北极涛动的年代际变化及其气候影响

北极涛动(Arctic Oscillation,AO)是北半球热带外地区大气环流变率的主导模态,对北半球以及区域尺度气温变化具有重要影响.AO可在没有外强迫条件下通过d波流相互作用形成,因此它被认为是全球气候系统内部变率的重要组成部分.研究年代际尺度上AO的变化及其气候影响,可加深对当前北半球气候变化规律的物理理解,也...     

Population increase impacts the climate,using the sensitive Arctic as an example

The global population during the last 100 years has increased from 2 to 7.7 billion, causing an increase in greenhouse gases in the atmosphere. In order to see how population increase is directly related to physical variables of the climate, this Perspective article places observations and scenarios of climate change into context and puts forth a statistical modeling study on how the sensitive Arctic climate responds to the increasing population. The relationships between population, Arctic sea-ice extent (SIE), and surface air temperature (SAT) are very strong, with the increasing population explaining 96% of the decreasing SIE and about 80% of the increasing SAT in the Arctic. Our projection for the SIE using the population as a “proxy predictor” for a projected population of 10 billion people on the Earth in 2100, yields a SIE of 9.30 and 8.21 million km² for a linear and squared relationship, respectively, indicating no “tipping point” for the annual ice extent in this century. This adds another dimension to climate understanding for the public at large using population as a proxy variable, instead of the more abstract CO₂ parameter. This also indicates that it is important to attempt to limit the ongoing increase in population, which is the main cause of the greenhouse gas emissions, in addition to reducing per capita emissions by an exponential increase in implementing renewable energy, a formidable challenge in this century.     

Possible impacts of climate change on debris-flow activity in the Swiss Alps

This study uses a long dataset of past debris flows from eight high-elevation catchments in the Swiss Alps for which triggering conditions since AD 1864 have been reconstructed. The torrents under investigation have unlimited sediment supply and the triggering of debris flows is thus mainly controlled by climatic factors. Based on point-based downscaled climate scenarios for meteorological stations located next to the catchments and for the periods 2001–2050 and 2051–2100, we study the evolution of temperature and rainfall above specific thresholds (10, 20, 30, 40 and 50 mm) and durations (1, 2 or 3 days). We conclude that the drier conditions in future summers and the wetting of springs, falls and early winters are likely to have significant impacts on the behavior of debris flows. Based on the current understanding of debris-flow systems and their reaction to rainfall inputs, one might expect only slight changes in the overall frequency of events by the mid-21^st century, but possibly an increase in the overall magnitude of debris flows due to larger volumes of sediment delivered to the channels and an increase in extreme precipitation events. In the second half of the 21^st century, the number of days with conditions favorable for the release of debris flows will likely decrease, especially in summer. The anticipated increase of rainfall during the shoulder seasons (March, April, November, December) is not expected to compensate for the decrease in future heavy summer rainfall over 2 or 3 days.     

The impact of Arctic sea ice on the Arctic energy budget and on the climate of the Northern mid-latitudes

The atmospheric general circulation model EC-EARTH-IFS has been applied to investigate the influence of both a reduced and a removed Arctic sea ice cover on the Arctic energy budget and on the climate of the Northern mid-latitudes. Three 40-year simulations driven by original and modified ERA-40 sea surface temperatures and sea ice concentrations have been performed at T255L62 resolution, corresponding to 79?km horizontal resolution. Simulated changes between sensitivity and reference experiments are most pronounced over the Arctic itself where the reduced or removed sea ice leads to strongly increased upward heat and longwave radiation fluxes and precipitation in winter. In summer, the most pronounced change is the stronger absorption of shortwave radiation which is enhanced by optically thinner clouds. Averaged over the year and over the area north of 70° N, the negative energy imbalance at the top of the atmosphere decreases by about 10?W/m² in both sensitivity experiments. The energy transport across 70° N is reduced. Changes are not restricted to the Arctic. Less extreme cold events and less precipitation are simulated in sub-Arctic and Northern mid-latitude regions in winter.     

