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1.
The “overshoot scenario” is an emissions scenario in which CO2 concentration in the atmosphere temporarily exceeds some pre-defined, “dangerous” threshold (before being reduced to non-dangerous levels). Support for this idea comes from its potential to achieve a balance between the burdens of current and future generations in dealing with global warming. Before it can be considered a viable policy, the overshoot scenario needs to be examined in terms of its impacts on the global climate and the environment. In, particular, it must be determined if climate change cause by the overshoot scenario is reversible or not, since crossing that “dangerous” CO2 threshold could result in climate change from which we might not be able to recover. In this study, we quantify the change in several climatic and environmental variables under the overshoot scenario using a global climate model of intermediate complexity. Compared to earlier studies on the overshoot scenario, we have an explicit carbon cycle model that allows us to represent carbon-climate feedbacks and force the climate model more realistically with CO2 emissions rates rather than with prescribed atmospheric pCO2. Our standard CO2 emissions rate is calculated on the basis of historical atmospheric pCO2 data and the WRE S650 non-overshoot stabilization profile. It starts from the preindustrial year 1760, peaks in the year 2056, and ends in the year 2300. A variety of overshoot scenarios were constructed by increasing the amplitude of the control emissions peak but decreasing the peak duration so that the cumulative emissions remain essentially constant. Sensitivity simulations of various overshoot scenarios in our model show that many aspects of the global climate are largely reversible by year 2300. The significance of the reversibility, which takes roughly 200 years in our experiments, depends on the time horizon with which it is viewed or the number of future generations for whom equity is sought. At times when the overshoot scenario has emissions rates higher then the control scenario, the transient changes in atmospheric and oceanic temperatures and surface ocean pH can be significant, even for moderate overshoot scenarios that remain within IPCC SRES emissions scenarios. The large transient changes and the centennial timescale of climate reversibility suggest that the overshoot might not be the best mitigation approach, even if it technically follows the optimal economic path.  相似文献   

2.
In a microwave background polarization map that covers only part of the sky, it is impossible to separate the E and B components perfectly. This difficulty in general makes it more difficult to detect the B component in a data set. Any polarization map can be separated in a unique way into “pure E”, “pure B” and “ambiguous” components. Power that resides in the pure E(B) component is guaranteed to be produced by E(B) modes, but there is no way to tell whether the ambiguous component comes from E or B modes. A polarization map can be separated into the three components either by finding an orthonormal basis for each component, or directly in real space by using Green functions or other methods.  相似文献   

3.
We present results of a study of the so-called “stickiness” regions where orbits in mappings and dynamical systems stay for very long times near an island and then escape to the surrounding chaotic region. First we investigated the standard map in the form xi+1 = xi+yi+1 and yi+1 = yi+K/2π · sin(2πxi) with a stochasticity parameter K = 5, where only two islands of regular motion survive. We checked now many consecutive points—for special initial conditions of the mapping—stay within a certain region around the island. For an orbit on an invariant curve all the points remain forever inside this region, but outside the “last invariant curve” this number changes significantly even for very small changes in the initial conditions. In our study we found out that there exist two regions of “sticky” orbits around the invariant curves: A small region I confined by Cantori with small holes and an extended region II is outside these cantori which has an interesting fractal character. Investigating also the Sitnikov-Problem where two equally massive primary bodies move on elliptical Keplerian orbits, and a third massless body oscillates through the barycentre of the two primaries perpendicularly to the plane of the primaries—a similar behaviour of the stickiness region was found. Although no clearly defined border between the two stickiness regions was found in the latter problem the fractal character of the outer region was confirmed.  相似文献   

