Climatic impact of carbon sequestration through reforestation

《京都议定书》允许通过重新植树造林创造碳汇来抵消化石燃料使用产生的二氧化碳排放。这是允许的，因为排放之后迅速吸收二氧化碳，或者不排放和吸收，对大气中的二氧化碳具有相同的影响。然而，由于植树造林引起地表属性(即地表反照率或反射率)的变化，对气候的影响是不同的。特别是，许多C汇活动可能会对气候产生直接的变暖效应，同时从大气中清除二氧化碳。由于与碳循环其他部分的相互作用，创建碳汇对二氧化碳的影响随着时间的推移而减少，而只要重新造林持续下去，重新造林引起的地表反射率变化所产生的辐射效应就会一直存在。到目前为止，加拿大的政策分析侧重于加拿大和中国(加拿大可能参与并获得一些信贷)可能重新造林的问题。加拿大和中国的重新造林对气候的净气候影响还没有得到严格的评估，尽管已经评估了可能产生的潜在碳汇。拟议研究的目的是评估净影响及其随时间的变化情况。拟议的研究将包括：(I)在加拿大和中国用于评估碳固存潜力的特定地理植被/碳储存模式中增加辐射转移计算能力；(Ii)在植被模式之上增加一个具有辐射转移计算的大气柱；(Iii)将上述模式的地理分布实施与简单的气候和碳循环模式相结合，以评估碳固存与碳循环其他部分的相互作用；以及(4)使用最先进的大气环流模式，通过云层的变化来评估植树造林的间接辐射效应。

The Kyoto Protocol allows for emissions of CO2 from fossil fuel use to be offset through the creation of carbon sinks through reforestation. This is allowed because emission followed by prompt absorption of CO2, or no emission and absorption, have identical effects on atmospheric CO2. However, the climatic impacts are not the same because of alterations in the surface properties (namely, the surface albedo or reflectivity) through reforestation. In particular, many C-sink activities likely have a direct warming effect on climate, while removing CO2 from the atmosphere. The impact on CO2 of creating a C sink decreases over time due to interactions with other parts of the carbon cycle, while the radiative effect through alterations in the surface  reflectivity due to reforestation persist as long as the reforestation persists. Canadian policy analysis to date has focused on possible reforestation in Canada and in China (for which Canada might participate and receive some credit). The net climatic impact of reforestation in Canada and in China on climate has not been rigorously assessed, although the potential C sink that could be created has been assessed. The purpose of the proposed research is to provide an assessment of net effects and how they would change over time. The proposed research will consist of (i) adding the capability of radiative transfer calculation to a geographically-specific vegetation/C-storage model that has been used in Canada and in China to assess the potential for C sequestration; (ii) to add an atmosphere column with radiative transfer calculations over top of the vegetation model; (iii) to couple a geographically-distributed implementation of the above models to simple climate and carbon-cycle models so as to assess the interactions of C sequestration with other parts of the carbon cycle; and (iv) to use a state-of-the-art atmospheric general circulation model to assess indirect radiative effects of reforestation through changes in clouds.