Publication Date:
2021-07-21
Description:
Global greening trends have been widely reported based on long‐term remote sensing data of terrestrial ecosystems. Typically, a hypothesis test is performed for each grid cell; this leads to multiple hypothesis testing and false positive trend detection. We reanalyze global greening and account for this issue with a novel statistical method that allows robust inference on greening regions. Based on leaf area index (LAI) data, our methods reduce the detected greening from 35.2% to 15.3% of the terrestrial land surface; this reduction is most notable in nonwoody vegetation. Our results confirm several greening regions (China, India, Europe, Sahel, North America, Brazil, and Siberia), that are also supported by independent data products. We also report evidence for an increasing seasonal amplitude in LAI north of 35°N. Considering the widespread use of spatially replicated trend tests in global change research, we recommend adopting the proposed multiple testing procedure to control false positive outcomes.
Description:
Plain Language Summary:
Using satellite data, recent studies have detected an increase in vegetation greenness around the globe. These studies attribute this vegetation increase to different factors, such as warming or land use change. However, we argue that the commonly used analysis method is detecting too many regions with trends. In this work, we reanalyze vegetation data using the leaf area index, which measures the area occupied by leaves in any given area. With our refined methods, we too detect greening regions around the world, however these regions are smaller and less abundant. Our research introduces a step in the statistical analysis that increases the reliability of the detected vegetation greening. This can help establish more consensus on what the main contributing factors are for the observed vegetation increase.
Description:
Key Points:
Many studies have consistently reported on global greening trends, but repeatedly without rigorous significance testing.
Although global greening has been overestimated, significant greening can still be rigorously detected.
We observe an increase in the seasonal amplitude of leaf area index around the glob.
Keywords:
581.9
;
910.285
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Global Greening
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Leaf Area Index (LAI)
;
Multiple Testing
;
Statistical significance
Type:
article
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