Long-term summer temperature reconstruction inferred from tree-ring records from the Eastern Carpathians

The first 1,000 year long Carpathian tree-ring width chronology was established based on living and subfossil stone pine (Pinus cembra L.) samples from an upper timberline forest located in Calimani Mts. (Romania). Tree-ring data were standardized using the regional curve standardization method in order to preserve the low and medium frequency climate signals. The de-trended index strongly correlates with summer mean temperature both at annual and decadal scales. The Calimani summer mean temperature anomalies were reconstructed for the period ad 1163-2005 applying the rescaling method. This new climate proxy from the Carpathians shows similar fluctuations to other North Hemispheric temperature reconstructions, but with periods of distinct differences. The fingerprint of Little Ice Age in the Calimani area is visible between ad 1370 and 1630 followed by lagged cold decades in ad 1820 and 1840. The recent warming is evident only after the 1980s in our reconstruction.     

Torneträsk tree-ring width and density ad 500–2004: a test of climatic sensitivity and a new 1500-year reconstruction of north Fennoscandian summers

This paper presents updated tree-ring width (TRW) and maximum density (MXD) from Torneträsk in northern Sweden, now covering the period ad 500–2004. By including data from relatively young trees for the most recent period, a previously noted decline in recent MXD is eliminated. Non-climatological growth trends in the data are removed using Regional Curve Standardization (RCS), thus producing TRW and MXD chronologies with preserved low-frequency variability. The chronologies are calibrated using local and regional instrumental climate records. A bootstrapped response function analysis using regional climate data shows that tree growth is forced by April–August temperatures and that the regression weights for MXD are much stronger than for TRW. The robustness of the reconstruction equation is verified by independent temperature data and shows that 63–64% of the instrumental inter-annual variation is captured by the tree-ring data. This is a significant improvement compared to previously published reconstructions based on tree-ring data from Torneträsk. A divergence phenomenon around ad 1800, expressed as an increase in TRW that is not paralleled by temperature and MXD, is most likely an effect of major changes in the density of the pine population at this northern tree-line site. The bias introduced by this TRW phenomenon is assessed by producing a summer temperature reconstruction based on MXD exclusively. The new data show generally higher temperature estimates than previous reconstructions based on Torneträsk tree-ring data. The late-twentieth century, however, is not exceptionally warm in the new record: On decadal-to-centennial timescales, periods around ad 750, 1000, 1400, and 1750 were equally warm, or warmer. The 200-year long warm period centered on ad 1000 was significantly warmer than the late-twentieth century (p < 0.05) and is supported by other local and regional paleoclimate data. The new tree-ring evidence from Torneträsk suggests that this “Medieval Warm Period” in northern Fennoscandia was much warmer than previously recognized.     

Improving a tree-ring reconstruction from west-central Scandinavia: 900?years of warm-season temperatures

Dendroclimatological sampling of Scots pine (Pinus sylvestris L.) has been made in the province of J?mtland, in the west-central Scandinavian mountains, since the 1970s. The tree-ring width (TRW) chronology spans several thousand years and has been used to reconstruct June?CAugust temperatures back to 1632 bc. A maximum latewood density (MXD) dataset, covering the period ad 1107?C1827 (with gap 1292?C1315) was presented in the 1980s by Fritz Schweingruber. Here we combine these historical MXD data with recently collected MXD data covering ad 1292?C2006 into a single reconstruction of April?CSeptember temperatures for the period ad 1107?C2006. Regional curve standardization (RCS) provides more low-frequency variability than ??non-RCS?? and stronger correlation with local seasonal temperatures (51% variance explained). The MXD chronology shows a stronger relationship with temperatures than the TRW data, but the two chronologies show similar multi-decadal variations back to ad 1500. According to the MXD chronology, the period since ad 1930 and around ad 1150?C1200 were the warmest during the last 900?years. Due to large uncertainties in the early part of the combined MXD chronology, it is not possible to conclude which period was the warmest. More sampling of trees growing near the tree-line is needed to further improve the MXD chronology.     

