首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 93 毫秒
1.
Approximately 1700 Pg of soil carbon (C) are stored in the northern circumpolar permafrost zone, more than twice as much C than in the atmosphere. The overall amount, rate, and form of C released to the atmosphere in a warmer world will influence the strength of the permafrost C feedback to climate change. We used a survey to quantify variability in the perception of the vulnerability of permafrost C to climate change. Experts were asked to provide quantitative estimates of permafrost change in response to four scenarios of warming. For the highest warming scenario (RCP 8.5), experts hypothesized that C release from permafrost zone soils could be 19–45 Pg C by 2040, 162–288 Pg C by 2100, and 381–616 Pg C by 2300 in CO2 equivalent using 100-year CH4 global warming potential (GWP). These values become 50 % larger using 20-year CH4 GWP, with a third to a half of expected climate forcing coming from CH4 even though CH4 was only 2.3 % of the expected C release. Experts projected that two-thirds of this release could be avoided under the lowest warming scenario (RCP 2.6). These results highlight the potential risk from permafrost thaw and serve to frame a hypothesis about the magnitude of this feedback to climate change. However, the level of emissions proposed here are unlikely to overshadow the impact of fossil fuel burning, which will continue to be the main source of C emissions and climate forcing.  相似文献   

2.
Climate policies must consider radiative forcing from Kyoto greenhouse gases, as well as other forcing constituents, such as aerosols and tropospheric ozone that result from air pollutants. Non-Kyoto forcing constituents contribute negative, as well as positive forcing, and overall increases in total forcing result in increases in global average temperature. Non-Kyoto forcing modeling is a relatively new component of climate management scenarios. This paper describes and assesses current non-Kyoto radiative forcing modeling within five integrated assessment models. The study finds negative forcing from aerosols masking (offsetting) approximately 25 % of positive forcing in the near-term in reference non-climate policy projections. However, masking is projected to decline rapidly to 5–10 % by 2100 with increasing Kyoto emissions and assumed reductions in air pollution—with the later declining to as much as 50 % and 80 % below today’s levels by 2050 and 2100 respectively. Together they imply declining importance of non-Kyoto forcing over time. There are however significant uncertainties and large differences across models in projected non-Kyoto emissions and forcing. A look into the modeling reveals differences in base conditions, relationships between Kyoto and non-Kyoto emissions, pollution control assumptions, and other fundamental modeling. In addition, under climate policy scenarios, we find air pollution and resulting non-Kyoto forcing reduced to levels below those produced by air pollution policies alone—e.g., China sulfur emissions fall an additional 45–85 % by 2050. None of the models actively manage non-Kyoto forcing for climate implications. Nonetheless, non-Kyoto forcing may be influencing mitigation results, including allowable carbon dioxide emissions, and further evaluation is merited.  相似文献   

3.
Benefit–cost analysis can serve as an informative input into the policy-making process, but only to the degree it characterizes the major impacts of the regulation under consideration. Recently, the US, amongst other nations, has begun to use estimates of the social cost of CO2 (SC-CO2) to develop analyses that more fully capture the climate change impacts of GHG abatement. The SC-CO2 represents the aggregate willingness to pay to avoid the damages associated with an additional tonne of CO2 emissions. In comparison, the social costs of non-CO2 GHGs have received little attention from researchers and policy analysts, despite their non-negligible climate impact. This article addresses this issue by developing a set of social cost estimates for two highly prevalent non-CO2 GHGs, methane and nitrous oxide. By extending existing integrated assessment models, it is possible to develop a set of social cost estimates for these gases that are consistent with the SC-CO2 estimates currently in use by the US federal government.Policy relevanceWithin the benefit–cost analyses that inform the design of major regulations, all Federal agencies within the US Government (USG) use a set of agreed upon SC-CO2 estimates to value the impact of CO2 emissions changes. However, the value of changes in non-CO2 GHG emissions has not been included in USG policy analysis to date. This article addresses that omission by developing a set of social cost estimates for two highly prevalent non-CO2 GHGs, methane and nitrous oxide. These new estimates are designed to be compatible with the USG SC-CO2 estimates currently in use and may therefore be directly applied to value emissions changes for these non-CO2 gases within the benefit–cost analyses used to evaluate future policies.  相似文献   

