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More Carbon Dioxide is not necessarily good for plants.

Posted on 18 April 2011 by villabolo

An argument, made by those who deny man made Global Warming, is that the Carbon Dioxide that is being released by the burning of fossil fuels is actually good for the environment. Their argument is based on the logic that, if plants need CO2 for their growth, then more of it should be better. We should expect our crops to become more abundant and our flowers to grow taller and bloom brighter.

However, this "more is better" philosophy is not the way things work in the real world. There is an older, wiser saying that goes, "Too much of a good thing can be a bad thing." For example, if a doctor tells you to take one pill of a certain medicine, taking four is not likely to heal you four times faster or make you four times better. It's more likely to make you sick.

It is possible to help increase the growth of some plants with extra CO2, under controlled conditions, inside of greenhouses. It is based on this that 'skeptics' make their claims. However, such claims are simplistic. They fail to take into account that once you increase one substance that plants need, you automatically increase their requirements for other substances. It also fails to take into account that a warmer earth will have an increase in deserts and other arid lands which would reduce the area available for crops. 

Plants cannot live on CO2 alone. They get their bulk from more solid substances like water and organic matter. This organic matter comes from decomposing plants and animals or from man made fertilizers. It is a simple task to increase water and fertilizer and protect against insects in an enclosed greenhouse but what about doing it in the open air, throughout the entire Earth?

What would be the effects of an increase of CO2 on agriculture and plant growth in general? The following points make it clear.

1. The worse problem, by far, is that increasing CO2 will increase temperatures throughout the Earth. This will make deserts and other types of dry land grow. While deserts increase in size, other eco-zones, whether tropical, forest or grassland will try to migrate towards the poles. However, soil conditions will not necessarily favor their growth even at optimum temperatures.

2. CO2 enhanced plants will need extra water both to maintain their larger growth as well as to compensate for greater moisture evaporation as the heat increases. Where will it come from? Rainwater is not sufficient for current agriculture and the aquifers they rely on are running dry throughout the Earth (1, 2).

On the other hand, as predicted by Global Warming, we are receiving intense storms with increased rain throughout of the world. One would think that this should be good for agriculture. Unfortunately, when rain falls down very quickly, it does not have time to soak into the ground. Instead, it builds up above the soil then floods causing damage to the crops. The water also floods into creeks, then rivers, and finally out into the ocean carrying off large amounts of soil and fertilizer.

3. Unlike Nature, our way of agriculture does not self fertilize by recycling all dead plants, animals and their waste. Instead we have to be constantly producing artificial fertilizers from natural gas which will eventually start running out. By increasing the need for such fertilizer you will shorten the supply of natural gas creating competition between the heating of our homes and the growing of our food. This will drive the prices of both up.

4. Too high a concentration of CO2 causes a reduction of photosynthesis in certain of plants. There is also evidence from the past of major damage to a wide variety of plants species from a sudden rise in CO2 (See illustrations below). Higher concentrations of CO2 also reduce the nutritional quality of some staples, such as wheat.

 5. When plants do benefit from increased Carbon Dioxide, it is only in enclosed areas, strictly isolated from insects. However, when the growth of Soybeans is boosted out in the open, it creates major changes in its chemistry that makes it more vulnerable to insects, as the illustration below shows.

Figure 1: Plant defenses go down as carbon dioxide levels go up, the researchers found. Soybeans grown at elevated CO2 levels attract many more adult Japanese beetles than plants grown at current atmospheric carbon dioxide levels. Science Daily; March 25, 2008. (Credit: Photo courtesy of Evan Delucia)

Figure 2: More than 55 million years ago, the Earth experienced a rapid jump in global Carbon Dioxide levels that raised temperatures across the planet. Now, researchers studying plants from that time have found that the rising temperatures may have boosted the foraging of insects. As modern temperatures continue to rise, the researchers believe the planet could see increasing crop damage and forest devastation. Science Daily; Feb. 15, 2008.

Figure 3: Global Warming reduces plant productivity. As Carbon Dioxide increases, vegetation in Northern Latitudes also increases. However, this does not compensate for decreases of vegetation in Southern Latitudes. The overall amount of vegetation worldwide declines 

In conclusion, it would be reckless to keep adding CO2 to the atmosphere. Assuming there are any positive impacts on agriculture in the short term, they will be overwhelmed by the negative impacts of climate change.

