共查询到20条相似文献，搜索用时 46 毫秒
1.
Solomon S Daniel JS Neely RR Vernier JP Dutton EG Thomason LW 《Science (New York, N.Y.)》2011,333(6044):866-870
Recent measurements demonstrate that the "background" stratospheric aerosol layer is persistently variable rather than constant, even in the absence of major volcanic eruptions. Several independent data sets show that stratospheric aerosols have increased in abundance since 2000. Near-global satellite aerosol data imply a negative radiative forcing due to stratospheric aerosol changes over this period of about -0.1 watt per square meter, reducing the recent global warming that would otherwise have occurred. Observations from earlier periods are limited but suggest an additional negative radiative forcing of about -0.1 watt per square meter from 1960 to 1990. Climate model projections neglecting these changes would continue to overestimate the radiative forcing and global warming in coming decades if these aerosols remain present at current values or increase. 相似文献
2.
PV Hobbs JS Reid RA Kotchenruther RJ Ferek R Weiss 《Science (New York, N.Y.)》1997,275(5307):1776-1778
Airborne measurements in smoke from biomass burning in Brazil have yielded optical parameters that permit an improved assessment of the effects of smoke on Earth's radiation balance. The global-mean direct radiative forcing due to smoke from biomass burning worldwide is estimated to be no more than about -0.3 watt per square meter (cooling), compared with +2.45 watts per square meter (warming) due to anthropogenic greenhouse gases. On regional scales, direct radiative forcing due to smoke can be large and might indirectly affect global climate. 相似文献
3.
Impacts of atmospheric anthropogenic nitrogen on the open ocean 总被引：3，自引：0，他引：3
Duce RA LaRoche J Altieri K Arrigo KR Baker AR Capone DG Cornell S Dentener F Galloway J Ganeshram RS Geider RJ Jickells T Kuypers MM Langlois R Liss PS Liu SM Middelburg JJ Moore CM Nickovic S Oschlies A Pedersen T Prospero J Schlitzer R Seitzinger S Sorensen LL Uematsu M Ulloa O Voss M Ward B Zamora L 《Science (New York, N.Y.)》2008,320(5878):893-897
Increasing quantities of atmospheric anthropogenic fixed nitrogen entering the open ocean could account for up to about a third of the ocean's external (nonrecycled) nitrogen supply and up to approximately 3% of the annual new marine biological production, approximately 0.3 petagram of carbon per year. This input could account for the production of up to approximately 1.6 teragrams of nitrous oxide (N2O) per year. Although approximately 10% of the ocean's drawdown of atmospheric anthropogenic carbon dioxide may result from this atmospheric nitrogen fertilization, leading to a decrease in radiative forcing, up to about two-thirds of this amount may be offset by the increase in N2O emissions. The effects of increasing atmospheric nitrogen deposition are expected to continue to grow in the future. 相似文献
4.
The impact of boreal forest fire on climate warming 总被引：1，自引：0，他引：1
Randerson JT Liu H Flanner MG Chambers SD Jin Y Hess PG Pfister G Mack MC Treseder KK Welp LR Chapin FS Harden JW Goulden ML Lyons E Neff JC Schuur EA Zender CS 《Science (New York, N.Y.)》2006,314(5802):1130-1132
We report measurements and analysis of a boreal forest fire, integrating the effects of greenhouse gases, aerosols, black carbon deposition on snow and sea ice, and postfire changes in surface albedo. The net effect of all agents was to increase radiative forcing during the first year (34 +/- 31 Watts per square meter of burned area), but to decrease radiative forcing when averaged over an 80-year fire cycle (-2.3 +/- 2.2 Watts per square meter) because multidecadal increases in surface albedo had a larger impact than fire-emitted greenhouse gases. This result implies that future increases in boreal fire may not accelerate climate warming. 相似文献
5.
