An assessment of the carbon balance of Arctic tundra: comparisons among observations, process models, and atmospheric inversions
An assessment of the carbon balance of Arctic tundra: comparisons among observations, process models, and atmospheric inversions
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DOI：
10.5194/bg-9-3185-2012
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发表时间：
2012-01-01
期刊：
影响因子：
4.9
通讯作者：
Yi, Y.
中科院分区：
文献类型：
--
作者：
McGuire, A. D.;Christensen, T. R.;Yi, Y.
虽然北极苔原估计仅覆盖全球陆地表面的8%，但目前储存在苔原土壤中的巨大且潜在不稳定的碳库在气候变暖的情况下有可能产生大量碳排放。这些以二氧化碳和甲烷两种形式存在的具有辐射活性的温室气体的排放可能加剧全球变暖。考虑到这些生态系统对气候变化的潜在敏感性，以及北极在下一个世纪将经历明显变暖的预期，评估冻原地区碳交换的响应是否可能增强或减轻变暖是很重要的。在这项研究中，我们比较了1990年和2006年之间的观测，区域和全球应用的过程为基础的陆地生物圈模型，大气反演模型之间的北极苔原碳交换的分析。通量观测和反演模型的综合表明，北极苔原和大气之间的CO2年交换有很大的不确定性，不能从中性平衡区分。基于过程的模型模拟的合奏的平均估计表明，北极苔原作为大气CO2的汇在最近几十年，但根据不确定性的估计，它不能确定与信心，这些生态系统是否代表一个弱或强汇。与20世纪90年代相比，21世纪初苔原的温度上升了0.6摄氏度。与1990年代相比，观测、基于过程的模型和反演模型的中心估计值都确定了2000年代更强的汇。一些过程模型表明，这是因为净初级生产增加更多的响应变暖比异养呼吸。同样，基于区域过程的模型的观测和应用表明，北极苔原的甲烷排放量从1990年代到2000年代有所增加，这是因为甲烷排放量对温度升高的敏感性。根据我们对观测、基于过程的模型和反演模型的估计的分析，我们估计，北极苔原是大气CO2的汇，年平均为110 Tg C（-1）（汇为291 Tg C yr（-1）与源为80 Tg C yr（-1）之间的不确定性）和大气中CH 4源为19 Tg C yr（-1）（8和29 Tg C yr（-1）来源之间的不确定性）。在这项研究中进行的一套分析表明，重要的是要减少观测，基于过程的模型和反演的不确定性，以更好地了解北极苔原影响大气CO2和CH 4浓度的程度。减少不确定性可通过以下方式实现：（1）战略性地设置更多的CO2和CH 4监测站，以减少反演中的不确定性，（2）改进CO2和CH 4交换地面测量观测网络，以了解对干扰的反应以及气候和水文变异梯度之间的交换，以及（3）将信息从增强的观测网络有效地转移到基于过程的模式中，以改进对北极苔原到大气的CO2和CH 4交换的模拟。
Although Arctic tundra has been estimated to cover only 8% of the global land surface, the large and potentially labile carbon pools currently stored in tundra soils have the potential for large emissions of carbon (C) under a warming climate. These emissions as radiatively active greenhouse gases in the form of both CO2 and CH4 could amplify global warming. Given the potential sensitivity of these ecosystems to climate change and the expectation that the Arctic will experience appreciable warming over the next century, it is important to assess whether responses of C exchange in tundra regions are likely to enhance or mitigate warming. In this study we compared analyses of C exchange of Arctic tundra between 1990 and 2006 among observations, regional and global applications of process-based terrestrial biosphere models, and atmospheric inversion models. Syntheses of flux observations and inversion models indicate that the annual exchange of CO2 between Arctic tundra and the atmosphere has large uncertainties that cannot be distinguished from neutral balance. The mean estimate from an ensemble of process-based model simulations suggests that Arctic tundra has acted as a sink for atmospheric CO2 in recent decades, but based on the uncertainty estimates it cannot be determined with confidence whether these ecosystems represent a weak or a strong sink. Tundra was 0.6 A degrees C warmer in the 2000s compared to the 1990s. The central estimates of the observations, process-based models, and inversion models each identify stronger sinks in the 2000s compared with the 1990s. Some of the process models indicate that this occurred because net primary production increased more in response to warming than heterotrophic respiration. Similarly, the observations and the applications of regional process-based models suggest that CH4 emissions from Arctic tundra have increased from the 1990s to 2000s because of the sensitivity of CH4 emissions to warmer temperatures. Based on our analyses of the estimates from observations, process-based models, and inversion models, we estimate that Arctic tundra was a sink for atmospheric CO2 of 110 Tg C yr(-1) (uncertainty between a sink of 291 Tg C yr(-1) and a source of 80 Tg C yr(-1)) and a source of CH4 to the atmosphere of 19 Tg C yr(-1) (uncertainty between sources of 8 and 29 Tg C yr(-1)). The suite of analyses conducted in this study indicate that it is important to reduce uncertainties in the observations, process-based models, and inversions in order to better understand the degree to which Arctic tundra is influencing atmospheric CO2 and CH4 concentrations. The reduction of uncertainties can be accomplished through (1) the strategic placement of more CO2 and CH4 monitoring stations to reduce uncertainties in inversions, (2) improved observation networks of ground-based measurements of CO2 and CH4 exchange to understand exchange in response to disturbance and across gradients of climatic and hydrological variability, and (3) the effective transfer of information from enhanced observation networks into process-based models to improve the simulation of CO2 and CH4 exchange from Arctic tundra to the atmosphere.