Plants, both through decay and respiration, are responsible for over half of the world’s annual carbon dioxide emissions.
I mention this fact for one reason and that is to communicate the power of the biosphere upon the atmosphere.
Usually, when discussed in the context of climate change, we talk about the opposite phenomenon, which is the power of the atmosphere on the biosphere. Specifically, the increased growth rate of plants in response to increased levels of atmospheric carbon dioxide.
But that focus on the biological benefits of carbon dioxide has limited our view. How does the biosphere affect the climate? Or, to be more precise, how does the changing biosphere, in response to carbon dioxide emissions, affect the climate?
I would like to propose a new climate feedback for the IPCC. Unfortunately for their organization this is a negative climate feedback. My proposition is a simple one based on these facts:
1) As carbon dioxide levels increase plants need to keep less stomata (pores) open to absorb adequate levels of carbon dioxide
2) With less stomata open plants will lose less water due to transpiration
3) This means less water vapor in the atmosphere – less of a powerful greenhouse gas (WUWT?).
Simply put, higher levels of carbon dioxide, all other things being equal (which we know they aren’t), will decrease levels of water vapor in the atmosphere and therefore the greenhouse effect. This effect will obviously be shown above land rather than the oceans, but then again, the atmosphere above the oceans is already very humid, far overpowering carbon dioxide.
Is this a powerful effect? I don’t know. But keep in mind the first sentence in this article before dismissing its magnitude out of hand. It is certainly something I’d like to see tested under strictly controlled conditions.
The effect would probably be logarithmic in nature, just like the radiative forcing of carbon dioxide is logarithmic, because plants can only grow and store so much water in the limited amount of real estate we have. However, plants do have another interesting, but somewhat predictable response to carbon dioxide – they increase the size of their root systems.
Since their leaves are more capable of supplying the needed carbon the limiting factor for growth becomes the minerals extracted by their roots.
Solution: Grow more and deeper roots.
That is one way the extra water might be stored.
Of course, in his book, A Many-Colored Glass, Freeman Dyson discusses the effects of these more intricate root systems. He postulates that as plants grow more roots and less shoots that their ultimate decay will return more of the carbon to the soil and less to the atmosphere.
That could certainly throw a damper on their multi-century long predictions of atmospheric carbon dioxide levels, especially, and again I defer to Dyson,when he calculates that half of the landmass on Earth would only have increase in thickness by 1/100th of an inch per year in order to absorb every last drop of our carbon dioxide emissions.
Conclusion:
This example was meant to demonstrate how little we know about the climate and, more importantly, the things we didn’t even realize we didn’t know. How many more mysteries are out there befuddling climate models and their predictions?
As simple as this example is, it is still far more complex than the calculations regarding carbon dioxide.
Or is it?
When clouds precipitate away their moisture, releasing heat towards both Heaven and Earth, wouldn’t the carbon dioxide reflect some of that heat back up towards space? Or would those conditions necessarily require a high amount of water vapor in the air which would drown out that effect?
I don’t know. Maybe it is a stupid question – or perhaps just another unknown unknown.
Cheers,
James Padgett
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Yet another in the growing list of questions the Warmistas must,
perforce, assiduously ignore.
In fact, they’re out of fundamental questions
because they already know the Answer:
Satanic Gases be gone!
You have a hypothesis, but will it will stand up to scrutiny?
Evapotranspiration accounts for about 10% of water vapour entering the atmosphere (see link). 90% comes from direct evaporation from land and water bodies. So, even if it were true that evapotranspiration decreases due to increased CO2, that effect would have to overcome increased evaporation due to higher temperature. And as 90% of water vapour comes from evaporation, that’s a lot to overcome. And evapotranspiration also increases due to higher temperature. So, even ignoring evaporation, if both temperature and CO2 rise, the direct effect of temperature will counteract the indirect effect of CO2 on evapotranspiration.
Before saying “more research is needed”, you should look to see if it has already been done. My guess is that it is already well known among experts that this effect is insignificant. I am ready to be proven wrong on that.
http://ga.water.usgs.gov/edu/watercycleevapotranspiration.html
And of course increased plant growth means more photosynthesis and therefore energy absorption from the radiation budget…
[Note – RW – there has been another commenter using this handle here occasionally over the past year whose behaviour and contentious comments resulted in warnings from Anthony. Just warning you to be prepared to politely deflect any replies that may be the result of this person’s reputation or perhaps be prepared to change your handle ~jove, mod]
Correction: in my previous post, for “evapotranspiration” read “tranpiration”. Evapotranspiration includes evaporation. I stand by the logic, but used the wrong term.
