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1.
HD40307g is the closest potentially habitable planet discovered today orbiting a K2V star and will be a prime target for future TPF-like missions if its existence is confirmed.Although the atmosphere of HD40307g should be denser and contain more CO2 judging from the amount of radiation it receives from its star,it is unknown how dense and how much CO2 the planetary atmosphere should have.Thus more knowledge on its atmosphere is useful.For HD40307g to have Earth-like climate(288 K global mean surface temperature),we obtain the following combination of atmospheric pressure and CO2 mixing ratio:(1)10-bar+3%CO2;(2)5-bar+10%CO2;(3)3-bar+30%CO2.  相似文献   

2.
This paper surveys the history of the Earth's climate and deals with facts, techniques, and causes. A review of climatic history since the origin of the Earth demonstrates the changes and variability of our climate along different scales. These variations can probably be fully understood only when taking into account both external forcing and non-linear interactions between the components of the climatic system: atmosphere, oceans, cryosphere, lithosphere, and biosphere. At least, as far as boundary conditions and forcing are concerned for the 108 to 109 yr time scale, atmospheric composition, solar evolution, and tectonism have to be considered, while variations of the Earth's orbital elements, and subsequently of the insolation, best explain the glacial-interglacial occurrences during the Quaternary Period. For shorter time scales, volcanic dust, solar activity, sea surface temperatures, and atmosphere-ocean autovariations have to be taken into account. Furthermore, the man-made effects have now to be considered: atmospheric loading of dust and air pollution particles, changes in surface albedo, and mainly the increasing rise of atmospheric CO2 and other trace gases adding to a greenhouse effect.This man-made warming effect of future CO2 increase will probably emerge as a clearly recognizable trend against the background of natural climatic fluctuations by the end of this century. This carbon dioxide induced super-interglacial will be superimposed on the expected natural long-term cooling trend of the ice age chronology.  相似文献   

3.
The global rate of fossil fuel combustion continues to rise, but the amount of CO2 accumulating in the atmosphere has not increased accordingly. The causes for this discrepancy are widely debated. Particularly, the location and drivers for the interannual variability of atmospheric CO2 are highly uncertain. Here we examine links between global atmospheric CO2 growth rate (CGR) and the climate anomalies of biomes based on (1986–1995) global climate data of ten years and accompanying satellite data sets. Our results show that four biomes, the tropical rainforest, tropical savanna, C4 grassland and boreal forest, and their responses to climate anomalies, are the major climate-sensitive CO2 sinks/sources that control the CGR. The nature and magnitude by which these biomes respond to climate anomalies are generally not the same. However, one common influence did emerge from our analysis; the extremely high CGR observed for the one extreme El Niño year was caused by the response of the tropical biomes (rainforest, savanna and C4 grassland) to temperature.  相似文献   

4.
The greenhouse effect on the Earth is identified by the difference between the effective radiating temperature of the planet and its surface temperature. The difference between the energy emitted by the surface and that emitted upward to space by the upper atmosphere quantifies it; it can therefore be defined as the long wave energy trapped in the atmosphere. Climate forcing and the response of the climate system within which climate feedback mechanisms are contained, will be defined in this review. Quantitative examples will illustrate what could happen if the greenhouse effect is perturbed by the human activities, in particular if atmospheric CO2 concentrations would double in the future. Recent measurements by satellites of the greenhouse effect will be given. The net cooling effect of clouds on the Earth and whether or not there will be less cooling by clouds as the planet warms, are discussed following a series of papers recently published by Ramanathan and his collaborators.  相似文献   