4.
The non-CO2 climate impact of aviation (NOx and contrails) is assessed and emissions weighting factors (EWFs) i.e., the factor by which aviation CO2 emissions should be multiplied to get the CO2-equivalent emissions for annual fleet average conditions are estimated. The EWFs are estimated using two economic metrics. One is based on the relative damage cost between non-CO2 forcers and CO2. The other is based on the cost-effective valuation between the non-CO2 forcers and CO2 given an upper ceiling on the global annual average surface temperature (set at 2?K above pre-industrial levels). We also estimate EWFs using three physical metrics, Global Warming Potential (GWP), Global Temperature change Potential (GTP) and Sustained GTP (SGTP) and compare our results with the economics based metrics. Given best estimates on the forcing contributions from CO2, contrails and NOx from aviation and by using a discount rate of 3%/year, the RDC based metric gives an EWF equal to 1.4 (slightly higher than EWFs based on GWP and SGTP using a 100?year time horizon). EWF using the cost-effective approach depends on the time that remains before stabilization occurs. It is roughly equal to unity until a few years before the temperature reaches its ceiling, and approximately 2 when stabilization has taken place. EWFs based on GTP resemble those based on CETO when the time left to when stabilization occurs is sufficiently large. Once stabilization has occurred CETO values resemble RDC based values. If aviation-induced cirrus clouds are included, uncertainties increase and the EWFs for GWP, SGTP and RDC based metrics end up in the range 1.3–2.9, while EWFs for GTP and CETO remain close to unity in the near term.  相似文献   

5.
Minimizing the future impacts of climate change requires reducing the greenhouse gas (GHG) load in the atmosphere. Anthropogenic emissions include many types of GHG’s as well as particulates such as black carbon and sulfate aerosols, each of which has a different effect on the atmosphere, and a different atmospheric lifetime. Several recent studies have advocated for the importance of short timescales when comparing the climate impact of different climate pollutants, placing a high relative value on short-lived pollutants, such as methane (CH4) and black carbon (BC) versus carbon dioxide (CO2). These studies have generated confusion over how to value changes in temperature that occur over short versus long timescales. We show the temperature changes that result from exchanging CO2 for CH4 using a variety of commonly suggested metrics to illustrate the trade-offs involved in potential carbon trading mechanisms that place a high value on CH4 emissions. Reducing CH4 emissions today would lead to a climate cooling of approximately ~0.5 °C, but this value will not change greatly if we delay reducing CH4 emissions by years or decades. This is not true for CO2, for which the climate is influenced by cumulative emissions. Any delay in reducing CO2 emissions is likely to lead to higher cumulative emissions, and more warming. The exact warming resulting from this delay depends on the trajectory of future CO2 emissions but using one business-as usual-projection we estimate an increase of 3/4 °C for every 15-year delay in CO2 mitigation. Overvaluing the influence of CH4 emissions on climate could easily result in our “locking” the earth into a warmer temperature trajectory, one that is temporarily masked by the short-term cooling effects of the CH4 reductions, but then persists for many generations.  相似文献   

6.
Uncertainties in climate stabilization   总被引：1，自引：1，他引：0  
The atmospheric composition, temperature and sea level implications out to 2300 of new reference and cost-optimized stabilization emissions scenarios produced using three different Integrated Assessment (IA) models are described and assessed. Stabilization is defined in terms of radiative forcing targets for the sum of gases potentially controlled under the Kyoto Protocol. For the most stringent stabilization case (“Level 1” with CO2 concentration stabilizing at about 450 ppm), peak CO2 emissions occur close to today, implying (in the absence of a substantial CO2 concentration overshoot) a need for immediate CO2 emissions abatement if we wish to stabilize at this level. In the extended reference case, CO2 stabilizes at about 1,000 ppm in 2200—but even to achieve this target requires large and rapid CO2 emissions reductions over the twenty-second century. Future temperature changes for the Level 1 stabilization case differ noticeably between the IA models even when a common set of climate model parameters is used (largely a result of different assumptions for non-Kyoto gases). For the Level 1 stabilization case, there is a probability of approximately 50% that warming from pre-industrial times will be less than (or more than) 2°C. For one of the IA models, warming in the Level 1 case is actually greater out to 2040 than in the reference case due to the effect of decreasing SO2 emissions that occur as a side effect of the policy-driven reduction in CO2 emissions. This effect is less noticeable for the other stabilization cases, but still leads to policies having virtually no effect on global-mean temperatures out to around 2060. Sea level rise uncertainties are very large. For example, for the Level 1 stabilization case, increases range from 8 to 120 cm for changes over 2000 to 2300.  相似文献   

