Drier summers cancel out the CO2 uptake enhancement induced by warmer springs
Drier summers cancel out the CO2 uptake enhancement induced by warmer springs
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DOI：
10.1073/pnas.0501647102
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发表时间：
2005-08-02
影响因子：
11.1
通讯作者：
Fung, I
中科院分区：
文献类型：
--
作者：
Angert, A;Biraud, S;Fung, I
以前的研究报告指出，根据卫星观测，北方陆地植被的光合作用活动有所增加。在此期间，北方半球大气中每年减少的二氧化碳的季节性循环幅度（生物圈活动的一个指标）也有所增加。我们发现，通过分析每年的趋势CO2记录的季节，初夏（6月）CO2浓度确实从1985年到1991年下降，他们继续减少，从1994年到2002年。这种减少表明春季净二氧化碳吸收加速。然而，在夏末的CO2最低浓度（净生长季节吸收的指标）自1994年以来没有表现出积极的趋势，表明在夏季较低的CO2净吸收抵消了在春季增强吸收。使用最近的卫星归一化差异植被指数数据集和气候数据，我们表明，这种较低的夏季吸收可能是在中高纬度地区的炎热和干燥的夏季的结果，表明气候变暖并不一定导致较高的CO2生长季节吸收，即使在高纬度生态系统被认为是温度限制。
An increase in photosynthetic activity of the northern hemisphere terrestrial vegetation, as derived from satellite observations, has been reported in previous studies. The amplitude of the seasonal cycle of the annually detrended atmospheric CO2 in the northern hemisphere (an indicator of biospheric activity) also increased during that period. We found, by analyzing the annually detrended CO2 record by season, that early summer (June) CO2 concentrations indeed decreased from 1985 to 1991, and they have continued to decrease from 1994 up to 2002. This decrease indicates accelerating springtime net CO2 uptake. However, the CO2 minimum concentration in late summer (an indicator of net growing-season uptake) showed no positive trend since 1994, indicating that lower net CO2 uptake during summer cancelled out the enhanced uptake during spring. Using a recent satellite normalized difference vegetation index data set and climate data, we show that this lower summer uptake is probably the result of hotter and drier summers in both mid and high latitudes, demonstrating that a warming climate does not necessarily lead to higher CO2 growing-season uptake, even in high-latitude ecosystems that are considered to be temperature limited.