5.
Increases in atmospheric CO2 concentration not only affects climate variables such as precipitation and air temperature, but also affects intrinsic ecosystem physiological properties such as bulk stomatal conductance and intercellular CO2 concentration. De-convolving these two effects remains uncertain in biosphere–atmosphere water and carbon cycling. Using a simplified analytical net ecosystem CO2 exchange (NEE) model, tested with recently collected flux measurements in a humid grassland ecosystem in Ireland, we assess how much projected climate shifts affect net canopy photosynthesis (A) without physiological adjustments and contrast those findings with published field data on physiological adjustments for several grassland ecosystems. Our analysis suggests that the intrinsic grassland ecosystem physiological adjustment of A is about 45 times more important than the resulting climatic forcing shifts from the IS92a scenario (and a doubling of atmospheric CO2 concentration). Also, our analysis shows that increase in precipitation results in concomitant decrease in the two climate variables—net radiation and vapor pressure deficit, and these decreases have opposite (and almost canceling) effects on A. Implications to afforestation policy and future experimental efforts to quantify the carbon sink from humid grassland ecosystems are also discussed.  相似文献   

6.
Data on the content of the 14C cosmogenic isotope in tree rings, which were obtained as a result of laboratory measurements, are often used when solar activity (SA) is reconstructed for previous epochs, in which direct observations are absent. However, these data contain information not only about SA variations but also about changes in the Earth climatic parameters, such as the global temperature and the CO2 content in the Earth’s atmosphere. The effect of these variations on the 14C isotope content in different natural reservoirs after the last glacial termination to the middle of the Holocene is considered. The global temperature and the CO2 content increased on this time interval. In this case the 14C absolute content in the atmosphere increased on this time interval, even though the 14С to 12С isotope concentration ratio (as described by the Δ14С parameter) decreased. These variations in the radiocarbon absolute content can be caused by its redistribution between natural reservoirs. It has been indicated that such a redistribution is possible only when the rate of carbon exchange between the ocean and atmosphere depends on temperature. The values of the corresponding temperature coefficient for the 17–10 ka BC time interval, which make it possible to describe the carbon redistribution between the ocean and atmosphere, have been obtained.  相似文献   

7.
The climate warming is mainly due to the increase in concentrations of anthropogenic greenhouse gases, of which CO2 is the most important one responsible for radiative forcing of the climate. In order to reduce the great estimation uncertainty of atmospheric CO2 concentrations, several CO2-related satellites have been successfully launched and many future greenhouse gas monitoring missions are planned. In this paper, we review the development of CO2 retrieval algorithms, spatial interpolation methods and ground observations. The main findings include: 1) current CO2 retrieval algorithms only partially account for atmospheric scattering effects; 2) the accurate estimation of the vertical profile of greenhouse gas concentrations is a long-term challenge for remote sensing techniques; 3) ground-based observations are too sparse to accurately infer CO2 concentrations on regional scales; and 4) accuracy is the primary challenge of satellite estimation of CO2 concentrations. These findings, taken as a whole, point to the need to develop a high accuracy method for simulation of carbon sources and sinks on the basis of the fundamental theorem of Earth’s surface modelling, which is able to efficiently fuse space- and ground-based measurements on the one hand and work with atmospheric transport models on the other hand.  相似文献   

8.
Solar geoengineering has been proposed as a potential mechanism to counteract global warming. Here we use the University of Victoria Earth System Model (UVic) to simulate the effect of idealized sunshade geoengineering on the global carbon cycle. We conduct two simulations. The first is the A2 simulation, where the model is driven by prescribed emission scenario based on the SRES A2 CO2 emission pathway. The second is the solar geoengineering simulation in which the model is driven by the A2 CO2 emission scenario combined with sunshade solar geoengineering. In the model, solar geoengineering is represented by a spatially uniform reduction in solar insolation that is implemented at year 2020 to offset CO2-induced global mean surface temperature change. Our results show that solar geoengineering increases global carbon uptake relative to A2, in particular CO2 uptake by the terrestrial biosphere. The increase in land carbon uptake is mainly associated with increased net primary production (NPP) in the tropics in the geoengineering simulation, which prevents excess warming in tropics. By year 2100, solar geoengineering decreases A2-simulated atmospheric CO2 by 110 ppm (12%) and causes a 60% (251 Pg C) increase in land carbon accumulation compared to A2. Solar geoengineering also prevents the reduction in ocean oxygen concentration caused by increased ocean temperatures and decreased ocean ventilation, but reduces global ocean NPP. Our results suggest that to fully access the climate effect of solar geoengineering, the response of the global carbon cycle should be taken into account.  相似文献   