7.
Political leaders in numerous nations argue for an upper limit of the global average surface temperature of 2 K above the pre-industrial level, in order to attempt to avoid the most serious impacts of climate change. This paper analyzes what this limit implies in terms of radiative forcing, emissions pathways and abatement costs, for a range of assumptions on rate of ocean heat uptake and climate sensitivity. The primary aim is to analyze the importance of ocean heat uptake for radiative forcing pathways that temporarily overshoot the long-run stabilization forcing, yet keep the temperature increase at or below the 2 K limit. In order to generate such pathways, an integrated climate-economy model, MiMiC, is used, in which the emissions pathways generated represent the least-cost solution of stabilizing the global average surface temperature at 2 K above the pre-industrial level. We find that the level of overshoot can be substantial. For example, the level of overshoot in radiative forcing in 2100 ranges from about 0.2 to 1 W/m2, where the value depends strongly and positively on the effective diffusivity of heat in the oceans. Measured in relative terms, the level of radiative forcing overshoot above its longrun equilibrium level in 2100 is 20% to 60% for high values of climate sensitivity (i.e., about 4.5 K) and 8% to 30% for low values of climate sensitivity (i.e., about 2 K). In addition, for cases in which the radiative forcing level can be directly stabilized at the equilibrium level associated with a specific climate sensitivity and the 2 K limit, the net present value abatement cost is roughly cut by half if overshoot pathways are considered instead of stabilization of radiative forcing at the equilibrium level without an overshoot.  相似文献   

8.
Combining policies to remove carbon dioxide (CO2) from the atmosphere with policies to reduce emissions could decrease CO2 concentrations faster than possible via natural processes. We model the optimal selection of a dynamic portfolio of abatement, research and development (R&D), and negative emission policies under an exogenous CO2 constraint and with stochastic technological change. We find that near-term abatement is not sensitive to the availability of R&D policies, but the anticipated availability of negative emission strategies can reduce the near-term abatement optimally undertaken to meet 2°C temperature limits. Further, planning to deploy negative emission technologies shifts optimal R&D funding from ??carbon-free?? technologies into ??emission intensity?? technologies. Making negative emission strategies available enables an 80% reduction in the cost of keeping year 2100 CO2 concentrations near their current level. However, negative emission strategies are less important if the possibility of tipping points rules out using late-century net negative emissions to temporarily overshoot the CO2 constraint earlier in the century.  相似文献   

9.
Combining bioenergy and carbon dioxide (CO2) capture and storage (CCS) technologies (BECCS) has the potential to remove CO2 from the atmosphere while producing useful energy. BECCS has played a central role in scenarios that reduce climate forcing to low levels such as 2.6 Wm?2. In this paper we consider whether BECCS is essential to limiting radiative forcing (RF) to 2.6 Wm?2 by 2100 using the Global Change Assessment Model, a closely coupled model of biogeophysical and human Earth systems. We show that BECCS can potentially reduce the cost of limiting RF to 2.6 Wm?2 by 2100 but that a variety of technology combinations that do not include BECCS can also achieve this goal, under appropriate emissions mitigation policies. We note that with appropriate supporting land-use policies terrestrial sequestration could deliver carbon storage ranging from 200 to 700 PgCO2-equiavalent over the 21st century. We explore substantial delays in participation by some geopolitical regions. We find that the value of BECCS is substantially higher under delay and that delay results in higher transient RF and climate change. However, when major regions postponed mitigation indefinitely, it was impossible to return RF to 2.6 Wm?2 by 2100. Neither finite land resources nor finite potential geologic storage capacity represented a meaningful technical limit on the ability of BECCS to contribute to emissions mitigation in the numerical experiments reported in this paper.  相似文献   

