Aerosol and ozone changes as forcing for climate evolution between 1850 and 2100

Global aerosol and ozone distributions and their associated radiative forcings were simulated between 1850 and 2100 following a recent historical emission dataset and under the representative concentration pathways (RCP) for the future. These simulations were used in an Earth System Model to account for the changes in both radiatively and chemically active compounds, when simulating the climate evolution. The past negative stratospheric ozone trends result in a negative climate forcing culminating at ?0.15 W m^?2 in the 1990s. In the meantime, the tropospheric ozone burden increase generates a positive climate forcing peaking at 0.41 W m^?2. The future evolution of ozone strongly depends on the RCP scenario considered. In RCP4.5 and RCP6.0, the evolution of both stratospheric and tropospheric ozone generate relatively weak radiative forcing changes until 2060–2070 followed by a relative 30 % decrease in radiative forcing by 2100. In contrast, RCP8.5 and RCP2.6 model projections exhibit strongly different ozone radiative forcing trajectories. In the RCP2.6 scenario, both effects (stratospheric ozone, a negative forcing, and tropospheric ozone, a positive forcing) decline towards 1950s values while they both get stronger in the RCP8.5 scenario. Over the twentieth century, the evolution of the total aerosol burden is characterized by a strong increase after World War II until the middle of the 1980s followed by a stabilization during the last decade due to the strong decrease in sulfates in OECD countries since the 1970s. The cooling effects reach their maximal values in 1980, with ?0.34 and ?0.28 W m^?2 respectively for direct and indirect total radiative forcings. According to the RCP scenarios, the aerosol content, after peaking around 2010, is projected to decline strongly and monotonically during the twenty-first century for the RCP8.5, 4.5 and 2.6 scenarios. While for RCP6.0 the decline occurs later, after peaking around 2050. As a consequence the relative importance of the total cooling effect of aerosols becomes weaker throughout the twenty-first century compared with the positive forcing of greenhouse gases. Nevertheless, both surface ozone and aerosol content show very different regional features depending on the future scenario considered. Hence, in 2050, surface ozone changes vary between ?12 and +12 ppbv over Asia depending on the RCP projection, whereas the regional direct aerosol radiative forcing can locally exceed ?3 W m^?2.     

Regional and global projections of twenty-first century glacier mass changes in response to climate scenarios from global climate models

A large component of present-day sea-level rise is due to the melt of glaciers other than the ice sheets. Recent projections of their contribution to global sea-level rise for the twenty-first century range between 70 and 180 mm, but bear significant uncertainty due to poor glacier inventory and lack of hypsometric data. Here, we aim to update the projections and improve quantification of their uncertainties by using a recently released global inventory containing outlines of almost every glacier in the world. We model volume change for each glacier in response to transient spatially-differentiated temperature and precipitation projections from 14 global climate models with two emission scenarios (RCP4.5 and RCP8.5) prepared for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. The multi-model mean suggests sea-level rise of 155 ± 41 mm (RCP4.5) and 216 ± 44 mm (RCP8.5) over the period 2006–2100, reducing the current global glacier volume by 29 or 41 %. The largest contributors to projected global volume loss are the glaciers in the Canadian and Russian Arctic, Alaska, and glaciers peripheral to the Antarctic and Greenland ice sheets. Although small contributors to global volume loss, glaciers in Central Europe, low-latitude South America, Caucasus, North Asia, and Western Canada and US are projected to lose more than 80 % of their volume by 2100. However, large uncertainties in the projections remain due to the choice of global climate model and emission scenario. With a series of sensitivity tests we quantify additional uncertainties due to the calibration of our model with sparsely observed glacier mass changes. This gives an upper bound for the uncertainty range of ±84 mm sea-level rise by 2100 for each projection.     