Atmospheric lifetimes of long-lived halogenated species 总被引：1，自引：0，他引：1
The atmospheric lifetimes of the fluorinated gases CF(4), C(2)F(6), c-C(4)F(8), (CF(3))(2)c-C(4)F(6), C(5)F(12), C(6)F(14), C(2)F(5)Cl, C(2)F(4)C(12), CF(3)Cl, and SF(6) are of concern because of the effects that these long-lived compounds acting as greenhouse gases can have on global climate. The possible atmospheric loss processes of these gases were assessed by determining the rate coefficients for the reactions of these gases with O((1)D), H, and OH and the absorption cross sections at 121.6 nanometers in the laboratory and using these data as input to a two-dimensional atmospheric model. The lifetimes of all the studied perfluoro compounds are >2000 years, and those of CF(3)Cl, CF(3)CF(2)Cl, and CF(2)ClCF(2)Cl are >300 years. If released into the atmosphere, these molecules will accumulate and their effects will persist for centuries or millennia. 相似文献
6.
Urban air pollution and smoke from fires have been modeled to reduce cloud formation by absorbing sunlight, thereby cooling the surface and heating the atmosphere. Satellite data over the Amazon region during the biomass burning season showed that scattered cumulus cloud cover was reduced from 38%in clean conditions to 0%for heavy smoke (optical depth of 1.3). This response to the smoke radiative effect reverses the regional smoke instantaneous forcing of climate from -28 watts per square meter in cloud-free conditions to +8 watts per square meter once the reduction of cloud cover is accounted for. 相似文献
7.
UV-B辐射胁迫对细叶青冈幼苗叶绿素荧光特性的影响 总被引：1，自引：0，他引：1
通过对在自然生境(CK)、辐射UV-B增强(+10％)和辐射UV-B减弱(-80％)三种条件下的细叶青冈幼苗叶绿素含量、荧光参数Fv/Fm、Fv/Fo和φPSⅡ的测定研究,探讨UV-B辐射胁迫对细叶青冈生长的影响.结果表明,细叶青冈幼苗在辐射UV-B减弱胁迫下叶绿素含量、荧光参数Fv/Fm、Fv/Fo和φPSⅡ均高于辐... 相似文献
8.
Trace gases have been measured, by electron-capture gas chromatography and gas chromatography-mass spectrometry techniques, at the South Pole (SP) in Antarctica and in the U.S. Pacific Northwest (PNW) ( approximately 45 degrees N) during January of each year from 1975 to 1980. These measurements show that the concentrations of CCl(3)F, CCl(2)F(2), and CH(3)CCl(3) have increased exponentially at substantial rates. The concentration of CCl(3)F increased at 12 percent per year at the SP and at 8 percent per year in the PNW; CCl(2)F(2) increased at about 9 percent per year at both locations, and CH(3)CCl(3) increased at 17 percent per year at the SP and 11.6 percent per year at the PNW site. There is some evidence that CCl(4) ( approximately 3 percent per year) and N(2)O (0.1 to 0.5 percent per year) may also have increased. Concentrations of nine other trace gases of importance in atmospheric chemistry are also being measured at these two locations. Results of the measurements of CHClF(2)(F-22), C(2)Cl(3)F(3)(F-113), SF(6), C(2)-hydrocarbons, and CH(3)Cl are reported here. 相似文献
9.
Orton GS Friedson AJ Baines KH Martin TZ West RA Caldwell J Hammel HB Bergstralh JT Malcom ME Golisch WF Griep DM Kaminski CD Tokunaga AT Baron R Shure M 《Science (New York, N.Y.)》1991,252(5005):537-542
The spatial organization and time dependence of Jupiter's stratospheric temperatures have been measured by observing thermal emission from the 7.8-micrometer CH(4) band. These temperatures, observed through the greater part of a Jovian year, exhibit the influence of seasonal radiative forcing. Distinct bands of high temperature are located at the poles and mid-latitudes, while the equator alternates between warm and cold with a period of approximately 4 years. Substantial longitudinal variability is often observed within the warm mid-latitude bands, and occasionally elsewhere on the planet. This variability includes small, localized structures, as well as large-scale waves with wavelengths longer than approximately 30,000 kilometers. The amplitudes of the waves vary on a time scale of approximately 1 month; structures on a smaller scale may have lifetimes of only days. Waves observed in 1985, 1987, and 1988 propagated with group velocities less than +/-30 meters per second. 相似文献
10.