10.
A fast simple climate modelling approach is developed for predicting and helping to understand general circulation model (GCM) simulations. We show that the simple model reproduces the GCM results accurately, for global mean surface air temperature change and global-mean heat uptake projections from 9 GCMs in the fifth coupled model inter-comparison project (CMIP5). This implies that understanding gained from idealised CO2 step experiments is applicable to policy-relevant scenario projections. Our approach is conceptually simple. It works by using the climate response to a CO2 step change taken directly from a GCM experiment. With radiative forcing from non-CO2 constituents obtained by adapting the Forster and Taylor method, we use our method to estimate results for CMIP5 representative concentration pathway (RCP) experiments for cases not run by the GCMs. We estimate differences between pairs of RCPs rather than RCP anomalies relative to the pre-industrial state. This gives better results because it makes greater use of available GCM projections. The GCMs exhibit differences in radiative forcing, which we incorporate in the simple model. We analyse the thus-completed ensemble of RCP projections. The ensemble mean changes between 1986–2005 and 2080–2099 for global temperature (heat uptake) are, for RCP8.5: 3.8 K (2.3 × 1024 J); for RCP6.0: 2.3 K (1.6 × 1024 J); for RCP4.5: 2.0 K (1.6 × 1024 J); for RCP2.6: 1.1 K (1.3 × 1024 J). The relative spread (standard deviation/ensemble mean) for these scenarios is around 0.2 and 0.15 for temperature and heat uptake respectively. We quantify the relative effect of mitigation action, through reduced emissions, via the time-dependent ratios (change in RCPx)/(change in RCP8.5), using changes with respect to pre-industrial conditions. We find that the effects of mitigation on global-mean temperature change and heat uptake are very similar across these different GCMs.  相似文献   

11.
In this paper we study the impact of alternative metrics on short- and long-term multi-gas emission reduction strategies and the associated global and regional economic costs and emissions budgets. We compare global warming potentials with three different time horizons (20, 100, 500 years), global temperature change potential and global cost potentials with and without temperature overshoot. We find that the choice of metric has a relatively small impact on the CO2 budget compatible with the 2° target and therefore on global costs. However it substantially influences mid-term emission levels of CH4, which may either rise or decline in the next decades as compared to today’s levels. Though CO2 budgets are not affected much, we find changes in CO2 prices which substantially affect regional costs. Lower CO2 prices lead to more fossil fuel use and therefore higher resource prices on the global market. This increases profits of fossil-fuel exporters. Due to the different weights of non-CO2 emissions associated with different metrics, there are large differences in nominal CO2 equivalent budgets, which do not necessarily imply large differences in the budgets of the single gases. This may induce large shifts in emission permit trade, especially in regions where agriculture with its high associated CH4 emissions plays an important role. Furthermore it makes it important to determine CO2 equivalence budgets with respect to the chosen metric. Our results suggest that for limiting warming to 2 °C in 2100, the currently used GWP100 performs well in terms of global mitigation costs despite its conceptual simplicity.  相似文献   

12.
Metrics are often used to compare the climate impacts of emissions from various sources, sectors or nations. These are usually based on global-mean input, and so there is the potential that important information on smaller scales is lost. Assuming a non-linear dependence of the climate impact on local surface temperature change, we explore the loss of information about regional variability that results from using global-mean input in the specific case of heterogeneous changes in ozone, methane and aerosol concentrations resulting from emissions from road traffic, aviation and shipping. Results from equilibrium simulations with two general circulation models are used. An alternative metric for capturing the regional climate impacts is investigated. We find that the application of a metric that is first calculated locally and then averaged globally captures a more complete and informative signal of climate impact than one that uses global-mean input. The loss of information when heterogeneity is ignored is largest in the case of aviation. Further investigation of the spatial distribution of temperature change indicates that although the pattern of temperature response does not closely match the pattern of the forcing, the forcing pattern still influences the response pattern on a hemispheric scale. When the short-lived transport forcing is superimposed on present-day anthropogenic CO2 forcing, the heterogeneity in the temperature response to CO2 dominates. This suggests that the importance of including regional climate impacts in global metrics depends on whether small sectors are considered in isolation or as part of the overall climate change.  相似文献   