4.
A typical question in climate change analysis is whether a certain observed climate characteristic, like a pronounced anomaly or an interdecadal trend, is an indicator of anthropogenic climate change or still in the range of natural variability. Many climatic features are described by one-dimensional index time series, like for instance the global mean temperature or circulation indices. Here, we present a Bayesian classification approach applied to the time series of the northern annular mode (NAM), which is the leading mode of Northern Hemisphere climate variability. After a pronounced negative phase during the 1950s and 1960s, the observed NAM index reveals a distinct positive trend, which is also simulated by various climate model simulations under enhanced greenhouse conditions. The objective of this study is to decide whether the observed temporal evolution of the NAM may be an indicator of global warming. Given a set of prior probabilities for disturbed and undisturbed climate scenarios, the Bayesian decision theorem decides whether the observed NAM trend is classified in a control climate, a greenhouse-gas plus sulphate aerosol climate or a purely greenhouse-gas induced climate as derived from multi-model ensemble simulations.The three climate scenarios are well separated from each other in terms of the 30-year NAM trends. The multi-model ensembles contain a weak but statistically significant climate change signal in the form of an intensification of the NAM. The Bayesian classification suggests that the greenhouse-gas scenario is the most probable explanation for the observed NAM trend since 1960, even if a high prior probability is assigned to the control climate. However, there are still large uncertainties in this classification result because some periods at the end of the 19th century and during the “warm” 1920s are also classified in an anthropogenic climate, although natural forcings are likely responsible for this early NAM intensification. This demonstrates a basic shortcoming of the Bayesian decision theorem when it is based on one-dimensional index time series like the NAM index.  相似文献   

5.
Since October 1990, 3 weeks after the launch of the Ulysses spacecraft, the dust detector onboard recorded impacts of cosmic dust particles. Besides dust impacts, the detector recorded noise from a variety of sources. So far, a very rigid scheme had been applied to eliminate noise from impact data. The data labeled “big” dust impacts previously led to the identification of interstellar dust and of dust streams from Jupiter. The analysis presented here is concerned with data of signals of small amplitudes which are strongly contaminated by noise. Impacts identified in this data set are called “small” impacts. It is shown that dust impacts can be clearly distinguished from noise for most of the events due to the multi-coincidence characteristics of the instrument. 516 “small” impacts have been identified. For an additional 119 events, strong arguments can be given that they are probably small dust impacts. Thereby, the total number of dust impacts increases from 333 to 968 in the time period from 28 October 1990 to 31 December 1992. This increase permits a better statistical analysis, especially of the Jupiter dust streams which consist mostly of small and fast particles. Additional dust streams have been identified between the already known streams before and after Jupiter flyby. The dependence of the deflection from the Jupiter direction, the stream intensity and width on Jupiter distance support the assertion that they have been emitted from the Jovian system. The masses of the 635 “small” dust particles range from 6 × 10−17 to 3 × 10−10 g with a mean value of 1 × 10−12 g, which compares to a range from 1 × 10−16 to 4 × 10−9 g with a mean value of 2 × 10−11 g for the previously identified 333 “big” dust particles.  相似文献   

6.
Lunar Clinopyroxene and Plagioclase: Surface Distribution and Composition   总被引：2，自引：0，他引：2  
The Clementine UVVIS images and the spectral and chemical (mineral) characteristics of lunar soil samples previously measured by the Lunar Samples Characterization Consortium were used to map the plagioclase and clinopyroxene abundance in the lunar surface material. An excess of plagioclase was found in young highland craters (e.g., in the crater Tycho) and in their ray systems. For clinopyroxenes, analogous behavior was observed in mare craters (e.g., in the crater Aristarchus). The maps for the FeO and Al2O3 bulk contents and the contents of these oxides in plagioclase and clinopyroxene were estimated by the same technique. These maps were compared to each other and to the predicted distribution of the lunar regolith maturity. The regolith of highland ray systems (e.g., the Tycho crater system) is characterized not only by low maturity but also by peculiar iron and aluminum contents: the lower the soil maturity degree, the smaller the iron content and the greater the aluminum content. This is confirmed by the data for the lunar soil samples from the Apollo 16 landing site. A cluster analysis of the “clinopyroxene content-maturity” and “plagioclase content-maturity” correlation diagrams allowed the mineral mapping of the lunar surface to be performed.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 4, 2005, pp. 291–303.Original Russian Text Copyright © 2005 by Shkuratov, Kaydash, Pieters.  相似文献   

