亚热带湿润区农业用地热环境效应及其生物物理因子分析

为分析亚热带湿润区农业用地对区域气候的影响,以江西省为例,基于2003—2019年的MODIS地表温度数据,将天然林地作为参照,分析了亚热带湿润地区农业用地热环境效应的时空变化特征及其与主要生物物理因子的关系。结果表明:(1)与天然林地相比,农业用地在白天具有明显的增温效应,年均增温幅度达1.9 ℃;夜间降温效应明显。(2)农业用地热环境效应随季节变化明显,特别是在夜晚,主要表现为农业用地在夏季的夜晚具有微弱的增温效应。(3)2003—2019年,农业用地白天增温和夜晚降温效应均呈增加态势。(4)农业用地热环境效应在白天主要受蒸散的控制,在夜晚主要受蒸散和反照率的共同控制。     

Offset of the potential carbon sink from boreal forestation by decreases in surface albedo

Carbon uptake by forestation is one method proposed to reduce net carbon dioxide emissions to the atmosphere and so limit the radiative forcing of climate change. But the overall impact of forestation on climate will also depend on other effects associated with the creation of new forests. In particular, the albedo of a forested landscape is generally lower than that of cultivated land, especially when snow is lying, and decreasing albedo exerts a positive radiative forcing on climate. Here I simulate the radiative forcings associated with changes in surface albedo as a result of forestation in temperate and boreal forest areas, and translate these forcings into equivalent changes in local carbon stock for comparison with estimated carbon sequestration potentials. I suggest that in many boreal forest areas, the positive forcing induced by decreases in albedo can offset the negative forcing that is expected from carbon sequestration. Some high-latitude forestation activities may therefore increase climate change, rather than mitigating it as intended.     

Recognition of climatic effects of land use/land cover change under global warming

Greenhouse gas emissions and land use/land cover change (LUCC) are two human activities notably affecting climate change. Will temperature and precipitation increase significantly during global warming resulting in more pronounced LUCC climatic effects? Considering the interannual forcing of these two factors, the NCAR Community Atmosphere Model (CAM4.0) was used in this study to investigate the importance of climatological background to LUCC impacts. Experiments based on the difference in the background climate, the greenhouse gas concentrations in 1850 and in the present age indicate contrary changes in climate sensitivity through estimations of the radiative forcing associated with LUCC, which are 0.54°C/(W/m²) and ?0.26°C/(W/m²), respectively. Therefore, the background climate appears to play an important role in the regional impact of LUCC, especially at higher latitudes. In addition, global warming predominantly influences snow-albedo feedback in the mid-latitudes, thus determining the impact of LUCC, whereas the regional difference in precipitation caused by global warming is responsible for the differing climate response to LUCC in the tropics and subtropics.     

Global warming and climate forcing by recent albedo changes on Mars

For hundreds of years, scientists have tracked the changing appearance of Mars, first by hand drawings and later by photographs. Because of this historical record, many classical albedo patterns have long been known to shift in appearance over time. Decadal variations of the martian surface albedo are generally attributed to removal and deposition of small amounts of relatively bright dust on the surface. Large swaths of the surface (up to 56 million km2) have been observed to darken or brighten by 10 per cent or more. It is unknown, however, how these albedo changes affect wind circulation, dust transport and the feedback between these processes and the martian climate. Here we present predictions from a Mars general circulation model, indicating that the observed interannual albedo alterations strongly influence the martian environment. Results indicate enhanced wind stress in recently darkened areas and decreased wind stress in brightened areas, producing a positive feedback system in which the albedo changes strengthen the winds that generate the changes. The simulations also predict a net annual global warming of surface air temperatures by approximately 0.65 K, enhancing dust lifting by increasing the likelihood of dust devil generation. The increase in global dust lifting by both wind stress and dust devils may affect the mechanisms that trigger large dust storm initiation, a poorly understood phenomenon, unique to Mars. In addition, predicted increases in summertime air temperatures at high southern latitudes would contribute to the rapid and steady scarp retreat that has been observed in the south polar residual ice for the past four Mars years. Our results suggest that documented albedo changes affect recent climate change and large-scale weather patterns on Mars, and thus albedo variations are a necessary component of future atmospheric and climate studies.     