Projected hydroclimate changes over Andean basins in central Chile from downscaled CMIP5 models under the low and high emission scenarios

This study examines the projections of hydroclimatic regimes and extremes over Andean basins in central Chile (～ 30–40° S) under a low and high emission scenarios (RCP2.6 and RCP8.5, respectively). A gridded daily precipitation and temperature dataset based on observations is used to drive and validate the VIC macro-scale hydrological model in the region of interest. Historical and future simulations from 19 climate models participating in CMIP5 have been adjusted with the observational dataset and then used to make hydrological projections. By the end of the century, there is a large difference between the scenarios, with projected warming of ～ + 1.2 °C (RCP2.6), ～ +?3.5 °C (RCP8.5) and drying of ～ ? 3% (RCP2.6), ～ ? 30% (RCP8.5). Following the strong drying and warming projected in this region under the RCP8.5 scenario, the VIC model simulates decreases in annual runoff of about 40% by the end of the century. Such strong regional effect of climate change may have large implications for the water resources of this region. Even under the low emission scenario, the Andes snowpack is projected to decrease by 35–45% by mid-century. In more snowmelt-dominated areas, the projected hydrological changes under RCP8.5 go together with more loss in the snowpack (75–85%) and a temporal shift in the center timing of runoff to earlier dates (up to 5 weeks by the end of the century). The severity and frequency of extreme hydroclimatic events are also projected to increase in the future. The occurrence of extended droughts, such as the recently experienced mega-drought (2010–2015), increases from one to up to five events per 100 years under RCP8.5. Concurrently, probability density function of 3-day peak runoff indicates an increase in the frequency of flood events. The estimated return periods of 3-day peak runoff events depict more drastic changes and increase in the flood risk as higher recurrence intervals are considered by mid-century under RCP2.6 and RCP8.5, and by the end of the century under RCP8.5.     

Sources of uncertainty in projections of twenty-first century westerly wind changes over the Amundsen Sea,West Antarctica,in CMIP5 climate models

The influence of changes in winds over the Amundsen Sea has been shown to be a potentially key mechanism in explaining rapid loss of ice from major glaciers in West Antarctica, which is having a significant impact on global sea level. Here, Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model data are used to assess twenty-first century projections in westerly winds over the Amundsen Sea (U _AS ). The importance of model uncertainty and internal climate variability in RCP4.5 and RCP8.5 scenario projections are quantified and potential sources of model uncertainty are considered. For the decade 2090–2099 the CMIP5 models show an ensemble mean twenty-first century response in annual mean U _AS of 0.3 and 0.7 m s^?1 following the RCP4.5 and RCP8.5 scenarios respectively. However, as a consequence of large internal climate variability over the Amundsen Sea, it takes until around 2030 (2065) for the RCP8.5 response to exceed one (two) standard deviation(s) of decadal internal variability. In all scenarios and seasons the model uncertainty is large. However the present-day climatological zonal wind bias over the whole South Pacific, which is important for tropical teleconnections, is strongly related to inter-model differences in projected change in U _AS (more skilful models show larger U _AS increases). This relationship is significant in winter (r = ?0.56) and spring (r = ?0.65), when the influence of the tropics on the Amundsen Sea region is known to be important. Horizontal grid spacing and present day sea ice extent are not significant sources of inter-model spread.     

Abrupt CO2 experiments as tools for predicting and understanding CMIP5 representative concentration pathway projections