The simulation of Arctic clouds and their influence on the winter surface temperature in present-day climate in the CMIP3 multi-model dataset

We investigate the influence of clouds on the surface energy budget and surface temperature in the sea-ice covered parts of the ocean north of the Arctic circle in present-day climate in nine global climate models participating in the Coupled Model Intercomparison Project phase 3, CMIP3. Monthly mean simulated surface skin temperature, radiative fluxes and cloud parameters are evaluated using retrievals from the extended AVHHR Polar Pathfinder (APP-x) product. We analyzed the annual cycle but the main focus is on the winter, in which large parts of the region experience polar night. We find a smaller across-model spread as well as better agreement with observations during summer than during winter in the simulated climatological annual cycles of total cloudiness and surface skin temperature. The across-model spread in liquid and ice water paths is substantial during the whole year. These results qualitatively agree with earlier studies on the present-day Arctic climate in GCMs. The climatological ensemble model mean annual cycle of surface cloud forcing shows good agreement with observations in summer. However, during winter the insulating effect of clouds tends to be underestimated in models. During winter, most of the models as well as the observations show higher monthly mean total cloud fractions, associated with larger positive surface cloud forcing. Most models also show good correlation between the surface cloud forcing and the vertically integrated ice and liquid cloud condensate. The wintertime ensemble model mean total cloud fraction (69%) shows excellent agreement with observations. The across-model spread in the winter mean cloudiness is substantial (36?C94%) however and several models significantly underestimate the cloud liquid water content. If the two models not showing any relationship between cloudiness and surface cloud forcing are disregarded, a tentative across-model relation exists, in such a way that models that simulate large winter mean cloudiness also show larger surface cloud forcing. Even though the across-model spread in wintertime surface cloud forcing is large, no clear relation to the surface temperature is found. This indicates that other processes, not explicitly cloud related, are important for the simulated across-model spread in surface temperature.     

Human activity and climate variability impacts on sediment discharge and runoff in the Yellow River of China

Theoretical and Applied Climatology - We analyze the variability of sediment discharge and runoff in the Hekou–Longmen segment in the middle reaches of the Yellow River, China. Our analysis...     

The influence of the Arctic Oscillation on winter temperatures in Iran

Summary The impact of the Arctic Oscillation (AO) on the winter surface air temperature (SAT) over Iran is demonstrated. Winter SAT data for 50 years (1951–2000) are analyzed for the negative and the positive AO phases. Using the Median Sequential Correlation Analysis (MSCA) technique it is shown that the winter SAT is negatively correlated to the winter AO index for most parts of Iran. The winter AO index accounts for about 14% to 46% of the winter SAT variance. The positive (negative) SAT anomaly is found to be associated with the onset of the negative (positive) phase. The overall probability of below long-term mean temperature during the positive and the negative phases are estimated to be around 70% and 25%, respectively. For the negative phase, westerly winds that originate from the warm Atlantic regions increase over Iran and consequently positive temperature anomalies are found across the country. The positive AO phase is accompanied by northerly winds that allow continental polar and arctic air masses to move into Iran, producing below normal temperatures. The summer AO is found to explain about 25–32% of the winter SAT variance in Iran. The reason for this is explained by the significant correlation (+0.38) between the summer and the following winter AO indices. These results indicate that the summer climate is linked to changes in atmospheric circulation which persist through to the following autumn and winter.     

The implications of climate policy for the impacts of climate change on global water resources

This paper assesses the implications of climate policy for exposure to water resources stresses. It compares a Reference scenario which leads to an increase in global mean temperature of 4 °C by the end of the 21st century with a Mitigation scenario which stabilises greenhouse gas concentrations at around 450 ppm CO₂e and leads to a 2 °C increase in 2100. Associated changes in river runoff are simulated using a global hydrological model, for four spatial patterns of change in temperature and rainfall. There is a considerable difference in hydrological change between these four patterns, but the percentages of change avoided at the global scale are relatively robust. By the 2050s, the Mitigation scenario typically avoids between 16 and 30% of the change in runoff under the Reference scenario, and by 2100 it avoids between 43 and 65%. Two different measures of exposure to water resources stress are calculated, based on resources per capita and the ratio of withdrawals to resources. Using the first measure, the Mitigation scenario avoids 8-17% of the impact in 2050 and 20-31% in 2100; with the second measure, the avoided impacts are 5-21% and 15-47% respectively. However, at the same time, the Mitigation scenario also reduces the positive impacts of climate change on water scarcity in other areas. The absolute numbers and locations of people affected by climate change and climate policy vary considerably between the four climate model patterns.     