全球变暖趋缓研究进展

近十几年来,全球年平均表面温度上升趋势显示出停滞状态,即全球变暖趋缓,这引起了国际社会的广泛关注,同时也引发了对全球变暖的质疑,各国气候学家正努力就全球变暖趋缓的事实、原因及其可能影响展开研究。本文综述了目前国内外对全球变暖趋缓的研究结果。多数科学家认可近十几年来全球变暖停滞的事实,并认为太阳活动处于低位相、大气气溶胶（自然和人为）增加以及海洋吸收热量是变暖停滞的可能影响因子,其中海洋（尤其是700米以下的深海）对热量的储存可能是变暖停滞的关键。国际耦合模式比较计划第5阶段中的模式并未精确地描述各种有利降温影响因子的近期位相演变,因而其模拟的近期增暖趋势较观测偏强。由此推断,变暖停滞主要是自然因素造成的,并且预测变暖趋缓将在近几年或几十年内结束（依赖于太平洋年代际振荡的位相转变）,未来气温将仍主要受到温室气体增加的影响而表现出明显的上升趋势。因此,目前的全球变暖趋缓不大可能改变到本世纪末全球大幅度变暖带来的风险。本综述展望未来的研究热点包括:精确估算全球气温和海洋热含量的变率及其不确定性,海洋年代际信号（太平洋以及大西洋的年代际振荡）的转型机制,存储在深海的热量将在何时返回海洋表面及其对区域气候的潜在影响。     

Multiproxy summer and winter surface air temperature field reconstructions for southern South America covering the past centuries

We statistically reconstruct austral summer (winter) surface air temperature fields back to ad 900 (1706) using 22 (20) annually resolved predictors from natural and human archives from southern South America (SSA). This represents the first regional-scale climate field reconstruction for parts of the Southern Hemisphere at this high temporal resolution. We apply three different reconstruction techniques: multivariate principal component regression, composite plus scaling, and regularized expectation maximization. There is generally good agreement between the results of the three methods on interannual and decadal timescales. The field reconstructions allow us to describe differences and similarities in the temperature evolution of different sub-regions of SSA. The reconstructed SSA mean summer temperatures between 900 and 1350 are mostly above the 1901?C1995 climatology. After 1350, we reconstruct a sharp transition to colder conditions, which last until approximately 1700. The summers in the eighteenth century are relatively warm with a subsequent cold relapse peaking around 1850. In the twentieth century, summer temperatures reach conditions similar to earlier warm periods. The winter temperatures in the eighteenth and nineteenth centuries were mostly below the twentieth century average. The uncertainties of our reconstructions are generally largest in the eastern lowlands of SSA, where the coverage with proxy data is poorest. Verifications with independent summer temperature proxies and instrumental measurements suggest that the interannual and multi-decadal variations of SSA temperatures are well captured by our reconstructions. This new dataset can be used for data/model comparison and data assimilation as well as for detection and attribution studies at sub-continental scales.     

Non-uniform interhemispheric temperature trends over the past 550 years

The warming trend over the last century in the northern hemisphere (NH) was interrupted by cooling from ad 1940 to 1975, a period during which the southern hemisphere experienced pronounced warming. The cause of these departures from steady warming at multidecadal timescales are unclear; the prevailing explanation is that they are driven by non-uniformity in external forcings but recent models suggest internal climate drivers may play a key role. Paleoclimate datasets can help provide a long-term perspective. Here we use tree-rings to reconstruct New Zealand mean annual temperature over the last 550 years and demonstrate that this has frequently cycled out-of-phase with NH mean annual temperature at a periodicity of around 30–60 years. Hence, observed multidecadal fluctuations around the recent warming trend have precedents in the past, strongly implicating natural climate variation as their cause. We consider the implications of these changes in understanding and modelling future climate change.     

Numerical Simulation of Global Temperature Change during the 20th Century with the IAP／LASG GOALS Model

The IAP/LASG GOALS coupled model is used to simulate the climate change during the 20th century using historical greenhouse gases concentrations, the mass mixing ratio of sulfate aerosols simulated by a CTM model, and reconstruction of solar variability spanning the period 1900 to 1997. Four simulations, including a control simulation and three forcing simulations, are conducted. Comparison with the observational record for the period indicates that the three forcing experiments simulate reasonable temporal and spatial distributions of the temperature change. The global warming during the 20th century is caused mainly by increasing greenhouse gas concentration especially since the late 1980s; sulfate aerosols offset a portion of the global warming and the reduction of global temperature is up to about 0.11℃ over the century; additionally, the effect of solar variability is not negligible in the simulation of climate change over the 20th century.     

