Long memory in temperature reconstructions

Ever since H. E. Hurst brought the concept of long memory time series to prominence in his study of river flows the origins of the so-called Hurst phenomena have remained elusive. Two sets of competing models have been proposed. The fractional Gaussian noises and their discrete time counter-part, the fractionally integrated processes, possess genuine long memory in the sense that the present state of a system has a temporal dependence on all past states. The alternative to these genuine long memory models are models which are non-stationary in the mean but for physical reasons are constrained to lie in a bounded range, hence on visual inspection appear to be stationary. In these models the long memory is merely an artifact of the method of analysis. There are now a growing number of millenial scale temperature reconstructions available. In this paper we present a new way of looking at long memory in these reconstructions and proxies, which gives support to them being described by the non-stationary models. The implications for climatic change are that the temperature time series are not mean reverting. There is no evidence to support the idea that the observed rise in global temperatures are a natural fluctuation which will reverse in the near future.     

Secular trends in high northern latitude temperature reconstructions based on tree rings

Boreal tree-ring records from high latitude North America, Scandinavia and Russia provide baseline data reflecting long-term trends in Arctic annual temperature. Reconstructions from 1682–1968 indicate the latter part and termination of the Little Ice Age and that the northern regions are now warmer by comparison. The resulting high-resolution, extended temperature time series allows examination of underlying causes of climatic change not possible using only the instrumental record. The recent recorded data for the Arctic show recovery from the cooling in the 1950's–1960's. The overall evaluation confirms that the high northern latitudes are now in an anomalously warm state relative to the past three centuries.     

Surface temperature in NW Europe during the Younger Dryas: AGCM simulation compared with temperature reconstructions

 During the Younger Dryas (YD) the climate in NW Europe returned to near-glacial conditions. To improve our understanding of climate variability during this cold interval, we compare an AGCM simulation of this climate, performed with the ECHAM model, with temperature reconstructions for NW Europe based on geological and paleoecological records. Maps for the mean winter, summer and annual temperature are presented. The simulated winters are consistent with reconstructions in the northern part of the study area. A strong deviation is noted in Ireland and England, where the simulation is too warm by at least 10 °C. It appears that the N Atlantic was cooler than prescribed in the YD simulation, including a southward expansion of the sea-ice margin. The comparison for the summer shows a too warm continental Europe in the simulation. Supposedly, these anomalously warm conditions are caused by the AGCM’s response to the prescribed increased summer insolation. The region of maximum summer cooling is similar in both the simulation and reconstruction, i.e., S Sweden. We suggest that this is due to the local cooling effect of the Scandinavian ice sheet. Compared to the present climate a considerable increase of the annual temperature range is inferred, especially for regions close to the Atlantic Ocean. Received: 20 November 1996 / Accepted: 8 July 1997     

Comparison of instrumental and interpolated meteorological data-based summer temperature reconstructions on Mt. Taibai in the Qinling Mountains,northwestern China

Theoretical and Applied Climatology - Previous dendroclimatical studies have been based on the relationship between tree growth and instrumental climate data recorded at lower land meteorological...     

Long-term patterns of solar irradiance forcing in model experiments and proxy based surface temperature reconstructions

Comparisons are made of long-term empirical and model-estimated patterns of solar irradiance forcing during a 200-year period (1650-1850), which precedes any apparent anthropogenic influence on climate. This interval encompasses a considerable range (approximately 4 W/m²) of estimated variation in solar output, including the "Maunder" and "Dalton" Minima of solar irradiance, and an intervening interval of relatively high values of irradiance, but does not encroach into the industrial era wherein it is difficult to separate solar and anthropogenic influences. Particular emphasis is placed on comparing empirical and modeled patterns of forced surface temperature variation. The empirical patterns bear a greater similarity to the pattern of forced response of a coupled ocean-atmosphere general circulation model (AOGCM) than with an independent model simulation result using an ocean with specified heat transport, both in terms of the spatial pattern of response and implied global mean sensitivity to forcing. Heightened sensitivity in the western Pacific warm pool apparent in the empirical response pattern, is not observed in the forced response of the coupled model. It is possible that this pattern is the result of feedback processes not currently reproduced in course-resolution coupled models. The greatest empirical response is found at the multidecadal-to-century (> 40 year period) time scale, for which the forcing is dominated by the roughly 90-year Gleissberg Cycle of irradiance. This indicates a global-mean sensitivity (approximately 0.3 K/W/m²), which is close to the coupled model result (approximately 0.4 K/W/m²). At decadal time scales (8-25 year period), for which the forcing is dominated by the 11-year and 22-year period solar cycles), the temperature sensitivity is moderately reduced, and its spatial pattern of response is dominated by an apparent resonance with known decadal modes of climate variability.     

