8 ms·

Tropical forests are approaching critical temperature thresholds

84 points by myshpa 3y ago

sbate1987 3y ago
[dead]
kentosi-dw 3y ago
"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/
mentalpiracy 3y ago
This is good data, but I think "approaching" is doing a lot of heavy lifting in this title - more than is supported by the abstract: >>> Using an empirical model incorporating these dynamics (validated with warming experiment data), we found that tropical forests can withstand up to a 3.9 ± 0.5 °C increase in air temperatures before a potential tipping point in metabolic function, but remaining uncertainty in the plasticity and range of Tcrit in tropical trees and the effect of leaf death on tree death could drastically change this prediction. 3.9 ± 0.5 °C is a lot of runway; likely moreso than we have with other ecosystems. This isn't good by any means, but significantly less dire than other threats.
- jacquesm 3y ago
  And when it's 45 degrees you'll be right there saying that there is nothing we can do about it now, so we should just accept it?
  - belval 3y ago
    Pretty sure that what he's saying is that if we need a 4C increase to trigger mass die-off of tropical forests it's mostly irrelevant since at +4C we enter a lot of other catastrophic scenarios. It's like if you discovered that when your house is on fire the windows will break. It's interesting on the scientific merits but if your house is on fire the whole building is at stake so it was already understood that the windows will break.
    - sdenton4 3y ago
      To be sure, when it's mass die off of one of the planets major carbon sinks we're talking about, it's good to pay more attention to the low end of the confidence interval...
    - jacquesm 3y ago
      No, it's not that. It's that there are multiple factors that put those forests at risk and all of them need to be mitigated to the point that they are safe for the foreseeable future. Deforestation is a huge problem, but this temperature effect has the potential to kill off entire forests in one go. So even if it is a little bit over the horizon assuming that you are going to be able to save some of the forests you'll still lose them. So you need to have multiple lines of attack at once, otherwise you will fail.
veave 3y ago
>photosynthetic machinery in tropical trees begins to fail averages approximately 46.7 °C >have midday peak temperatures of approximately 34 °C during dry periods, with a long high-temperature tail that can exceed 40 °C So basically they have found absolutely nothing of concern

84 points by myshpa 3y ago

sbate1987 3y ago

[dead]

"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/

mentalpiracy 3y ago

This is good data, but I think "approaching" is doing a lot of heavy lifting in this title - more than is supported by the abstract: >>> Using an empirical model incorporating these dynamics (validated with warming experiment data), we found that tropical forests can withstand up to a 3.9 ± 0.5 °C increase in air temperatures before a potential tipping point in metabolic function, but remaining uncertainty in the plasticity and range of Tcrit in tropical trees and the effect of leaf death on tree death could drastically change this prediction. 3.9 ± 0.5 °C is a lot of runway; likely moreso than we have with other ecosystems. This isn't good by any means, but significantly less dire than other threats.

jacquesm 3y ago
And when it's 45 degrees you'll be right there saying that there is nothing we can do about it now, so we should just accept it?
- belval 3y ago
  Pretty sure that what he's saying is that if we need a 4C increase to trigger mass die-off of tropical forests it's mostly irrelevant since at +4C we enter a lot of other catastrophic scenarios. It's like if you discovered that when your house is on fire the windows will break. It's interesting on the scientific merits but if your house is on fire the whole building is at stake so it was already understood that the windows will break.
  - sdenton4 3y ago
    To be sure, when it's mass die off of one of the planets major carbon sinks we're talking about, it's good to pay more attention to the low end of the confidence interval...
  - jacquesm 3y ago
    No, it's not that. It's that there are multiple factors that put those forests at risk and all of them need to be mitigated to the point that they are safe for the foreseeable future. Deforestation is a huge problem, but this temperature effect has the potential to kill off entire forests in one go. So even if it is a little bit over the horizon assuming that you are going to be able to save some of the forests you'll still lose them. So you need to have multiple lines of attack at once, otherwise you will fail.

veave 3y ago

>photosynthetic machinery in tropical trees begins to fail averages approximately 46.7 °C >have midday peak temperatures of approximately 34 °C during dry periods, with a long high-temperature tail that can exceed 40 °C So basically they have found absolutely nothing of concern