[目的]通过对辐射强迫下亚热带典型树种秃瓣杜英幼苗的生长及光合生理的研究,初步探讨植物对于辐射强迫的生理响应及适应性机理,进而揭示辐射变化对亚热带森林树种的影响。[方法]试验设置3个处理水平,即对照组(100%自然光)、弱辐射强迫(39%自然光)、强辐射强迫(16%自然光),对秃瓣杜英不同时期的叶绿素相对含量、光合作用参数等进行测定,分析不同处理梯度对秃瓣杜英株高、地径、叶绿素含量、气体交换参数、光响应曲线参数的影响。[结果]不同处理下秃瓣杜英的地径生长量为:对照组弱辐射强迫组强辐射强迫组,株高生长量在处理前期为:强辐射强迫组弱辐射强迫组对照组,在处理后期无明显变化规律;叶绿素相对含量表现为:强辐射强迫强弱辐射强迫对照组,辐射强迫处理下,秃瓣杜英的光补偿点(LCP)、光饱和点(LSP)和最大净光合速率(Amax)均降低,强辐射强迫处理下,秃瓣杜英的气孔导度(Gs)、蒸腾速率(Tr)显著小于对照组;表观光量子效率(AQY)和暗呼吸速率(Rd)变化规律不明显。[结论]综合来说,辐射强迫引起环境因子的变化,对秃瓣杜英的地径和株高生长量、叶绿素相对含量、光合生理参数有显著影响,但随着秃瓣杜英逐渐适应了这种变化,后期其对地径和株高增量的影响不显著,表明秃瓣杜英能一定程度上适应这种辐射强迫环境,在一定时期内生长正常。 相似文献
11.
[目的]通过对辐射强迫下亚热带典型树种秃瓣杜英幼苗的生长及光合生理的研究,初步探讨植物对于辐射强迫的生理响应及适应性机理,进而揭示辐射变化对亚热带森林树种的影响。[方法]试验设置 3 个处理水平,即对照组(100%自然光)、弱辐射强迫(39%自然光)、强辐射强迫(16%自然光),对秃瓣杜英不同时期的叶绿素相对含量、光合作用参数等进行测定,分析不同处理梯度对秃瓣杜英株高、地径、叶绿素含量、气体交换参数、光响应曲线参数的影响。[结果]不同处理下秃瓣杜英的地径生长量为:对照组>弱辐射强迫组>强辐射强迫组,株高生长量在处理前期为:强辐射强迫组>弱辐射强迫组>对照组,在处理后期无明显变化规律;叶绿素相对含量表现为:强辐射强迫>强弱辐射强迫>对照组,辐射强迫处理下,秃瓣杜英的光补偿点(LCP)、光饱和点(LSP)和最大净光合速率(Amax)均降低,强辐射强迫处理下,秃瓣杜英的气孔导度(Gs)、蒸腾速率(Tr)显著小于对照组;表观光量子效率(AQY)和暗呼吸速率(Rd)变化规律不明显。[结论]综合来说,辐射强迫引起环境因子的变化,对秃瓣杜英的地径和株高生长量、叶绿素相对含量、光合生理参数有显著影响,但随着秃瓣杜英逐渐适应了这种变化,后期其对地径和株高增量的影响不显著,表明秃瓣杜英能一定程度上适应这种辐射强迫环境,在一定时期内生长正常。 相似文献
12.