A comparison of the Medieval Warm Period, Little Ice Age and 20th century warming simulated by the FGOALS climate system model

To compare differences among the Medieval Warm Period (MWP), Little Ice Age (LIA), and 20th century global warming (20CW), six sets of transient and equilibrium simulations were generated using the climate system model FGOALS_gl. This model was developed by the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences. The results indicate that MWP warming is evident on a global scale, except for at mid-latitudes of the North Pacific. However, the magnitude of the warming is weaker than that in the 20th century. The warming in the high latitudes of the Northern Hemisphere is stronger than that in the Southern Hemisphere. The LIA cooling is also evident on a global scale, with a strong cooling over the high Eurasian continent, while the cooling center is over the Arctic domain. Both the MWP and the 20CW experiments exhibit the strongest warming anomalies in the middle troposphere around 200?C300 hPa, but the cooling center of the LIA experiment is seen in the polar surface of the Northern Hemisphere. A comparison of model simulation against the reconstruction indicates that model??s performance in simulating the surface air temperature changes during the warm periods is better than that during the cold periods. The consistencies between model and reconstruction in lower latitudes are better than those in high latitudes. Comparison of the inter-annual variability mode of East Asian summer monsoon (EASM) rainfall during the MWP, LIA and 20CW reveals a similar rainfall anomalies pattern. However, the time spectra of the principal component during the three typical periods of the last millennium are different, and the quasi-biannual oscillation is more evident during the two warm periods. At a centennial time scale, the external mode of the EASM variability driven by the changes of effective solar radiation is determined by the changes of large scale land-sea thermal contrast. The rainfall anomalies over the east of 110°E exhibit a meridional homogeneous change pattern, which is different from the meridional out-of-phase change of rainfall anomalies associated with the internal mode.     

基于遥感和GIS的日最高最低气温估算

气温是气象要素的重要组成部分,广泛用于全球气候变化、资源环境分析及灾害预警等多个领域.随着卫星遥感技术的发展,气温的估算趋向于遥感或遥感和GIS结合的方法.本文以浙江省为研究区域,利用了36个站点2013年逐日每10min一次的自动气象站气温观测数据和MODIS地表温度及其他参数产品,选用多元线性回归(自变量为地表温度、归一化植被指数、地表反照率、经度、纬度和高程)、温度植被指数以及多元线性回归插值方法进行气温估算,建立了研究区日最高气温最低气温估算模型,并比较了几种气温估算方法在研究区的适用性.结果表明:3种方法最高气温估算的决定系数(R~2)分别为0.96、0.91、0.97,均方根误差(R_(MSE))分别为1.84、2.75、1.49℃;多元线性回归和多元线性回归插值法最低气温估算的R~2分别为0.87、0.91,R_(MSE)分别为3.33、2.93℃,两者均为多元线性回归插值法得到的结果最好.空间分布结果显示,多元线性回归插值法能很好地反映由地形不同所带来的细节差异.     

基于地表裸露度和地表反照率影响的喀斯特地区热环境变化分析

在自然和人为因素的影响下,喀斯特地区地表覆盖受到破坏,导致大面积地表裸露,同时影响着地表反照率的变化,进而引起周围地表温度发生改变。以典型喀斯特区域安顺市为例,基于大气校正法反演2006—2017年地表温度,并结合同时期的地表裸露度和地表反照率变化情况分析喀斯特地区热环境变化特征。结果表明:地表裸露度、地表反照率与地表温度在空间上整体变化趋势相一致,是影响地表温度的因素之一;在时间上呈持续下降趋势,地表裸露度总体下降了53%,地表反照率和地表温度分别下降了37.1%和2.4%,表明热环境得到有效改善;地表裸露度,地表反照率与地表温度均呈线性正相关,地表温度随着地表裸露度和地表反照率的增加而上升,反之,地表温度则会降低。     

基于多源遥感的森林变化对区域温度影响的监测方法研究进展

人类活动通过改变土地覆被促成森林面积变化,推动碳收支和地表能量平衡发生相应变化,进而影响全球和区域尺度的气候。现有森林变化对区域温度的影响研究主要集中在有限精度的森林变化数据与温度数据结合的简单统计方法,但高可靠度的森林变化及其生物物理过程对区域温度的影响研究表明,准确、全面地理解森林与气候之间的生物物理相互作用机制,能为森林生态系统的全面评估提供科学支撑。笔者综合分析了基于多源遥感的森林变化结合其生物物理过程对区域温度影响的多种监测方法,结果发现:①多源中高分辨率森林变化数据的有限可用性一直阻碍着对温度变化影响的精准量化;②集成遥感观测数据的多种方法在量化森林变化的生物物理机制对于区域温度变化影响的评价不一致。因此,森林变化的生物物理机制及其温度效应是一个值得深入分析的问题。未来需要充分发挥多种数据源合理集成后用于解释森林响应气候效应方面的交叉优势,理解生物物理机制与生物化学机制共同作用下的森林变化、碳循环与气候的交互关系,并通过森林生态系统的合理经营与管理实现其气候效益最大化。     