13.
Climate is simulated for reference and mitigation emissions scenarios from Integrated Assessment Models using the Bern2.5CC carbon cycle–climate model. Mitigation options encompass all major radiative forcing agents. Temperature change is attributed to forcings using an impulse–response substitute of Bern2.5CC. The contribution of CO2 to global warming increases over the century in all scenarios. Non-CO2 mitigation measures add to the abatement of global warming. The share of mitigation carried by CO2, however, increases when radiative forcing targets are lowered, and increases after 2000 in all mitigation scenarios. Thus, non-CO2 mitigation is limited and net CO2 emissions must eventually subside. Mitigation rapidly reduces the sulfate aerosol loading and associated cooling, partly masking Greenhouse Gas mitigation over the coming decades. A profound effect of mitigation on CO2 concentration, radiative forcing, temperatures and the rate of climate change emerges in the second half of the century.  相似文献   

14.
100-year Global Warming Potentials (GWPs) are used almost universally to compare emissions of greenhouse gases in national inventories and reduction targets. GWPs have been criticised on several grounds, but little work has been done to determine global mitigation costs under alternative physics-based metrics . We used the integrated assessment model MESSAGE to compare emission pathways and abatement costs for fixed and time-dependent variants of the Global Temperature Change Potential (GTP) with those based on GWPs, for a policy goal of limiting the radiative forcing to a specified level in the year 2100. We find that fixed 100-year GTPs would increase global abatement costs (discounted and aggregated over the 21st century) under this policy goal by 5–20 % relative to 100-year GWPs, whereas time-varying GTPs would reduce costs by about 5 %. These cost differences are smaller than differences arising from alternative assumptions regarding agricultural mitigation potential and much smaller than those arising from alternative radiative forcing targets. Using the land-use model GLOBIOM, we show that alternative metrics affect food production differently in different world regions depending on regional characteristics of future land-use change to meet growing food demand. We conclude that under scenarios of complete participation, the choice of metric has a limited impact on global abatement costs but could be important for the political economy of regional and sectoral participation in collective mitigation efforts, in particular changing costs and gains over time for agriculture and energy-intensive sectors.  相似文献   

15.
This paper synthesizes results of the multi-model Energy Modeling Forum 27 (EMF27) with a focus on climate policy scenarios. The study included two harmonized long-term climate targets of 450 ppm CO2-e (enforced in 2100) and 550 pm CO2-e (not-to-exceed) as well as two more fragmented policies based on national and regional emissions targets. Stabilizing atmospheric GHG concentrations at 450 and 550 ppm CO2-e requires a dramatic reduction of carbon emissions compared to baseline levels. Mitigation pathways for the 450 CO2-e target are largely overlapping with the 550 CO2-e pathways in the first half of the century, and the lower level is achieved through rapid reductions in atmospheric concentrations in the second half of the century aided by negative anthropogenic carbon flows. A fragmented scenario designed to extrapolate current levels of ambition into the future falls short of the emissions reductions required under the harmonized targets. In a more aggressive scenario intended to capture a break from observed levels of stringency, emissions are still somewhat higher in the second half due to unabated emissions from non-participating countries, emphasizing that a phase-out of global emissions in the long term can only be reached with full global participation. A key finding is that a large range of energy-related CO2 emissions can be compatible with a given long-term target, depending on assumptions about carbon cycle response, non-CO2 and land use CO2 emissions abatement, partly explaining the spread in mitigation costs.  相似文献   