Lobert JM Butler JH Montzka SA Geller LS Myers RC Elkins JW 《Science (New York, N.Y.)》1995,267(5200):1002-1005
Surface waters along a cruise track in the East Pacific Ocean were undersaturated in methyl bromide (CH(3)Br) in most areas except for coastal and upwelling regions, with saturation anomalies ranging from + 100 percent in coastal waters to -50 percent in open ocean areas, representing a regionally weighted mean of -16 (-13 to -20) percent. The partial lifetime of atmospheric CH(3)Br with respect to calculated oceanic degradation along this cruise track is 3.0 (2.9 to 3.6) years. The global, mean dry mole fraction of CH3Br in the atmosphere was 9.8 +/- 0.6 parts per trillion, with an interhemispheric ratio of 1.31 +/- 0.08. These data indicate that approximately 8 percent (0.2 parts per trillion) of the observed interhemispheric difference in atmospheric CH3Br could be attributed to an uneven global distribution of oceanic sources and sinks. 相似文献
13.
Cloud-radiative forcing and climate: results from the Earth radiation budget experiment 总被引：10，自引：0，他引：10
Ramanathan V Cess RD Harrison EF Minnis P Barkstrom BR Ahmad E Hartmann D 《Science (New York, N.Y.)》1989,243(4887):57-63
The study of climate and climate change is hindered by a lack of information on the effect of clouds on the radiation balance of the earth, referred to as the cloud-radiative forcing. Quantitative estimates of the global distributions of cloud-radiative forcing have been obtained from the spaceborne Earth Radiation Budget Experiment (ERBE) launched in 1984. For the April 1985 period, the global shortwave cloud forcing [-44.5 watts per square meter (W/m(2))] due to the enhancement of planetary albedo, exceeded in magnitude the longwave cloud forcing (31.3 W/m(2)) resulting from the greenhouse effect of clouds. Thus, clouds had a net cooling effect on the earth. This cooling effect is large over the mid-and high-latitude oceans, with values reaching -100 W/m(2). The monthly averaged longwave cloud forcing reached maximum values of 50 to 100 W/m(2) over the convectively disturbed regions of the tropics. However, this heating effect is nearly canceled by a correspondingly large negative shortwave cloud forcing, which indicates the delicately balanced state of the tropics. The size of the observed net cloud forcing is about four times as large as the expected value of radiative forcing from a doubling of CO(2). The shortwave and longwave components of cloud forcing are about ten times as large as those for a CO(2) doubling. Hence, small changes in the cloud-radiative forcing fields can play a significant role as a climate feedback mechanism. For example, during past glaciations a migration toward the equator of the field of strong, negative cloud-radiative forcing, in response to a similar migration of cooler waters, could have significantly amplified oceanic cooling and continental glaciation. 相似文献
14.
McConnell JR Edwards R Kok GL Flanner MG Zender CS Saltzman ES Banta JR Pasteris DR Carter MM Kahl JD 《Science (New York, N.Y.)》2007,317(5843):1381-1384
Black carbon (BC) from biomass and fossil fuel combustion alters chemical and physical properties of the atmosphere and snow albedo, yet little is known about its emission or deposition histories. Measurements of BC, vanillic acid, and non-sea-salt sulfur in ice cores indicate that sources and concentrations of BC in Greenland precipitation varied greatly since 1788 as a result of boreal forest fires and industrial activities. Beginning about 1850, industrial emissions resulted in a sevenfold increase in ice-core BC concentrations, with most change occurring in winter. BC concentrations after about 1951 were lower but increasing. At its maximum from 1906 to 1910, estimated surface climate forcing in early summer from BC in Arctic snow was about 3 watts per square meter, which is eight times the typical preindustrial forcing value. 相似文献
15.
An analysis of high-resolution microwave images of Saturn and Saturn's individual rings is presented. Radio interferometric observations of Saturn taken at the Very Large Array in New Mexico at wavelengths of 2 and 6 centimeters reveal interesting new features in both the atmosphere and rings. The resulting maps show an increase in brightness temperature of about 3 K from equator to pole at both wavelengths, while the 6-centimeter map shows a bright band at northern mid-latitudes. The data are consistent with a radiative transfer model of the atmosphere that constrains the well-mixed, fully saturated, NH(3) mixing ratio to be 1.2 x 10(-4) in a region just below the NH(3) clouds, while the observed bright band indicates a 25 percent relative decrease of NH(3) in northern mid-latitudes. Brightness temperatures for the classical rings are presented. Ring brightness shows a variation with azimuth and is linearly polarized at an average value of about 5 percent. The variations in ring polarization suggest that at least 20 percent of the ring brightness is the result of a single scattering process. 相似文献
16.