A fast simple climate modelling approach is developed for predicting and helping to understand general circulation model (GCM) simulations. We show that the simple model reproduces the GCM results accurately, for global mean surface air temperature change and global-mean heat uptake projections from 9 GCMs in the fifth coupled model inter-comparison project (CMIP5). This implies that understanding gained from idealised CO₂ step experiments is applicable to policy-relevant scenario projections. Our approach is conceptually simple. It works by using the climate response to a CO₂ step change taken directly from a GCM experiment. With radiative forcing from non-CO₂ constituents obtained by adapting the Forster and Taylor method, we use our method to estimate results for CMIP5 representative concentration pathway (RCP) experiments for cases not run by the GCMs. We estimate differences between pairs of RCPs rather than RCP anomalies relative to the pre-industrial state. This gives better results because it makes greater use of available GCM projections. The GCMs exhibit differences in radiative forcing, which we incorporate in the simple model. We analyse the thus-completed ensemble of RCP projections. The ensemble mean changes between 1986–2005 and 2080–2099 for global temperature (heat uptake) are, for RCP8.5: 3.8 K (2.3 × 10²⁴ J); for RCP6.0: 2.3 K (1.6 × 10²⁴ J); for RCP4.5: 2.0 K (1.6 × 10²⁴ J); for RCP2.6: 1.1 K (1.3 × 10²⁴ J). The relative spread (standard deviation/ensemble mean) for these scenarios is around 0.2 and 0.15 for temperature and heat uptake respectively. We quantify the relative effect of mitigation action, through reduced emissions, via the time-dependent ratios (change in RCPx)/(change in RCP8.5), using changes with respect to pre-industrial conditions. We find that the effects of mitigation on global-mean temperature change and heat uptake are very similar across these different GCMs.     

Climate-model induced differences in the 21st century global and regional glacier contributions to sea-level rise

The large uncertainty in future global glacier volume projections partly results from a substantial range in future climate conditions projected by global climate models. This study addresses the effect of global and regional differences in climate input data on the projected twenty-first century glacier contribution to sea-level rise. Glacier volume changes are calculated with a surface mass balance model combined with volume-area scaling, applied to 89 glaciers in different climatic regions. The mass balance model is based on a simplified energy balance approach, with separated contributions by net solar radiation and the combined other fluxes. Future mass balance is calculated from anomalies in air temperature, precipitation and atmospheric transmissivity, taken from eight global climate models forced with the A1B emission scenario. Regional and global sea-level contributions are obtained by scaling the volume changes at the modelled glaciers to all glaciers larger than 0.1 km² outside the Greenland and Antarctic ice sheets. This results in a global value of 0.102 ± 0.028 m (multi-model mean and standard deviation) relative sea-level equivalent for the period 2012–2099, corresponding to 18 ± 5 % of the estimated total volume of glaciers. Glaciers in the Antarctic, Alaska, Central Asia and Greenland together account for 65 ± 4 % of the total multi-model mean projected sea-level rise. The projected sea-level contribution is 35 ± 17 % larger when only anomalies in air temperature are taken into account, demonstrating an important compensating effect by increased precipitation and possibly reduced atmospheric transmissivity. The variability in projected precipitation and atmospheric transmissivity changes is especially large in the Arctic regions, making the sea-level contribution for these regions particularly sensitive to the climate model used. Including additional uncertainties in the modelling procedure and the input data, the total uncertainty estimate for the future projections becomes ±0.063 m.     

Analysis of aerosol distribution variations over China for the period 2045–2050 under different Representative Concentration Pathway scenarios: 不同代表性浓度路径情景下 2045-2050 年中国气溶胶分布变化的分析