北京地区城市化对辐射强迫的影响估算

能引起城市区域辐射强迫的因素较多,但是目前城市化引起的辐射强迫的相关研究较少.本文利用GLASS 反照率遥感数据和CERES地表短波辐射数据计算了近10年来北京地区城市化过程引起的辐射强迫,讨论了辐射强迫 的空间分布规律及数量统计特征.基于2000、2010年2期的Globeland30土地分类数据提取了城市边缘区,并结合辐射 强迫遥感数据计算了主城核心区、內缘区、各级外缘区的辐射强迫,探究了土地覆盖变化强迫因子、气候等其他强迫因子 的相对贡献大小.结果表明:近10年北京市全区域的辐射强迫为2.52 W·m-2,表现为增温效应,其中土地覆被不变区 域产生的辐射强迫为2.51W·m-2,耕地、林地是2种主要辐射强迫源;土地覆被变化区域产生的辐射强迫为2.67 W· m-2,非植被类型之间的土地覆被变化引起的平均辐射强迫为2.23W·m-2,有植被参与的土地覆被变化区域产生的辐 射强迫为2.95W·m-2;主城核心区的辐射强迫为-1.16W·m-2,表现为降温效应;辐射强迫变化与距离主城区的距离 呈先增大后减小的变化趋势.研究结果可为城市区域的辐射强迫研究提供参考,有助于了解北京市区域气候分布差异      

Atmospheric science: stratospheric cooling and the troposphere

Satellite observations of tropospheric temperatures seem to show less warming than surface temperatures, contrary to physical predictions. Fu et al. show that statistical correction for the effect of stratospheric cooling brings the satellite-based estimates of tropospheric warming into closer agreement with observations of surface warming. Here we apply the method of Fu et al. to output from a state-of-the-art coupled climate model and show that simulated tropospheric temperature trends are consistent with those observed and that their method is robust.     

Acclimatization of soil respiration to warming in a tall grass prairie.

The latest report by the Intergovernmental Panel on Climate Change (IPCC) predicts a 1.4-5.8 degrees C average increase in the global surface temperature over the period 1990 to 2100 (ref. 1). These estimates of future warming are greater than earlier projections, which is partly due to incorporation of a positive feedback. This feedback results from further release of greenhouse gases from terrestrial ecosystems in response to climatic warming. The feedback mechanism is usually based on the assumption that observed sensitivity of soil respiration to temperature under current climate conditions would hold in a warmer climate. However, this assumption has not been carefully examined. We have therefore conducted an experiment in a tall grass prairie ecosystem in the US Great Plains to study the response of soil respiration (the sum of root and heterotrophic respiration) to artificial warming of about 2 degrees C. Our observations indicate that the temperature sensitivity of soil respiration decreases--or acclimatizes--under warming and that the acclimatization is greater at high temperatures. This acclimatization of soil respiration to warming may therefore weaken the positive feedback between the terrestrial carbon cycle and climate.     

Observations of increased tropical rainfall preceded by air passage over forests

Vegetation affects precipitation patterns by mediating moisture, energy and trace-gas fluxes between the surface and atmosphere. When forests are replaced by pasture or crops, evapotranspiration of moisture from soil and vegetation is often diminished, leading to reduced atmospheric humidity and potentially suppressing precipitation. Climate models predict that large-scale tropical deforestation causes reduced regional precipitation, although the magnitude of the effect is model and resolution dependent. In contrast, observational studies have linked deforestation to increased precipitation locally but have been unable to explore the impact of large-scale deforestation. Here we use satellite remote-sensing data of tropical precipitation and vegetation, combined with simulated atmospheric transport patterns, to assess the pan-tropical effect of forests on tropical rainfall. We find that for more than 60 per cent of the tropical land surface (latitudes 30 degrees south to 30 degrees north), air that has passed over extensive vegetation in the preceding few days produces at least twice as much rain as air that has passed over little vegetation. We demonstrate that this empirical correlation is consistent with evapotranspiration maintaining atmospheric moisture in air that passes over extensive vegetation. We combine these empirical relationships with current trends of Amazonian deforestation to estimate reductions of 12 and 21 per cent in wet-season and dry-season precipitation respectively across the Amazon basin by 2050, due to less-efficient moisture recycling. Our observation-based results complement similar estimates from climate models, in which the physical mechanisms and feedbacks at work could be explored in more detail.     

