August Mean Temperature Research Articles

Millennium-long summer temperature variations in the European Alps as reconstructed from tree rings

Abstract. This paper presents a reconstruction of the summer temperatures over the Greater Alpine Region (44.05°–47.41° N, 6.43°–13° E) during the last millennium based on a network of 38 multi-centennial larch and stone pine chronologies. Tree ring series are standardized using an Adaptative Regional Growth Curve, which attempts to remove the age effect from the low frequency variations in the series. The proxies are calibrated using the June to August mean temperatures from the HISTALP high-elevation temperature time series spanning the 1818–2003. The method combines an analogue technique, which is able to extend the too short tree-ring series, an artificial neural network technique for an optimal non-linear calibration including a bootstrap technique for calculating error assessment on the reconstruction. About 50% of the temperature variance is reconstructed. Low-elevation instrumental data back to 1760 compared to their instrumental target data reveal divergence between (warmer) early instrumental measurements and (colder) proxy estimates. The proxy record indicates cool conditions, from the mid-11th century to the mid-12th century, related to the Oort solar minimum followed by a short Medieval Warm Period (1200–1420). The Little Ice Age (1420–1830) appears particularly cold between 1420 and 1820 with summers that are 0.8 °C cooler than the 1901–2000 period. The new record suggests that the persistency of the late 20th century warming trend is unprecedented. It also reveals significant similarities with other alpine reconstructions.

Reconstruction des températures estivales dans les alpes françaises au moyen de données dendrochronologiques (749-2008 AD)

To date, in the Alps, only three reconstructions extend back prior to 1000 AD. This lack is related to the scarcity of wood material in the western and southern parts of the Alps, especially during the early part of the last millennium. On the basis of a dense tree-ring width network (34 unpublished multi centennial larch chronologies), this paper attempts, for the first time, a reconstruction of the summer temperatures over the French Alps. This network combine 548 tree-ring width series from living trees, dead trees and construction wood. All sites sampled are located near tree-line in high-altitude forest stands. The Adaptative Regional Growth Curve standardization method was applied to preserve interannual to multicentennial variations in this high-elevation proxy data-set. The proxies are calibrated using the June to August mean temperatures from the last revised version of the HISTALP database. The method combines an analogue technique, which is able to extend the too short tree-ring series, an artificial neural network technique for an optimal non-linear calibration including a bootstrap technique for calculating error assessment on the reconstruction. About 50% of the temperature variance is reconstructed. The proxy record evidences a prolonged Medieval Warm Period persisting until 1500 with warm periods that resemble twentieth century conditions but also cold phases before 1000 synchronous to the Swiss glacier advances. The Little Ice Age is rather mild until 1660 if compared to other alpine reconstructions. Then, summers are 0. 7°C cooler than the 1961—1990 mean until 1920.

Spatial and temporal stability of the climatic signal in northern Fennoscandian pine tree‐ring width and maximum density

The spatial and temporal stability of the climatic signal in pine tree‐ring width and maximum density is examined using data from four sites in northern Sweden and Finland. Moving‐window multiple linear regression, using monthly and daily climate data, indicates that ring widths at all sites have been strongly controlled by July temperatures throughout the past century. The relationship between maximum density and temperature is stronger but much less stable across both space and time. Shifts in the hottest part of the summer do not explain large shifts in the period most strongly influencing density. It is concluded that palaeoclimate reconstructions based on northern Fennoscandian pine tree‐ring width chronologies should be restricted to the temperature of midsummer (July), whereas maximum density should be used to reconstruct the temperature of a longer growth season (June to August). They thus provide different and complementary palaeoclimate signals. At all four sites, the correlation between maximum density and June to August mean temperature is lowest in the latter half of the 20th century, but split sample tests with strong verification statistics (RE and CE) show that this represents a quantitative change in the strength of the correlation with climate, rather than a qualitative change in the nature of that relationship, and thus does not invalidate climate reconstructions.

Analyses of the impact of changes in atmospheric deposition and climate on forest growth in European monitoring plots: A stand growth approach

