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Wouldn’t that reduce the available sunlight for photosynthesis? The problem is that we’re trapping more heat per photon. Reducing the amount of photosynthesis

Wouldn’t that reduce the available sunlight for photosynthesis? The problem is that we’re trapping more heat per photon. Reducing the amount of photosynthesis might reduce the carbon fixation by plants. Not sure if that’d be a good idea.

merpnderp 5y ago
The extra carbon in the air has already made plants more productive so there’s some offset already.
- IntrepidWorm 5y ago
  This seems plausible, but I'm curious if you have a citation?
  - chrisco255 5y ago
    https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth/ https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fer...
- ncmncm 5y ago
  Invasive weeds and vines, mainly. Poison ivy, kudzu, and virginia creeper grow faster. Most plants cannot use all the carbon they already get. Instead, they get less able to compete as the weeds choke them.
  - chrisco255 5y ago
    Not true at all. Most plants can use additional carbon all the way to 1000+ PPM. Some all the way to 2000PPM. Quotes below, sources below that: - CO2 increased leaf area, water use efficiency, and harvest index (in tomatoes) [1] - Optimal levels for tomatoes may be 2 to 5 times the normal atmospheric levels (1000 to 1500 ppm CO2 versus ambient levels of 350 ppm) [2] - Combining increases in CO2 with fertilization and irrigation could greatly enhance leaf area which when coupled to observed increases in net photosynthesis as a result of elevated CO2 could greatly increase productivity of loblolly pine trees. [3] - demonstrating an optimal CO2 concentration of 889.6, 909.4, and 894.2 ppm for aboveground, belowground, and total biomass, respectively, and 967.8 ppm for leaf photosynthesis (in winter wheat) [4] [1] https://www.sciencedirect.com/science/article/abs/pii/S0378377419320463 https://www.sciencedirect.com/science/article/abs/pii/S03783... [2] https://cals.arizona.edu/hydroponictomatoes/nutritio.htm https://cals.arizona.edu/hydroponictomatoes/nutritio.htm [3] https://link.springer.com/article/10.1007/s004680050111 https://link.springer.com/article/10.1007/s004680050111 [4] https://pubmed.ncbi.nlm.nih.gov/26253981/ https://pubmed.ncbi.nlm.nih.gov/26253981/
    - monort 5y ago
      Elevated CO2 concentration favors plants with C3 pathway, because they appeared when CO2 ppm was much higher, than today. Plants with more recent C4 pathway (evolved around 25 million years ago), do not respond as much to CO2. https://www.sciencedirect.com/science/article/pii/S1978301916303400 https://www.sciencedirect.com/science/article/pii/S197830191...
      - ncmncm 5y ago
        For reference, corn (maize) is C4. And sugar cane. High-fructose corn syrup and cane sugar happen to represent the greatest public health disaster since smallpox was eradicated and smoking started down.
qzw 5y ago
Sounds like most of the brighter clouds generated would be over the ocean in this particular scenario, so shouldn’t affect plants too much.
- privong 5y ago
  > Sounds like most of the brighter clouds generated would be over the ocean in this particular scenario, so shouldn’t affect plants too much. Phytoplankton rely on photosynthesis and are the food for a large fraction of marine life (either directly or indirectly).
- robbedpeter 5y ago
  Just plankton and algae and the largest ecosystem on the planet, right? There's always a gotcha, because nature is a chaotic, complex system that is mathematically impossible to account for all the consequences of exercising leverage.
  - qzw 5y ago
    I did think of that, but then also thought that since oceanic plant life move around with currents, they wouldn't be deprived of sunlight all the time. But yes, as you point out, nobody knows all the consequences. It sounds like they're actually doing research and experiments to validate their idea, so whatever model they use will hopefully take these kinds of secondary and tertiary effects into account.
- ratww 5y ago
  "Scientists estimate that 50-80% of the oxygen production on Earth comes from the ocean. The majority of this production is from oceanic plankton — drifting plants, algae, and some bacteria that can photosynthesize" https://oceanservice.noaa.gov/facts/ocean-oxygen.html https://oceanservice.noaa.gov/facts/ocean-oxygen.html
davesmylie 5y ago
Typically I can't find any reliable stats on the spot, but I recall the reduction in photosynthesis from ordinary heavy cloud cover alone can be up to 85% - with most photosynthesis happening whilst there is only light (or even no) cloud cover. Probably this would have minimal effect on light cloud cover and there is already not a great deal happening during heavy cloud.
labster 5y ago
Photosynthesis is largely limited by water availability. Plants only uptake CO2 when they can open stomata, which is when they won’t dry out.
- bobbytit 5y ago
  Photosynthesis is limited by the availability of light, water, co2 and warmth.
  - willis936 5y ago
    This is like saying my computer's performance in a game is limited by CPU, GPU, and RAM while my CPU is maxed out 90% of the time.
    - bobbytit 5y ago
      So CO2 is the equivalent of your CPU. It is currently nowhere near what is needed to run at full efficiency. Look at the lower levels of a forest or the inside of a thick bush and then try and tell me that light is not a limiting factor.
    - bobbytit 5y ago
      Precisely. A plant is unable to perform to its full potential unless it is raised in an enclosed environment with supplemental CO2 at the ideal temperature and with adequate light and water. Plants outside never have enough carbon dioxide, though they often have more than they need of the other factors.
    - marcosdumay 5y ago
      If you go and reduce your RAM because the limit is elsewhere, you may find out that it quickly becomes the bottleneck.
- chrisco255 5y ago
  Most species experience fertilization effect from CO2 all the way to 1000+ PPM, some to 2000PPM. Higher CO2 concentration reduces the loss of water, since the stomata don't need to be open as long. https://en.wikipedia.org/wiki/Stomatal_conductance https://en.wikipedia.org/wiki/Stomatal_conductance

merpnderp 5y ago

The extra carbon in the air has already made plants more productive so there’s some offset already.