Smoke invigoration versus inhibition of clouds over the Amazon 总被引：3，自引：0，他引：3
The effect of anthropogenic aerosols on clouds is one of the most important and least understood aspects of human-induced climate change. Small changes in the amount of cloud coverage can produce a climate forcing equivalent in magnitude and opposite in sign to that caused by anthropogenic greenhouse gases, and changes in cloud height can shift the effect of clouds from cooling to warming. Focusing on the Amazon, we show a smooth transition between two opposing effects of aerosols on clouds: the microphysical and the radiative. We show how a feedback between the optical properties of aerosols and the cloud fraction can modify the aerosol forcing, changing the total radiative energy and redistributing it over the atmospheric column. 相似文献
17.
Simulation of early 20th century global warming 总被引：3，自引：0，他引：3
The observed global warming of the past century occurred primarily in two distinct 20-year periods, from 1925 to 1944 and from 1978 to the present. Although the latter warming is often attributed to a human-induced increase of greenhouse gases, causes of the earlier warming are less clear because this period precedes the time of strongest increases in human-induced greenhouse gas (radiative) forcing. Results from a set of six integrations of a coupled ocean-atmosphere climate model suggest that the warming of the early 20th century could have resulted from a combination of human-induced radiative forcing and an unusually large realization of internal multidecadal variability of the coupled ocean-atmosphere system. This conclusion is dependent on the model's climate sensitivity, internal variability, and the specification of the time-varying human-induced radiative forcing. 相似文献
18.
Atmospheric dimethyl sulfide (DMS) measurements were made on the Atlantic Coast of the United States at Wallops Island and Cape Henry, Virginia, during June 1975. The very low concentrations, typically less than 30 parts per trillion observed at the Cape Henry site, were thought to result from the smog chemistry associated with the Norfolk metropolitan area. Atmospheric DMS concentrations at the Wallops Island site were much higher, having a geometric mean of 58 parts per trillion and a geometric standard deviation of 2.1. At this site the DMS source strength was estimated to be 6 milligrams of sulfur per square meter per year. Because of wind conditions during this experiment, the DMS source strength is thought to be representative of the DMS source strength of the ocean in the Wallops Island area and is much less than the 130 milligrams of sulfur per square meter per year needed to balance the ocean-atmosphere portion of the global sulfur budget. 相似文献
19.
Mahowald N 《Science (New York, N.Y.)》2011,334(6057):794-796
The net effect of anthropogenic aerosols on climate is usually considered the sum of the direct radiative effect of anthropogenic aerosols, plus the indirect effect of these aerosols through aerosol-cloud interactions. However, an additional impact of aerosols on a longer time scale is their indirect effect on climate through biogeochemical feedbacks, largely due to changes in the atmospheric concentration of CO(2). Aerosols can affect land and ocean biogeochemical cycles by physical forcing or by adding nutrients and pollutants to ecosystems. The net biogeochemical effect of aerosols is estimated to be equivalent to a radiative forcing of -0.5 ± 0.4 watts per square meter, which suggests that reaching lower carbon targets will be even costlier than previously estimated. 相似文献
20.
在观察叶甲科昆虫生物学特性的工作中,我们曾发现过鸡血藤黄叶甲 Gonioctena fulva(Mots)伪胎生的生殖方式,即每次生殖时,常先产一粒卵,再胎生出幼虫。1984年初夏,又发现同一属的十三星角胫叶甲 Gonioctena tredecimmaculata(Jacoby)营胎生生殖,这种生殖方式在叶甲科中是少见的。为此,我们于1984—1985年对其生物学特性作了较系统的观察,结果报道如下。 相似文献