16.
Today's climate policy is based on the assumption that the location of emissions reductions has no impact on the overall climate effect. However, this may not be the case since reductions of greenhouse gases generally will lead to changes in emissions of short-lived gases and aerosols. Abatement measures may be primarily targeted at reducing CO2, but may also simultaneously reduce emissions of NOx, CO, CH4 and SO2 and aerosols. Emissions of these species may cause significant additional radiative forcing. We have used a global 3-D chemical transport model and a radiative transfer model to study the impact on climate in terms of radiative forcing for a realistic change in location of the emissions from large-scale sources. Based on an assumed 10% reduction in CO2 emissions, reductions in the emissions of other species have been estimated. Climate impact for the SRES A1B scenario is compared to two reduction cases, with the main focus on a case with emission reductions between 2010 and 2030, but also a case with sustained emission reductions. The emission reductions are applied to four different regions (Europe, China, South Asia, and South America). In terms of integrated radiative forcing (over 100 yr), the total effect (including only the direct effect of aerosols) is always smaller than for CO2 alone. Large variations between the regions are found (53–86% of the CO2 effect). Inclusion of the indirect effects of sulphate aerosols reduces the net effect of measures towards zero. The global temperature responses, calculated with a simple energy balance model, show an initial additional warming of different magnitude between the regions followed by a more uniform reduction in the warming later. A major part of the regional differences can be attributed to differences related to aerosols, while ozone and changes in methane lifetime make relatively small contributions. Emission reductions in a different sector (e.g. transportation instead of large-scale sources) might change this conclusion since the NOx to SO2 ratio in the emissions is significantly higher for transportation than for large-scale sources. The total climate effect of abatement measures thus depends on (i) which gases and aerosols are affected by the measure, (ii) the lifetime of the measure implemented, (iii) time horizon over which the effects are considered, and (iv) the chemical, physical and meteorological conditions in the region. There are important policy implications of the results. Equal effects of a measure cannot be assumed if the measure is implemented in a different region and if several gases are affected. Thus, the design of emission reduction measures should be considered thoroughly before implementation.  相似文献   

17.
We use the global atmospheric GCM aerosol model ECHAM5-HAM to asses possible impacts of future air pollution mitigation strategies on climate. Air quality control strategies focus on the reduction of aerosol emissions. Here we investigate the extreme case of a maximum feasible end-of-pipe abatement of aerosols in the near term future (2030) in combination with increasing greenhouse gas (GHG) concentrations. The temperature response of increasing GHG concentrations and reduced aerosol emissions leads to a global annual mean equilibrium temperature response of 2.18 K. When aerosols are maximally abated only in the Industry and Powerplant sector, while other sectors stay with currently enforced regulations, the temperature response is 1.89 K. A maximum feasible abatement applied in the Domestic and Transport sector, while other sectors remain with the current legislation, leads to a temperature response of 1.39 K. Increasing GHG concentrations alone lead to a temperature response of 1.20 K. We also simulate 2–5% increases in global mean precipitation among all scenarios considered, and the hydrological sensitivity is found to be significantly higher for aerosols than for GHGs. Our study, thus highlights the huge potential impact of future air pollution mitigation strategies on climate and supports the need for urgent GHG emission reductions. GHG and aerosol forcings are not independent as both affect and are influenced by changes in the hydrological cycle. However, within the given range of changes in aerosol emissions and GHG concentrations considered in this study, the climate response towards increasing GHG concentrations and decreasing aerosols emissions is additive.  相似文献   

18.
The global three-dimensional Lagrangian chemistry-transport model STOCHEM has been used to follow changes in the tropospheric distributions of methane CH4 and ozone O3 following the emission of pulses of the oxides of nitrogen NO x . Month-long emission pulses of NO x produce deficits in CH4 mixing ratios that bring about negative radiative forcing (climate cooling) and decay away with e-folding times of 10–15 years. They also produce short-term excesses in O3 mixing ratios that bring about positive radiative forcing (climate warming) that decay over several months to produce deficits, with their attendant negative radiative forcing (climate cooling) that decays away in step with the CH4 deficits. Total time-integrated net radiative forcing is markedly influenced by cancellation between the negative CH4 and long-term O3 contributions and the positive short-term O3 contribution to leave a small negative residual. Consequently, total net radiative forcing from NO x emission pulses and the global warming potentials derived from them, show a strong dependence on the magnitudes, locations and seasons of the emissions. These dependences are illustrated using the Asian continent as an example and demonstrate that there is no simple robust relationship between continental-scale NO x emissions and globally-integrated radiative forcing. We find that the magnitude of the time-integrated radiative forcing from NO x -driven CH4 depletion tends to approach and outweigh that from ozone enhancement, leaving net time-integrated radiative forcings and global warming potentials negative (climate cooling) in contrast to the situation for aircraft NO x (climate warming). Control of man-made surface NO x emissions alone may lead to positive radiative forcing (climate warming).  相似文献   