9.
Projections of future climate change by climate system models depend on the sensitivities of models to specified greenhouse gases.To reveal and understand the different climate sensitivities of two versions of LASG/IAP climate system model FGOALS-g2 and FGOALS-s2,we investigate the global mean surface air temperature responses to idealized CO2 forcing by using the output of abruptly quadrupling CO2 experiments.The Gregory-style regression method is used to estimate the"radiative forcing"of quadrupled CO2 and equilibrium sensitivity.The model response is separated into a fast-response stage associated with the CO2 forcing during the first 20 years,and a slow-response stage post the first 20 years.The results show that the radiative forcing of CO2 is overestimated due to the positive water-vapor feedback and underestimated due to the fast cloud processes.The rapid response of water vapor in FGOALS-s2 is responsible for the stronger radiative forcing of CO2.The climate sensitivity,defined as the equilibrium temperature change under doubled CO2 forcing,is about 3.7 K in FGOALS-g2 and4.5 K in FGOALS-s2.The larger sensitivity of FGOALS-s2 is due mainly to the weaker negative longwave clear-sky feedback and stronger positive shortwave clear-sky feedback at the fast-response stage,because of the more rapid response of water vapor increase and sea-ice decrease in FGOALS-s2 than in FGOALS-g2.At the slow-response stage,similar to the fast-response stage,net negative clear-sky feedback is weaker in FGOALS-s2.Nevertheless,the total negative feedback is larger in FGOALS-s2 due to a larger negative shortwave cloud feedback that involves a larger response of total cloud fraction and condensed water path increase.The uncertainties of estimated forcing and net feedback mainly come from the shortwave cloud processes.  相似文献   

10.
Carbonates capping Neoproterozoic glacial deposits contain peculiar sedimentological features and geochemical anomalies ascribed to extraordinary environmental conditions in the snowball Earth aftermath. It is commonly assumed that post-snowball climate dominated by CO2 partial pressures several hundred times greater than modern levels, would be characterized by extreme temperatures, a vigorous hydrological cycle, and associated high continental weathering rates. However, the climate in the aftermath of a global glaciation has never been rigorously modelled. Here, we use a hierarchy of numerical models, from an atmospheric general circulation model to a mechanistic model describing continental weathering processes, to explore characteristics of the Earth system during the supergreenhouse climate following a snowball glaciation. These models suggest that the hydrological cycle intensifies only moderately in response to the elevated greenhouse. Indeed, constraints imposed by the surface energy budget sharply limit global mean evaporation once the temperature has warmed sufficiently that the evaporation approaches the total absorbed solar radiation. Even at 400 times the present day pressure of atmospheric CO2, continental runoff is only 1.2 times the modern runoff. Under these conditions and accounting for the grinding of the continental surface by the ice sheet during the snowball event, the simulated maximum discharge of dissolved elements from continental weathering into the ocean is approximately 10 times greater than the modern flux. Consequently, it takes millions of years for the silicate weathering cycle to reduce post-snowball CO2 levels to background Neoproterozoic levels. Regarding the origin of the cap dolostones, we show that continental weathering alone does not supply enough cations during the snowball melting phase to account for their observed volume.  相似文献   

11.
A CO2-weathering model has been used to explore the possible evolution of the Earth’s climate as the Sun steadily brightened throughout geologic time. The results of the model calculations can be described in terms of three, qualitatively different, “Megaclimates”. Mega-climate 1 resulted from a period of rapid outgassing in the early Archean, with high, but declining, temperatures caused by the small weathering rates on a largely water-covered planet. Mega-climate 2 began about 3 Gyear ago as major continental land masses developed, increasing the weathering rate in the early Proterozoic and thereby depleting the atmospheric CO2 concentration. This process produced the first Precambrian glaciations about 2.3 Gyear ago. During Mega-climate 2, evolutionary biological processes increased the surface weatherability in incremental steps and plate tectonics modulated the CO2 outgassing rate with an estimated period of 150 Myear (approximately one-half the period for the formation and breakup of super continents). Throughout Mega-climate 2 the surface temperature was controlled by variations in the atmospheric CO2 level allowing transitions between glacial and non-glacial conditions. The results of the model for Mega-climate 2 are in agreement with the occurrence (and absence) of glaciations in the geologic record. Extending the model to the future suggests that CO2 control of the Earth’s temperature will no longer be able to compensate for a solar flux that continues to increase. The present level of atmospheric CO2 is so small that further reduction in CO2 cannot prevent the Earth from experiencing Mega-climate 3 with steadily increasing surface temperatures caused by the continued brightening of the Sun. During Mega-climate 3, the main danger to the biosphere would come not from an increasing temperature but from a decreasing (rather than an increasing) CO2 level which could, in time, fall below 0.5 PAL, causing serious damage to the biosphere. Fortunately, the rates of change due to solar brightening are slow enough that Mega-climate 3 appears to pose no threat to the biosphere for the next 0.5-2 Gyear.  相似文献   