The impacts of climate change on tribal traditional foods

American Indian and Alaska Native tribes are uniquely affected by climate change. Indigenous peoples have depended on a wide variety of native fungi, plant and animal species for food, medicine, ceremonies, community and economic health for countless generations. Climate change stands to impact the species and ecosystems that constitute tribal traditional foods that are vital to tribal culture, economy and traditional ways of life. This paper examines the impacts of climate change on tribal traditional foods by providing cultural context for the importance of traditional foods to tribal culture, recognizing that tribal access to traditional food resources is strongly influenced by the legal and regulatory relationship with the federal government, and examining the multi-faceted relationship that tribes have with places, ecological processes and species. Tribal participation in local, regional and national climate change adaption strategies, with a focus on food-based resources, can inform and strengthen the ability of both tribes and other governmental resource managers to address and adapt to climate change impacts.     

The influence of tropical Pacific forcing on the Arctic Oscillation

The potential role of tropical Pacific forcing in driving the seasonal variability of the Arctic Oscillation (AO) is explored using both observational data and a simple general circulation model (SGCM). A lead–lag regression technique is first applied to the monthly averaged sea surface temperature (SST) and the AO index. The AO maximum is found to be related to a negative SST anomaly over the tropical Pacific three months earlier. A singular value decomposition (SVD) analysis is then performed on the tropical Pacific SST and the sea level pressure (SLP) over the Northern Hemisphere. An AO-like atmospheric pattern and its associated SST appear as the second pair of SVD modes. Ensemble integrations are carried out with the SGCM to test the atmospheric response to different tropical Pacific forcings. The atmospheric response to the linear fit of the model’s empirical forcing associated with the SST variability in the second SVD modes strongly projects onto the AO. Idealized thermal forcings are then designed based on the regression of the seasonally averaged tropical Pacific precipitation against the AO index. Results indicate that forcing anomalies over the western tropical Pacific are more effective in generating an AO-like response while those over the eastern tropical Pacific tend to produce a Pacific-North American (PNA)-like response. The physical mechanisms responsible for the energy transport from the tropical Pacific to the extratropical North Atlantic are investigated using wave activity flux and vorticity forcing formalisms. The energy from the western tropical Pacific forcing tends to propagate zonally to the North Atlantic because of the jet stream waveguide effect while the transport of the energy from the eastern tropical Pacific forcing mostly concentrates over the PNA area. The linearized SGCM results show that nonlinear processes are involved in the generation of the forced AO-like pattern.     

IPCC AR6报告解读：人类活动对气候系统的影响

2021年8月9日,IPCC发布了第六次评估报告(AR6)第一工作组报告,报告第三章“人类活动对气候系统的影响”定量评估了人类活动对气候系统的影响程度以及气候模式对观测到的平均气候、气候变化和气候变率的模拟性能。报告基于气候系统的多个圈层变量的综合评估明确指出,毋庸置疑的是,自工业化以来人为影响已经使大气、海洋和陆地升温;支撑本次评估的国际耦合模式比较计划第六阶段（CMIP6）气候模式模拟的大多数大尺度气候指标的近期平均气候,相比前一次评估报告（AR5）中的CMIP5模式结果有所改进。报告在更广泛的领域和区域提供了更多证据表明气候系统中的人类活动影响,但受制于观测、模式与过程认知的不足,在大气、海洋、冰冻圈、生物圈及气候变率模态的多个指标变化中人为影响的贡献方面仍然存在不确定性甚至缺少研究。     

The impacts of climate change on agricultural production systems in China

Climate change can bring positive and negative effects on Chinese agriculture, but negative impacts tend to dominate. The annual mean surface temperature has risen about 0.5–0.8 °C. The precipitation trends have not been identified during the past 100 years in China, although the frequency and intensity of extreme weather/climate events have increased, especially of drought. Water scarcity, more frequent and serious outbreaks of insects and diseases, and soil degradation caused by climate change have impacted agro-environmental conditions. However, temperature rise prolonged the crop growth seasons and cold damages have reduced in Northeast China. The projection of climate change indicates that the surface temperature will continue to increase with about 3.9 to 6.0 °C and precipitation is expected to increase by 9 to 11 % at the end of 21st century in China. Climate warming will provide more heat and as a consequence, the boundary of the triple-cropping system (TCS) will extend northwards by as much as 200 to 300 km, from the Yangtze River Valley to the Yellow River Basin, and the current double-cropping system (DCS) will move to the central part of China, into the current single cropping system (SCS) area which will decrease in SCS surface area of 23.1 % by 2050. Climate warming will also affect the optimum location for the cultivation of China’s main crop varieties. If no measures are taken to adapt to climate changes, compared with the potential yield in 1961–1990, yields of irrigated wheat, corn and rice are projected to decrease by 2.2–6.7 %, 0.4 %–11.9 % and 4.3–12.4 % respectively in the 2050s. Climate warming will enhance potential evaporation and reduce the availability of soil moisture, thus causing a greater need for agricultural irrigation, intensifying the conflict between water supply and demand, especially in arid and semi-arid areas of China. With adequate irrigation, the extent of the reduction in yield of China’s corn and wheat can be improved by 5 % to 15 %, and rice by 5 % or so than the potential yield in 1961–1990. Adaptive measures can reduce the agricultural loss under climate change. If effective measures are taken in a timely way, then climate change in the next 30–50 years will not have a significant influence on China’s food security.     