7.
Increases in the partial pressure of carbon dioxide (pCO2) in the atmosphere will significantly affect a wide variety of terrestrial fauna and flora. Because of tight atmospheric–oceanic coupling, shallow-water marine species are also expected to be affected by increases in atmospheric carbon dioxide concentrations. One proposed way to slow increases in atmospheric pCO2 is to sequester CO2 in the deep sea. Thus, over the next few centuries marine species will be exposed to changing seawater chemistry caused by ocean–atmospheric exchange and/or deep-ocean sequestration. This initial case study on one allogromiid foraminiferal species (Allogromia laticollaris) was conducted to begin to ascertain the effect of elevated pCO2 on benthic Foraminifera, which are a major meiofaunal constituent of shallow- and deep-water marine communities. Cultures of this thecate foraminiferan protist were used for 10–14-day experiments. Experimental treatments were executed in an incubator that controlled CO2 (15 000; 30 000; 60 000; 90 000; 200 000 ppm), temperature and humidity; atmospheric controls (i.e., ~ 375 ppm CO2) were executed simultaneously. Although the experimental elevated pCO2 values are far above foreseeable surface water pCO2, they were selected to represent the spectrum of conditions expected for the benthos if deep-sea CO2 sequestration becomes a reality. Survival was assessed in two independent ways: pseudopodial presence/absence and measurement of adenosine triphosphate (ATP), which is an indicator of cellular energy. Substantial proportions of A. laticollaris populations survived 200 000 ppm CO2 although the mean of the median [ATP] of survivors was statistically lower for this treatment than for that of atmospheric control specimens. After individuals that had been incubated in 200 000 ppm CO2 for 12 days were transferred to atmospheric conditions for ~ 24 h, the [ATP] of live specimens (survivors) approximated those of the comparable atmospheric control treatment. Incubation in 200 000 ppm CO2 also resulted in reproduction by some individuals. Results suggest that certain Foraminifera are able to tolerate deep-sea CO2 sequestration and perhaps thrive as a result of elevated pCO2 that is predicted for the next few centuries, in a high-pCO2 world. Thus, allogromiid foraminiferal “blooms” may result from climate change. Furthermore, because allogromiids consume a variety of prey, it is likely that they will be major players in ecosystem dynamics of future coastal sedimentary environments.  相似文献   

8.
ASTRON has demonstrated the capabilities of a 4 m2, dense phased array antenna (Bij de Vaate et al., 2002) for radio astronomy, as part of the Thousand Element Array project (ThEA). Although it proved the principle, a definitive answer related to the viability of the dense phased array approach for the SKA could not be given, due to the limited collecting area of the array considered. A larger demonstrator has therefore been defined, known as “Electronic Multi-Beam Radio Astronomy Concept”, EMBRACE, which will have an area of 625 m2, operate in the band 0.4–1.550 GHz and have at least two independent and steerable beams. With this collecting area EMBRACE can function as a radio astronomy instrument whose sensitivity is comparable to that of a 25-m diameter dish. The collecting area also represents a significant percentage area (∼10%) of an individual SKA “station.” This paper presents the plans for the realisation of the EMBRACE demonstrator.  相似文献   

9.
The response of the Earth's global mean vertical atmospheric temperature structure to large increases in the atmospheric CO2 concentration was examined using a 1-D radiative-convective atmospheric model. It was found that the greenhouse warming of the terrestrial surface can be strongly inhibited by the development of a more isothermal, moister and higher troposphere than at present. The saturation of the strong CO2 infrared bands for high CO2 concentrations further inhibits the greenhouse warming to such an extent that a runaway greenhouse fuelled only by a rise in the atmospheric CO2 is not possible. However, a continuously rising solar-constant does eventually lead to a runaway.  相似文献   