The regional air quality modeling system RAMS-CMAQ was applied to simulate the aerosol concentration for the period 2045–2050 over China based on the downscaled meteorological field of three RCP scenarios from CESM (NCAR's Community Earth System Model) in CMIP5. The downscaling simulation of the meteorological field of the three RCP scenarios showed that, compared with that under RCP2.6, the difference in near-surface temperature between North and South China is weakened and the wind speed increases over North and South China and decreases over central China under RCP4.5 and RCP8.5. Under RCP2.6, from 2045 to 2050, the modeled average PM_2.5 concentration is highest, with a value of 40–50 µg m⁻³, over the North China Plain, part of the Yangtze River Delta, and the Sichuan Basin. Meanwhile, it is 30–40 µg m⁻³ over central China and part of the Pearl River Delta. Compared with RCP2.6, PM_2.5 increases by 4–12 µg m⁻³ under both RCP4.5 and RCP8.5, of which the SO₄²⁻ and NH₄⁺ concentration increases under both RCP4.5 and RCP8.5; the NO₃⁻ concentration decreases under RCP4.5 and increases under RCP8.5; and the black carbon concentration changes very slightly, and organic carbon concentration decreases, under RCP4.5 and RCP8.5, with some increase over part of Southwest and Southeast China under RCP8.5. The difference between RCP4.5 and RCP2.6 and the difference between RCP8.5 and RCP2.6 have similar annual variation for different aerosol species, indicating that the impact of climate change on different species tends to be consistent.摘要基于来自于 CMIP5 中 CESM 模式的三种 RCP 情景下的气象场的降尺度模拟, 应用区域空气质量模式系统 RAMS-CMAQ 模拟 2045-2050 年中国地区气溶胶浓度.三种 RCP 情景下气象场的降尺度模拟表明, 与 RCP2.6 相比, 在 RCP4.5 和 RCP8.5 下, 华北和华南的近地表温度差减小, 风速在华北和华南地区增加, 在中部地区下降. RCP2.6 情景下, 模拟的 2045 年到 2050 年平均的 PM _2.5浓度在华北平原, 长三角的部分地区和四川盆地最高, 约为 40-50 µg m^–3, 在中国中部和珠三角的部分地区约为 30-40 µg m^–3. 与 RCP2.6 相比, 在 RCP4.5 和 RCP8.5 下, PM_2.5增加了 4-12 µg m^–3, 其中在 RCP4.5 和 RCP8.5 下, SO₄^2–和 NH₄⁺的浓度增加, 在 RCP4.5 下, NO^3–浓度降低, 在 RCP8.5 下, NO^3–浓度升高, 在 RCP4.5 和 RCP8.5 下, BC 浓度变化很小, 而 OC 浓度下降, 其中在 RCP8.5 下, 西南和东南部分地区的 OC 有所增加.不同的气溶胶物种浓度在 RCP4.5 和 RCP2.6 之间的差异以及 RCP8.5 和 RCP2.6 之间的差异具有相似的年度变化, 这表明气候变化对不同物种的影响趋于一致.     

Projection of snow cover changes over China under RCP scenarios

Snow cover changes in the middle (2040–2059) and end (2080–2099) of the twenty-first century over China were investigated with a regional climate model, nested within the global model BCC_CSM1.1. The simulations had been conducted for the period of 1950–2099 under the RCP4.5 and RCP8.5 scenarios. Results show that the model perform well in representing contemporary (1986–2005) spatial distributions of snow cover days (SCDs) and snow water equivalent (SWE). However, some differences between observation and simulation were detected. Under the RCP4.5 scenarios, SCDs are shortened by 10–20 and 20–40 days during the middle and end of the twenty-first century, respectively. Whereas simulated SWE is lowered by 0.1–10 mm in most areas over the Tibetan Plateau (TP). On the other hand, the spatial distributions of SWE are reversed between the middle and end terms in the northeast China. Furthermore, compared with the changes of RCP4.5 scenario, SCDs are reduced by 5–20 days in the middle period under RCP8.5 scenario with even larger decreasing amplitude in the end term. SWE was lowered by 0.1–2.5 mm in most areas except the northeast of China in middle term under RCP8.5 scenario. The great center of SCDs and SWE changes are always located over TP. The regional mean of SCDs and SWE for the TP and for China display a declining trend from 2006 to 2099 with more pronounced changes in the TP than in China as a whole. Under the RCP8.5 scenario, the changes are enhanced compared to those under RCP4.5.     

