[HN Gopher] Tropical forests are approaching critical temperatur...
___________________________________________________________________
Tropical forests are approaching critical temperature thresholds
Author : myshpa
Score : 66 points
Date : 2023-08-25 19:32 UTC (3 hours ago)
(HTM) web link (www.nature.com)
(TXT) w3m dump (www.nature.com)
| sbate1987 wrote:
| [dead]
| kentosi-dw wrote:
| "The critical temperature beyond which photosynthetic machinery
| in tropical trees begins to fail averages approximately 46.7
| degC"
|
| I know the tropics are hot, but the idea of accepting ~45c as
| "average" sounds insane.
| mentalpiracy wrote:
| 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 degC during dry periods, with
| a long high-temperature tail that can exceed 40 degC.
| p_j_w wrote:
| > 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), you may want to
| hold off on that thankfulness.
| rolph wrote:
| 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/PMC10422931/
| TheOtherHobbes wrote:
| 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.
| oceanplexian wrote:
| 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.
| jacquesm wrote:
| 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 wrote:
| 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-i.
| ..
|
| https://www.frontiersin.org/articles/10.3389/fpls.2021.71539.
| ..
|
| https://www.sciencedirect.com/topics/pharmacology-
| toxicology...
|
| https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism
| mentalpiracy wrote:
| 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 degC 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 degC 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.
| Retric wrote:
| It's not 4C when there's this much uncertainty involved.
|
| The concern isn't hitting X temperature and everything
| instantly fails it's looking for the lowest temperature where
| positive feedback loop occurs. That feedback temperature might
| be 3.4C or it might be 0.4C, this study hasn't discovered a
| specific answer just a very critical threshold we are fairly
| close to where bad stuff occurs.
|
| "Leaf thermocouple data from multiple sites across the tropics
| suggest that even within pixels of moderate temperatures, upper
| canopy leaves exceed Tcrit 0.01% of the time." So it's a rare
| event right now. Perhaps at +0.8C such extreme events become
| common enough for large local die offs to occur. When coupled
| with tree lifespan you actually get widespread cumulative
| damage much sooner than expected. Or perhaps it's not a
| problem, we don't have a definitive answer just one study.
| hedora wrote:
| Yeah; by the time we are at 3.4C (the bottom of that range),
| we're already to the point where a large percentage of people
| are climate refugees. In addition to many currently-inhabited
| places being too hot for humans to survive, the Atlantic
| current will have already collapsed, so bug chunks of Western
| Europe will probably be under a glacier.
| jacquesm wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| mentalpiracy wrote:
| I plainly did not say that there was nothing to do about it,
| but I appreciate your enthusiastic defense of the forests.
| Unless we stop clear-cutting in the short term, there won't
| be any rainforests left by the time the temperatures hit 45C.
| jacquesm wrote:
| Both are a problem. The time to act is _now_ not when the
| temperatures are so high that the trend alone + momentum
| will be enough to reach the point of no return. We _really_
| need those trees. So instead of trying to dismiss the
| article you could do a better job at making the case for
| action instead of pretending that there is 'plenty of
| room' when clearly there isn't. Because even in this
| comment you give another reason to say it's pointless and
| that we _will_ hit 45 degrees.
|
| Clearcutting rainforest is a huge problem, bigger so
| because the rich countries arguing that the poor countries
| shouldn't be doing this after clearcutting their own land
| is hypocritical to the extreme. But rising temperatures are
| by themselves also a huge problem and this is an
| 'either/or' situation, which means we need to tackle _all_
| of these in ways that last.
| mentalpiracy wrote:
| Genuine question: would you please quote where I
| dismissed the entire study? (note that I have slightly
| modified the wording of the first sentence since your
| original reply - the original phrasing was: >>>
| "approaching" is doing a lot of heavy lifting in this
| title - far more than is supported by the abstract (imo)
| )
|
| I was critical of a single word in the title.
| jacquesm wrote:
| That's exactly the problem though: rather than to build
| upon the ideas in the article all you did was find fault
| with a single word, and that drove your comment. Instead,
| if you were to take this serious you could approach it
| constructively rather than destructively. It's maybe a
| bit more work but I think the cumulative effect of that
| would result in a much better discussion around the
| subject matter.
|
| 6 degrees difference sounds like it is huge, right? But:
| that's 6 degrees with a margin of error, and with a
| difference per species (it is an _average_!) that further
| enlarges that margin for error. Then there are possible
| feedback mechanisms to contend with, as well as various
| local effects. Rather than to just accentuate the fact
| that 'approaching' is doing the heavy lifting it would
| be trivial to point out that this is how scientists
| communicate around things they are not 100% sure of (and
| that includes most things), but meanwhile us silly
| laypeople should not assume that because the statement is
| made carefully that it still is a warning and so can't be
| dismissed out of hand. That is more typing but it takes
| you out of 'dismissal', which is how I read your original
| comment, especially with the 'far more' in there which is
| - ironically - doing a lot of heavy lifting in your
| original comment.
| veave wrote:
| >photosynthetic machinery in tropical trees begins to fail
| averages approximately 46.7 degC
|
| >have midday peak temperatures of approximately 34 degC during
| dry periods, with a long high-temperature tail that can exceed 40
| degC
|
| So basically they have found absolutely nothing of concern
___________________________________________________________________
(page generated 2023-08-25 23:02 UTC)