It will simply increase the size of deserts and decrease the amount of arable land. It will also increase the requirements for water and soil fertility as well as plant damage from insects.

Increasing CO2 levels would only be beneficial inside of highly controlled, enclosed spaces like greenhouses.

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Comments 151 to 200 out of 248:

  1. LukeW at 05:33 AM, good to see someone with their feet firmly on the ground and enough nouse to know whether it is dry or wet. There is a project that is collecting all available anecdotal evidence from journals etc to reconstruct as best possible, the early climate of Australia prior to the official record period. If you are not already aware of it these addresses should lead you to information about it. http://www.australiangeographic.com.au/journal/first-fleet-logs-reveal-climate-patterns.htm http://climatehistory.com.au/2010/12/02/volunteers-dig-up-tales-of-wild-weather-and-insect-plagues/
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  2. villabolo at 07:34 AM, the flooding event you are referring to was not due to the La Nina alone, but rather to the combination of La Nina and a negative IOD. That combination merely replicated the conditions last bought in 1975, but also to some extent in 1942, 1933, 1917, 1916,1909,1906, and yet to be established prior to that. The difference now is that the ENSO and IOD are very close to being able to be accurately forecast 2 years out, and as has been happening, those who follow such forecasts are able to plan ahead with more confidence than those who don't, and so not everyone got caught out.
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  3. johnd wrote : "If you are not already aware of it these addresses should lead you to information about it. http://www.australiangeographic.com.au/journal/first-fleet-logs-reveal-climate-patterns.htm http://climatehistory.com.au/2010/12/02/volunteers-dig-up-tales-of-wild-weather-and-insect-plagues/" This is pure gold, as far as so-called skepticism is concerned. Any project involving the BOM and Met Office (two of the organisation most hateful to the so-called skeptics - due to their important leadership in that all-encompassing conspiracy, apparently), has a built-in rejection clause when the results are not as desirable as required for continuing obfuscation, i.e. "It was always going to be biased, fraudulent and untrustworthy - the BOM and Met Office are involved !"
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  4. Luke, John and Villabolo, If I may be so bold--could we please move the discussion back to the topic at hand? Arguing about what ifs and the IOD and ENSO (yes, I was guilty of that earlier too) is not helpful.
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  5. JMurphy at 08:34 AM, once again you've overlooked the obvious. It is a University of Melbourne project, coincidently it was they who provided the FACE PowerPoint presentation I referenced earlier. Given the objective is to collect data that is beyond that contained in the official BOM records, BOM will be more of a beneficary rather than a contributor.
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  6. Back to the issue at hand-in spite of all the hand-waving & obfuscation being done by John D, BP & Luke, the fact remains that attempts to claim that enriched CO2 will be beneficial for agriculture are overly simplistic-as they ignore all the other negative impacts that might well result from either enriched CO2 directly, or from changes in hydrology & temperature that will result. These facts are backed up even by the results of the FACE trials in which they place so much faith-even though said trials do little to simulate expected changes in temperature & hydrology. Drops in nutrition, resistance to insect pests & increased soil-borne pathogens have all been shown to occur under eCO2 *alone*-which will almost certainly have a negative impact on crop yields & increase the cost of cropping for farmers. Certainly, just the known dangers to agriculture posed by increasing CO2 emissions should be sufficient to make us want to pursue a more prudent approach to the burning of fossil fuels. In Denial World, however, the risks are entirely worth it if it means a continued reliance on fossil fuels.
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  7. That map in the Horsham FACE trial is also nothing to be optimistic about. Almost the entire map shows areas with declining yields between now & 2050-with some areas only expected to decline by 2070, & only a few smatterings of areas that expect to see a yield increase between now & 2070. Again, what the people running the FACE trial are telling us is *very* different from what John D is trying to sell it as.
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  8. Marcus at 09:20 AM, we've discussed the Horsham FACE trials in depth some time back in another thread, and you claimed to have studied and understood the results. Why then are you now claiming they did little to simulate expected changes in temperature and precipitation when it so clearly was a integral part of the trials? Do you recall that, or didn't the results make it clear enough for you?