12.
Understanding climate change is an active topic of research. Much of the observed increase in global surface temperature over the past 150 years occurred prior to the 1940s and after the 1980s. The main causes invoked are solar variability, changes in atmospheric greenhouse gas content or sulfur due to natural or anthropogenic action, or internal variability of the coupled ocean–atmosphere system. Magnetism has seldom been invoked, and evidence for connections between climate and magnetic field variations have received little attention. We review evidence for correlations which could suggest such (causal or non-causal) connections at various time scales (recent secular variation ∼ 10–100 yr, historical and archeomagnetic change ∼ 100–5000 yr, and excursions and reversals ∼ 103–106 yr), and attempt to suggest mechanisms. Evidence for correlations, which invoke Milankovic forcing in the core, either directly or through changes in ice distribution and moments of inertia of the Earth, is still tenuous. Correlation between decadal changes in amplitude of geomagnetic variations of external origin, solar irradiance and global temperature is stronger. It suggests that solar irradiance could have been a major forcing function of climate until the mid-1980s, when “anomalous” warming becomes apparent. The most intriguing feature may be the recently proposed archeomagnetic jerks, i.e. fairly abrupt (∼ 100 yr long) geomagnetic field variations found at irregular intervals over the past few millennia, using the archeological record from Europe to the Middle East. These seem to correlate with significant climatic events in the eastern North Atlantic region. A proposed mechanism involves variations in the geometry of the geomagnetic field (f.i. tilt of the dipole to lower latitudes), resulting in enhanced cosmic-ray induced nucleation of clouds. No forcing factor, be it changes in CO2 concentration in the atmosphere or changes in cosmic ray flux modulated by solar activity and geomagnetism, or possibly other factors, can at present be neglected or shown to be the overwhelming single driver of climate change in past centuries. Intensive data acquisition is required to further probe indications that the Earth's and Sun's magnetic fields may have significant bearing on climate change at certain time scales.  相似文献   

13.
A study of the contribution to global climate change from China’s CO2 emission is conducted using the FIO-ESM v1.0 climate model. A series of sensitivity experiments are performed to identify two kinds of contributions to global climate change of China’s CO2 emission due to fossil fuel combustion: one is the pure contribution which is the historical climate response from the sensitivity experiment forced only by China’s CO2 emission, the other is the accumulative contribution which is proposed in this research and defined as the difference of historical climate responses between the experiments forced by all countries’ CO2 emission and other countries’ CO2 emission excluding China. The pure contribution approach considers the total CO2 discharged by China, while the accumulative contribution approach considers not only the discharge amount of China but also the discharge order of China and other countries. The latter is a more realistic approach to quantify the contribution of CO2 emission to the historical change of atmospheric CO2 concentration, surface air temperature (SAT), sea surface temperature (SST) and sea ice coverage in the Arctic. Model results show that from the accumulative perspective, the ratio of the contribution of CO2 emission from China for the increase of atmospheric CO2 concentration, SAT and SST, and the decrease of the sea ice coverage in the Arctic to that from all other countries excluding China varies from 8% to 92%, 5% to 95%, 9% to 91% and 18% to 82%, respectively. Here we take the contribution of China’s CO2 emission as an example, the contribution of CO2 emission from any other country or area can be evaluated by the same approach.  相似文献   