Long-term hydroclimatic variability in monsoon shadow zone of western Himalaya, India

Tree-ring-width data of Himalayan cedar [Cedrus deodara (Roxb.) G. Don] from 11 homogeneous moisture stressed sites in the monsoon shadow zone of the western Himalaya were used to develop a mean chronology extending back to ad 1353. The chronology developed using Regional Curve Standardization method is the first from the Himalayan region of India showing centennial-scale variations. The calibration of ring-width chronology with instrumental precipitation data available from stations close to the tree ring sampling sites showed strong, direct relationship with March?CApril?CMay?CJune (MAMJ) precipitation. This strong relationship was used to supplement the instrumental precipitation data back to ad 1410. The precipitation reconstruction showed extended period of drought in fifteenth and sixteenth centuries. Increasingly pluvial conditions were recorded since eighteenth century, with the highest precipitation in the early part of the nineteenth century. The decreasing trend in reconstructed precipitation in the last decade of the twentieth century, consistent with the instrumental records, is associated with the decreasing trend in frequency of western disturbances. MAMJ precipitation over the monsoon shadow zone in the western Himalaya is directly associated with the North Atlantic Oscillation (NAO) and NINO3-SST index of El Nino-Southern Oscillation (ENSO), the leading modes of climate variability influencing climate over large parts of the Northern Hemisphere. However, the relationship between ENSO and MAMJ precipitation collapsed completely during 1930?C1960. The breakdown in this relationship is associated with the warm phase of Atlantic Multidecadal Oscillation (AMO). A spectral analysis of reconstructed MAMJ precipitation indicates frequencies in the range of the variability associated with modes of NAO, ENSO and AMO.     

Simulation of the influence of solar radiation variations on the global climate with an ocean-atmosphere general circulation model

 Two simulations with a global coupled ocean-atmosphere circulation model have been carried out to study the potential impact of solar variability on climate. The Hoyt and Schatten estimate of solar variability from 1700 to 1992 has been used to force the model. Results indicate that the near-surface temperature simulated by the model is dominated by the long periodic solar fluctuations (Gleissberg cycle), with global mean temperatures varying by about 0.5 K. Further results indicate that solar variability and an increase in greenhouse gases both induce to a first approximation a comparable pattern of surface temperature change, i.e., an increase of the land-sea contrast. However, the solar-induced warming pattern in annual means and summer is more centered over the subtropics, compared to a more uniform warming associated with the increase in greenhouse gases. The observed temperature rise over the most recent 30 and 100 years is larger than the trend in the solar forcing simulation during the same period, indicating a strong likelihood that, if the model forcing and response is realistic, other factors have contributed to the observed warming. Since the pattern of the recent observed warming agrees better with the greenhouse warming pattern than with the solar variability response, it is likely that one of these factors is the increase of the atmospheric greenhouse gas concentration. Received: 14 October 1996 / Accepted: 9 May 1997     

Early summer temperature reconstruction in the eastern Tibetan plateau since ad 1440 using tree-ring width of Sabina tibetica

Long climate records are scarce on the Tibetan Plateau for understanding the climate variability on long-term context. Here we presented an early summer (May?CJune) temperature reconstruction since ad 1440 for Qamdo area using tree rings of Sabina tibetica. The reconstruction accounted for 64% of the variance in the instrumental record. It showed warm periods during 1501?C1514, 1528?C1538, 1598?C1609, 1624?C1636, 1650?C1668, 1695?C1705, 1752?C1762, 1794?C1804, 1878?C1890, 1909?C1921, 1938?C1949, and 1979?C1991. Cool early summer occurred during 1440?C1454, 1482?C1500, 1515?C1527, 1576?C1597, 1610?C1621, 1669?C1679, 1706?C1716, 1782?C1793, 1863?C1873, 1894?C1908, and 1922?C1937. Comparison with other proxy or meteorological records suggested that there is obvious spatial variability in the May?CJune temperature variations along the eastern margin of the Tibetan Plateau.     