Scales of climate impacts

Climates, ecosystems, and societies interact over a tremendous range of temporal and spatial scales. Scholarly work on climate impacts has tended to emphasize different questions, variables, and modes of explanation depending on the primary scale of interest. Much of the current debate on cause and effect, vulnerability, marginality, and the like stems from uncritical or unconscious efforts to transfer experience, conclusions, and insights across scales. This paper sketches a perspective from which the relative temporal and spatial dimensions of climatic, ecological, and social processes can be more clearly perceived, and their potential interactions more critically evaluated. Quantitative estimates of a variety of characteristic scales are derived and compared, leading to specific recommendations for the design of climate impact studies.A longer version of this paper (Clark, 1985), with complete documentation of data sources, was presented at the Social Science Research Council's Conference on Forecasting in the Social and Natural Sciences (Boulder, Colorado, June 10–13, 1984).     

Direct human influence of irrigation on atmospheric water vapour and climate

Human activity increases the atmospheric water vapour content in an indirect way through climate feedbacks. We conclude here that human activity also has a direct influence on the water vapour concentration through irrigation. In idealised simulations we estimate a global mean radiative forcing in the range of 0.03 to +0.1 Wm^–2 due to the increase in water vapour from irrigation. However, because the water cycle is embodied in the climate system, irrigation has a more complex influence on climate. We also simulate a change in the temperature vertical profile and a large surface cooling of up to 0.8 K over irrigated land areas. This is of opposite sign than expected from the radiative forcing alone, and this questions the applicability of the radiative forcing concept for such a climatic perturbation. Further, this study shows stronger links than previously recognised between climate change and freshwater scarcity which are environmental issues of paramount importance for the twenty first century.     

Arctic radiation deficit and climate variability

One of the generally accepted climatic effects of stratospheric aerosol injection is the reduction of the global radiation in high latitudes by an order of 5% during El Chichon type eruptions. To test the effect of a high-latitude radiation deficit on global climate, a GCM experiment was performed with the ECMWF T21 atmosphere general circulation model (AGCM). The results provide physically-consistent evidence that this radiation deficit is a possible external forcing factor for severe climatic anomalies not only in the area directly affected by the reduced radiation, but also in the tropics. The most important factor is the creation of enhanced snow cover in regions of Asia that are distant from the location of the introduced radiation anomaly. The simulated results show certain features that are well known from observations in weak monsoon years, i.e. the weakened easterly jet in the upper troposphere over northern India, prolonged winter monsoon conditions, and prevailing anticyclonic vorticity anomalies over the entire Indian summer monsoon region. Over the western Pacific at the end of boreal winter (May), increased convective activity leads to a negative Walker circulation anomaly with westerly wind anomalies near the surface and easterly anomalies in the upper troposphere. This is known as one of the most important anomalies at the beginning of an El Niño/Southern Oscillation (ENSO) event.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil     

The variation of warm pool in the equatorial western pacific and its impacts on climate

1.IntroductionSincetheEINinoeventwasregardedasaresultoftheair--seainteraction(Bjerknes,1969;RasmussonandWallace,1983;Philander,1990),thetropicalPacifichasbeenPaidmuchattentionbymeteorologistsintheclimaticstudies.Particularly,thereisthehighestoceantemperatureintheequatorialwesternPacific,theuwarmpool",andthestrongestconvectionandatmosphericheatingareovertheequatorialwesternPacific,sothattheequatorialwesternPacificisveryimportanttotheclimaticvariationintheglobe.Thenumericalsimulationwithasi…