10.
Greenhouse gas emissions from a managed grassland   总被引：3，自引：0，他引：3  
Managed grasslands contribute to global warming by the exchange of the greenhouse gases carbon dioxide, nitrous oxide and methane. To reduce uncertainties of the global warming potential of European grasslands and to assess potential mitigation options, an integrated approach quantifying fluxes from all three gases is needed. Greenhouse gas emissions from a grassland site in the SE of Scotland were measured in 2002 and 2003. Closed static chambers were used for N2O and CH4 flux measurements, and samples were analysed by gas chromatography. Closed dynamic chambers were used for soil respiration measurements, using infrared gas analysis. Three organic manures and two inorganic fertilizers were applied at a rate of 300 kg N ha−1 a−1 (available N) and compared with a zero-N control on grassland plots in a replicated experimental design. Soil respiration from plots receiving manure was up to 1.6 times larger than CO2 release from control plots and up to 1.7 times larger compared to inorganic treatments (p<0.05). A highly significant (p<0.001) effect of fertilizer and manure treatments on N2O release was observed. Release of N2O from plots receiving inorganic fertilizers resulted in short term peaks of up to 388 g N2O–N ha−1 day−1. However losses from plots receiving organic manures were both longer lasting and greater in magnitude, with an emission of up to 3488 g N2O–N ha−1 day−1 from the sewage sludge treatments. During the 2002 growing season the cumulative total N2O flux from manure treatments was 25 times larger than that from mineral fertilizers. CH4 emissions were only significantly increased (p<0.001) for a short period following applications of cattle slurry. Although soil respiration in manure plots was high, model predictions and micrometeorological flux measurements at an adjacent site suggest that all plots receiving fertilizer or manure acted as a sink for CO2. Therefore in terms of global warming potentials the contribution of N2O from manure treatments becomes particularly important. There were considerable variations in N2O and CO2 fluxes between years, which was related to annual variations in soil temperature and rainfall.  相似文献   

11.
S.A. Stern  L. Trafton 《Icarus》1984,57(2):231-240
Cosmic abundance, vapor pressure, and molecular weight considerations restrict the likely gas candidates for Pluto's atmosphere to Ne, N2, CO, O2, and Ar, in addition to the already detected CH4. The vapor pressures and cosmic abundances of these gases indicate that all except Ne should be saturated in Pluto's atmosphere. The vapor pressure of Ne is so high that the existence of solid or liquid Ne on Pluto's surface is very unlikely; cosmic abundance arguments imply that Ne cannot attain saturation in Pluto's atmosphere. At both perihelion, N2 should dominate the saturated gases. CO2 should have the next highest mixing ratio, followed by O2 and Ar. CH4 should have the smallest mixing ratio. Because vapor pressures of these gases vary with temperature at diverse rates, the bulk and constituent mixing ratios of Pluto's atmosphere should vary with season. Between perihelion and aphelion, the column abundance of CH4 may change by a factor of 260 while that of N2 changes by only a factor of 52. The potential seasonal variation of Pluto's atmosphere was investigated by considering the behavior of these gases when individually mixed with CH4. The effects of diurnal and latitudinal variation of insolation and eclipses on the atmosphere also were investigated. Seasonal effects are shown to dominate. It was shown that the atmospheric bulk may not be a minimum near aphelion but rather at intermediate distances from the Sun during summer/winter inadequate ice deposits may allow the atmosphere to collapse by freezing out over winter latitudes. If the atmosphere does not collapse, its weight is sufficient to keep it distributed uniformly around Pluto's surface. In this case, the atmosphere tends to regulate the surface temperature to a seasonally dependent value which is uniform over the globe.Finally, the likely global circulation regimes for each model atmosphere as a function of temperature were investigated and it was concluded that if CH4, O2, or CO dominates the atmosphere, Pluto will exhibit cyclic variations between an axially symmetric circulation system at perihelion and a baroclinic wave regime at aphelion. However, if N2 dominates, as is likely, the wave regime should hold continuously. If the atmosphere collapses to a thin halo during summer/winter seasons, only a weak, symmetric circulation should occur.  相似文献   

