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IPCC AR6: Global Greening, Unspun Edition

08 Dec 2021 | Science Notes

You’ll have to dig deep into the IPCC Report to find a brief mention of the fact that despite all this catastrophic climate change, the planet is getting greener. You’d think the greens would be happy. Even if they aren’t we are, because we like plants and trees. Herewith, from Section 2.3.4.3.3, the IPCC AR6 on Global Greening: “Vegetation index data derived from [satellites] depicts increases in aspects of vegetation greenness (i.e., green leaf area and/or mass) over the past four decades (--). NDVI [Normalized Difference Vegetation Index] increased globally from the early 1980s through the early 2010s (--). Pan et al. (2018a) found NDVI increases over about 70% of the Earth’s vegetated surface through 2013, and Osborne et al. (2018) noted strong upward changes in NDVI in the circumpolar Arctic through 2016. Globally integrated Leaf Area Index (LAI) also rose from the early 1980s through at least the early 2010s (--) and probably through near-present; for example, (--) documented an LAI increase over one-third of the global vegetated area from 2000–2017.”

Although less frequently analysed for temporal trends, Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) likewise increased over many global land areas (particularly China, India, and Eastern Europe) in the past two decades (Figure 2.33) (--). There are also documented changes in specific vegetation types, such as a 7% rise in global tree cover for 1982–2016 (--) and an expansion of shrub extent in the Arctic tundra over 1982–2017 (--). The increased greening is largely consistent with CO2 fertilization at the global scale, with other changes being noteworthy at the regional level (--); examples include agricultural intensification in China and India (--) and temperature increases in the northern high latitudes (--) and in other areas such as the Loess Plateau in central China (--). Notably, some areas (such as parts of Amazonia, central Asia, and the Congo basin) have experienced browning (i.e., decreases in green leaf area and/or mass) (--). Because rates of browning have exceeded rates of greening in some regions since the late 1990s, the increase in global greening has been somewhat slower in the last two decades (--).

Global-scale linear trends differ substantially across products for the same periods and trend metrics used (--). Several factors contribute to this large span in estimated changes. Remotely sensed vegetation products vary in their spatial and temporal completeness as well as resolution and are sensitive to contamination from atmospheric composition, clouds, snow cover, and anisotropy, as well as orbital changes and sensor degradations (--). Ground-based measurements suitable for calibration and validation are scarce before 2000 (--), and the recalibration of satellite records (e.g., as in from MODIS Collection 5 to 6) can affect trends (--). It is possible that the increase in greenness over 2000–2015 is larger than the increase in gross primary production (based on flux tower measurements and MODIS Collection 6 data) (--). Land use changes and altered disturbance regimes (e.g. floods, fires, diseases) may mask large-scale signals (--). In addition, there is a plethora of models for the identification of phenological metrics from satellite data as well as a variety of statistical techniques for analysing historical changes (--).

In summary, there is high confidence that vegetation greenness (i.e., green leaf area and/or mass) has increased globally since the early 1980s. However, there is low confidence in the magnitude of this increase owing to the large range in available estimates.

One comment on “IPCC AR6: Global Greening, Unspun Edition”

  1. Clever how they could not state an amount of greening or even a range. Too much fodder for us deniers. NASA 2016 LIA study estimated an 18% greening about the size of the continental USA between 1980 and 2010. Extrapolating back to 1960 and forward to 2020 one could estimate a 30% global greening since 1960 mainly due to that horrible pollutant CO2. But that must never be discussed.

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