| In the trend of global warming, the increase of greenhouse gases concentrations has a very important influence on the ground the energy balance and global climate change, which has aroused widespread concern. In order to ease the global warming, we must limit the emissions of these gases. Thus, these long-lived greenhouse gases these gases that mainly contribute to global warming, such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), et al., are included in the "Kyoto Protocol" and are required to control their emissions. Based on the previous work, this study will apply the GWP, GTP and other measurement methods to study two important long-lived greenhouse gases:methane (CH4) and nitrous oxide (N2O), calculating their radiative forcing, as well as GWP and GTP in the next 10 to 500 years. And the above different methods of measurement will be compared and evaluated.Using 998-band long-wave radiation transfer model based on k-distribution method and two sets data of atmospheric profiles, this study calculates the global mean instantaneous radiation efficiency and stratospheric adjusted radiation efficiency of CO2, CH4 and N2O under the clear sky as well as ones under the cloudy sky. It can be obtained from results as follows. Firstly, after adjustment of stratospheric temperature, the radiation efficiencies of CO2, CH4 and N2O are all relatively reduced; this depends on the negative gain of the net radiation fluxes of the tropopause affected by the temperature profile after the stratospheric temperature adjustment. Secondly, compared with the IPCC (2007) results, the radiation efficiencies of CO2, CH4 and N2O before the atmospheric lifetime adjustment are all relatively higher. Through analysis, the cause attributing to the above phenomenon may be:the updated data of greenhouse gases concentration adopted in this paper, which is more than the data used in IPCC (2007), and the effect from the discrepancy between different models schemes.Moreover, according to the newly calculated radiation efficiencies of CO2, CH4 and N2O, the GWP and GTP in the next 20,100,500 years are computed, and the changes of surface temperature in the next 500 years by pulse emission and sustain emission are calculated. The results show that:Firstly, compared with the same amount of gas under pulse emission, the values of GWP of CH4 and N2O are both significantly larger than ones of GTPP. This is because that, compared to some gas like SF6, which can stay in the atmosphere for thousands or even millions of years, the atmospheric lifetime of CH4 and N2O are relatively shorter. So the effects on climate change by the pulse emissions are greatly overestimated through their GWP values. Secondly, by contrasting the values of GWP and GTPS, it can be found that the difference between them is smaller than the difference between the values of GTPP and GWP of the same gas during the same period. And with the expansion of time range, the difference between GTPS and GWP decreases gradually.In reality, CH4, N2O emissions are increasing constantly, and GTPS are just used to consider the relative impact on surface temperature by sustaining emissions. By comparison and analysis, it can be acknowledged that, GTPS is the optimum solution among all the methods of evaluating the impact on global climate by emissions of a certain kind of long-lived greenhouse gases like CH4 and N2O. So using this method can provide good technical support for the nations for policy-making and industrial adjustment aimed to the very industry and agriculture which now emit these greenhouse gases continuously.
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