emission rates of biogenic VOC are estimated to be in the region of the Alps which has the largest forest coverage in Switzerland and the major part of these forests consists of Norway spruce. The total annual biogenic VOC emission rate of 87 ktonnes y^–1 coming from the forests is significantly higher than those from other studies where calculations were carried out by classifying the forests as deciduous and coniferous. The difference is attributed to the high leaf biomass densities of Norway spruce and fir (abies alba) trees which have a strong effect on the results when speciation of trees is taken into account. Besides the annual rate, emission rates were calculated for a specific period during July 4–6, 1991 when a photochemical smog episode was investigated in the Swiss field experiment POLLUMET. Emission rates estimated for that period agree well with those calculated for July using the average temperatures over the last 10 years.     

Satellite-derived outgoing longwave radiation,surface temperature and sea ice concentration off the coast of Adélie-Land,Eastern Antarctica

Summary Outgoing longwave radiation (OLR) as seen from satellite (NOAA-series), and sea ice concentration in Mer Dumont d'Urville, Eastern Antarctica were analyzed. For the time period 1974–1990 available radiative flux data showed a slight increase of 1.8 W/m² or 1% for the period. If thistrend should continue — trends over a 16-year period in any geophysical data is a rather questionable concept in isolation — a 4°C warming would be observed from space for this polar region over a century. The observed increase is, however, in agreement with Dumont d'Urville, the only ground station within the study area, which displayed a similar temperature increase (Periard and Pettré, 1991). Further it is in agreement with the general temperature increase which has been observed for the high southern latitudes (Boden et al., 1990). In addition, models of climatic change due to increased CO₂ and other trace gases predict for polar regions values of similar size.Sea ice concentration showed a slight decrease for the time period 1974–1989, for which data were available. However, a relationship existed between the radiative flux and the ice concentration, not only for the actual data, but also for the deviation series with the annual cycles removed. A correlation factor of –0.74 was found; the sensitivity for an increase of 10% in ice concentration was –2.9 W/m². This represents a temperature change as seen from space of about 1°C for a 10% change in sea ice concentration.With 7 Figures     

Fennoscandian summers from ad 500: temperature changes on short and long timescales

Quantitative estimates of 1480 years of summer temperatures in northern Fennoscandia have previously been derived from continuous treering records from northern Sweden. Here we show the results of spectral analyses of these data. Only a few peaks in the spectra are consistently significant when the data are analyzed over a number of sub-periods. Relatively timestable peaks are apparent at periods of 2.1, 2.5, 3.1, 3.6, 4.8, 32–33 and for a range between 55–100 years. These results offer no strong evidence for solar-related forcing of summer temperatures in these regions. Our previously published reconstruction was limited in its ability to represent long-timescale temperature change because of the method used to standardize the original tree-ring data. Here we employ an alternative standardization technique which enables us to capture temperature change on longer timescales. Considerable variance is now reconstructed on timescales of several centuries. In comparison with modern normals (1951–70) generally extended periods when cool conditions prevailed, prior to the start of the instrumental record, include 500–700, 790–870, 1110–1150, 1190–1360, 1570–1750 (A.D.) with the most significant cold troughs centred on about 660, 800, 1140, 1580–1620 and 1640. Predominantly warm conditions occurred in 720–790, 870–1110 and 1360–1570 with peaks of warmth around 750, 930, 990, 1060, 1090, 1160, 1410, 1430, 1760 and 1820.This paper was presented at Clima Locarno 90, the International Conference on Past and Present Climate Dynamics: Reconstruction of Rates of Change, held in Locarno, Switzerland, September 24 to 28, 1991, organized by the Swiss National Climate Program — ProClim, with support from the Swiss Academy of Sciences. Guest editor for these papers is Dr. K. Kelts Offprint requests to: KR Briffa     