Short-term climatic impacts of afforestation in the East Asian monsoon region

The influence of changes in vegetation cover on short-term climate over the East Asian monsoon region is simulated using the Community Climate System Model Version 3.5.The results show the annual mean surface air temperature significantly decreases by 0.93°C in response to afforestation over the East Asian monsoon region.Also,surface air temperature decreases by 1.46 and 0.40°C in summer and winter,respectively.The cooling is caused by enhanced evapotranspiration(ET) produced by increased forest cover.Evapotranspiration is greater in summer than in winter,so summer cooling is greater than winter cooling.The annual mean precipitation increases in response to afforestation,with a maximum of 7% in April.Water vapor increases significantly because of greater latent heat flux release.Meanwhile,afforestation leads to higher surface roughness,which decreases surface wind speed and induces an ascending air motion.These factors can produce more clouds and precipitation.Moreover,the surface albedo and the reflective solar radiation are reduced in response to afforestation.     

Irregular tropical glacier retreat over the Holocene epoch driven by progressive warming

The causes and timing of tropical glacier fluctuations during the Holocene epoch (10,000 years ago to present) are poorly understood. Yet constraining their sensitivity to changes in climate is important, as these glaciers are both sensitive indicators of climate change and serve as water reservoirs for highland regions. Studies have so far documented extra-tropical glacier fluctuations, but in the tropics, glacier-climate relationships are insufficiently understood. Here we present a (10)Be chronology for the past 11,000?years (11?kyr), using 57 moraines from the Bolivian Telata glacier (in the Cordillera Real mountain range). This chronology indicates that Telata glacier retreated irregularly. A rapid and strong melting from the maximum extent occurred from 10.8?±?0.9 to 8.5?±?0.4?kyr ago, followed by a slower retreat until the Little Ice Age, about 200 years ago. A dramatic increase in the rate of retreat occurred over the twentieth century. A glacier-climate model indicates that, relative to modern climate, annual mean temperature for the Telata glacier region was -3.3?±?0.8 °C cooler at 11?kyr ago and remained -2.1?±?0.8 °C cooler until the end of the Little Ice Age. We suggest that long-term warming of the eastern tropical Pacific and increased atmospheric temperature in response to enhanced austral summer insolation were the main drivers for the long-term Holocene retreat of glaciers in the southern tropics.     

35 ka BP climate simulations in East Asia and probing the mechanisms of climate changes

Interglacial or postglacial climates are all of charac-teristic of warmer conditions. However, if condition asso-ciated with the warm feature is wetter or drier than today,it would produce different impacts on natural environ-ments and human society. Quaternary studies found thatclimate with warm-dry or warm-wet conditions had oc-curred in China during the last 40—30 ka BP[1]. For ex-ample, it was warmer than the present during themid-Holocene (3—8 ka BP) and the late phases of MarineIsot…     

青藏高原对全球大气温度和水汽分布的影响

利用耦合的气候模式CESM, 定量研究青藏高原对全球大气温度和水汽分布的影响。通过对比采用真实地形的参考实验(Real)和去掉青藏高原的敏感性实验(NoTibet)发现, 去掉青藏高原会使北半球大气变冷、变干, 对南半球的影响不明显。北半球中高纬度从地表至平流层均有强烈降温, 地表的降温中心在北大西洋, 年平均降温幅度达5ºC, 高空的降温中心在100 hPa的平流层, 年平均降温幅度达2ºC。北大西洋和南亚地区湿度减少, 南大西洋和东非地区湿度增加。北半球变冷主要是海洋向北经向热量输送减少的结果, 一方面增强了北半球的经向温度梯度, 导致Hadley环流增强, 加强了中低纬地区向北的大气热量输送, 部分补偿了海洋向北减少的热量输送, 维持了北半球中低纬度的能量平衡; 另一方面, 使得北半球中高纬度蒸发作用减弱, 大气中水汽含量减少, 北半球变得寒冷干燥。初步的研究表明, 青藏高原对北半球气候有重大影响, 影响范围可达北半球高纬度地区。     

