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> The world will be greener in a high-CO2 environment. There’s no legitimate argument over that fact. However it's important to remember that world isn't a hig

by jgraham 9mo ago

> The world will be greener in a high-CO2 environment. There’s no legitimate argument over that fact. However it's important to remember that world isn't a high school physics experiment, and you can't easily separate out CO2 concentration from the other impacts of increased CO2: | Climate change can prolong the plant growing season and expand the areas suitable for crop planting, as well as promote crop photosynthesis thanks to increased atmospheric carbon dioxide concentrations. However, an excessive carbon dioxide concentration in the atmosphere may lead to unbalanced nutrient absorption in crops and hinder photosynthesis, respiration, and transpiration, thus affecting crop yields. Irregular precipitation patterns and extreme weather events such as droughts and floods can lead to hypoxia and nutrient loss in the plant roots. An increase in the frequency of extreme weather events directly damages plants and expands the range of diseases and pests. In addition, climate change will also affect soil moisture content, temperature, microbial activity, nutrient cycling, and quality, thus affecting plant growth. [https://www.mdpi.com/2073-4395/14/6/1236 https://www.mdpi.com/2073-4395/14/6/1236] In global models of climate change the overall impact on plant growth is significant, but not positive: | Global above ground biomass is projected to decline by 4 to 16% under a 2 °C increase in climate warming [https://www.pnas.org/doi/10.1073/pnas.2420379122 https://www.pnas.org/doi/10.1073/pnas.2420379122] > Certainly it’s more favorable for growth of plants that make food That does not seem to be what agricultural researchers believe: | In wheat a mean daily temperature of 35°C caused total failure of the plant, while exposure to short episodes (2–5 days) of HS (>24°C) at the reproductive stage (start of flowering) resulted in substantial damage to floret fertility leading to an estimated 6.0 ± 2.9% loss in global yield with each degree-Celsius (°C) increase in temperature | Although it might be argued that the ‘fertilization effect’ of increasing CO2 concentration may benefit crop biomass thus raising the possibility of an increased food production, emerging evidence has demonstrated a reduction in crop yield if increased CO2 is combined with high temperature and/or water scarcity, making a net increase in crop productivity unlikely | When the combination of drought and heatwave is considered, production losses considering cereals including wheat (−11.3%), barley (−12.1%) and maize (−12.5%), and for non-cereals: oil crops (−8.4%), olives (−6.2%), vegetables (−3.5%), roots and tubers (−4.5%), sugar beet (−8.8%), among others [https://pmc.ncbi.nlm.nih.gov/articles/PMC10796516/ https://pmc.ncbi.nlm.nih.gov/articles/PMC10796516/]

timr 9mo ago
[flagged]
- beej71 9mo ago
  > 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.
  - deleted 9mo ago
    [deleted]
- jgraham 9mo ago
  > 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.

by jgraham 9mo ago

timr 9mo ago

[flagged]

beej71 9mo ago
> 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.
- deleted 9mo ago
  [deleted]
jgraham 9mo ago
> 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.