I have a lot of respect for Dyson but even if I’d never heard of him, your question makes sense. I hope we can hear from plant experts or people who know whether/how the experiments have been done or could/should be done. There is plenty of data showing how plants thrive with more CO2, but how that translates to demonstrations outside a greenhouse with complex ecosystems over time, I don’t know. I do know that the AGW camp are unlikely to volunteer to fund the research…
Could you please elaborate, how this is supposed to be “new”?
A simple search for “stomata” in ipcc.ch turns up this section of the TAR
http://www.ipcc.ch/ipccreports/tar/wg1/289.htm
In a recent GCM study, tropical photosynthesis and transpiration rates were calculated to change only slightly under a CO2 concentration of 700 ppm, while the additional surface net radiation due to global warming was mainly returned to the atmosphere as sensible heat flux, boosting warming over the tropical continents by 0.4 to 0.9°C above the direct greenhouse warming of 1.7°C (Sellers et al., 1996a). It has been hypothesised that this effect may be partially countered by increased vegetation growth (Betts et al., 1997), but it is not clear to what extent this would be significant in already densely vegetated areas such as the tropical forests. To what extent can we trust these new models and their predictions?
Absolutely right to seek negative feedback mechanisms which have maintained a viable biosphere for four billion years. The alarmists (with their wickedly misleading “tipping point” expression) claim there’s positive feedback; unstable equilibrium. Wrong!
This is the philosophical divide between the two camps.
John B
What makes you think that decreased transpiration has to “overcome” the 90% of vapour from other sources? Water vapour causes somewhere up to 95% of the greenhouse effect. Our own activities account for between about 0.3 and 1%. So it is entirely possible that a reduction in evapotranspiration of about 3% would wipe out all human influence on the greenhouse effect.
Since palaeo-stomata studies suggest fairly large variations in response to carbon dioxide levels, this is far from unlikely, and could easily overcome the increase in evaporation from the very small temperature increases some parts of the world are seeing.
It isn’t even the first time this hypothesis is brought up on WUWT:
http://wattsupwiththat.com/2011/03/04/negative-water-vapor-feedback-in-plant-evapotranspiration-found/
Bluegrue
Under what conditions? Were the plants grown for several generations under increased carbon-dioxide concentrations? What plant types were studied, all of them? Did they increase the range of the plants that responded most to carbon dioxide, at the expense of those that responded least? Did they assume an increased range for all plants that grow better with higher carbon dioxide (at the moment we are in a carbon dioxide crisis, with very low levels compared to earlier periods in the Earth’s history; this has been detrimental to some classes of plants)?
Such studies are often (of necessity) far too restricted to say much of any use about the real world.
Another limiting factor for plant growth: Warmth. An experiment was done that found that leaves maintain a fairly consistent temperature inside their leaves as they grow. I think it was around 21 C, and this was only for one type of plant. Other plants might have different optimal internal temperatures, but what about those that prefer 21C? As the lower troposphere warms from the average 14C, then plants won’t have to work so hard to bring their leaf internal temperatures up to 21C. Warmer temperatures could promote more growth if warmth was a bottle neck or ‘lowest plank in the barrel’ that limited growth.
I love the idea of more roots in a CO2 enriched growing environment because of lack of minerals in the growing medium. That lays question to the claim that daffodils, for example, from certain companies are better simply because they have larger root systems.
John M Reynolds
From what I have read Plants are CO2 neutral. ie All the CO2 that plants can use is absorbed through photosynthesis . High CO2 levels increases growth but eventually all plants die and the CO2 is released in to atmosphere. No net change.
The important item is timing. Low CO2 level means stunted growth and I suspect shorter life spans. High CO2 leads to a greater quantity of foliage , increased life spans of plants and a greater turn over of water ( transpiration) . Leading to a higher humidity, increased rain and in turn greater plant growth.
The age of the Dinosaurs – higher CO2 levels – higher temps – higher rainfall. The greatest quantity and most diverse amount of life on this planet.
Be nice to have those conditions back again.
Instead we are looking at an Ice Age. Real Deal.
The greatest moderator of CO2 is the Ocean. As temps fall water absorbs CO2.
As water temps increase CO2 is released. This has the effect of increasing plant growth
As water temps decrease CO2 is absorbed. Ocean temps and levels are decreasing.
That can only mean 2 things.
1 – Ocean levels go down – Ice quantity in the world is going up. ( where is the water going)
2 – Ocean temps are dropping – CO2 levels will soon start to decrease as oceans start to absorb the CO2.
I have just read that New York is expecting the earliest/greatest snow fall for 150 years.
Again, how much of an effect does a 0.7/288 degrees K change have on the evaporative budget?
Most important climate change factor and ‘known unknown’ is the sun’s input, but not the usually considered TSI, cosmic rays, UV, etc.
http://www.vukcevic.talktalk.net/CDr.htm
the rest are minor factors or indirect consequences.