During the last 15 years a number of studies have shown increasing forest growth in central Europe, rather than a decline as was expected due to negative effects of air pollution. We have here used data from intensive monitoring plots spread over Europe for a five year period in order to examine the influence of environmental factors on forest growth. Evaluations focussed on the influence of nitrogen, sulphur and acid deposition, temperatures, precipitation and on a drought index calculated as deviation from the long-term mean. The study included the main tree species Norway spruce, Scots pine, common beech as well as European and sessile oak and was based on data from 363 plots. As many other factors besides nitrogen and temperature influence tree growth, expected stem volume increments were modelled using site productivity, stand age and a stand density index. Relative volume increment was then calculated as actual increment in % of expected increment. The site productivity, assumed to be given by site conditions and past environmental conditions, was either taken from expert estimates or computed from site index curves from northern, central and southern Europe. The model explained between 18% and 39% of the variance with site productivity being positively related and age negatively related to actual increment. The various models and statistical approaches were fairly consistent, and indicated a fertilizing effect of nitrogen deposition, with slightly above one percent increase in volume increment per kg of nitrogen deposition per ha and year. This was most clear for spruce and pine, and most pronounced for plots having soil C/N ratios above 25. Also, we found a positive relationship between relative increment and summer temperature, i.e. May–August mean temperature deviation from the 1961–1990 means. The cause–effect relationship here is, however, less certain. Other influences were uncertain. Possibly, sulphur and acid deposition have effects on growth, but these effects are obscured by, and outweighed by the positive effect of nitrogen deposition, because of collinearity between these variables. Drought effects were uncertain also, and one reason for this might be large uncertainties in the precipitation data: precipitation measured on some 50% of the plots correlated poorly with the precipitation data obtained from Europe-wide databases. The major finding of this study was a positive relationship between higher than normal volume increment on one hand and nitrogen deposition on the other hand.

Multiple stable isotopes from oak trees in southwestern Scotland and the potential for stable isotope dendroclimatology in maritime climatic regions

Across much of Europe, Eurasia and N. America there exist networks of long tree-ring chronologies which, under favourable circumstances, may be used to provide a record of palaeoclimate information. A proportion of these tree-ring archives, primarily those collected for archaeological dating purposes, represent a significant and largely untapped palaeoenvironmental archive. Such records may be unsuitable for palaeoclimatic reconstruction based solely upon their physical characteristics (ring width and density) owing to weak or poorly expressed climatic forcing. This is especially true of oak chronologies from maritime regions. This study explores the potential for extracting a climate signal from such chronologies by comparing the stable isotope ratios of C, H and O from the rings of common oak ( Quercus robur) trees in southwestern Scotland, with local and regional meteorological data. Summer (growing season) climate influences all three isotopes and the relationships identified are consistent with published empirical and mechanistic studies. The climate signal appears strongest in O and weakest in H. The C and O series, in combination, explain 31% of the variance in July–August mean temperature measured locally and 26% when compared with a homogenised gridded dataset for the period AD1957-2002. Over longer timescales the combination of C and O isotopes may also preserve a significant low-frequency signal (July–August r 2 = 0.57, 9-year running mean AD1879–1998). These findings demonstrate the potential of stable isotope dendroclimatology for investigating climatic change from oak chronologies in maritime regions.

January to August temperature variability since 1776 inferred from tree-ring width of Pinus tabulaeformis in Helan Mountain

Tree-ring standardized chronologies are developed by 78 cores collected from the eastern and western Helan Mountain. Statistical analysis shows that both the STD and RES chronologies correlate negatively with the temperature of different periods of early half year, especially with January to August mean (JA) temperature, which means that JA temperature is one of the predominant limiting factors of tree growth in the Helan Mountain. Based on this analysis, we reconstructed JA temperature, and the explained variance is 43.3% (F=21.422, p<0.001). The comparatively high temperature periods in the reconstruction were: 1805–1818, 1828–1857, 1899–1907, 1919–1931 and 1968–1995; and the comparatively low temperature periods happened in 1858–1872, 1883–1895 and 1935–1953. Ten-year moving average curve shows three slow uplifting trends: 1766–1853, 1862–1931 and 1944–1995. Each temperature increase was followed by a sudden temperature decrease about 10 years, that is to say, the JA temperature in the Helan Mountain is characterized by slow increase and sudden decrease. The 70-and 10.77-year periodicities detected in the temperature series correspond to the Gleissberg (80-year) and Schwabe (11-year) periodicities of solar activity respectively, the 2.11–2.62 years cycles are considered to be influenced by QBO (Quasi-Biennial-Oscillation) and the local environmental change.

A 1052-year tree-ring proxy for Alpine summer temperatures

A June–August Alpine temperature proxy series is developed back to AD 951 using 1,527 ring-width measurements from living trees and relict wood. The reconstruction is composed of larch data from four Alpine valleys in Switzerland and pine data from the western Austrian Alps. These regions are situated in high elevation Alpine environments where a spatially homogenous summer temperature signal exists. In an attempt to capture the full frequency range of summer temperatures over the past millennium, from inter-annual to multi-centennial scales, the regional curve standardization technique is applied to the ring width measurements. Correlations of 0.65 and 0.86 after decadal smoothing, with high elevation meteorological stations since 1864 indicate an optimal response of the RCS chronology to June–August mean temperatures. The proxy record reveals warm conditions from before AD 1000 into the thirteenth century, followed by a prolonged cool period, reaching minimum values in the 1820s, and a warming trend into the twentieth century. This latter trend and the higher frequency variations compare well with the actual high elevation temperature record. The new central Alpine proxy suggests that summer temperatures during the last decade are unprecedented over the past millennium. It also reveals significant similarities at inter-decadal to multi-centennial frequencies with large-scale temperature reconstructions, however, deviating during certain periods from H.H. Lamb‘s European/North Atlantic temperature history.