A surface air temperature response function for earth's atmosphere

A property of Earth's atmosphere called thesurface air temperature response function is defined to be the change in surface air temperature that results from a change in radiant energy absorbed at the planet's surface. It is experimentally evaluated by three independent techniques to yield a value over land of 0.172 K (Wm^–2)^–1 while one of these techniques yields a value about half that great for stations on the extreme west coast of the United States. Computing an appropriate global upper limit from these two results yields a value of 0.113 K (Wm^–2)^–1, which compares well with a fourth technique that yields a mean global value of 0.097 K (Wm^–2)^–1. The results imply an unexpected time-scale invariant response function.Contribution from Agricultural Research Service, Science and Education, U.S. Department of Agriculture.     

Calibration of the climatic signal in a new pollen sequence from La Grande Pile

A new core, GPXX, from La Grande Pile (Vosges, France) has enabled a more precise evaluation of pollen data concerning the last climatic cycle at this site and has enabled reconstruction of the monthly temperature and precipitation. This paper shows that the various components of the reconstructed climatic signal are clearly separated and that they are coherent with the vegetation dynamics. The Eemian interglacial was influenced first by an oceanic climate and second by a more continental one. The two interstadials, St-Germain I and II, were mainly continental. These three temperate periods ended with a cool and humid transition period dominated by boreal forests, which may have been favourable to ice accretion. The Dansgaard-Oeschger oscillations from 55 to 25 Kyr BP are not significantly recorded in La Grande Pile.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Drought frequency in central California since 101 B.C. recorded in giant sequoia tree rings

Well replicated tree-ring width index chronologies have been developed for giant sequoia at three sites in the Sierra Nevada, California. Extreme low-growth events in these chronologies correspond with regional drought events in the twentieth century in the San Joaquin drainage, in which the giant sequoia sites are located. This relationship is based upon comparison of tree-ring indices with August Palmer Drought Severity Indices for California Climate Division 5. Ring-width indices in the lowest decile from each site were compared. The frequency of low-growth events which occurred at all three sites in the same year is reconstructed from 101 B.C. to A.D. 1988. The inferred frequency of severe drought events changes through time, sometimes suddenly. The period from roughly 1850 to 1950 had one of the lowest frequencies of drought of any one hundred year period in the 2089 year record. The twentieth century so far has had a below-average frequency of extreme droughts.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Major wet interval in white mountains medieval warm period evidenced inδ 13C of bristlecone pine tree rings

A long ¹³C chronology was developed from bristlecone pine (Pinus longaeva) at the Methuselah Walk site in the White Mountains of California. The chronology represents cellulose from five-year ring groups pooled from multiple radii of multiple trees. The most dramatic isotopic event in the chronology appears from A.D. 1080–1129, when ¹³C values are depressed to levels ~ 2 below the mean for the period A.D. 925–1654. This isotopic excursion appears to represent a real event and is not an artifact of sampling circumstances; in fact, a similar excursion occurs in a previously-reported, independent ¹³C chronology from bristlecone pine. By carbon isotope fractionation models, the shift to low ¹³C values is consistent with abundant soil moisture, permitting leaf stomata to remain open, and allowing ready access of CO₂ from which carbon fixation may discriminate more effectively against¹³C in favor of¹²C. According to this model, the¹³C-depleted 50-yr isotopic excursion represents the wettest period in the White Mountains in the past 1000 yr, during which isotope-reconstructed July Palmer Drought Severity Indices averaged ~ +2.2.     