中国东北南部地区冬季气温异常的海气背景分析

利用1951—2005年中国沈阳、通化、营口、丹东气温和北半球500 hPa高度及北太平洋海温资料,分析了中国东北南部地区冬季气温的异常变化及其海气背景。结果表明:中国东北南部地区冬季气温具有明显的年代际变化特征;冬季异常冷暖年份,其同期与前期500 hPa高度和海温距平场分布具有明显不同;前期春季(3—5月)贝加尔湖高压和西太平洋副热带高压的强弱变化,西风漂流区海温、赤道东太平洋关键区海温及2个海区海温距平差,对中国东北南部地区冬季气温的异常变化均具有较好的预测指示意义。前期夏季(7—9月)赤道东太平洋关键区海温对中国东北南部地区冬季气温异常变化具有指示性。     

Fading temperature sensitivity of Alpine tree growth at its Mediterranean margin and associated effects on large-scale climate reconstructions

A millennium-long tree-ring width chronology of living and dead larch (Larix decidua Mill.) specimens from the Maritime French Alps was introduced 35?years ago. This record has been included in various large-scale temperature reconstructions, though recent analyses revealed only weak associations with regional summer temperatures. Calibration and verification trials against instrumental measurements were, however, limited by the original record’s early ending in 1974. Here we introduce an update of this widely considered chronology until 2007 and back into medieval times. A total of 297 new larch samples from high-elevation settings in the southern French Alps were included, and the combined 398 measurement series allowed effects of tree-ring detrending and chronology development to be explored. Comparisons with meteorological temperature, precipitation and drought indices revealed weak and temporally inconsistent climate sensitivity. To further place these local findings in a biogeographic context, we used >3,000 larch trees from 61 locations across the Alpine arc. This unique network approach confirmed fading temperature sensitivity with decreasing latitude, and thus questioned the overall reliability of ring width-based temperature reconstructions in the Mediterranean region. Our results further emphasize the pending need to develop chronologies from maximum latewood densities and stable isotope ratios across the lower latitudes, and to carefully evaluate ecological site conditions and methodological data restrictions prior to compiling local data into global networks.     

Monthly, seasonal and annual temperature reconstructions for Central Europe derived from documentary evidence and instrumental records since AD 1500

Monthly temperature series for Central Europe back to AD 1500 are developed from documentary index series from Germany, Switzerland and the Czech Republic (1500–1854) and 11 instrumental temperature records (1760–2007). Documentary evidence from the Low Countries, the Carpathian Basin and Poland are used for cross-checking for earlier centuries. The instrumental station records are corrected for inhomogeneities, including insufficient radiation protection of early thermometers and the urban heat island effect. For overlapping period (1760–1854), the documentary data series correlate with instrumental temperatures, most strongly in winter (86% explained variance in January) and least in autumn (56% in September). For annual average temperatures, 81% of the variance is explained. Verification statistics indicate high reconstruction skill for most months and seasons. The last 20 years (since 1988) stand out as very likely the warmest 20-year period, accounting for the calibration uncertainty and decreases in proxy data quality before the calibration period. The new reconstruction displays a previously unobserved long-term decrease in DJF, MAM and JJA temperature variability over last five centuries. Compiled monthly, seasonal and annual series can be used to improve the robustness of gridded large-scale European temperature reconstructions and possible impact studies. Further improvement of the reconstruction would be achieved if documentary data from other European countries are further developed.     