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  9. Villabo - you remain unread as to how major droughts break in Australia, decadal influences, and the importance of major floods in recharging rivers and groundwater. Sorry but it's our underlying lot in life and our natural ecology (exclude Europeans) is adapted to it. Las Ninas are not evenly spread either. So good luck finding a climate change signal in there with the current time series ! Sorry to harp on off-topic. But more to the point extrapolating from CO2 fertilsation to other AGW doom and gloom issues is also off topic. As for CO2 - all I have said is that the jury is still out and things are quite complex. FACE experiments are indeed equivocal and not as good as laboratory studies. As for declines in quality of foodstuffs - well let the plant breeders work at it. You'll be surprised. Don't assume that the current varieties are all you'll have in the future. Same would have been said 100 years ago. I would be more concerned about natural systems - unknown interactions of C3 woodies overtaking C4s by basic metabolic efficiency. Impact of frost from CO2 sensitivity on natural species. But some nation states may win out of AGW on crops and extra CO2. It's Liebig's law of the Minimum. In general I think extra rainfall and temperature will help C3 crops. The way things are going - hope you're one of those nation states. There won't be a global deal on CO2 mitigation and adapation is where we're at. Time to prepare.
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  10. "Why then are you now claiming they did little to simulate expected changes in temperature and precipitation when it so clearly was a integral part of the trials" Yes I recall the study, & I remember thinking at the time that it was a pretty poor recreation of the kind of conditions that we expect to see in 20-40 years time. You've clearly forgotten that. You've also clearly forgotten that the yield increases you cited were *only* seen under the more ideal conditions (regular sowing times & under irrigated agriculture). Likewise you forgot how they mentioned that they were already seeing the impacts of acclimation after just 3 years. Lastly, you seem to forget that the leader of the project was incredibly downbeat about the results in the summary he presented at the time. I think you should make a better effort to understand the FACE trial, & its implications, yourself before you accuse me of a lack of understanding.
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  11. Might I also suggest, John D, that you stop misrepresenting what I said before. I clearly said they did *little* to simulate future conditions-I did *not* say they did nothing at all to simulate it. In fact, as poor a simulation as I believe this to be, it went further than any of the other FACE trials I looked at-which seem to look strictly at eCO2 alone. Again, all the yield boosts you mentioned came from the more ideal conditions + eCO2, yet still the message they present is grim-with future soil-borne disease issues, acclimation issues, poor nitrogen use efficiency & predicted drops in yields across the majority of Victoria between now & 2070. Of course, being in denial, you've chosen to focus only on the numbers which you think "prove" your case.
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  12. As CO2 rises and the world warms, weather patterns change (dry to wet and wet to dry) geographically as the tropics widen and in essential character as drought and deluge becomes the way of the weather. There will be winners and losers in the eco-systems present, as exampled by this years Amazon drought and (in some areas) drought breaking rains in Austrialia. Yet overall it appears the sinks are shrinking and going to shrink further. "Their efficiency in removing CO2 emissions from the atmosphere is expected to decrease in the future under increasing atmospheric CO2 because of their response to elevated CO2 levels, warming and other climate changes. Recent evidence from observations and models suggests that the efficiency of the sinks could have already decreased in the past few decades, but the uncertainties are very large" Trends in the land and ocean carbon uptake Corinne Le Que´ re´ 1,2 Current Opinion in Environmental Sustainability 2010, 2:219–224 Also keep in mind that all the models used to estimate safe CO2 emissions and future carbon cycle behaviour don't include permafrost release and keep increasing the sinks. Then add in ocean warming, rain_forrest droughts, ozone effects, pest increases, the nitrogen situation (reactive nitrogen additions to the land have been a net negative radiative forcing for the 50 years and have significanlty increase primary production), etc...etc Then consider that the Pliocene was 3-5C (1.8-3C in a hundred years of 350ppm or 2090) than present on 350ppm and we're at 390ppm. Stop all emissions today and the gradual uptake by the sinks (~100-200years) will remove another 10-20% of the 110ppm addition of Co2 there has been, so taking it down to an equilibrium of ~370ppm a level at which it will then stay at for eons. Of course as always it is slightly more complicated for as the atmospheric CO2 falls the sinks re-release the carbon they stored, meaning we don't get away with that easy and will still have take all the CO2 out of the atmosphere to get to 350ppm (40ppm or 20 years of current emissions). Then add in the 7-14ppm release per 1C that occurs as the world warms and massive losses to biodiversity that are occuring due to other human past times (meaning eco-systems are unhealthy and vulnerable) making biosphere carbon release much more likely. So the reality is to get anywhere near 2C, and not be facing traumatic change, there is a need to at get least 40ppm of CO2 out the atmosphere as of now, i.e. forget having a carbon budget the human race already has a huge carbon debt and every ounce of carbon from now on just adds more to it. Prevention is better and cure and more effective the earlier it is done so