12.
This paper presents our results for full 3-D simulations of very-high to ultra-high energy electromagnetic cascades – and the associated coherent Cherenkov radiation – as might be produced by high-energy neutrino interactions in dense media. Using “thinning” techniques, we develop an algorithm based on the existing “ZHS” code, and demonstrate that the new “ZHS-thinned” code can produce fast and accurate results for showers up to . Using ZHS-thinned, we develop new parameterisations for the radiation from showers in ice, salt, and the lunar regolith, with a separate treatment of the megaregolith (deep regolith). Our parameterisations include for the first time a method to simulate fluctuations in shower length induced by the LPM effect. Our results, which avoid the pit-falls of scaling simulations from lower energies, allow improved calculations of the detection probability for experiments searching for high-energy neutrinos using the radio technique.  相似文献   

13.
《Astroparticle Physics》2004,20(6):641-652
The cosmic ray primary composition in the energy range between 1015 and 1016 eV, i.e., around the “knee” of the primary spectrum, has been studied through the combined measurements of the EAS-TOP air shower array (2005 m a.s.l., 105 m2 collecting area) and the MACRO underground detector (963 m a.s.l., 3100 m w.e. of minimum rock overburden, 920 m2 effective area) at the National Gran Sasso Laboratories. The used observables are the air shower size (Ne) measured by EAS-TOP and the muon number (Nμ) recorded by MACRO. The two detectors are separated on average by 1200 m of rock, and located at a respective zenith angle of about 30°. The energy threshold at the surface for muons reaching the MACRO depth is approximately 1.3 TeV. Such muons are produced in the early stages of the shower development and in a kinematic region quite different from the one relevant for the usual Nμ−Ne studies. The measurement leads to a primary composition becoming heavier at the knee of the primary spectrum, the knee itself resulting from the steepening of the spectrum of a primary light component (p, He) of Δγ=0.7±0.4 at E04×1015 eV. The result confirms the ones reported from the observation of the low energy muons at the surface (typically in the GeV energy range), showing that the conclusions do not depend on the production region kinematics. Thus, the hadronic interaction model used (CORSIKA/QGSJET) provides consistent composition results from data related to secondaries produced in a rapidity region exceeding the central one. Such an evolution of the composition in the knee region supports the “standard” galactic acceleration/propagation models that imply rigidity dependent breaks of the different components, and therefore breaks occurring at lower energies in the spectra of the light nuclei.  相似文献   

14.
Interannual variability of regional climate was investigated on a seasonal basis. Observations and two global climate model (GCM) simulations were intercompared to identify model biases and climate change signals due to the enhanced greenhouse effect. Observed record length varies from 40 to 100 years, while the model output comes from two 100-year equilibrium climate simulations corresponding to atmospheric greenhouse gas concentrations at observed 1990 and projected 2050 levels. The GCM includes an atmosphere based on the NCAR CCM1 with the addition of the radiative effects of CH4, N2O and CFCs, a bulk layer land surface and a mixed-layer ocean with thermodynamic sea-ice and fixed meridional oceanic heat transport.Because comparisons of interannual variability are sensitive to the time period chosen, a climate ensemble technique has been developed. This technique provides comparisons between variance ratios of two time series for all possible contiguous sub-periods of a fixed length. The time autocorrelation is thus preserved within each sub-period. The optimal sub-period length was found to be 30 years, based on which robust statistics of the ensemble were obtained to identify substantial differences in interannual variability that are both physically important and statistically significant.Several aspects of observed interannual variability were reproduced by the GCM. These include: global surface air temperature; Arctic sea-ice extent; and regional variability of surface air temperature, sea level pressure and 500 mb height over about one quarter of the observed data domains. Substantial biases, however, exist over broad regions, where strong seasonality and systematic links between variables were identified. For instance, during summer substantially greater model variability was found for both surface air temperature and sea-level pressure over land areas between 20–50°N, while this tendency was confined to 20–30°N in other seasons. When greenhouse gas concentrations increase, atmospheric moisture variability is substantially larger over areas that experience the greatest surface warming. This corresponds to an intensified hydrologic cycle and, hence, regional increases in precipitation variability. Surface air temperature variability increases where hydrologic processes vary greatly or where mean soil moisture is much reduced. In contrast, temperature variability decreases substantially where sea-ice melts completely. These results indicate that regional changes in interannual variability due to the enhanced greenhouse effect are associated with mechanisms that depend on the variable and season.  相似文献   

