Unexpected changes to the global methane budget over the past 2000 years

We report a 2000-year Antarctic ice-core record of stable carbon isotope measurements in atmospheric methane (delta13CH4). Large delta13CH4 variations indicate that the methane budget varied unexpectedly during the late preindustrial Holocene (circa 0 to 1700 A.D.). During the first thousand years (0 to 1000 A.D.), delta13CH4 was at least 2 per mil enriched compared to expected values, and during the following 700 years, an about 2 per mil depletion occurred. Our modeled methane source partitioning implies that biomass burning emissions were high from 0 to 1000 A.D. but reduced by almost approximately 40% over the next 700 years. We suggest that both human activities and natural climate change influenced preindustrial biomass burning emissions and that these emissions have been previously understated in late preindustrial Holocene methane budget research.     

Oxygen isotope constraints on the sulfur cycle over the past 10 million years

Oxygen isotopes in marine sulfate (delta18O(SO4)) measured in marine barite show variability over the past 10 million years, including a 5 per mil decrease during the Plio-Pleistocene, with near-constant values during the Miocene that are slightly enriched over the modern ocean. A numerical model suggests that sea level fluctuations during Plio-Pleistocene glacial cycles affected the sulfur cycle by reducing the area of continental shelves and increasing the oxidative weathering of pyrite. The data also require that sulfate concentrations were 10 to 20% lower in the late Miocene than today.     

Abrupt temperature changes in the Western Mediterranean over the past 250,000 years

A continuous high-resolution Western Mediterranean sea surface temperature (SST) alkenone record spanning the past 250,000 years shows that abrupt changes were more common at warming than at cooling. During marine isotope stage (MIS) 6, SST oscillated following a stadial-interstadial pattern but at lower intensities and rates of change than in the Dansgaard/Oeschger events of MIS 3. Some of the most prominent events occurred over MISs 5 and 7, after prolonged warm periods of high stability. Climate during the whole period was predominantly maintained in interglacial-interstadial conditions, whereas the duration of stadials was much shorter.     

Tropical forests and the global carbon cycle

New data on the three major determinants of the carbon release from tropical forest clearing are used in a computer model that simulates land use change and its effects on the carbon content of vegetation and soil in order to calculate the net flux of carbon dioxide between tropical ecosystems and the atmosphere. The model also permits testing the sensitivity of the calculated flux to uncertainties in these data. The tropics were a net source of at least 0.4 x 10(15) grams but not more than 1.6 x 10(15) grams of carbon in 1980, considerably less than previous estimates. Decreases in soil organic matter were responsible for 0.1 x 10(15) to 0.3 x 10(15) grams of the release, while the burning and decay of cleared vegetation accounted for 0.3 x 10(15) to 1.3 x 10(15) grams. These estimates are lower than many previous ones because lower biomass estimates and slightly lower land clearing rates were used and because ecosystem recovery processes were included. These new estimates of the biotic release allow for the possibility of a balanced global budget given the large remaining uncertainties in the marine, terrestrial, and fossil fuel components of the carbon cycle.     

Causes of climate change over the past 1000 years

Recent reconstructions of Northern Hemisphere temperatures and climate forcing over the past 1000 years allow the warming of the 20th century to be placed within a historical context and various mechanisms of climate change to be tested. Comparisons of observations with simulations from an energy balance climate model indicate that as much as 41 to 64% of preanthropogenic (pre-1850) decadal-scale temperature variations was due to changes in solar irradiance and volcanism. Removal of the forced response from reconstructed temperature time series yields residuals that show similar variability to those of control runs of coupled models, thereby lending support to the models' value as estimates of low-frequency variability in the climate system. Removal of all forcing except greenhouse gases from the approximately 1000-year time series results in a residual with a very large late-20th-century warming that closely agrees with the response predicted from greenhouse gas forcing. The combination of a unique level of temperature increase in the late 20th century and improved constraints on the role of natural variability provides further evidence that the greenhouse effect has already established itself above the level of natural variability in the climate system. A 21st-century global warming projection far exceeds the natural variability of the past 1000 years and is greater than the best estimate of global temperature change for the last interglacial.     

Orbital and millennial Antarctic climate variability over the past 800,000 years

A high-resolution deuterium profile is now available along the entire European Project for Ice Coring in Antarctica Dome C ice core, extending this climate record back to marine isotope stage 20.2, approximately 800,000 years ago. Experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation. We assessed the general correspondence between Dansgaard-Oeschger events and their smoothed Antarctic counterparts for this Dome C record, which reveals the presence of such features with similar amplitudes during previous glacial periods. We suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records.     