Multi-fingerprint detection and attribution analysis of greenhouse gas, greenhouse gas-plus-aerosol and solar forced climate change

 A multi-fingerprint analysis is applied to the detection and attribution of anthropogenic climate change. While a single fingerprint is optimal for the detection of climate change, further tests of the statistical consistency of the detected climate change signal with model predictions for different candidate forcing mechanisms require the simultaneous application of several fingerprints. Model-predicted climate change signals are derived from three anthropogenic global warming simulations for the period 1880 to 2049 and two simulations forced by estimated changes in solar radiation from 1700 to 1992. In the first global warming simulation, the forcing is by greenhouse gas only, while in the remaining two simulations the direct influence of sulfate aerosols is also included. From the climate change signals of the greenhouse gas only and the average of the two greenhouse gas-plus-aerosol simulations, two optimized fingerprint patterns are derived by weighting the model-predicted climate change patterns towards low-noise directions. The optimized fingerprint patterns are then applied as a filter to the observed near-surface temperature trend patterns, yielding several detection variables. The space-time structure of natural climate variability needed to determine the optimal fingerprint pattern and the resultant signal-to-noise ratio of the detection variable is estimated from several multi-century control simulations with different CGCMs and from instrumental data over the last 136 y. Applying the combined greenhouse gas-plus-aerosol fingerprint in the same way as the greenhouse gas only fingerprint in a previous work, the recent 30-y trends (1966–1995) of annual mean near surface temperature are again found to represent a significant climate change at the 97.5% confidence level. However, using both the greenhouse gas and the combined forcing fingerprints in a two-pattern analysis, a substantially better agreement between observations and the climate model prediction is found for the combined forcing simulation. Anticipating that the influence of the aerosol forcing is strongest for longer term temperature trends in summer, application of the detection and attribution test to the latest observed 50-y trend pattern of summer temperature yielded statistical consistency with the greenhouse gas-plus-aerosol simulation with respect to both the pattern and amplitude of the signal. In contrast, the observations are inconsistent with the greenhouse-gas only climate change signal at a 95% confidence level for all estimates of climate variability. The observed trend 1943–1992 is furthermore inconsistent with a hypothesized solar radiation change alone at an estimated 90% confidence level. Thus, in contrast to the single pattern analysis, the two pattern analysis is able to discriminate between different forcing hypotheses in the observed climate change signal. The results are subject to uncertainties associated with the forcing history, which is poorly known for the solar and aerosol forcing, the possible omission of other important forcings, and inevitable model errors in the computation of the response to the forcing. Further uncertainties in the estimated significance levels arise from the use of model internal variability simulations and relatively short instrumental observations (after subtraction of an estimated greenhouse gas signal) to estimate the natural climate variability. The resulting confidence limits accordingly vary for different estimates using different variability data. Despite these uncertainties, however, we consider our results sufficiently robust to have some confidence in our finding that the observed climate change is consistent with a combined greenhouse gas and aerosol forcing, but inconsistent with greenhouse gas or solar forcing alone. Received: 28 April 1996 / Accepted: 27 January 1997     

Coupled North Atlantic slope water forcing on Gulf of Maine temperatures over the past millennium

To investigate ocean variability during the last millennium in the Western Gulf of Maine (GOM), we collected a 142-year-old living bivalve (Arctica islandica L.) in 2004, and three fossil A. islandica shells (calibrated ¹⁴C_AMS = 1030 ± 78 ad; 1320 ± 45 ad; 1357 ± 40 ad) for stable isotope and growth increment analysis. A statistically significant relationship exists between modern GOM temperature records [shell isotope-derived (30 m) (r = ?0.79; P < 0.007), Prince 5 (50 m) (r = ?0.72; P < 0.019), Boothbay Harbor SST (r = ?0.76; P < 0.011)], and Labrador Current (LC) transport data from the Eastern Newfoundland Slope during 1993–2003. In all cases, as LC transport increased, GOM water temperatures decreased the following year. Decadal trends in the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) influence GOM water temperatures in the most recent period, with water temperatures decreasing during NAO and AMO negative modes most likely linked to LC transport and Gulf Stream interaction. Mean shell-derived isotopic changes (δ¹⁸O_c) during the last 1,000 years were +0.47‰ and likely reflect a 1–2°C cooling from 1000 ad to present. Based on these results, we suggest that observed cooling in the GOM during the last millennium was due to increased transport and/or cooling of the LC, and decreased Gulf Stream influence on the GOM.     