The global-scale impacts of climate change on water resources and flooding under new climate and socio-economic scenarios

This paper presents a preliminary assessment of the relative effects of rate of climate change (four Representative Concentration Pathways - RCPs), assumed future population (five Shared Socio-economic Pathways - SSPs), and pattern of climate change (19 CMIP5 climate models) on regional and global exposure to water resources stress and river flooding. Uncertainty in projected future impacts of climate change on exposure to water stress and river flooding is dominated by uncertainty in the projected spatial and seasonal pattern of change in climate. There is little clear difference in impact between RCP2.6, RCP4.5 and RCP6.0 in 2050, and between RCP4.5 and RCP6.0 in 2080. Impacts under RCP8.5 are greater than under the other RCPs in 2050 and 2080. For a given RCP, there is a difference in the absolute numbers of people exposed to increased water resources stress or increased river flood frequency between the five SSPs. With the ‘middle-of-the-road’ SSP2, climate change by 2050 would increase exposure to water resources stress for between approximately 920 and 3,400 million people under the highest RCP, and increase exposure to river flood risk for between 100 and 580 million people. Under RCP2.6, exposure to increased water scarcity would be reduced in 2050 by 22-24 %, compared to impacts under the RCP8.5, and exposure to increased flood frequency would be reduced by around 16 %. The implications of climate change for actual future losses and adaptation depend not only on the numbers of people exposed to changes in risk, but also on the qualitative characteristics of future worlds as described in the different SSPs. The difference in ‘actual’ impact between SSPs will therefore be greater than the differences in numbers of people exposed to impact.     

RCP 8.5��A scenario of comparatively high greenhouse gas emissions

This paper summarizes the main characteristics of the RCP8.5 scenario. The RCP8.5 combines assumptions about high population and relatively slow income growth with modest rates of technological change and energy intensity improvements, leading in the long term to high energy demand and GHG emissions in absence of climate change policies. Compared to the total set of Representative Concentration Pathways (RCPs), RCP8.5 thus corresponds to the pathway with the highest greenhouse gas emissions. Using the IIASA Integrated Assessment Framework and the MESSAGE model for the development of the RCP8.5, we focus in this paper on two important extensions compared to earlier scenarios: 1) the development of spatially explicit air pollution projections, and 2) enhancements in the land-use and land-cover change projections. In addition, we explore scenario variants that use RCP8.5 as a baseline, and assume different degrees of greenhouse gas mitigation policies to reduce radiative forcing. Based on our modeling framework, we find it technically possible to limit forcing from RCP8.5 to lower levels comparable to the other RCPs (2.6 to 6 W/m²). Our scenario analysis further indicates that climate policy-induced changes of global energy supply and demand may lead to significant co-benefits for other policy priorities, such as local air pollution.     

Historical change and future scenarios of sea level rise in Macau and adjacent waters

Against a background of climate change, Macau is very exposed to sea level rise(SLR) because of its low elevation,small size, and ongoing land reclamation. Therefore, we evaluate sea level changes in Macau, both historical and, especially,possible future scenarios, aiming to provide knowledge and a framework to help accommodate and protect against future SLR. Sea level in Macau is now rising at an accelerated rate: 1.35 mm yr-1over 1925–2010 and jumping to 4.2 mm yr-1over 1970–2010, which outpaces the rise in global mean sea level. In addition, vertical land movement in Macau contributes little to local sea level change. In the future, the rate of SLR in Macau will be about 20% higher than the global average, as a consequence of a greater local warming tendency and strengthened northward winds. Specifically, the sea level is projected to rise 8–12, 22–51 and 35–118 cm by 2020, 2060 and 2100, respectively, depending on the emissions scenario and climate sensitivity. Under the +8.5 W m-2Representative Concentration Pathway(RCP8.5) scenario the increase in sea level by2100 will reach 65–118 cm—double that under RCP2.6. Moreover, the SLR will accelerate under RCP6.0 and RCP8.5, while remaining at a moderate and steady rate under RCP4.5 and RCP2.6. The key source of uncertainty stems from the emissions scenario and climate sensitivity, among which the discrepancies in SLR are small during the first half of the 21 st century but begin to diverge thereafter.     