Climate change and woodland caribou in Northwestern Ontario: a risk analysis

Woodland caribou (Rangifer tarandus caribou) range occupancy and populations have declined in northwestern (NW) Ontario over the last 100 years primarily due to human-induced factors. Recovery efforts are underway to halt this decline by reducing risk factors. Climate forecasts suggest a 4—5 oC increase in May—August mean temperature over the next century with little change in precipitation. Resulting increases in extreme weather events and increased fire weather severity will likely increase the amount of forest burned, reduce the area of older forest, alter distribution and abundance of forest tree species and plant communities, and increase abundance of alternate prey. The reduced amount of older forest preferred by caribou will be in greater demand by the forest industry leading to more conflict over ecological and economic values. Most of these factors will increase risk to caribou survival. Although forests may experience enhanced productivity, forest management practices will try to adapt harvest, regeneration, silviculture and fire management practices to both maintain economic benefits and increase the ability of forests to sequester carbon. The interaction of climate-induced forest change and forest management practices adds uncertainty to caribou conservation efforts at the southern edge of its current range. This uncertainty reinforces the need for a precautionary approach to forest management, increased research and monitoring effort, sustained emphasis on caribou recovery, and careful rationalization of restoration efforts where greatest opportunities for success may be realized.

Comparison of living-tree and subfossil ringwidths with summer temperatures from 18 th, 19 th and 20 th centuries in Northern Finland

Summary This work seeks to analyse the importance of summer-temperatures an the tree-ring growth of Scots pine ( Pinus sylvestris L.) during the past three centuries. Three living-tree chronologies, subfossil pine chronology and one composite tree-ring chronology were constructed from latitudinal and altitudinal forest-limits of pine in northern Finland and compared with meteorological data comes from three localities. These data include early instrumental temperature observations from 18 th and 19 th centuries. The modern meteorological data covers the period from 1860 to present. Response functions were derived by means of Pearson correlations using five subperiods as follows: 1738–1748, 1802–1822, 1825–1835, 1861–1926 and 1927–1992. It was demonstrated that the correlations between ringwidths and mid-summer (July) temperatures did not vary significantly as a function of time. Early(June) and late-summer (August) mean temperatures were secondary in relation to mid-summer temperatures in controlling the radial growth. Early-summer temperatures governed pine radial growth most clearly during the 19 th century, whereas late-summer temperatures had strongest influence an ring-widths during the 18 th century and later part of the 20 th century. There was no clear signature of temporally reduced sensitivity of Scots pine ring-widths to mid-summer temperatures over the periods of early meteorological observations. Subfossil pine chronology, constructed using pines recovered from small Jakes along the forest-limit zone, showed a consistent pattern of response to summer-temperatures in relation to living-tree chronologies.

A Mesoscale Study of Corn-Weather Response on Cash-Grain Farms

Abstract Weather records for 49 locations and detailed agronomic data from 60 farms in a 400-mi2 area in central Illinois were used to study corn-weather relations exhibited by actual farming operations in a typical agricultural area of the American Corn Belt. Weekly, monthly and seasonal rainfall and temperature values plus agronomic data were correlated with corn yields during 1955–1963. The results are of added importance because the data sample was from a period when new agronomic practices, which could alter corn-weather relationships established in previous studies, were being widely employed. July and August mean temperatures and cumulative degrees above 90F during July and August had the strongest correlations with corn yield, −0.50, −0.69 and −0.51, respectively. July rainfall had a stronger association with yields than rainfall in any other month, but it was considerably less than the association for July temperature. Weekly rainfalls and temperatures in early June and early August correlated mo...

The Periodic Fluctuations of About 7-Years for August Mean Pressure and Temperature in the Northern Hemisphere

In our previous reports, stochastical studies were tried for the fluctuations of monthly mean temperature and pressure for August at the various stations in the neighbourhood of Japan. Significant periodic fluctuations of about 7-years were detected then. Such periodicity was distinct in the middle latitudes and was presented in the zonal oscillation of North Pacific High. In this paper, we have tried the statistical investigation for the periodicity in monthly mean situation in the Northern Hemisphere. The results obtained are as follows.1) The periodicity of about 7-years for the monthly mean pressure and temperature for August are stochastically significant in Central and Southern Europe, and for August mean pressure in Southern India, Java and Sumatra.2) The periodic fluctuations of 7-years for August mean pressure in Europe are everywhere in phase, but for the temperature, they are inverse between Greenwich and Alexandria.3) The periodic fluctuations of 7-years for August mean pressure in Europe and India are also in phase.4) The periodic fluctuations of 7-years for August. mean pressure in Europe are ahead of Japan for several years.