means stopping all fossil carbon emissions asap and transforming land use such that, it not only becomes an enhanced carbon sink but also provides sustainable food, fuel and materials. Even with all that the temperature rise is still likely to rise to at least to 1.5C so major adaptations are already necessary and they will have a carbon cost. Everything that needs fossil fuels to exist (e.g. wind turbines) are extra carbon costs, and as to have any chance of reachign 350ppm all FF emissions really have to stop asap so payback Fossil carbon displacement is a false accounting. Considering basically everything is totally fossil fuels dependent at present and to date CO2 emissions just keep going up (yes 2009 dipped but 2010 rose to the challenge again) both suggestive that all actions so far have been futile; Does anyone have any suggestions?
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    Moderator Response: Converted to hyperlink
  13. "... all actions so far have been futile; Does anyone have any suggestions? " Suggestions only make sense when the problem statement is properly couched. The first question... which is the bigger problem, CO2 toxicity, or climate change? I dont pretend to know the answer to this question, but getting this straight upfront might make a difference.
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  14. "In general I think extra rainfall and temperature will help C3 crops." What you *think* is irrelevant, unless you can back it up with hard *evidence* Luke. Extra rainfall is not much good if it comes after a decade of drought, & as a deluge-yet that is *exactly* what is being predicted here in Australia. warmer temperatures are likely to lead to more rapid ripening, most likely before the plants reach maximum biomass. Also, as with John D, you're choosing to ignore the potential impacts of eCO2 on both soil-borne diseases & insect pests-not to mention the impacts on weeds (which are, themselves, predominantly C3 plants). As to your claims regarding breeding new varieties-you are aware of the kind of time, money & effort that this takes, aren't you? I'd suggest that *not* stuffing up our climate would be far more cost-effective than adaptation. Still, it never ceases to amaze me the lengths some people here will go to defend the interests of the fossil fuel industry.
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  15. Marcus at 11:19 AM, I have a better suggestion, instead of you claiming that I have misrepresented you, why don't we all go back and examine word for word what I wrote and compare it to what you claim that I wrote and see just who is misrepresenting who. There is little humour to be had when a reader misrepresents what someone else has written, but it becomes a big joke when that reader fails to understand just what they have written and so misrepresent themselves, but worse then that, go on to attack those who faithfully quoted what was actually said.
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  16. Interesting that BP & johnd both seized on one paper I linked to in my earlier post (the FACE trial paper) yet apparently failed to take the rest of my advice (" In fact, that issue has several (free access) review papers on climate effects on agriculture that several commentators here would benefit from reading...") For example: http://jxb.oxfordjournals.org/content/60/10/2827.abstract Integrating pests and pathogens into the climate change/food security debate. Gregory et al. (2009) Abstract: "...Globally atmospheric [CO2] has increased, and in northern latitudes mean temperature at many locations has increased by about 1.0–1.4 °C with accompanying changes in pest and pathogen incidence and to farming practices. Many pests and pathogens exhibit considerable capacity for generating, recombining, and selecting fit combinations of variants in key pathogenicity, fitness, and aggressiveness traits that there is little doubt that any new opportunities resulting from climate change will be exploited by them..." johnd says: "Apparently apart from myself and BP few others have bothered to read any of those recommended..." I think that should read "Apparently including myself and BP few others have bothered to read..."
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  17. A couple more references germane to the debate: Impact of Elevated Levels of Atmospheric CO2 and Herbivory on Flavonoids of Soybean (Glycine max Linnaeus) O'Neill et al. (2010) Journal of Chemical Ecology 36 pp 35-45 Abstract: "Plants grown under elevated CO2 conditions experience physiological changes, particularly in phytochemical content, that can influence their suitability as food for insects. Flavonoids are important plant defense compounds and antioxidants that can have a large effect on leaf palatability and herbivore longevity ... Insects feeding on G. max foliage growing under elevated levels of CO2 may derive additional antioxidant benefits from their host plants as a consequence of the change in ratios of flavonoid classes. This nutritional benefit could lead to increased herbivore longevity and increased damage to soybean (and perhaps other crop plants) in the future." Elevated CO2 lessens predation of Chrysopa sinica on Aphis gossypii. Gao et al. (2010) Entomologia Experimentalis et Applicata 135 pp 135-140 Abstract: "... The predatory ability of larvae in the third instar and the total larval stage of C. sinica that fed on A. gossypii were significantly lower in elevated CO2 environments. The number of aphids consumed by first-generation lacewing population did not change significantly with different CO2 treatments; however, significantly fewer aphids were consumed by the second generation of the lacewing population with elevated CO2. We speculate that A. gossypii may become a more serious pest under an environment with elevated CO2 concentrations because of the reduced predatory ability of C. sinica on A. gossypii."