Evidence for an early Holocene climatic optimum in the Antarctic deep ice-core record

In the interpretation of the Antarctic deep ice-core data, little attention has been given to the Holocene part of the records. As far as translation of the stable isotope content in terms of temperature is concerned, this can be understood because expected temperature changes may be obscured by isotopic noise of various origins and because no ¹⁴C dating has yet been available for this type of sequence. In this article, we focus on the Dome C and Vostok cores and on a new 850-m long ice core drilled out at Komsomolskaïa by the Soviet Antarctic Expeditions. These three sites are located in East Antarctica, on the Antarctic plateau, in a region essentially undisturbed by ice-flow conditions, so that their detailed intercomparison may allow us to identify the climatically significant isotopic signal. Our results compare well with the proximal records of Southern Hemisphere high latitudes and support the existence of a warmer climatic optimum between 10 and 6 ka y BP. Maximum temperatures are reached just at the end of the last deglaciation, which confirms previous observations at high latitudes, in contrast with later dates for the Atlantic and hypsithermal optima in Europe and North America.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Organic carbon accumulation rates in the Holocene and glacial Arabian Sea: implications for O2-consumption in the deep-sea and atmospheric CO2 variations

Variations in the deep-sea carbon reservoir have been invoked to explain the observed atmospheric carbon dioxide (CO₂) changes during glacial-interglacial cycles. In order to distinguish between the quantity of organic matter remineralized in the deep-sea and that permanently removed into sediments, we compared the bulk- and organic carbon-accumulation rates in Holocene and glacial sediments deposited below the oxygen minimum layer with total- and organic carbon fluxes to the deep Arabian Sea from continuous sediment trap deployments. This comparison shows that the mass of organic carbon remineralized at the sediment water interface is mainly a function of the bulk sediment flux. The oxygen consumed by the organic carbon remineralization is of the order of the observed oxygen deficiency of the modern deep Arabian Sea water. We use the evidence from the northern Indian Ocean to speculate on the possible effect of abiogenic mineral flux on the removal of organic carbon from upper layers of the world ocean to the deep-sea. We assume that if the bulk accumulation rate (not primary productivity) influences the flux of organic carbon (that is fixed from the atmosphere by marine organisms), then mineral matter flux will exert a significant control over atmospheric CO₂ contents. Model calculations incorporating transient changes in global bulk flux, caused by natural or anthropogenic changes, show that significant proportions of the observed changes in atmospheric CO₂ contents can be explained by this mechanism.This paper was presented at Clima Locarno 90, the International Conference on Past and Present Climate Dynamics: Reconstruction of Rates of Change, held in Locarno, Switzerland, September 24 to 28, 1991, organized by the Swiss National Climate Program — ProClim, with support from the Swiss Academy of Sciences. Guest editor for these papers is Dr. K. Kelts Offprint requests to: F Sirocko     

Monthly air temperature trends in Switzerland 1901–2000 and 1975–2004

Summary We analysed long-term temperature trends based on 12 homogenised series of monthly temperature data in Switzerland at elevations between 316 m.a.s.l. and 2490 m.a.s.l for the 20^th century (1901–2000) and for the last thirty years (1975–2004). Comparisons were made between these two periods, with changes standardised to decadal trends. Our results show mean decadal trends of +0.135 °C during the 20^th century and +0.57 °C based on the last three decades only. These trends are more than twice as high as the averaged temperature trends in the Northern Hemisphere. Most stations behave quite similarly, indicating that the increasing trends are linked to large-scale rather than local processes. Seasonal analyses show that the greatest temperature increase in the 1975–2004 period occurred during spring and summer whereas they were particularly weak in spring during the 20^th century. Recent temperature increases are as much related to increases in maximum temperatures as to increases in minimum temperature, a trend that was not apparent in the 1901–2000 period. The different seasonal warming rates may have important consequences for vegetation, natural disasters, human health, and energy consumption, amongst others. The strong increase in summer temperatures helps to explain the accelerated glacier retreat in the Alps since 1980. Authors’ addresses: Martine Rebetez, WSL Swiss Federal Research Institute, 1015 Lausanne, Switzerland; Michael Reinhard, Laboratory of Ecological Systems (ECOS), EPFL Swiss Federal Institute of Technology, 1015 Lausanne, Switzerland.     