15.
In this paper we investigate both the global and the local hydrodynamics of axisymmetric accretion disks around young stellar objects under the simultaneous action of viscosity, self-gravity and pressure forces. For simplicity, we take for the global model a polytropic equation of state, make the infinitely thin disk approximation and characterize the surface density and temperature profiles in the disk as power laws in the radial distance r from the protostar. We solve the problem of the general density profile of a Keplerian disk showing that self-gravity could not be an important factor for the fast formation of the rocky cores of giant gaseous planets in our solar system. Under the hypothesis that the unperturbed rotation curve of the disk is nearly Keplerian throughout the radial extent, we can estimate with our polytropic model a lower limit for the resulting masses Md(r) of stable disks up to 100 AU. These masses are in the range of the so-called minimum mass solar nebular (d/Ms ≈ 0.01–0.02).By adopting a simplified viscosity model, where the height-integrated turbulent dynamical viscosity ν is a function of the surface density σ like η ∝ σΓ, we derive in the local shearing sheet model linearized evolution equations for small density perturbations describing both a diffusion process and the propagation of acoustic density waves. We solve a special initial value problem and calculate the appropriate Green's function. The analytical solutions so obtained describe in the case Γ < 0 the successive formation of quasi-stationary ring-shaped density structures in a disk with a definite mode of maximum instability, whereas in the case Γ > Γc the density wave equation describes the propagation of an “overstable” ring-shaped acoustic density wavelet to the outer ranges of the accretion disk. Whereas the group velocity of the wave packet is subsonic, the phase velocities of individual wave crests in the wave packet are supersonic. The mode of maximum instability, the growth rate and the number of growing waves in the wavelet are controlled by Γ and α. Our present knowledge concerning turbulent viscosity in protoplanetary disks is not sufficient to decide whether or not the case Γ > Γc is realized.The suggested structuring processes in the linear theory should initiate in the non-linear regime the formation of narrow ring-shaped density shock waves moving through the protoplanetary disk. These non-linear waves could produce extremely spatially and temporally heterogeneous temperature regions in the disk. We speculate that ring-shaped density waves, excited by inner boundary conditions and which have dominated the disk's evolution at early times, are responsible both for the fast growth of dust to planetesimals and at least for the rapid accretion of the rocky cores of giant gaseous planets in the protoplanetary accretion disk (shock wave trigger hypothesis). We derive provisional scaling rules for planetary systems regarding the spacing of orbits as a function of the mass ratio of the protoplanetary disk to the protostar. However, further analytical work and linear as well as nonlinear numerical simulations of density waves excited by inner boundary conditions are needed to consolidate the results and speculations of our linear wave mechanics in the future.  相似文献   

16.
The recent assessment by the Intergovernmental Panel on Climate Change (IPCC) has emphasized that understanding the institutional context in which policies are made and implemented is critical to define sustainable development paths from a climate change perspective. Nevertheless, while the importance of social, political and cultural factors is getting more recognition in some parts of the world, little is known about the human dimensions or the contexts in which they operate in the affluent oil economies of the Arabian Peninsula. Policies that implicitly subsidize or support a wasteful and environmentally destructive use of resources are still pervasive, while noteworthy environmental improvements still face formidable political and institutional constraints to the adaptation of the necessary far reaching and multisectoral approach. The principal aim of this paper is to identify some of the major shortcomings within the special context of the Arab Gulf states' socio-cultural environment in support of appropriate development pathways. Conclusions highlight that past and current policy recommendations for mitigating environmental threats are likely to be ineffective. This is because they are based on the unverified assumption that Western-derived standards of conduct, specifically the normative concept of ”good governance” and ”democracy”, will be adopted in non-Western politico-cultural contexts.  相似文献   