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  18. Well gee Marcus - why don't you look up the photosynthetic temperature optima for many common C3 crops. Then put yourself on the US/Canadian border. It's not that hard.
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  19. John D-here are my exact words, quoted verbatim: "These facts are backed up even by the results of the FACE trials in which they place so much faith-even though said trials do little to simulate expected changes in temperature & hydrology." Notice that I don't actually mention the Horsham trial specifically John? So indeed, you've misrepresented my position even more grossly than even I realized. I will admit that the Horsham trial goes further than any other FACE trial to try & simulate conditions of a warmer world but, seriously, no current field conditions can properly compare with the conditions being predicted for 20-50 years from now-& I'll bet you dollars to donuts that the investigators would agree with me. None of which changes the fact that (a) none of the other FACE trials I've read about simulate conditions of a warmer world-only eCO2 vs aCO2; (b) the yield increases you cited previously, from the Horsham Trial, were those from the irrigated, early sowing crops, not the rain-fed crops sown later in the year; (c) that several FACE trials-including the Horsham trial-have highlighted issues of increased pests, increased soil-borne diseases & reduced nutritional values in an eCO2 world. The fact that you would rather engage in a pedantic attack on my words rather than address the points that I-& many others here-have raised about the extremely simplistic "CO2 is plant food" meme says a great deal to me about your agenda. It also highlights the fact that, until you address the *real* issues, we'd all be better off just ignoring you.
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  20. Plant production is often limited by local exhaustion of carbon dioxide, an essential nutrient, in the immediate vicinity of photosynthesising leaves during calm periods of bright sunshine. Windy countries, such as mine, have an advantage here. Furthermore, there is plenty of evidence that the maniac photosynthetic rate of most plants (why this is so isn't known - it is up to 10X that required) causes global depletion of carbon dioxide for no good purpose. A great number of studies have shown that increased carbon dioxide content stimulates plants. I know of no study that shows "harm" to plants from increased CO2 - there is diminution once the concentration reaches very high levels, but harm, no. I have read recent reports stating that the higher levels of CO2 at present are resulting in greater primary production - not less. As for running out of nutrients - we may be, though that is not established. At present we use extract the plant nutrients we need form concentrated sources, such as mineral rich deposits. However, as need arises we will obtain them from dispersed sources, such as the ocean. The technology already exists to do much of this. It has to be borne in mind that there is no less of any element in existence today. Each is cycled in geological time. Our technology will be able to circumvent this in the future and greatly increase the rate of recycling and reuse. The water issues are ones of misuse and misallocation, rather than overuse. If we give up scientific farming (which has increased production on most US farms by 300% in a lifetime) then people will have to starve. Between 1 B and 3 B will have insufficient food. Do the Greens want that? I don't. Let's find good scientific and technical solutions to our problems, and not rely on unsubstantiated polemic.
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  21. orchestia at 06:32 AM, what you say is right, unfortunately the faith that technology will overcome many of the challenges for agriculture is not shared by those who only see doom and gloom. The debate on whether CO2 has a fertilisation effect on plant growth has advanced considerably. Whereas not so long ago many would not accept that it was real, despite evidence of it having being used commercially for decades, or the evidence shown by results of the FACE trials. Most do now concede that it is not only real, but results in quite significant improved growth. However many who now have no other argument and must accept it as real, now focus on other aspects such as availability of nutrients, pest and diseases, or the ability of plants to adapt With regards to the pests and diseases, they must somehow think that the rapid and ongoing research that has allowed the spectacular advances so far is suddenly going to stopped, that science is suddenly going to enter a new dark age. I don't share that pessimism. When they focus on nutrient availability, it seems that most of their concerns is about nitrogen based fertilisers which seems ludicrous given there is an almost unlimited supply that again technology is helping to improve access to. I do however have concerns for the supply of the likes of phosphorous, potassium, sulphur etc as nature does not provide any natural replenishment and our wasteful lifestyle is wilfully squandering about half of what is required to produce the food that sustains them. However with the will, technology will help over come some this also. Isn't it amazing the lengths that people go to recycle things that aren't so essential, newspapers, soft drink cans and bottles, but ignore the basic nutrients essential to life.