Potential Soil C Sequestration on U.S. Agricultural Soils

Soil carbon sequestration has been suggested as a means to help mitigate atmospheric CO₂ increases, however there is limited knowledge aboutthe magnitude of the mitigation potential. Field studies across the U.S. provide information on soil C stock changes that result from changes in agricultural management. However, data from such studies are not readily extrapolated to changes at a national scale because soils, climate, and management regimes vary locally and regionally. We used a modified version of the Intergovernmental Panel on Climate Change (IPCC) soil organic C inventory method, together with the National Resources Inventory (NRI) and other data, to estimate agricultural soil C sequestration potential in the conterminous U.S. The IPCC method estimates soil C stock changes associated with changes in land use and/or land management practices. In the U.S., the NRI provides a detailed record of land use and management activities on agricultural land that can be used to implement the IPCC method. We analyzed potential soil C storage from increased adoption of no-till, decreased fallow operations, conversion of highly erodible land to grassland, and increased use of cover crops in annual cropping systems. The results represent potentials that do not explicitly consider the economic feasibility of proposed agricultural production changes, but provide an indication of the biophysical potential of soil C sequestration as a guide to policy makers. Our analysis suggests that U.S. cropland soils have the potential to increase sequestered soil C by an additional 60–70 Tg (10¹²g) C yr^{– 1}, over present rates of 17 Tg C yr^–1(estimated using the IPCC method), with widespread adoption of soil C sequestering management practices. Adoption of no-till on all currently annually cropped area (129Mha) would increase soil C sequestration by 47 Tg C yr^–1. Alternatively, use of no-till on 50% of annual cropland, with reduced tillage practices on the other 50%, would sequester less – about37 Tg C yr^–1. Elimination of summer fallow practices and conversionof highly erodible cropland to perennial grass cover could sequester around 20 and 28Tg C yr^–1, respectively. The soil C sequestration potentialfrom including a winter cover crop on annual cropping systems was estimated at 40Tg C yr^–1. All rates were estimated for a fifteen-yearprojection period, and annual rates of soil C accumulations would be expected to decrease substantially over longer time periods. The total sequestration potential we have estimated for the projection period (83 Tg C yr^–1) represents about 5% of 1999total U.S. CO₂ emissions or nearly double estimated CO₂ emissionsfrom agricultural production (43 Tg C yr^–1). For purposes ofstabilizing or reducing CO₂ emissions, e.g., by 7% of 1990 levels asoriginally called for in the Kyoto Protocol, total potential soil C sequestration would represent 15% of that reduction level from projected 2008 emissions(2008 total greenhouse gas emissions less 93% of 1990 greenhouse gasemissions). Thus, our analysis suggests that agricultural soil C sequestration could play a meaningful, but not predominant, role in helping mitigate greenhouse gas increases.     

Younger dryas and holocene glacier fluctuations and equilibrium-line altitude variations in the Jostedalsbre region,western Norway

Reconstructed Younger Dryas (11000-10000 y BP) valley- and cirque glaciers west of the Jostedalsbre ice cap suggest an equilibrium-line altitude (ELA) depression of 450±50 m compared to the present level. The mid-Preboreal (9500±200 y BP) deglaciation was characterized by vertical wastage, indicating that the ELA was above the summit plateaus. During the Erdalen event (9100±200 y BP) marginal moraines were formed up to 1 km beyond the Little Ice Age (LIA) moraines which lie in front of the present valley outlet glaciers of the Jostedalsbre ice cap. The average ELA lowering during this event is calculated to 325 m below the modern level. Lithostratigraphic and paleobotanical studies show that the Hypsithermal (ca. 8000-6000 y BP) ELA was about 450 m higher than at present. As a result, Jostedalsbreen probably disappeared entirely during that period. The glacier reformed about 5300 y BP. The ELA intersected the modern mean equilibrium line altitude five times from ca. 2600 y BP to the present. The outlet valley glaciers reached their maximum Neoglacial extent during the LIA in the mid-18th century, when the ELA was depressed 100–150 m below the present level.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program