Temperature variability in China in an ensemble simulation for the last 1,200?years

Regional temperature anomalies in China during 800?C2005 ad in an ensemble simulation with the atmosphere?Cocean general circulation model ECHAM5/MPIOM subject to anthropogenic and natural forcings are compared to reconstructions. In a mutual assessment of three reconstructed data sets and two ensemble simulations with different solar forcings, a reconstructed data set and a simulated ensemble for weak solar variability are selected for further comparison. Temperature variability in the selected simulated and reconstructed data shows a continuous power spectrum with weak long-term memory. The simulation reveals weak long-term anomaly periods known as the Medieval Warm Period (MWP), the Little Ice Age (LIA), and the Modern Warming (MW) in the three considered regions: Northeast, Southeast, and West China. The ensemble spread yields an uncertainty of ±0.5°C in all regions. The simulated temperature varies nearly synchronously in all three regions, whereas reconstructed data hint to increased decadal variability in the West and centennial variability in the Northeast. Cold periods are found in 1200?C1300 and in 1600?C1900 ad in all regions. The coldest anomalies which are caused by volcanic eruptions in the beginnings of the thirteenth and the nineteenth centuries are only partly consistent with reconstructed data. After 1800, the annual cycle reduces in the Northeast and on the Tibetan plateau, whereas the eastern Pacific shows an enhanced summer?Cwinter contrast.     

Climate model simulation of anthropogenic influence on greenhouse-induced climate change (early agriculture to modern): the role of ocean feedbacks

We present further steps in our analysis of the early anthropogenic hypothesis (Ruddiman, Clim Change 61:261–293, 2003) that increased levels of greenhouse gases in the current interglacial, compared to lower levels in previous interglacials, were initiated by early agricultural activities, and that these increases caused a warming of climate long before the industrial era (～1750). These steps include updating observations of greenhouse gas and climate trends from earlier interglacials, reviewing recent estimates of greenhouse gas emissions from early agriculture, and describing a simulation by a climate model with a dynamic ocean forced by the low levels of greenhouse gases typical of previous interglacials in order to gauge the magnitude of the climate change for an inferred (natural) low greenhouse gas level relative to a high present day level. We conduct two time slice (equilibrium) simulations using present day orbital forcing and two levels of greenhouse gas forcing: the estimated low (natural) levels of previous interglacials, and the high levels of the present (control). By comparing the former to the latter, we estimate how much colder the climate would be without the combined greenhouse gas forcing of the early agriculture era (inferred from differences between this interglacial and previous interglacials) and the industrial era (the period since ～1750). With the low greenhouse gas levels, the global average surface temperature is 2.7 K lower than present day—ranging from ～2 K lower in the tropics to 4–8 K lower in polar regions. These changes are large, and larger than those reported in a pre-industrial (～1750) simulation with this model, because the imposed low greenhouse gas levels (CH₄ = 450 ppb, CO₂ = 240 ppm) are lower than both pre-industrial (CH₄ = 760 ppb, CO₂ = 280 ppm) and modern control (CH₄ = 1,714 ppb, CO₂ = 355 ppm) values. The area of year-round snowcover is larger, as found in our previous simulations and some other modeling studies, indicating that a state of incipient glaciation would exist given the current configuration of earth’s orbit (reduced insolation in northern hemisphere summer) and the imposed low levels of greenhouse gases. We include comparisons of these snowcover maps with known locations of earlier glacial inception and with locations of twentieth century glaciers and ice caps. In two earlier studies, we used climate models consisting of atmosphere, land surface, and a shallow mixed-layer ocean (Ruddiman et al., Quat Sci Rev 25:1–10, 2005; Vavrus et al., Quat Sci Rev 27:1410–1425, 2008). Here, we replaced the mixed-layer ocean with a complete dynamic ocean. While the simulated climate of the atmosphere and the surface with this improved model configuration is similar to our earlier results (Vavrus et al., Quat Sci Rev 27:1410–1425, 2008), the added information from the full dynamical ocean is of particular interest. The global and vertically-averaged ocean temperature is 1.25 K lower, the area of sea ice is larger, and there is less upwelling in the Southern Ocean. From these results, we infer that natural ocean feedbacks could have amplified the greenhouse gas changes initiated by early agriculture and possibly account for an additional increment of CO₂ increase beyond that attributed directly to early agricultural, as proposed by Ruddiman (Rev Geophys 45:RG4001, 2007). However, a full test of the early anthropogenic hypothesis will require additional observations and simulations with models that include ocean and land carbon cycles and other refinements elaborated herein.     