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  22. Wow John D, you still don't get it, do you? The whole *point* of this thread is to show that the impacts of future global warming go well beyond the simplistic "CO2 = more biomass" mantra spouted by the Denialists. No one that I know of here has questioned that, under the right circumstances, enriching the CO2 content of the atmosphere will lead to some increase in *total* plant biomass (not necessarily seed/fruit)-at least in the short to medium term. However, the thing you & your ilk still refuse to accept is that, outside of a controlled environment, an enriched CO2 atmosphere will have a number of negative effects on crop yields-from the impacts of pests & disease, to the impacts of global warming on the activity of Rubisco Activase, to the effects of changed hydrology (droughts & floods). The combined effects of these negatives will almost certainly be enough to offset the straight yield increases garnered from eCO2-especially after acclimation sets in. Now *yes*, maybe some of these negatives can be overcome through the development of new farming techniques-at least in the First World. Of course these measures won't come cheap, & will either send many farmers to the wall or significantly increase the cost of staple food items. Of course, the attitude of you & your ilk is that this is a perfectly good price to pay-so long as the interests of the fossil fuel industry aren't hurt. The rest of us, however, think that it would be much more cost-effective to *not* perform massive experiments on our atmosphere & climatic systems.
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  23. Gentlemen; this discussion has been beaten to death. I understand that my illustrations and video, which take up a large segment of my post, concern the productivity of plants under higher CO2 levels. However, it is not the most important issue in a world which would have as low as 500 ppm of CO2. The issue in point #5 is: "5. The worse problem, by far, is that increasing CO2 will increase temperatures throughout the Earth; making deserts and other types of dry land grow. While deserts increase in size, other eco-zones, whether tropical, forest or grassland will try to migrate towards the poles. However, soil conditions will not necessarily favor their growth even at optimum temperatures. This will seriously decrease the amount of land useful for agriculture." (Last sentence recently added.) Of course, we're quite aware of the counter-arguments, made on this thread, concerning "losers and winners". What we should be discussing is whether or not the losers will far exceed the winners. I offer two points in counter-rebuttal to the implicit assumption of this "losers and winners" argument, that the outcome would somehow balance each other. 1. How much land taken out of commission, or substantially reduced in growing ability, will there be by an increase in aridity. This compared to any theoretical increase in abundance in food crops. 2. I believe this has been mentioned before on this thread. What would be the effects of mass migrations and invasions of those lands with 'enhanced productivity' compared to any benefits to the 'blessed' lands or its inhabitants? In my opinion, this would be an effect equaling or, more likely surpassing, any actual benefits; let alone deficits. I will add an illustration to my desertification point for the purpose of emphasizing its importance. I'll also be adding another brief point concerning AGW caused human migration and invasion. In any case, it's time to switch subjects; PLEASE.
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  24. villabolo#173: "making deserts and other types of dry land grow." Dry land burns really well. "This is a situation of historic proportions," said Victoria Koenig, public information officer with the Texas Forest Service, in a phone interview with AccuWeather.com Tuesday. "The fuels are so dry. The winds are astronomical. The behavior of the winds is a perplexing situation. It's never been like this before."
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  25. I'm with Marcus. Johnd, your characterization of the arc of this debate bears no resemblance to what I have observed, although I suspect we fly in different circles. Biogeochemical models have built in CO2 fertilization in response to increasing CO2 since the 80's, with different responses for C-3 and C-4 plants. The FACE experiments were designed to parameterize those models under a range of conditions, and to test for acclimation and ecosystem level knock-on effects. What really came out of the FACE experiments though was how variable plants were in this respect, and how tricky it is to generalize about responses more specific than photosynthesis. In the end, the effects of CO2 (0-50%, depending on plant) are small and variable compared to responses to precipitation. Why? Well, there is a ceiling to the CO2 effect, it is fully realized for only some species under very specific circumstances (high nutrients, high water, high light). The effect is even less notable for net ecosystem productivity. Water limitation, by contrast is a hard limit for plants, and is very hard to overcome technologically without consequences (ask the people in the Owens "River" Valley!). Variation in precip results in 2 orders of magnitude variation in primary production between ecosystems. That trumps CO2 as a limiting factor every time. Expansion of arid zones will not be compensated on a global level by CO2 fertilization. Seeing how we've dealt so far with famine induced by precipitation in Africa, I'm also not as optimistic about application of technology or of the political will to address the problem in places where rich people don't tread.