17.
The effect of gateways on ocean circulation patterns in the Cenozoic   总被引：1，自引：0，他引：1  
Both geological data and climate model studies indicate that substantially different patterns of the global ocean circulation have existed throughout the Cenozoic. In a climate model study of the late Oligocene [von der Heydt, A., Dijkstra, H.A. (2006). Effect of ocean gateways on the global ocean circulation in the late Oligocene and early Miocene. Paleoceanography, 21, PA1011] a “northern sinking” type of circulation was found, with (shallow) deep water formation in both the North Pacific Ocean and the North Atlantic Ocean. This is in contrast to the present-day “conveyor” circulation, where there is deep water formation in the North Atlantic but not in the North Pacific. In order to explain these differences, we use an ocean general circulation model for idealized two-basin flows and study the effect of asymmetries in the continental geometry on the circulation patterns. Two types of asymmetry are considered: (i) the relative northward extent of the Pacific and the Atlantic basin, and (ii) the existence of a circum-global gateway at low latitudes. The more northward extent of the Pacific basin in the Oligocene makes the Conveyor solution less likely and facilitates deep water formation in the North Pacific compared to the North Atlantic. The low-latitude gateway on the other hand, allows salinity and heat exchange between the two main ocean basins and therefore leads to deep water formation in both the North Atlantic and the North Pacific.  相似文献   

18.
This paper examines the economic and ethical dimensions of climate policy in light of existing knowledge of the impacts of global warming and the costs of greenhouse gas emissions abatement. We find that the criterion of economic efficiency, operationalized through cost-benefit analysis, is ill-equipped to cope with the pervasive uncertainties and issues of intergenerational fairness that characterize climate change. In contrast, the concept of sustainable development—that today's policies should ensure that future generations enjoy life opportunities undiminished relative to the present—is a normative criterion that explicitly addresses the uncertainties and distributional aspects of global environmental change. If one interprets the sustainability criterion to imply that it is morally wrong to impose catastrophic risks on unborn generations when reducing those risks would not noticeably diminish the quality of life of existing persons, a case can be made for significant steps to reduce greenhouse gas emissions.  相似文献   

19.
The Wilkinson Microwave Anisotropy Probe (WMAP) science team has released results from the first year of operation at the Earth–Sun L2 Lagrange point. The maps are consistent with previous observations but have much better sensitivity and angular resolution than the COBE DMR maps, and much better calibration accuracy and sky coverage than ground-based and balloon-borne experiments. The angular power spectra from these ground-based and balloon-borne experiments are consistent within their systematic and statistical uncertainties with the WMAP results. WMAP detected the large angular-scale correlation between the temperature and polarization anisotropies of the CMB caused by electron scattering since the Universe became reionized after the “Dark Ages”, giving a value for the electron scattering optical depth of 0.17 ± 0.04. The simplest ΛCDM model with n=1 and Ωtot=1 fixed provides an adequate fit to the WMAP data and gives parameters which are consistent with determinations of the Hubble constant and observations of the accelerating Universe using supernovae. The time-ordered data, maps, and power spectra from WMAP can be found at http://lambda.gsfc.nasa.gov along with 13 papers by the WMAP science team describing the results in detail.  相似文献   

20.
This paper is a comparison and compilation of lichenometric and geomorphic studies performed by two independent teams in the Cordillera Blanca, Peru, in 1996 and 2002 on 66 “Little Ice Age” moraines of 14 glaciers. Using eleven new control points, we recalibrated the initial rapid growth phase of the previously established Rhizocarpon subgenus Rhizocarpon growth curve. This curve was then used to estimate the age of “Little Ice Age” moraines. The time of deposition of the most prominent and numerous terminal and lateral moraines on the Pacific-facing side of the Cordillera Blanca (between AD 1590 and AD 1720) corresponds to the coldest and wettest phase in the tropical Andes as revealed by ice-core data. Less prominent advances occurred between AD 1780 and 1880.  相似文献   

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