Doubting Rich says:
October 29, 2011 at 4:50 am
John B
What makes you think that decreased transpiration has to “overcome” the 90% of vapour from other sources? Water vapour causes somewhere up to 95% of the greenhouse effect. Our own activities between about 0.3 and 1%. So it is entirely possible that a reduction in evapotranspiration of about 3% would wipe out all human influence on the greenhouse effect.
Since palaeo-stomata studies suggest fairly large variations in response to carbon dioxide levels, this is far from unlikely, and could easily overcome the increase in evaporation from the very small temperature increases some parts of the world are seeing.
————–
I fear you misunderstood me. 90% of water vapour comes from evaporation, Only 10% from transpiration. If temperature and CO2 rise, the predominant effect will be inreased water vapour from evaporation. That effect is what decreased transpiration, if it occurred at all, would have to overcome if the net effect were to be decreased water vapour.
And bluegrue is suggesting that it is already known that transpiration rates do not change significantly due to CO2 concentrations of up to 700ppm.
Paul Cantwell says:
October 29, 2011 at 5:01 am
From what I have read Plants are CO2 neutral. ie All the CO2 that plants can use is absorbed through photosynthesis . High CO2 levels increases growth but eventually all plants die and the CO2 is released in to atmosphere. No net change.
—————-
The carbon may eventually be released in the atmosphere, but it can take a long time. Fossil fuels are an example of carbon that was once in the atmosphere. As long as there as an increase in plant matter, the CO2 sink is larger..
When faced with more CO2 in the atmosphere, plants have 3 “options”
1. Keep capturing the same amount of CO2 as before, which means they won’t need to keep their stomata open as long –> less evaporation.
2. Keep their stomata open as long as before, which means they will absorbe more CO2 — > more plant growth.
3. A combination of the above.
The most common option is 3, by far. So there is both more plant growth and less evaporation.
More plants means a bigger CO2 sink.
Plants also release other chemicals that have a cooling effect.
See for example:
http://www.co2science.org/about/position/globalwarming.php
“Carbon dioxide is a powerful aerial fertilizer, directly enhancing the growth of almost all terrestrial plants and many aquatic plants as its atmospheric concentration rises. And just as increased algal productivity at sea increases the emission of sulfur gases to the atmosphere, ultimately leading to more and brighter clouds over the world’s oceans, so too do CO2-induced increases in terrestrial plant productivity lead to enhanced emissions of various sulfur gases over land, where they likewise ultimately cool the planet. In addition, many non-sulfur-based biogenic materials of the terrestrial environment play major roles as water- and ice-nucleating aerosols; and the airborne presence of these materials should also be enhanced by rising levels of atmospheric CO2. Hence, it is possible that incorporation of this multifaceted CO2-induced cooling effect into the suite of equations that comprise the current generation of global climate models might actually tip the climatic scales in favor of global cooling in the face of continued growth of anthropogenic CO2 emissions.”
The balance of water vapor in the atmosphere does not directly depend on the amount of evaporation. The capacity of the atmosphere to hold water vapor depends on the temperature, but the removal of water vapor from the atmosphere (rain) also depends on the relative humidity. If there is less rain, the replacement vapor due to evaporation does not have to be as large to maintain or even increase the absolute vapor content. Supporters of the CAGW hypothesis and many modelers assumed constant relative humidity, and thus increasing absolute water vapor content with increasing temperature. However, data shows not only dropping relative humidity with increasing temperature, but even dropping to near constant absolute water vapor levels at higher altitudes, which is the opposite of what is needed for positive feedback.
The point I am making here is that the evaporation level is not the only factor for amount of vapor in the atmosphere, so your point is moot.
Good hypothesis, James. Thanks for posting.
There are 2 things that make me a little bit puzzled.
a)
1) As carbon dioxide levels increase plants need to keep less stomata (pores) open to absorb adequate levels of carbon dioxide
I have to admit, I don’t know much about plants in this specific case. But that sounds quite illogical to me, because plants grow better at higher CO2 conditions and I can’t see, how that correlates with lesser stomata. This would rather mean a growth stagnation, which isn’t.
b)
3) This means less water vapor in the atmosphere – less of a powerful greenhouse gas
Water vapor level only changed insignificantly over the decades, and as John B. already adumbrated, water vapor seems to come mostly from ocean and land evaporation.
[Although I have to admit, that my room plants are very thirsty and need lots of water 🙂 ]
As for me, a very good explanation for interaction of water vapor an CO2 in the atmosphere maintaining a constant optical depth, is shown in the paper from Miskolczi:
http://www.met.hu/doc/idojaras/vol111001_01.pdf
And keep in mind, James, there are no stupid questions.
Only stupid answers from alarmists. 😉
“There are known knowns; there are things we know we know.
We also know there are known unknowns; that is to say we know there are some things we do not know.