天水市近63年极端温度变化特征分析

为了研究气候变暖对天水极端温度的影响,利用天水观测站1951年至2013年逐年的极端温度资料,运用气候倾向率、趋势系数、百分位法、滑动T检验等统计方法,分析极端温度对气候变暖的响应特征。结果表明：天水年极端最高（低）温度均呈显著性升高趋势,极端最高气温上升0.2℃/10a,极端最低气温上升0.3℃/10a,都通过了α=0.01的显著性检验;通过百分位法定义了极端温度的阈值,分析发现：极端最高气温与阈值的差值随时间序列的增加逐步增大,极端最低气温与阈值的差值随时间序列的增加逐步减少,对极端最高温度和极端最低温度利用滑动T检验法进行突变检验,在α=0.01显著性水平下,极端最低温度没有发生突变,而极端最高温度在1983年和1993年发生了两次十分明显的突变。     

沈阳市59年来气温变化及其突变性分析

利用沈阳市1951～2009年气温观测资料,采用线性倾向估计对沈阳市年平均气温、平均最高、最低气温的年际、年代际变化进行统计分析,并利用Mann-Kendall方法进行突变检测。结果表明,沈阳市年平均气温、最高、最低气温均呈上升趋势,其线性倾向率分别为0.231、0.181、0.218℃/10a;年平均气温、平均最高和最低气温的增温态势十分明显;平均最低气温的增温比平均最高气温更加显著。沈阳市年平均气温的突变点出现在1982年,年平均最高气温在1994年,年平均最低气温在1978年。     

The timing of high sea levels over the past 200,000 years

The (230)Th ages and (234)U/(238)U ratios were determined for Barbados corals that grew during periods of high sea level within the last 200,000 years. The similarity of the initial (234)U/(238)U ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine (234)U/(238)U ratio 83,000 and 200,000 years ago was within 2 per mil of the modern value. The accuracies of the (230)Th ages are evaluated on the basis of the (234)U/(238)U values and a model of the behavior of uranium and thorium isotopes during diagenesis. For the last three interglacial and two intervening interstadial periods, sea level peaked at or after peaks in summer insolation in the Northern Hemisphere. This overall pattern supports the idea that glacial-interglacial cycles are caused by changes in Earth's orbital geometry. The sea-level drop at the end of the penultimate interglacial, the last interglacial, and a subsequent interstadial period lagged behind the decrease in insolation by 5,000 to 10,000 years.     

The cause of decreased pan evaporation over the past 50 years

Changes in the global water cycle can cause major environmental and socioeconomic impacts. As the average global temperature increases, it is generally expected that the air will become drier and that evaporation from terrestrial water bodies will increase. Paradoxically, terrestrial observations over the past 50 years show the reverse. Here, we show that the decrease in evaporation is consistent with what one would expect from the observed large and widespread decreases in sunlight resulting from increasing cloud coverage and aerosol concentration.     

Rapid variability of seawater chemistry over the past 130 million years

Fluid inclusion data suggest that the composition of major elements in seawater changes slowly over geological time scales. This view contrasts with high-resolution isotope data that imply more rapid fluctuations of seawater chemistry. We used a non-steady-state box model of the global sulfur cycle to show that the global δ(34)S record can be explained by variable marine sulfate concentrations triggered by basin-scale evaporite precipitation and dissolution. The record is characterized by long phases of stasis, punctuated by short intervals of rapid change. Sulfate concentrations affect several important biological processes, including carbonate mineralogy, microbially mediated organic matter remineralization, sedimentary phosphorous regeneration, nitrogen fixation, and sulfate aerosol formation. These changes are likely to affect ocean productivity, the global carbon cycle, and climate.     

The impact of agricultural soil erosion on the global carbon cycle

Agricultural soil erosion is thought to perturb the global carbon cycle, but estimates of its effect range from a source of 1 petagram per year(-1) to a sink of the same magnitude. By using caesium-137 and carbon inventory measurements from a large-scale survey, we found consistent evidence for an erosion-induced sink of atmospheric carbon equivalent to approximately 26% of the carbon transported by erosion. Based on this relationship, we estimated a global carbon sink of 0.12 (range 0.06 to 0.27) petagrams of carbon per year(-1) resulting from erosion in the world's agricultural landscapes. Our analysis directly challenges the view that agricultural erosion represents an important source or sink for atmospheric CO2.     