“一带一路”区域未来气候变化预估

利用耦合模式比较计划第5阶段(CMIP5)提供的18个全球气候模式的模拟结果,预估了3种典型浓度路径(RCP2.6、RCP4.5、RCP8.5)下“一带一路”地区平均气候和极端气候的未来变化趋势。结果表明:在温室气体持续排放情景下,“一带一路”地区年平均气温在未来将会持续上升,升温幅度随温室气体浓度的增加而加大。在高温室气体排放情景(RCP8.5)下,到21世纪末期,平均气温将普遍升高5℃以上,其中北亚地区升幅最大,南亚和东南亚地区升幅最小。对于降水的变化,预估该区域大部分地区的年降水量将增加,其中西亚和北亚增加最为明显,而且在21世纪中期,RCP2.6情景下的增幅要比RCP4.5和RCP8.5情景下的偏大,而在21世纪后期,RCP8.5情景下降水的增幅比RCP2.6和RCP4.5情景下的偏大。未来极端温度也将呈升高的趋势,增温幅度高纬度地区大于低纬度地区、高排放情景大于低排放情景。而且在高纬度区域,极端低温的增暖幅度要大于极端高温的增幅。连续干旱日数在北亚和东亚总体呈现减少趋势,而在其他地区则呈增加趋势。极端强降水在“一带一路”区域总体上将增强,增强最明显的地区位于南亚、东南亚和东亚。     

基于NorESM1-M模式的中国东北地区2050s玉米气候生产潜力预估

利用NorESM1-M模式资料驱动AEZ模型模拟了21世纪中叶东北地区春玉米在雨养条件下的气候生产潜力。结果表明：在RCP2.6情景下,东北区域热量资源较1981-2010年有所改善,年平均气温增加1.72℃,≥ 10℃积温增加359.6℃;降水整体呈现略增加趋势且南部多于北部,全区平均增多56.9 mm,蒸散量增加10.0 mm;具有最大气候生产潜力的区域在辽宁省东部;与基准年相比,辽宁单产平均每公顷增加1100 kg。在RCP8.5情景下,东北区域热量资源进一步改善,黑龙江、辽宁和吉林三省≥ 10℃积温分别增加652.7℃、636.3℃和683.9℃,降水总量较RCP2.6情景增加但空间分布差异较大,全区维持增产趋势,辽宁、吉林和黑龙江增产百分比分别为3.3%、8.1%和20.0%。     

Impact of climate changes over the extratropical land on permafrost dynamics under RCP scenarios in the 21st century as simulated by the IAP RAS climate model

Estimates of possible climate changes and cryolithozone dynamics in the 21st century over the Northern Hemisphere land are obtained using the IAP RAS global climate model under the RCP scenarios. Annual mean warming over the northern extratropical land during the 21st century amounts to 1.2–5.3°C depending on the scenario. The area of the snow cover in February amounting currently to 46 million km² decreases to 33–42 million km² in the late 21st century. According to model estimates, the near-surface permafrost in the late 21st century persists in northern regions of West Siberia, in Transbaikalia, and Tibet even under the most aggressive RCP 8.5 scenario; under more moderate scenarios (RCP 6.0, RCP 4.5, and RCP 2.6), it remains in East Siberia and in some high-latitude regions of North America. The total near-surface permafrost area in the Northern Hemisphere in the current century decreases by 5.3–12.8 million km² depending on the scenario. The soil subsidence due to permafrost thawing in Central Siberia, Cisbaikalia, and North America can reach 0.5–0.8 m by the late 21st century.     

Assessment of projected agro-climatic indices over Awun river basin,Nigeria for the late twenty-first century