Influence of seasonality on glacier mass balance, and implications for palaeoclimate reconstructions

Climates inferred from former glacier geometries in some areas exhibit discrepancies with regional palaeoclimates predicted by General Circulation Models (GCMs) and modelling of palaeoecological data, possibly as a consequence of their differing treatments of climatic seasonality. Since glacier-based climate reconstructions potentially offer an important tool in the calibration of GCMs, which themselves need validation if used to predict future climate scenarios, we attempt to resolve mismatches between these techniques by (1) investigating the influence of seasonality on glacier mass balance, and (2) refining the methodology used for the derivation of glacier-based palaeoclimates. Focussing on the Younger Dryas stadial glaciation of Scotland, northeast Atlantic, we show that sea-ice amplified seasonality led to a significantly drier climate than has been suggested by glacier-based interpretations. This was characterised by a relatively short ablation season and the survival of a more substantial winter snowpack. We suggest that if palaeoglaciological studies were to account for changes in seasonal temperature and precipitation variability, their results would agree more closely with the cold, arid, northeast Atlantic palaeoenvironment predicted by atmospheric modelling and northwest European pollen studies, and would therefore provide more accurate constraints for GCM calibration.     

鲁中地区极端高温变化特征分析

基于1966—2015年鲁中地区8个气象站日最高气温、日最低气温和相对湿度气象观测资料,利用年最高气温、高温日数、极端高温日数、暖夜日数、炎热日数和高温热浪日数等指数,研究其极端高温天气变化特征。结果表明:鲁中地区近50 a年最高气温随时间变化呈增加趋势,1990年后增加趋势明显,有6 a左右的主要变化周期,主要空间变化规律一致;极端高温天气呈增强趋势,尤其在1990年以后,年炎热日数和轻度高温热浪日数最多出现在1994年,年高温日数最多出现在1997年,年极端高温、暖夜日数和重度高温热浪日数均出现在2005年;中部地区发生极端高温天气频率高,南部山区发生频率低。     

Estimation of multi-scale temporal variability of air and water temperature in the northeastern part of the Black Sea

Standard deviations of mesoscale, synoptic, seasonal, and interannual fluctuations of the air and water temperature are calculated from long-term measurements. The contributions of each type of fluctuation to the total temporal variability are estimated. The intraannual cycle of variability of monthly (long-term) means of mesoscale and synoptic fluctuations is considered.     

On exceptionally mild winters in Genoa,Italy

Summary Averages of air temperature, atmospheric pressure and rainfall measured at Genoa University Observatory for the winter (December to February) and December–March periods in the years 1987–88, 1988–89 and 1989–90 are examined. The average air temperature and the atmospheric pressure in these years were anomalously high while the rainfall was lower in 1988–89 and 1989–90. The results of an investigation performed to determine whether similar mild events occurred in the past are explained. Finally the possibility of more recent meteorological events being the result of an enhanced greenhouse effect is discussed.With 2 Figures     

Chemical characterization of cloud episodes at a ridge site in Tuscan Appennines, Italy

Cloudwater samples were collected from November 1992 to March 1995 in Vallombrosa, a mountain site of the Tuscan Apennines (central Italy). Chemical analyses show that all examined inorganic ions contributed significantly to the total ionic content (TIC). The ratio SO₄²⁻/NO₄⁻ ranged from 0.92 to 3.46 and was >1 for 86% of samples. There is a wide range in the chemical composition of the cloudwater. The total ionic content ranged from 640 to 7476 μeq l⁻¹ and pH from 3.17 to 6.22. The liquid water content (LWC) ranged from 0.06 to 0.94 g m⁻³ and electrical conductivity from 47 to 485 μΩ⁻¹. The total ionic content decreases while the liquid water content increases. Also analyzed were soluble trace metals (Fe, Pb, Cu, Mn, Cd, Al), synthetic anionic surfactants and the methanesulphonic acid. Chemical analyses evidenced in some cases a high concentration of organic matter. The meteorological analysis for a few samples of individual passages was carried out for the possibility of establishing a correspondence between meteorological events and chemical composition. The sources (marine, crustal and anthropogenic) of chemical components were deduced.     

Estimation of fog deposition on epiphytic bryophytes in a subtropical montane forest ecosystem in northeastern Taiwan

