Thank you Ugo, great summary. I would like to add that the cooling capacity of the forests are by design highest around the equator where much more solar energy comes in than in for instance the boreal forest areas, where the forest design is more geared towards maximizing photosynthesis in a short summer.
As far as I understand, the forest mechanism of “Air Cooling” (lowering the temperature over a huge area) works during the growing season of trees. In the northern hemisphere it is summer. The most solar radiation comes, the air temperature is highest - and it is during this season that forests transpirate, form clouds, additionally attract moisture from the oceans into the continents ("Biotic pump"), which leads to heavy summer precipitation, feeds rivers, etc. Apparently, in the equator zone, or 0-15 degrees South latitude - where the forests of the Amazon, Congo and Indonesia are located, the same “seasonal” peaks occur: when the temperature is highest, then “forest cooling” works.
"Most models predict major damage to forests in the next century if current climate trajectories are not ameliorated. Debate still remains as to the magnitude of stabilizing forces, such as tree acclimation and positive CO2-associated effects on water use, but most observational data suggest that forest decline is well under way." and "Other long-lived, sessile organisms such as corals appear to be poorly equipped to survive rapid changes, which raises questions about the vulnerability of contemporary forests to future climate change. The emerging view that, similar to corals, tree species have rather inflexible damage thresholds, particularly in terms of water stress, is especially concerning."
Whatever the contribution of forests for a cooler planet it may soon be gone.
Hi Ugo, as I understand it, the formation of water vapour doesn't release heat to space, rather the heat energy is transformed to another type of energy (latent heat) as it suspends the water. When that vapour condenses, the energy is released again as heat energy. hence the temperature moderating effect of water in the environment. But it's probably safe to say that many forms of water vapour do reflect heat to space due to increased albedo.
Yes, maybe I used the wrong terms. The point is that energy is released into space as infrared radiation. Let me check if I said it right, and thanks for the note.
I think the way I described it is correct. Heat is released in the form of molecular vibrations , but these vibrations decay in the form of infrared radiation that can be dispersed into space. It is a little complicated, but I'll see to describe it more explicitly.
Your discussion of transpiration in trees is not consistent with our considerable understanding of the mechanisms involved. You repeatedly refer to “pumping” of water in the leaves and from the roots. This is not at all what happens. You also say that trees cannot thermoregulate. This is not true. You may want to consult a modern plant physiology text.
Hello, Tom, thanks for this note. You are right: plants have a limited thermoregulation capability! I'll modify the post accordingly. About "pumping"; I think it is reasonable to use that word, since trees do pull water from roots to leaves -- of course it is not a mechanical pump, but a biophysical pump based on a pressure difference. But that's what pumps do! So, thanks again -- I keep learning things! Would you like to join our discussion group in these matters? Your expertise would be welcome.
We need to revegetate much of the planet while stopping ongoing deforestation. BUT, we need to listen to the science on how to do this rather than planting monocultures of species and planting in the wrong places. My latest post discusses this.
Thank you Ugo, great summary. I would like to add that the cooling capacity of the forests are by design highest around the equator where much more solar energy comes in than in for instance the boreal forest areas, where the forest design is more geared towards maximizing photosynthesis in a short summer.
As far as I understand, the forest mechanism of “Air Cooling” (lowering the temperature over a huge area) works during the growing season of trees. In the northern hemisphere it is summer. The most solar radiation comes, the air temperature is highest - and it is during this season that forests transpirate, form clouds, additionally attract moisture from the oceans into the continents ("Biotic pump"), which leads to heavy summer precipitation, feeds rivers, etc. Apparently, in the equator zone, or 0-15 degrees South latitude - where the forests of the Amazon, Congo and Indonesia are located, the same “seasonal” peaks occur: when the temperature is highest, then “forest cooling” works.
Correct. I added a note on this point
Adding to my pessimism is this: https://www.science.org/doi/10.1126/science.aat7631 which says:
"Most models predict major damage to forests in the next century if current climate trajectories are not ameliorated. Debate still remains as to the magnitude of stabilizing forces, such as tree acclimation and positive CO2-associated effects on water use, but most observational data suggest that forest decline is well under way." and "Other long-lived, sessile organisms such as corals appear to be poorly equipped to survive rapid changes, which raises questions about the vulnerability of contemporary forests to future climate change. The emerging view that, similar to corals, tree species have rather inflexible damage thresholds, particularly in terms of water stress, is especially concerning."
Whatever the contribution of forests for a cooler planet it may soon be gone.
Hi Ugo, as I understand it, the formation of water vapour doesn't release heat to space, rather the heat energy is transformed to another type of energy (latent heat) as it suspends the water. When that vapour condenses, the energy is released again as heat energy. hence the temperature moderating effect of water in the environment. But it's probably safe to say that many forms of water vapour do reflect heat to space due to increased albedo.
Yes, maybe I used the wrong terms. The point is that energy is released into space as infrared radiation. Let me check if I said it right, and thanks for the note.
I think the way I described it is correct. Heat is released in the form of molecular vibrations , but these vibrations decay in the form of infrared radiation that can be dispersed into space. It is a little complicated, but I'll see to describe it more explicitly.
Interesting. Carrying heat to higher latitudes can allow it to escape easier into space.
Your discussion of transpiration in trees is not consistent with our considerable understanding of the mechanisms involved. You repeatedly refer to “pumping” of water in the leaves and from the roots. This is not at all what happens. You also say that trees cannot thermoregulate. This is not true. You may want to consult a modern plant physiology text.
Hello, Tom, thanks for this note. You are right: plants have a limited thermoregulation capability! I'll modify the post accordingly. About "pumping"; I think it is reasonable to use that word, since trees do pull water from roots to leaves -- of course it is not a mechanical pump, but a biophysical pump based on a pressure difference. But that's what pumps do! So, thanks again -- I keep learning things! Would you like to join our discussion group in these matters? Your expertise would be welcome.
Yes, I'd be glad to join your discussion group. Let me know how.
Send me your email at ugo.bardi(thingette)unifi.it
We need to revegetate much of the planet while stopping ongoing deforestation. BUT, we need to listen to the science on how to do this rather than planting monocultures of species and planting in the wrong places. My latest post discusses this.
Nice post, Jonathan. Too bad that you don't mention the biophysical cooling effect of the water cycle. That's the point I am making in my post.
Thanks! Always more to include!
Thank You, Ugo. I'll include this on my blog.