14.
Abstract

A physically based model of moisture transfer in the soil-canopy-atmosphere system, fitted to measured data in wheat fields, was applied to calculate the sensitivity of evapotranspiration to the combined effect of possible CO2-induced climate changes and the direct impact of doubling CO2 content in the atmosphere. The impact of carbon dioxide was taken into account by changing the stomatal resistance and the leaf area index. Several climate change scenarios were used. Simulation studies showed that when the changes of a number of climatic and plant factors are considered, evapotranspiration responses can differ greatly from those that consider only temperature change. The temperature effect of the increase in CO2 content in the atmosphere can be compensated by changes in the physiological parameters of vegetation. Thus, under certain conditions, one can expect a decrease in evapotranspiration instead of an increase such as is predicted by a number of models which neglect the direct effects of CO2 on plant behaviour.  相似文献   

15.
An atmosphere–ocean climate box model is used to examine the influence of cloud feedback on the equilibria of the climate system. The model consists of three non-linear ordinary differential equations, which are simplified forms of the first law of thermodynamics for the atmosphere and ocean and the continuity equation for the atmospheric component of the hydrological cycle. The mass continuity equation expresses the cloud liquid water content as a function of the evaporation rate from the ocean surface and the precipitation rate. Cloud formation releases latent heat. The model clouds also absorb solar energy at a rate consistent with recent findings. The model simulates snow–ice albedo feedback, water vapour feedback and cloud feedback. The global mean precipitation and surface temperature are analysed as they respond to enhanced greenhouse warming. Model results show that cloud feedback can lead to the occurrence of multiple climate equilibria. Some of these are warmer than the present equilibrium, with increased precipitation, while others are colder, with reduced precipitation. If the cloud feedback is weak, enhanced greenhouse forcing leads to a small alteration of the present equilibrium. If the cloud feedback is strong enough, the climate system can be forced into a warmer and wetter equilibrium.  相似文献   

16.
Abstract

Global climate change can be reproduced in detail by using three-dimensional general circulation models (GCMs). However, such complex models require super-computers and extensive hours of computational time for a single attempt at reproducing long term climate change. An alternative approach is to make simplifying assumptions that retain the essential physics for the desired simulation. Energy balance and Radiative-convective models are examples of such models. The model in this study follows the simplified approach using physics-based climate processes as well as interactions between atmospheric and hydrological processes. The vertically and latitudinally averaged mean temperature and mean water vapour content between 30°N-50°N latitudes are considered as atmospheric state variables while soil and sea temperatures and water storage amount are considered for describing the behaviour of the hydrological system. Temperatures in both the atmosphere and ground are calculated by a thermal energy equation that considers the physically-based processes of shortwave radiation, longwave radiation, sensible heat flux, and latent heat flux. Precipitation and evaporation processes transport moisture between the atmosphere and ground. In this study, the radiation parameterization of the simplified climate model is tested in the investigation of the various effects of global warming due to doubling and quadrupling of CO2. Changes of temperature, soil water content, evaporation rate and precipitation rate are investigated by numerical experiments. The simplified climate model provides acceptable simulation of climate change and holds promise for practical investigations such as the interactions of physical processes in the evolution of drought phenomena.  相似文献   

17.
Ocean Drilling Program Leg 199 Site 1220 provides a continuous sedimentary section across the Paleocene/Eocene (P/E) transition in the carbonate‐bearing sediments on 56–57 Ma oceanic crust. The large negative δ13C shift in seawater is likely due to the disintegration of methane hydrate, which is expected to be rapidly changed to carbon dioxide in the atmosphere and well‐oxygenated seawater, leading to a reduction in deep‐sea pH. A pH decrease was very likely responsible for the emergence of agglutinated foraminiferal fauna as calcareous fauna was eliminated by acidification at the P/E transition at Site 1220. The absence of the more resistant calcareous benthic foraminifera and the presence of the planktonic foraminifera at Site 1220 is interesting and unique, which indicates that calcareous benthic foraminifera suffered greatly from living on the seafloor. Box model calculation demonstrates that, assuming the same mean alkalinity as today, pCO2 must increase from 280 ppm to about 410 ppm for the calcite undersaturation in the deep ocean and for the oversaturation in the surface ocean during the P/E transition. The calculated increased pCO2 coincides with paleo‐botanical evidence. The current global emission rate (～7.3 peta (1015) gC/y) of anthropogenic carbon input is approximately 30 times of the estimate at the P/E transition. The results at the P/E transition give an implication that the deep sea benthic fauna will be threatened in future in combination with ocean acidification, increased sea surface temperature and more stratified surface water.  相似文献   

