The climate mitigation target of limiting the temperature increase below 2 °C above the pre-industrial levels requires the efforts from all countries. Tracking the trajectory of the land carbon sink efficiency is thus crucial to evaluate the nationally determined contributions (NDCs). Here, we define the instantaneous land sink efficiency as the ratio of natural land carbon sinks to emissions from fossil fuel and land-use and land-cover change with a value of 1 indicating carbon neutrality to track its temporal dynamics in the past decades. Land sink efficiency has been decreasing during 1957–1990 because of the increased emissions from fossil fuel. After the effect of the Mt. Pinatubo eruption diminished (after 1994), the land sink efficiency firstly increased before 2009 and then began to decrease again after 2009. This reversal around 2009 is mostly attributed to changes in land sinks in tropical regions in response to climate variations. The decreasing trend of land sink efficiency in recent years reveals greater challenges in climate change mitigation, and that climate impacts on land carbon sinks must be accurately quantified to assess the effectiveness of regional scale climate mitigation policies.

中文翻译：

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土地碳汇效率的年代际变化

将温度升高限制在比工业化前水平高2°C以下的气候缓解目标需要所有国家的共同努力。因此，跟踪土地碳汇效率的轨迹对于评估国家确定的贡献（NDC）至关重要。在这里，我们将瞬时土地汇效率定义为自然土地碳汇与化石燃料和土地利用及土地覆被变化的排放之比，取值为1表示碳中性以追踪其过去几十年的时间动态。由于化石燃料排放量的增加，在1957年至1990年期间，土地吸收效率一直在下降。经过山的影响。皮纳图博火山喷发减少了（1994年以后），土地吸收效率在2009年之前先上升，然后在2009年以后又开始下降。2009年左右的逆转主要归因于热带地区因气候变化而引起的陆地汇聚变化。近年来，土地汇聚效率的下降趋势显示出缓解气候变化的挑战更大，而且必须准确量化气候变化对土地碳汇的影响，以评估区域规模减缓气候变化政策的有效性。