alt Hacker NewsYou spent a lot of words arguing with me about things I didn't say.
> you can't easily separate out CO2 concentration from the other impacts of increased CO2
...I never said you could? I explicitly said that there will be changes that require adaptation.
> Global above ground biomass is projected to decline by 4 to 16% under a 2 °C increase in climate warming
That paper is talking about a net reduction in biomass due to projected losses in places with temperature increases exceeding 10 degrees C. It's not just a model, it's science fiction -- it all hinges on the assumptions one makes regarding the proliferation of deserts, which is something we cannot currently predict.
Use the IPCC report instead of cherry-picking studies that support your opinions, and it's obvious that you're wrong. From AR6 Chapter 2, section 2.3.4.3.3 ("Global Greening and Browning") [1]:
> AR5 WGII briefly discussed changes in global vegetation greenness derived from satellite proxies for photosynthetic activity. Observed trends varied in their strength and consistency, and AR5 thus made no confidence statement on observed changes. SRCCL subsequently concluded that greening had increased globally over the past 2–3 decades (high confidence).
> Vegetation index data derived from AVHRR and MODIS depicts increases in aspects of vegetation greenness (i.e., green leaf area and/or mass) over the past four decades (Piao et al., 2020). NDVI increased globally from the early 1980s through the early 2010s (Liu et al., 2015c). 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 (Zhu et al., 2016; Forzieri et al., 2017; Jiang et al., 2017; Xiao et al., 2017) and probably through near-present; for example, Chen et al. (2019) 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) (Forkel et al., 2014; Gobron, 2018; Keenan & Riley, 2018). There are also documented changes in specific vegetation types, such as a 7% rise in global tree cover for 1982–2016 (Song et al., 2018) and an expansion of shrub extent in the Arctic tundra over 1982–2017 (Myers-Smith et al., 2020). The increased greening is largely consistent with CO2 fertilization at the global scale, with other changes being noteworthy at the regional level (Piao et al., 2020).
> 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.
Plant response to CO2 is not only logical, it's actually happening, and well-documented by a number of different lines of evidence. The only thing you can say in response is that, in the distant future, losses due to desertification might offset this growth. That's fine, it's an argument, but it's basically fortune telling given the scale of the system and the distance into the future. We don't even have the ability to quantify the differences we've observed since the 80s!
[1] https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6... (page 101 in that file)
Replies
> you can't easily separate out CO2 concentration from the other impacts of increased CO2 >> I never said you could?
I took the fact that you explicitly mentioned "high-CO2 environment" and claimed there was no room for argument over the "fact"s as an indication that you were trying to separate out the impact of CO2 from other factors caused by climate change such as heat stress and drought. If that wasn't the case then apologies for misunderstanding.
> That paper is talking about a net reduction in biomass due to projected losses in places with temperature increases exceeding 10 degrees C.
The abstract says:
| with great biomass reductions in regions where mean annual temperatures exceeded 10 °C
Unless the abstract is especially badly written that suggests that it's not 10°C _change_ but 2°C change leading to biomass loss in areas that are already at 10°C on average.
> IPCC report
Thanks, that's a useful reference! Do you have a link to the final report? That one seems to be a draft and I didn't find the right published version (but there are many so I'm sure I'm missing it).
I note the paragraph you quoted concludes:
> The increased greening is largely consistent with CO2 fertilization at the global scale, with other changes being noteworthy at the regional level (Piao et al., 2020); examples include agricultural intensification in China and India (Chen et al., 2019; Gao et al., 2019) and temperature increases in the northern high latitudes (Kong et al., 2017; Keenan and Riley, 2018) and in other areas such as the Loess Plateau in central China (Wang et al., 2018). 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) (Anderson et al., 2019; Gottschalk et al., 2016; Hoogakker et al., 2015). 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
So it sounds like a combination of the CO2 increases up to about the year 2000, along with agricultural intensification and various other factors have indeed increased the amount of plant cover, but we are already seeing changes to that picture with further rises to CO2 levels.
> You spent a lot of words arguing with me about things I didn't say.
Well you started with
> The world will be greener in a high-CO2 environment. There’s no legitimate argument over that fact.
And my central point is that the model you're implying there is one in which there's a monotonic relationship between CO2 levels and plant growth. However in reality things are clearly more complex than that, and there is indeed legitimate argument over what factors are dominant in different scenarios.
Your claim that things will only change over long-enough timescales so that you don't have to worry about also seems to lack evidence. In systems with significant feedback loops it seems dangerous to assume that changes will only happen slowly unless you're very confident that you fully understand all the system dynamics. With climate change it's clear that we don't fully understand the system, and some changes are happening faster than earlier models predicted. So _maybe_ we have a few centuries to figure out how to move global agriculture to northern latitudes, and deal with more variable conditions, but from a risk-analysis point of view it seems like a rather poor strategy.
> I _explicitly_ said that there will be changes that require adaptation.
I think this understates how incredibly expensive, violent, and deadly that adaptation will be.