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"The critical temperature beyond which photosynthetic machinery in tropical trees begins to fail averages approximately 46.7 °C" I know the tropics are hot, bu

"The critical temperature beyond which photosynthetic machinery in tropical trees begins to fail averages approximately 46.7 °C" I know the tropics are hot, but the idea of accepting ~45c as "average" sounds insane.

TheOtherHobbes 3y ago
It's the average temperature at which trees start to die, not the average temperature over a year. Just a couple of weeks at that temp will do a lot of damage. The point is that ~2C or so from the pre-warming baseline you start seeing signs of a mass die off. And ~4C or so the damage starts to become systemic and irreversible.
mentalpiracy 3y ago
45C average is insane! but thankfully a worst-case scenario - not the current situation. Here is the present day temperature readings, from the abstract: >>> Here we found that pantropical canopy temperatures independently triangulated from individual leaf thermocouples, pyrgeometers and remote sensing (ECOSTRESS) have midday peak temperatures of approximately 34 °C during dry periods, with a long high-temperature tail that can exceed 40 °C.
- p_j_w 3y ago
  > thankfully a worst-case scenario Considering that the models predicting the worst cases have tended to be more accurate (eg https://www.nature.com/articles/nature24672 https://www.nature.com/articles/nature24672), you may want to hold off on that thankfulness.
oceanplexian 3y ago
I live in a desert climate where it not only hits 46C, but does so for literally months on end. This article is utterly BS. Trees do fine, even an huge number of imported species from significantly cooler climates.
- rolph 3y ago
  how long does it take for dessert plants to produce biomass compared to same species in temperate conditions? Are you considering C-3 plants, C-4 plants, or CAM plants. https://www.khanacademy.org/science/biology/photosynthesis-in-plants/photorespiration--c3-c4-cam-plants/a/c3-c4-and-cam-plants-agriculture https://www.khanacademy.org/science/biology/photosynthesis-i... https://www.frontiersin.org/articles/10.3389/fpls.2021.715391 https://www.frontiersin.org/articles/10.3389/fpls.2021.71539... https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/c4-plant https://www.sciencedirect.com/topics/pharmacology-toxicology... https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism
- jacquesm 3y ago
  They survive, they're not 'doing fine', if they did you wouldn't live in a desert climate for long. High temperatures have a very visible effect on vegetation, so much so that you can trivially pick these out on satellite imagery.
rolph 3y ago
leaf temperature is the issue. photosynthetic machinery begins to denature at 30C leaf temperature, this is physiologic break even point. plants become stunted and just survive, rather than produce net gain of biomass https://www.ncbi.nlm.nih.gov/pmc/articles/PMC129275/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC129275/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10422931/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10422931/

TheOtherHobbes 3y ago

It's the average temperature at which trees start to die, not the average temperature over a year. Just a couple of weeks at that temp will do a lot of damage. The point is that ~2C or so from the pre-warming baseline you start seeing signs of a mass die off. And ~4C or so the damage starts to become systemic and irreversible.

mentalpiracy 3y ago

45C average is insane! but thankfully a worst-case scenario - not the current situation. Here is the present day temperature readings, from the abstract: >>> Here we found that pantropical canopy temperatures independently triangulated from individual leaf thermocouples, pyrgeometers and remote sensing (ECOSTRESS) have midday peak temperatures of approximately 34 °C during dry periods, with a long high-temperature tail that can exceed 40 °C.

p_j_w 3y ago
> thankfully a worst-case scenario Considering that the models predicting the worst cases have tended to be more accurate (eg https://www.nature.com/articles/nature24672 https://www.nature.com/articles/nature24672), you may want to hold off on that thankfulness.

oceanplexian 3y ago

I live in a desert climate where it not only hits 46C, but does so for literally months on end. This article is utterly BS. Trees do fine, even an huge number of imported species from significantly cooler climates.

rolph 3y ago
how long does it take for dessert plants to produce biomass compared to same species in temperate conditions? Are you considering C-3 plants, C-4 plants, or CAM plants. https://www.khanacademy.org/science/biology/photosynthesis-in-plants/photorespiration--c3-c4-cam-plants/a/c3-c4-and-cam-plants-agriculture https://www.khanacademy.org/science/biology/photosynthesis-i... https://www.frontiersin.org/articles/10.3389/fpls.2021.715391 https://www.frontiersin.org/articles/10.3389/fpls.2021.71539... https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/c4-plant https://www.sciencedirect.com/topics/pharmacology-toxicology... https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism
jacquesm 3y ago
They survive, they're not 'doing fine', if they did you wouldn't live in a desert climate for long. High temperatures have a very visible effect on vegetation, so much so that you can trivially pick these out on satellite imagery.

rolph 3y ago

leaf temperature is the issue. photosynthetic machinery begins to denature at 30C leaf temperature, this is physiologic break even point. plants become stunted and just survive, rather than produce net gain of biomass https://www.ncbi.nlm.nih.gov/pmc/articles/PMC129275/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC129275/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10422931/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10422931/