This paper examines changes in rainfall effectiveness indices of the Awun basin in Nigeria during the late twenty-first century for agricultural applications with outputs from high-resolution regional climate model (RCM) simulations. The RCM simulations are driven by two global climate models for a reference period (1985–2004) and a future period (2080–2099) and for RCP4.5 (a scenario with some mitigation) and RCP8.5 (a business as usual scenario) forcings. Simulations are provided for the control (1985–2004) and scenario (2080–2099) periods. Observations from synoptic station are used for bias-correction. Three indices being local onset date, seasonality index (SI), and hydrologic ratio (HR) are analyzed. Onset and HR are tested with two evapotranspiration (ET_p) models. Farmers’ perceptions are also collected to validate trends of rainfall indices for the present-day climate. We found that onset dates do not depend much on the ET_p models used, and farmers’ perceptions are consistent with predicted rainfall patterns. Present-day climate trend shows an early onset. However, onset is projected to be late in future and the delay will be magnified under the business as usual scenario. Indeed, average onset date is found on the 5th May for present-day while in the future, a delay about 4 and 8 weeks is projected under RCP4.5 and RCP8.5 scenarios respectively. SI is between 0.80 and 0.99, and HR is less than 0.75 for all scenarios, meaning respectively that (i) the rainy season will get shorter and (ii) the area will get drier in the future compared to the present-day. Local stakeholders are forewarned to prepare for potential response strategies. A continuous provision of forecast-based rainfall indices to support farmer’s decision making is also recommended.     

The RCP greenhouse gas concentrations and their extensions from 1765 to 2300

We present the greenhouse gas concentrations for the Representative Concentration Pathways (RCPs) and their extensions beyond 2100, the Extended Concentration Pathways (ECPs). These projections include all major anthropogenic greenhouse gases and are a result of a multi-year effort to produce new scenarios for climate change research. We combine a suite of atmospheric concentration observations and emissions estimates for greenhouse gases (GHGs) through the historical period (1750?C2005) with harmonized emissions projected by four different Integrated Assessment Models for 2005?C2100. As concentrations are somewhat dependent on the future climate itself (due to climate feedbacks in the carbon and other gas cycles), we emulate median response characteristics of models assessed in the IPCC Fourth Assessment Report using the reduced-complexity carbon cycle climate model MAGICC6. Projected ??best-estimate?? global-mean surface temperature increases (using inter alia a climate sensitivity of 3°C) range from 1.5°C by 2100 for the lowest of the four RCPs, called both RCP3-PD and RCP2.6, to 4.5°C for the highest one, RCP8.5, relative to pre-industrial levels. Beyond 2100, we present the ECPs that are simple extensions of the RCPs, based on the assumption of either smoothly stabilizing concentrations or constant emissions: For example, the lower RCP2.6 pathway represents a strong mitigation scenario and is extended by assuming constant emissions after 2100 (including net negative CO₂ emissions), leading to CO₂ concentrations returning to 360 ppm by 2300. We also present the GHG concentrations for one supplementary extension, which illustrates the stringent emissions implications of attempting to go back to ECP4.5 concentration levels by 2250 after emissions during the 21^st century followed the higher RCP6 scenario. Corresponding radiative forcing values are presented for the RCP and ECPs.     

CMIP5模式集合对中国区域性低温事件的模拟与预估

基于CMIP5逐日最低气温的模拟和预估数据,对中国区域性低温事件进行了研究。通过对中国区域性低温事件的历史模拟显示,模式集合的结果低估了中国区域性低温事件的变化趋势,但能够反映出与观测结果相同的减弱趋势,且比单个模式的结果更稳定,其空间分布与观测结果相似度也较高。在此基础上,采用模式集合方案对不同排放情景下（RCP2.6, RCP4.5, RCP8.5）的中国区域性低温事件进行了预估。结果显示,在RCP2.6排放情景下,中国区域性低温事件的减弱趋势较为缓和;在RCP4.5排放情景下,中国区域性低温事件呈现出显著的减弱趋势;在RCP8.5排放情景下,中国区域性低温事件的减弱趋势更明显。温室气体的排放可能主要影响中国区域性低温事件的强度和发生频次,对其空间分布影响较小。     