The fog meteorology, fog chemistry and fog deposition on epiphytic bryophytes were investigated from July 2000 to June 2001 in the Yuanyang Lake forest ecosystem. The elevation of the site ranges from 1650 to 2420 m, at which the high frequency of fog occurrence throughout the year has been thought to be of benefit to the establishment of the primary Taiwan yellow cypress forest [Chamaecyparis obtusa var. formosana (Hayata) Rehder] and to the extensive growth of the epiphytic bryophytes. A weather station including a visibility sensor and an active fog collector was installed for fog meteorological and chemical study. The fog deposition rate on epiphytic bryophytes was estimated by measuring the increase rate in plant weight when exposed to fog. Average fog duration of 4.7 and 11.0 h per day was measured in summer months (June to August) and the rest of the year, respectively. November 2000 was the foggiest month in which the average fog duration reached 14.9 h per day. The ionic composition of fog water revealed that the area was less polluted than expected from literature data. The in situ exposure experiments done with the dominant epiphytic bryophytes showed an average fog deposition rate of 0.63 g H₂O g⁻¹ d. w. h⁻¹, which approximated 0.17 mm h⁻¹ at the stand scale. The nutrient fluxes estimated for February 2001 showed that for all ions, more than 50% of the ecosystem input was through fog deposition. These results demonstrate the importance of epiphytic bryophytes and fog deposition in nutrient cycling of this subtropical montane forest ecosystem. The incorporation of fog study in the long-term ecosystem research projects is necessary in this area.     

Climate change scenarios for surface temperature in Emilia-Romagna (Italy) obtained using statistical downscaling models

Summary Possible changes of mean climate and the frequency of extreme temperature events in Emilia-Romagna, over the period 2070–2100 compared to 1960–1990, are assessed. A statistical downscaling technique, applied to HadAM3P experiments (control, A2 and B2 scenarios) performed at the Hadley Centre, is used to achieve this objective. The method applied consists of a multivariate regression based on Canonical Correlation Analysis (CCA), using as possible predictors mean sea level pressure (MSLP), geopotential height at 500 hPa (Z500) and temperature at 850 hPa (T850), and as predictands the seasonal mean values of minimum and maximum surface temperature (T_min and T_max), 90^th percentile of maximum temperature (T_max90), 10^th percentile of minimum temperature (T_min10), number of frost days (T_nfd) and heat wave duration (HWD) at the station level. First, the statistical model is optimised and calibrated using NCEP/NCAR reanalysis to evaluate the large-scale predictors. The observational data at 32 stations uniformly distributed over Emilia-Romagna are used to compute the local predictands. The results of the optimisation procedure reveal that T850 is the best predictor in most cases, and in combination with MSLP, is an optimum predictor for winter T_max90 and autumn T_min10. Finally, MSLP is the best predictor for spring T_min while Z500 is the best predictor for spring T_max90 and heat wave duration index, except during autumn. The ability of HadAM3P to simulate the present day spatial and temporal variability of the chosen predictors is tested using the control experiments. Finally, the downscaling model is applied to all model output experiments to obtain simulated present day and A2 and B2 scenario results at the local scale. Results show that significant increases can be expected to occur under scenario conditions in both maximum and minimum temperature, associated with a decrease in the number of frost days and with an increase in the heat wave duration index. The magnitude of the change is more significant for the A2 scenario than for the B2 scenario.     

非适宜气温和PM2.5及其协同作用对不同年龄段老年人死亡的影响

老年人群是脆弱群体的主体,非适宜气温和PM_2.5对不同年龄段老年人的危险性、滞后期、收获效应、协同作用可能存在相关规律,但是尚缺乏非适宜气温和PM_2.5对细分年龄段老年人的影响研究。本研究以中国老龄化最严重的江苏省南通市为例,收集了2012—2017年256037位65—104岁死亡者信息,并按年龄分为6组,运用广义相加模型和分布滞后非线性模型分别研究了非适宜气温、PM_2.5对各组人群的相对危险度、死亡归因分值和滞后期,以及二者的协同作用。结果显示:（1）随年龄增长,非适宜气温的相对危险度和归因分值不断升高,并且低温升高的幅度远高于高温,在90岁以上组分别达到高温的1.46和6.49倍,PM_2.5的相对危险度先降低后升高,高龄老人的主要危险因素是低温。（2）低温、高温分别具有9—12和3—6 d的滞后期,但是滞后期与年龄无关;PM_2.5的滞后期随年龄增长而延长。（3）仅在78岁以下观察到高温的收获效应,说明高温对78岁以上高龄老人的影响并不局限于身体脆弱者和患病者。（4）非适宜气温和PM_2.5存在协同作用,死亡人数随气温降低、升高、PM_2.5浓度升高而增多,但不同年龄的变化幅度有差异。研究结果可为制定老年人群在各个年龄对大气环境中的危险因素应对策略提供参考,但由于南通是老龄化最严重的地区,未来还需在其他地区做进一步的研究,增加结论的适用性。