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Impact of CO2 concentration changes on the biosphere-atmosphere system of West Africa

机译：CO2浓度变化对西非生物圈-大气系统的影响

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Vegetation dynamics plays a critical role in causing the decadal variability of precipitation over the Sahel region of West Africa. However, the potential impact of changes in CO2 concentration on vegetation dynamics and precipitation variability of this region has not been addressed by previous studies. In this paper, we explore the role of CO2 concentration in the regional climate system of West Africa using a zonally symmetric, synchronously coupled biosphere-atmosphere model. We first document the response of precipitation and vegetation to incremental changes of CO2 concentration; the impact of CO2 concentration on the variability of the regional biosphere-atmosphere system is then addressed using the second half of the twentieth century as an example. An increase of CO2 concentration causes the regional biosphere-atmosphere system to become wetter and greener, with the radiative effect of CO2 and improved plant-water relation dominant in the Sahelian grassland region and the direct enhancement of leaf carbon assimilation dominant in the tree-covered region to the south. Driven by the observed sea surface temperature (SST) of the tropical Atlantic Ocean during the period 1950-97 and with CO2 concentration prescribed at a pre-industrial level 300ppmv, the model simulates a persistent Sahel drought during the period of 1960s-1990s. The simulated drought takes place in the form of a transition of the coupled biosphere-atmosphere system from a wet/green regime in the 1950s to a dry/barren regime after the 1960s. This climate transition is triggered by SST forcing and materialized through vegetation-climate interactions. The same SST forcing does not produce such a persistent drought when a constant modem CO2 concentration of 350ppmv is specified, indicating that the biosphere-atmosphere system at higher CO2 level is more resilient to drought-inducing external forcings. This finding suggests that the regional climate in Sahel, which tends to alternate between dry and wet spells, may experience longer (or more frequent) wet episodes and shorter (or less frequent) dry episodes in the future than in the past. Our study has significant implications regarding the impact of climate change on regional socio-economic development. [References: 54]
机译：植被动力学在导致西非萨赫勒地区降水的年代际变化中起关键作用。但是，以前的研究并未解决二氧化碳浓度变化对该地区植被动态和降水变化的潜在影响。在本文中，我们使用区域对称，同步耦合的生物圈-大气模型探索了西非区域气候系统中二氧化碳浓度的作用。我们首先记录了降水和植被对CO2浓度递增变化的响应。然后以20世纪下半叶为例，探讨了CO2浓度对区域生物圈-大气系统变异性的影响。 CO2浓度的增加导致区域生物圈-大气系统变得更湿和更绿，在萨赫勒草原地区占主导地位的是CO2的辐射效应和改善的植物与水的关系，而在树木覆盖的树木中占主导地位的叶碳同化作用的直接增强南部地区。该模型由1950-97年间热带大西洋的观测海表温度（SST）驱动，并且在工业化前水平规定的CO2浓度为300ppmv的情况下，该模型模拟了1960-1990年代期间持续的萨赫勒干旱。模拟干旱以生物圈-大气耦合系统从1950年代的湿/绿状态过渡到1960年代后的干/荒状态的形式发生。这种气候转变是由SST强迫触发的，并通过植被-气候相互作用而得以实现。当指定恒定的现代CO2浓度为350ppmv时，相同的SST强迫不会产生这样的持续干旱，这表明较高CO2水平的生物圈-大气系统对干旱引起的外部强迫更具抵抗力。这一发现表明，萨赫勒地区的气候倾向于在干湿交替之间交替变化，与过去相比，未来可能会经历更长（或更频繁）的湿气发作和更短（或更不频繁）的干旱发作。我们的研究对气候变化对区域社会经济发展的影响具有重要意义。 [参考：54]

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