A transient climate change simulation with greenhouse gas and aerosol forcing: experimental design and comparison with the instrumental record for the twentieth century

 The Canadian Centre for Climate Modelling and Analysis (CCCma) global coupled model is used to investigate the potential climate effects of increasing greenhouse gas (GHG) concentrations and changes in sulfate aerosol loadings. The forcing scenario adopted closely resembles that of Mitchell et al. for both the greenhouse gas and aerosol components. Its implementation in the model and the resulting changes in forcing are described. Five simulations of 200 years in length, nominally for the years 1900 to 2100, are available for analysis. They consist of a control simulation without change in forcing, three independent simulations with the same greenhouse gas and aerosol changes, and a single simulation with greenhouse gas only forcing. Simulations of the evolution of temperature and precipitation from 1900 to the present are compared with available observations. Temperature and precipitation are primary climate variables with reasonable temporal and spatial coverage in the observational record for the period. The simulation of potential climate change from the present to the end of the twenty-first century, based on projected GHG and aerosol forcing changes, is discussed in a companion paper. For the historical period dealt with here, the GHG and aerosol forcing has changed relatively little compared to the forcing changes projected to the end of the twenty-first century. Nevertheless, the forced climate signal for temperature in the model is reasonably consistent with the observed global mean temperature from the instrumental record. This is true also for the trend in zonally averaged temperature as a function of latitude and for some aspects of the geographical and regional distributions of temperature. Despite the modest change in overall forcing, the difference between GHG+aerosol and GHG-only forcing is discernible in the temperature response for this period. Changes in precipitation, on the other hand, are much less evident in both the instrumental and simulated record. There is an apparent increasing trend in average precipitation in both the observations and the model results over that part of the land for which observations are available. Regional and geographical changes and trends (which are less affected by sampling considerations), if they exist, are masked by the large natural variability of precipitation in both model and observations. Received: 24 September 1998 / Accepted: 8 October 1999     

Past millennial solar forcing magnitude

A set of global climate model simulations for the last thousand years developed by the Max Planck Institute is compared with paleoclimate proxy data and instrumental data, focusing on surface temperatures for land areas between 30° and 75°N. The proxy data are obtained from six previously published Northern Hemispheric-scale temperature reconstructions, here re-calibrated for consistency, which are compared with the simulations utilizing a newly developed statistical framework for ranking several competing simulations by means of their statistical distance against past climate variations. The climate model simulations are driven by either “low” or “high” solar forcing amplitudes (0.1 and 0.25 % smaller total solar irradiance in the Maunder Minimum period compared to the present) in addition to several other known climate forcings of importance. Our results indicate that the high solar forcing amplitude results in a poorer match with the hemispheric-scale temperature reconstructions and lends stronger statistical support for the low-amplitude solar forcing. However, results are likely conditional upon the sensitivity of the climate model used and strongly dependent on the choice of temperature reconstruction, hence a greater consensus is needed regarding the reconstruction of past temperatures as this currently provides a great source of uncertainty.     

Solar Forcing of Global Climate Change Since The Mid-17th Century

Spacecraft measurements of the sun's total irradiance since 1980 have revealed a long-term variation that is roughly in phase with the 11-year solar cycle. Its origin is uncertain, but may be related to the overall level of solar magnetic activity as well as to the concurrent activity on the visible disk. A low-pass Gaussian filtered time series of the annual sunspot number has been developed as a suitable proxy for solar magnetic activity that contains a long-term component related to the average level of activity as well as a short-term component related to the current phase of the 11-year cycle. This time series is also assumed to be a proxy for solar total irradiance, and the irradiance is reconstructed for the period since 1617 based on the estimate from climatic evidence that global temperatures during the Maunder Minimum of solar activity, which coincided with one of the coldest periods of the Little Ice Age, were about 1 °C colder than modern temperatures. This irradiance variation is used as the variable radiative forcing function in a one-dimensional ocean–climate model, leading to a reconstruction of global temperatures over the same period, and to a suggestion that solar forcing and anthropogenic greenhouse-gas forcing made roughly equal contributions to the rise in global temperature that took place between 1900 and 1955. The importance of solar variability as a factor in climate change over the last few decades may have been underestimated in recent studies.     