Reconstruction of the Amazon Basin effective moisture availability over the past 14,000 years

Quantifying the moisture history of the Amazon Basin is essential for understanding the cause of rain forest diversity and its potential as a methane source. We reconstructed the Amazon River outflow history for the past 14,000 years to provide a moisture budget for the river drainage basin. The oxygen isotopic composition of planktonic foraminifera recovered from a marine sediment core in a region of Amazon River discharge shows that the Amazon Basin was extremely dry during the Younger Dryas, with the discharge reduced by at least 40% as compared with that of today. After the Younger Dryas, a meltwater-driven discharge event was followed by a steady increase in the Amazon Basin effective moisture throughout the Holocene.     

过去300年东北地区林地和草地覆盖变化

东北地区是我国森林、草场资源最为丰富的地区之一。近300年来,耕地扩张、森林砍伐、草地退化等所导致的显著土地覆盖变化会通过对陆-气之间碳通量和地表反照率的改变,进而对气候系统产生影响。该文采用历史文献分析、原始潜在植被恢复等方法,结合驱动力分析,重建了过去300年东北地区林地和草地自然覆盖变化状况。可提供空间分辨率至县、时间分辨率约为100年的东北地区林地和草地覆盖数据,为气候模拟、碳排放估计等相关研究提供真实的历史数据;得到对过去300年,东北地区林地和草地覆盖变化特征的认识:过去300年,东北地区林地、草地所占比例分别减少了约15％、10％;18—19世纪,东北的天然植被覆盖几乎处于原始状态,林地、草地减少的地区主要集中在辽东、辽西等农垦区;1900—1950年为林地、草地减少最为迅速的时期,辽东、辽西的天然植被几乎均被破坏殆尽,鸭绿江流域、长白山地区森林减少十分显著,草地界线已明显向西退缩;20世纪后半期,林地覆盖在空间上呈扩张趋势,局部地区仍在减少,而草地覆盖在空间上则一直呈缩小趋势。      

Impacts of climatic change and fishing on Pacific salmon abundance over the past 300 years

The effects of climate variability on Pacific salmon abundance are uncertain because historical records are short and are complicated by commercial harvesting and habitat alteration. We use lake sediment records of delta15N and biological indicators to reconstruct sockeye salmon abundance in the Bristol Bay and Kodiak Island regions of Alaska over the past 300 years. Marked shifts in populations occurred over decades during this period, and some pronounced changes appear to be related to climatic change. Variations in salmon returns due to climate or harvesting can have strong impacts on sockeye nursery lake productivity in systems where adult salmon carcasses are important nutrient sources.     

北京市近20年农业用水变化趋势及其影响因素

对1986-2007年北京市农业用水情况和影响其变化的相关指标进行主成分分析。结果表明:农作物播种面积、有效灌溉面积、种植业总产量、养殖业总产量和参考作物腾发量五大指标所代表的面积、产量、气候三大因素对北京市农业用水影响的贡献率依次为44.1%、35.2%和17.1%。具体分析各因素,发现近20年北京市农业用水量的降低主要是因为农作物播种面积和有效灌溉面积缩小,节水灌溉面积扩大以及节水技术进步;种植业单位产量用水量的减少,使农业用水量降低;种、养业等用水比例变化趋向合理,有利于北京市节水型农业结构的发展;但目前北京市参考作物腾发量呈上升趋势,将加大农业灌溉用水压力。     

全球变化研究热点——碳循环

40多年来,全世界的科研工作者已经在碳循环领域的各个方面做了大量的工作.本文总结了全球碳循环研究的最新进展,着重介绍了大气CO2浓度的变化及增长趋势,陆地生态系统和海洋对于大气CO2浓度变化及由此而引起的气候变化的反馈及其研究现状.同时,对许多固碳措施和技术方法也作了阐述.目前全球碳循环研究已经达到了系统集成的高度,因此集成研究将是21世纪碳循环研究的发展趋势.     

近30年广西土壤有机质演变特征

土壤有机质(SOM)是衡量农业生产力和土壤整体健康的重要指标,对促进区域粮食安全和缓解全球变暖下的粮食危机具有重要意义。为揭示1984—2009年广西全域SOM变化情况,基于广西第二次土壤普查项目(1984年)和广西测土配方施肥项目(2009年)两期数据,利用地统计学、动态度、分布指数等方法分析了广西土壤表层SOM时空演变特征及其在不同海拔高度上的分布状况。结果显示,近30年广西SOM总体含量大幅提升,各含量等级已由零散交错的不均匀分布演变为相对集中的连片分布,分布面积呈现：等级4(20～30 g·kg^-1)>等级5(30～40 g·kg^-1)>等级6(>40 g·kg^-1)>等级3(10～20 g·kg^-1)>等级1(≤6 g·kg^-1)>等级2(6～10 g·kg^-1),等级4和等级5所占比例分别由1984年的28.20%和18.73%提升至2009年的38.09%和36.19%。在变化速率方面,等级2减少最为迅速,...