18.
Direct evidence of the feedback between climate and weathering   总被引：1，自引：0，他引：1  
Long-term climate moderation is commonly attributed to chemical weathering; the higher the temperature and precipitation the faster the weathering rate. Weathering releases divalent cations to the ocean via riverine transport where they promote the drawdown of CO2 from the atmosphere by the precipitation and subsequent burial of carbonate minerals. To test this widely-held hypothesis, we performed a field study determining the weathering rates of 8 nearly pristine north-eastern Iceland river catchments with varying glacial cover over 44 years. The mean annual temperature and annual precipitation of these catchments varied by 3.2 to 4.5 °C and 80 to 530%, respectively during the study period. Statistically significant linear positive correlations were found between mean annual temperature and chemical weathering in all 8 catchments and between mean annual temperature and both mechanical weathering and runoff in 7 of the 8 catchments. For each degree of temperature increase, the runoff, mechanical weathering flux, and chemical weathering fluxes in these catchments are found to increase from 6 to 16%, 8 to 30%, and 4 to 14% respectively, depending on the catchment. In contrast, annual precipitation is less related to the measured fluxes; statistically significant correlations between annual precipitation and runoff, mechanical weathering, and chemical weathering were found for 3 of the least glaciated catchments. Mechanical and chemical weathering increased with time in all catchments over the 44 year period. These correlations were statistically significant for only 2 of the 8 catchments due to scatter in corresponding annual runoff and average annual temperature versus time plots. Taken together, these results 1) demonstrate a significant feedback between climate and Earth surface weathering, and 2) suggest that weathering rates are currently increasing with time due to global warming.  相似文献   

19.
Measurements of benthic foraminiferal cadmium:calcium (Cd/Ca) have indicated that the glacial–interglacial change in deep North Pacific phosphate (PO4) concentration was minimal, which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean. Here we present sedimentary redox-sensitive trace metal records from Ocean Drilling Program (ODP) Site 882 (NW subarctic Pacific, water depth 3244 m) to make inferences about changes in deep North Pacific oxygenation – and thus respired carbon storage – over the past 150,000 yr. These observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep-water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment. Our results suggest that the deep subarctic Pacific water mass was depleted in oxygen during glacial maxima, though it was not anoxic. We reconcile our results with the existing benthic foraminiferal Cd/Ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed, rather than remineralized. This change would have corresponded to an increase in the deep Pacific storage of respired carbon, which would have lowered atmospheric carbon dioxide (CO2) by sequestering CO2 away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea. The magnitude of change in preformed nutrients suggested by the North Pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pCO2.  相似文献   

20.
The effect of cloud feedback on the response of a radiative-convective model to a change in cloud model parameters, atmospheric CO2 concentration, and solar constant has been studied using two different parameterization schemes. The method for simulating the vertical distribution of both cloud cover and cloud optical thickness, which depends on the relative humidity and on the saturation mixing ratio of water vapor, respectively, is the same in both approaches, but the schemes differ with respect to modeling the water vapor profile. In scheme I atmospheric water vapor is coupled to surface parameters, while in scheme II an explicit balance equation for water vapor in the individual atmospheric layers is used. For both models the combined effect of feedbacks due to variations in lapse rate, cloud cover, and cloud optical thickness results in different relationships between changes in surface temperature, planetary temperature, and cloud cover. Specifically, for a CO2 doubling and a 2% increase in solar constant, in both models the surface warming is reduced by cloud feedback, in contrast to no feedback, with the greater reduction in scheme I as compared to that of scheme II.  相似文献   

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