A 694-year tree-ring based rainfall reconstruction from Himachal Pradesh, India

We developed ring-width chronologies of Cedrus deodara [(Roxb.) G. Don] and Pinus gerardiana (Wall. Ex. Lamb) from a homogeneous moisture stressed area in Kinnaur, Himachal Pradesh. Running correlation using a 50-year window with overlap of 25 years showed strong correlations between these species chronologies during the entire common period (ad 1310–2005). Response function analysis indicated that except for January–February, precipitation has a direct relationship with growth of these species. We therefore combined both the species chronologies to develop a statistically calibrated reconstruction of March–July precipitation that spans from ad 1310–2004, and explains 46% of the variance contained in the instrumental data from the calibration period 1951–1994. In the past 694 years of the reconstruction, the wettest period was in the twentieth century (1963–1992) and the driest in the eighteenth century (1773–1802). The relationships observed between reconstructed precipitation and Indian summer monsoon on interdecadal scale, SOI, PDO and NAO indicate the potential utility of such long-term reconstructions in understanding the large-scale climate variability. Multi-taper method (MTM) spectral analysis indicated significant (p < 0.05) spectral peaks at 2–4, 6, 8, 10, 30, 33, 37 and 40–42 years in the reconstructed precipitation data.     

温室气体、海表面温度、太阳常数及火山活动对中国地表气温影响之初探

利用全球大气环流模式CAM3.1,对近百年温室气体浓度、全球海表面温度、太阳常数的变化以及火山活动对我国地表气温所产生的影响进行了研究。全球海表面温度的升高及温室气体浓度的增加是导致中国年平均地表气温升高的部分因素。近百年我国年平均地表气温主要经历了两次年代际振荡并逐渐增温。第一次振荡的冷期为1910年代,随后变暖,1940年代达暖峰期。第二次振荡冷期发生于1950~1960年代,随后变暖,暖峰期发生在1990年代。太阳常数和全球海表面温度的两次振荡是造成这两次振荡主要因素,气温、太阳常数和全球海表面温度均发生了准60年周期的年代际振荡,气温振荡的位相落后于太阳常数和全球海表面温度的位相。20世纪20年代以前及60年代以后火山活动的活跃是导致1910年代和1960~1980年代出现冷期的原因之一。     

Process, Forcing, and Signal Analysis of Global Mean TemperatureVariations by Means of a Three-Box Energy Balance Model

An analytic solution of an energy balance model (EBM) is presented which can beused as a recursive filter for time series analysis. It is shown that the EBM can reproduce the solution of a coupled atmosphere-ocean general circulation model (AOGCM) experiment. Contrary to the AOGCM, the EBM easily allows for variations in climate sensitivity to satisfy the full range of uncertainty concerned with this parameter. The recursive filter is applied to two natural and two anthropogenic forcing mechanisms which are expressed in terms of heating rate anomaly time series: volcanism, solar activity, greenhouse gases (GHG), and anthropogenic tropospheric aerosols. Thus, we obtain modelled global mean temperature variations as a response to the different forcings and with respect to the uncertainty in the forcing approximations and climate sensitivity. In addition, it is shown that the observed (ENSO-corrected) global mean temperature time series within the period from 1866 to 1997 can be explained by the external forcings which have been considered and an additional white noise forcing. In this way we are able to separate different signals and compare them. As a result, global anthropogenic climate change due to GHG forcing can be detected at a high level of significance without considering spatial patterns of climate change but including natural forcing, which is usually not done. Furthermore, it is shown that solar forcing alone does not lead to significantclimate change, whereas solar and volcanic forcing together lead to a significant natural climate change signal. Anthropogenic climate change due to GHG forcing may partly be masked by anthropogenic aerosol cooling.