RegCM4对华北区域21世纪气候变化预估研究

利用国家气候中心完成的RegCM4区域气候模式在RCP4.5和RCP8.5两种排放路径下的气候变化动力降尺度试验结果,在检验模式对基准期(1986—2005年)气温和降水模拟能力基础上,进行华北区域21世纪气候变化预估分析。结果表明:RegCM4对华北区域基准期气温和降水的模拟能力较好。未来21世纪,两种情景下华北区域气温、降水、持续干期(consecutive dry days, CDD)和强降水量(R95p)变化逐渐增大,但变化幅度在高排放的RCP8.5情景下更为显著,其中近期(2021—2035年)、中期(2046—2065年)、远期(2080—2098年)RCP8.5情景下年平均气温分别升高1.77、3.44、5.82℃,年平均降水分别增加8.1%、14%、19.3%,CDD分别减少3、3、12 d, R95p分别增加30.8%、41.9%、69.8%。空间上,未来21世纪华北区域内年、冬季、夏季平均气温将一致升高,夏季升温幅度最大;年、冬季、夏季平均降水整体以增加为主,冬季降水增加幅度最大;CDD以减少为主,但近期和中期在山西和京津冀有所增加,而R95p以增加为主,表明21世纪华北区域干旱事件逐渐减少、极端降水事件不断增加。     

气候变化对河北坝上地区草地土壤风蚀扬尘季节和年排放速率的影响

以全球气候模式NorESM1-M产生的RCP2.6、RCP4.5、RCP6.0、RCP8.5气候变化情景数据和原环保部推荐的土壤风蚀扬尘计算方法,模拟分析了未来气候变化对河北坝上砂粘壤土、粘壤土、壤粘土、砂壤土、砂粘土和风沙土草地土壤风蚀扬尘总可悬浮颗粒物(Total Suspended Particle,TSP)、PM10和PM2.5的季节及年排放速率的影响。结果表明:气候变化影响下坝上地区气温上升,年降水量和风速波动较大、并存在上升和下降的趋势。相比基准情景,在RCP2.6、RCP4.5、RCP6.0和RCP8.5情景下,各土壤风蚀扬尘TSP、PM10和PM2.5季节排放速率在春季分别高15%、47%、28%和46%;秋季分别高17%、54%、45%和38%;冬季分别低36%、42%、39%和44%;夏季,在RCP2.6情景下低1%,在RCP4.5、RCP6.0和RCP8.5情景下分别高14%、3%和7%;未来气候变化情景下,各土壤风蚀扬尘TSP、PM10和PM2.5年排放速率分别高25%、54%、35%和54%。基准和未来气候变化情景下,土壤风蚀扬尘TSP、PM10和PM2.5的季节和年排放速率及其差异从高到低均依次为砂粘壤土、风沙土、砂壤土、粘壤土、壤粘土和砂粘土。表明未来气候变化将使河北坝上地区草地土壤风蚀扬尘排放速率增加,但存在季节和气候变化情景方面的差异。     

Temperature variations and rice yields in China: historical contributions and future trends

Temperature is the principal factor that determines rice growth, development and ultimately grain yield. In this study, normal growing-degree-days (NGDD) and killing growing-degree-days (KGDD) were used to capture the different effects of normal and extreme temperatures on rice yields, respectively. Based on these indexes, we assessed the contributions of temperature variations to county-level rice yields across China during the historical period (1980–2008), and estimated the potential exposure of rice to extreme temperature stress in the near future (2021–2050). The results showed that historical temperature variations had measurable impacts on rice yields with a distinct spatial pattern: for different regions, such variations had contributed much to the increased rice yields in Northeast China (Region I) (0.59 % yield year^?1) and some portions of the Yunnan-Guizhou Plateau (Region II) (0.34 % yield year^?1), but seriously hindered the improvements of rice yields in the Sichuan Basin (SB) (?0.29 % yield year^?1) and the southern cultivation areas (Region IV) (?0.17 % yield year^?1); for the entire country, half of the contributions were positive and the other half were negative, resulting in a balance pattern with an average of 0.01 % yield year^?1. Under the RCP8.5 scenario, climate warming during 2021–2050 would substantially reduce cold stress but increase heat stress in the rice planting areas across China. For the future period, Region I, II and eastern China would be continually exposed to more severe cold stress than the other regions; Region III (including SB and the mid-lower reaches of Yangtze River (MLRYR)) would be the hot spot of heat stress.