19.
The economics (or lack thereof) of aerosol geoengineering   总被引：1，自引：0，他引：1  
Anthropogenic greenhouse gas emissions are changing the Earth’s climate and impose substantial risks for current and future generations. What are scientifically sound, economically viable, and ethically defendable strategies to manage these climate risks? Ratified international agreements call for a reduction of greenhouse gas emissions to avoid dangerous anthropogenic interference with the climate system. Recent proposals, however, call for a different approach: to geoengineer climate by injecting aerosol precursors into the stratosphere. Published economic studies typically neglect the risks of aerosol geoengineering due to (i) the potential for a failure to sustain the aerosol forcing and (ii) the negative impacts associated with the aerosol forcing. Here we use a simple integrated assessment model of climate change to analyze potential economic impacts of aerosol geoengineering strategies over a wide range of uncertain parameters such as climate sensitivity, the economic damages due to climate change, and the economic damages due to aerosol geoengineering forcing. The simplicity of the model provides the advantages of parsimony and transparency, but it also imposes severe caveats on the interpretation of the results. For example, the analysis is based on a globally aggregated model and is hence silent on intragenerational distribution of costs and benefits. In addition, the analysis neglects the effects of learning and has a very simplistic representation of climate change impacts. Our analysis suggests three main conclusions. First, substituting aerosol geoengineering for CO2 abatement can be an economically ineffective strategy. One key to this finding is that a failure to sustain the aerosol forcing can lead to sizeable and abrupt climatic changes. The monetary damages due to such a discontinuous aerosol geoengineering can dominate the cost-benefit analysis because the monetary damages of climate change are expected to increase with the rate of change. Second, the relative contribution of aerosol geoengineering to an economically optimal portfolio hinges critically on, thus far, deeply uncertain estimates of the damages due to aerosol forcing. Even if we assume that aerosol forcing could be deployed continuously, the aerosol geoengineering does not considerably displace CO2 abatement in the simple economic optimal growth model until the damages due to the aerosol forcing are rather low. Third, substituting aerosol geoengineering for greenhouse gas emission abatement can fail an ethical test regarding intergenerational justice. Substituting aerosol geoengineering for greenhouse gas emissions abatements constitutes a conscious risk transfer to future generations, in violation of principles of intergenerational justice which demands that present generations should not create benefits for themselves in exchange for burdens on future generations.  相似文献   

20.
Methane emissions contribute to global baseline surface ozone concentrations; therefore reducing methane to address climate change has significant co-benefits for air quality and human health. We analyze the costs of reducing methane from 2005 to 2030, as might be motivated to reduce climate forcing, and the resulting benefits from lower surface ozone to 2060. We construct three plausible scenarios of methane emission reductions, relative to a base scenario, ranging from 75 to 180 Mton CH4 yr?1 decreased in 2030. Using compilations of the global availability of methane emission reductions, the least aggressive scenario (A) does not incur any positive marginal costs to 2030, while the most aggressive (C) requires discovery of new methane abatement technologies. The present value of implementation costs for Scenario B are nearly equal to Scenario A, as it implements cost-saving options more quickly, even though it adopts positive cost measures. We estimate the avoided premature human mortalities due to surface ozone decreases by combining transient full-chemistry simulations of these scenarios in a global atmospheric chemical transport model, with concentration-mortality relationships from a short-term epidemiologic study and projected global population. An estimated 38,000 premature mortalities are avoided globally in 2030 under Scenario B. As benefits of methane reduction are positive but costs are negative for Scenario A, it is justified regardless of how avoided mortalities are valued. The incremental benefits of Scenario B also far outweigh the incremental costs. Scenario C has incremental costs that roughly equal benefits, only when technological learning is assumed. Benefits within industrialized nations alone also exceed costs in Scenarios A and B, assuming that the lowest-cost emission reductions, including those in developing nations, are implemented. Monetized co-benefits of methane mitigation for human health are estimated to be $13–17 per ton CO2eq, with a wider range possible under alternative assumptions. Methane mitigation can be a cost-effective means of long-term and international air quality management, with concurrent benefits for climate.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号