IntrepidWorm 5y ago
This seems plausible, but I'm curious if you have a citation?
- chrisco255 5y ago
  https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth/ https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fer...
ncmncm 5y ago
Invasive weeds and vines, mainly. Poison ivy, kudzu, and virginia creeper grow faster. Most plants cannot use all the carbon they already get. Instead, they get less able to compete as the weeds choke them.
- chrisco255 5y ago
  Not true at all. Most plants can use additional carbon all the way to 1000+ PPM. Some all the way to 2000PPM. Quotes below, sources below that: - CO2 increased leaf area, water use efficiency, and harvest index (in tomatoes) [1] - Optimal levels for tomatoes may be 2 to 5 times the normal atmospheric levels (1000 to 1500 ppm CO2 versus ambient levels of 350 ppm) [2] - Combining increases in CO2 with fertilization and irrigation could greatly enhance leaf area which when coupled to observed increases in net photosynthesis as a result of elevated CO2 could greatly increase productivity of loblolly pine trees. [3] - demonstrating an optimal CO2 concentration of 889.6, 909.4, and 894.2 ppm for aboveground, belowground, and total biomass, respectively, and 967.8 ppm for leaf photosynthesis (in winter wheat) [4] [1] https://www.sciencedirect.com/science/article/abs/pii/S0378377419320463 https://www.sciencedirect.com/science/article/abs/pii/S03783... [2] https://cals.arizona.edu/hydroponictomatoes/nutritio.htm https://cals.arizona.edu/hydroponictomatoes/nutritio.htm [3] https://link.springer.com/article/10.1007/s004680050111 https://link.springer.com/article/10.1007/s004680050111 [4] https://pubmed.ncbi.nlm.nih.gov/26253981/ https://pubmed.ncbi.nlm.nih.gov/26253981/
  - monort 5y ago
    Elevated CO2 concentration favors plants with C3 pathway, because they appeared when CO2 ppm was much higher, than today. Plants with more recent C4 pathway (evolved around 25 million years ago), do not respond as much to CO2. https://www.sciencedirect.com/science/article/pii/S1978301916303400 https://www.sciencedirect.com/science/article/pii/S197830191...
    - ncmncm 5y ago
      For reference, corn (maize) is C4. And sugar cane. High-fructose corn syrup and cane sugar happen to represent the greatest public health disaster since smallpox was eradicated and smoking started down.

qzw 5y ago

Sounds like most of the brighter clouds generated would be over the ocean in this particular scenario, so shouldn’t affect plants too much.

privong 5y ago
> Sounds like most of the brighter clouds generated would be over the ocean in this particular scenario, so shouldn’t affect plants too much. Phytoplankton rely on photosynthesis and are the food for a large fraction of marine life (either directly or indirectly).
robbedpeter 5y ago
Just plankton and algae and the largest ecosystem on the planet, right? There's always a gotcha, because nature is a chaotic, complex system that is mathematically impossible to account for all the consequences of exercising leverage.
- qzw 5y ago
  I did think of that, but then also thought that since oceanic plant life move around with currents, they wouldn't be deprived of sunlight all the time. But yes, as you point out, nobody knows all the consequences. It sounds like they're actually doing research and experiments to validate their idea, so whatever model they use will hopefully take these kinds of secondary and tertiary effects into account.
ratww 5y ago
"Scientists estimate that 50-80% of the oxygen production on Earth comes from the ocean. The majority of this production is from oceanic plankton — drifting plants, algae, and some bacteria that can photosynthesize" https://oceanservice.noaa.gov/facts/ocean-oxygen.html https://oceanservice.noaa.gov/facts/ocean-oxygen.html

davesmylie 5y ago

Typically I can't find any reliable stats on the spot, but I recall the reduction in photosynthesis from ordinary heavy cloud cover alone can be up to 85% - with most photosynthesis happening whilst there is only light (or even no) cloud cover. Probably this would have minimal effect on light cloud cover and there is already not a great deal happening during heavy cloud.

labster 5y ago

Photosynthesis is largely limited by water availability. Plants only uptake CO2 when they can open stomata, which is when they won’t dry out.

bobbytit 5y ago
Photosynthesis is limited by the availability of light, water, co2 and warmth.
- willis936 5y ago
  This is like saying my computer's performance in a game is limited by CPU, GPU, and RAM while my CPU is maxed out 90% of the time.
  - bobbytit 5y ago
    So CO2 is the equivalent of your CPU. It is currently nowhere near what is needed to run at full efficiency. Look at the lower levels of a forest or the inside of a thick bush and then try and tell me that light is not a limiting factor.
  - bobbytit 5y ago
    Precisely. A plant is unable to perform to its full potential unless it is raised in an enclosed environment with supplemental CO2 at the ideal temperature and with adequate light and water. Plants outside never have enough carbon dioxide, though they often have more than they need of the other factors.
  - marcosdumay 5y ago
    If you go and reduce your RAM because the limit is elsewhere, you may find out that it quickly becomes the bottleneck.
chrisco255 5y ago
Most species experience fertilization effect from CO2 all the way to 1000+ PPM, some to 2000PPM. Higher CO2 concentration reduces the loss of water, since the stomata don't need to be open as long. https://en.wikipedia.org/wiki/Stomatal_conductance https://en.wikipedia.org/wiki/Stomatal_conductance