But there are also unknown unknowns – the ones we don’t know we don’t know. ”
—Former United States Secretary of Defense Donald Rumsfeld
Unknown unknowns:
1.The role of the thermohaline circulatory patterns on climate.
2.The cyclical nature of key emissions of the sun, notably CMEs and X-rated flares.
3. The amount of reafforestation, its type, its location and the rate of subsequent growth which humans, in their infinite wisdom, will allow to take place in the next 500 years.
4. The effect of a 30 year shift in the jet stream further south over the Atlantic, in particular its effect on desert- or semi-desert areas of N. Africa and Southern Europe,in terms of the levels of water in aquifers, the spread of vegetation within the deserts and changes in climate and local temperature which may or may not accrue as a result.
5. What the stable human population will end up being: 10 billion, 15 billion or 25 billion plus?
6. How effectively the oceans transfer heat from the surface layer to deeper levels, since Sea Surface Temperature is but a minor measure of the overall oceanic temperature index…..
7. How evolving levels of atmospheric pollutants will affect the atmospheric energy budget.
That’s just seven. No discussion of volcanoes, major oceanic pollution events, freak snows leaving widespread snow cover for an entire northern latitude summer etc etc.
c3 plants fix three carbon atoms during photosynthesis, c4 fix four. Most plants are c3 but we are presently growing more c4 plants commercially, thanks to maize. Additionally, we are bio-enineering c3 plants with c4 genes to make them more water efficient. Furthermore we are growing more maize and other oddities to produce ethanol. I doubt that all the co2 is released into the atmosphere when a plant dies, rather more will be “adsorbed” and remain in the topsoil.
I think there are plans to make rice a c4 plant, that could be interesting.
Cactus do not photosynthesize in real-time like c3 and c4 plants, rather, they store up what they need to perform a type of photosynthesis later, in low light or night.
bluegrue says:
October 29, 2011 at 4:04 am
In a recent GCM study, tropical photosynthesis and transpiration rates were calculated to change only slightly under a CO2 concentration of 700 ppm
==========================================================
..a recent study…GCM…calculated… Sigh!.
What do real experiments (plural) show when plants are grow in higher C02 environments?
To add a couple of more unknows that complicate the models, what are the mean residence times of carbon in the life cycles in the biosphere? Think about decaying leaf litter, phytoplankton, swamp gas, and methane hydrates. The actual residence time of CO2 in the atmosphere as a gas is probably a matter of days, but the “observed” environmental residence time depends on these cycles with the atmosphere.
“jmrSudbury
An experiment was done that found that leaves maintain a fairly consistent temperature inside their leaves as they grow. I think it was around 21 C, and this was only for one type of plant. Other plants might have different optimal internal temperatures, but what about those that prefer 21C? ”
Living organisms do have an ‘optimal internal temperature’, but not for the reason you think. There is a relationship between the rate a particular enzyme turns over and temperature, however, this is ‘tunable’ in evolutionary time; it would be very easy to tune all the biochemistry to 11 degrees or to 31 degrees. Enteric bacteria spend time inside intestines at 37 and then when pooped out, at ambient temperature; their biochemistry is tuned to be dynamic.
The operating temperature of a plant or animal is actually, surprise surprise, a compromize.
Plants and animals can generate heat by thermogenesis, which requires energy, and cool themselves by transpiration/panting/sweating, which also requires energy and resources.
The ‘optimal internal temperature’ of a particular species, sometimes the same species in a different location, represents the lowest energy cost required to buffer internal temperature using heating/cooling energy consuming processes.
The smaller you are, the less the payoff in the attempt. Bacteria quite simply don’t bother with this game and instead of buffering their temperature, they buffer their biochemistry. The bigger you are, the bigger the payoff. Having a constant internal temperature means that signaling pathways become increasingly refined, it is easier for cell to measure what is going on in different pathways and easier to fine tune them. Mammals are pretty much the masters of this, by removing (thermal) noise from their biochemistry, they can read/write information wonderfully.
Different mammals have different optima. The bigger you are there less your body temperature swings during the day/night cycle. Mammals also split themselves into two, a core body where all the important stuff happens (the organs) and the non-core extremities. Through the regulation of blood flow the core temperature is maintained and skin, for example, goes on a roller coaster ride.
There is a nice dog core body plot somewhere that shows the average rectal temperature of dog breeds vs. body mass. Large dogs have a lower working temperature than small dogs. It is easier for large to dog generate heat than to lose heat, so they sit on the left hand side of the curve, whereas with small dogs it is the opposite.
from John B
“Evapotranspiration accounts for about 10% of water vapour entering the atmosphere (see link). 90% comes from direct evaporation from land and water bodies.”
But increasing the leafy mass also shades the ground and thereby reduces the direct evaporation as well. There are researchers in the Midwest USA that suspect that the increasing planting density of corn the last 20 years has resulted in moderating the high temperatures.