A satellite view of aerosols in the climate system

Anthropogenic aerosols are intricately linked to the climate system and to the hydrologic cycle. The net effect of aerosols is to cool the climate system by reflecting sunlight. Depending on their composition, aerosols can also absorb sunlight in the atmosphere, further cooling the surface but warming the atmosphere in the process. These effects of aerosols on the temperature profile, along with the role of aerosols as cloud condensation nuclei, impact the hydrologic cycle, through changes in cloud cover, cloud properties and precipitation. Unravelling these feedbacks is particularly difficult because aerosols take a multitude of shapes and forms, ranging from desert dust to urban pollution, and because aerosol concentrations vary strongly over time and space. To accurately study aerosol distribution and composition therefore requires continuous observations from satellites, networks of ground-based instruments and dedicated field experiments. Increases in aerosol concentration and changes in their composition, driven by industrialization and an expanding population, may adversely affect the Earth's climate and water supply.     

水库对局地气候影响的数值模拟研究

大型水库建设改变了上游地区的地形高度和地表特征,必将对周边地区的局地气候产生影响.利用高分辨率边界层模式模拟研究了在高山峡谷地区由于水库建设可能导致的局地气候变化.结果表明:高山峡谷地区的水库将导致附近地区在冬季增温,增温幅度可达0.4～0.85℃,使春、夏、秋季降温,最大降温幅度可达2℃,但水库对附近地区气温的影响范围较小,影响温度0.1℃的水平范围约为2.5km,影响高度约500m;水库对气温影响的日变化规律冬季和其它季节不同,冬季使全天增温,白天增温幅度大,夜间增温幅度小,其余季节在夜间使气温增加,在白天使气温下降,夜间增温和白天降温的转换时刻大约在上午8时和晚间21时;在冬、春、夏和秋季,水库附近的相对湿度可分别增加约29.8%,37.2%,13.3%和20.3%,影响范围小于3km;水库将使附近的地面风速有明显增加,水库附近风速增加的幅度小于0.5m/s.     

Ecosystem carbon storage in arctic tundra reduced by long-term nutrient fertilization

Global warming is predicted to be most pronounced at high latitudes, and observational evidence over the past 25 years suggests that this warming is already under way. One-third of the global soil carbon pool is stored in northern latitudes, so there is considerable interest in understanding how the carbon balance of northern ecosystems will respond to climate warming. Observations of controls over plant productivity in tundra and boreal ecosystems have been used to build a conceptual model of response to warming, where warmer soils and increased decomposition of plant litter increase nutrient availability, which, in turn, stimulates plant production and increases ecosystem carbon storage. Here we present the results of a long-term fertilization experiment in Alaskan tundra, in which increased nutrient availability caused a net ecosystem loss of almost 2,000 grams of carbon per square meter over 20 years. We found that annual aboveground plant production doubled during the experiment. Losses of carbon and nitrogen from deep soil layers, however, were substantial and more than offset the increased carbon and nitrogen storage in plant biomass and litter. Our study suggests that projected release of soil nutrients associated with high-latitude warming may further amplify carbon release from soils, causing a net loss of ecosystem carbon and a positive feedback to climate warming.     

A climatologically significant aerosol longwave indirect effect in the Arctic

The warming of Arctic climate and decreases in sea ice thickness and extent observed over recent decades are believed to result from increased direct greenhouse gas forcing, changes in atmospheric dynamics having anthropogenic origin, and important positive reinforcements including ice-albedo and cloud-radiation feedbacks. The importance of cloud-radiation interactions is being investigated through advanced instrumentation deployed in the high Arctic since 1997 (refs 7, 8). These studies have established that clouds, via the dominance of longwave radiation, exert a net warming on the Arctic climate system throughout most of the year, except briefly during the summer. The Arctic region also experiences significant periodic influxes of anthropogenic aerosols, which originate from the industrial regions in lower latitudes. Here we use multisensor radiometric data to show that enhanced aerosol concentrations alter the microphysical properties of Arctic clouds, in a process known as the 'first indirect' effect. Under frequently occurring cloud types we find that this leads to an increase of an average 3.4 watts per square metre in the surface longwave fluxes. This is comparable to a warming effect from established greenhouse gases and implies that the observed longwave enhancement is climatologically significant.