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  26. Stephen Baines - I wholeheartedly agree. Johnd appears focused on technological seed/breed development to escape these consequences ("However with the will, technology will help over come some this also."), although he has put forward no actual data to support this - the FACE results appear to be exploring what is within the range of existing plant variants, rather than demonstrating that selective breeding can produce superplants. There does appear to be a small yield effect with increased CO2 for some species (wheat, yes, soybeans, no), fighting with decreased nutritional value, much larger hydrological changes and heat stress, with an end result of at best little change in productivity, but a more likely decrease thereof.
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  27. Why do you guys talk about weather eg euro heat wave as if its climate change? If that's true then the current temperature of the planet based on the UAH temperature record has not increased at all for the last 30 years.what I'm talking about is way closer to what the climate is than a local heat wave in europe.
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    Moderator Response: [mc] See the extreme weather thread for discussion of heat waves.
  28. adrian smits, the current UAH decadal trend is 0.049C, i.e. positive, no matter how you might want to look at it. Is that what you call a non-increase in temperature ? What would you call a negative trend, then - an increase in temperature ? But, looking at the data, I bet you were saying the same between 2008 and 2009; then you probably kept quiet for the last couple of yours; now you want to proclaim a non-increase in temperature; soon you'll be keeping quiet again. Must get confusing for you...
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    Moderator Response: [mc] Take this to Global warming stopped in ... or a similar temperature thread.
  29. Stephen Baines at 13:02 PM, irrespective of flying or otherwise in different circles, your comment on modeling and the FACE trials was merely elaborating on what I noted in post 50,johnd at 10:50 AM on 18 April. Possibly where we differ, certainly where I differ from some others, is rather than using the average results or those results that indicate potential problems to benchmark limitations and feed pessimism, it is the more positive results that will determine the future direction for ongoing research and development. I don't think those involved in conducting such trials have packed up and gone home just yet. On the matter of moisture, again I don't think we differ on it being the ultimate determinate. However given that a warmer world is generally accepted as being a wetter world, then it comes down to how distribution may alter. I believe one of the major factors in changing distribution patterns has been deforestation. The historical removal of forests from around areas of habitation, be it coastal or along river systems, drastically alters how far inland precipitation can penetrate,and where the runoff is subsequently directed, completely altering regional climates. Apart from such human induced changes, the distribution is basically determined by the pattern of differential SST's, both within each ocean basin, and adjoining basins. Given that researchers are only at the stage of being able to reliably forecast SST's 2 years ahead, I am not sure how much faith can be placed in some of the projections looking decades or centuries ahead, especially as the understanding of ocean current circulation is still in it's infancy.
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  30. KR at 13:10 PM, I don't know how you managed to, or why you've done it, but my comment that you highlighted was patently obviously referring to the sentence immediately prior to it regarding the squandering of essential nutrients, and not as you have misrepresented it. Go back and read carefully and it should become obvious. Despite that, regarding your comments on superplants, perhaps some of the existing varieties do qualify when compared to the earliest varieties in which they have had their origins. Think hybrid vigour, increased resistance to pests and diseases, and the ability to not only survive, but increase production under conditions previously considered impossible. Would that not make some of the existing varieties worthy of consideration as superplants?
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  31. JohnC I would like this Post to actually appear in the rebuttal section since I cannot make changes to it. I can only make changes to this post. I'm kind of confused.
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  32. I stumbled onto some very troubling information recently which indicates that (on average) the optimum temperature for photosynthesis in C3 plants is 76F (24.4C) and that a 10% drop in photosynthesis occurs for every degree F until 86 F (30C) is reached. At this point the stoma are 100% closed to prevent water loss. This means that the CO2 argument "high CO2 is good for plants" is false since higher CO2 levels will produce higher temperatures thus lowering agricultural productivity. The results of my Internet-based research (if you can call it research) can be viewed here: http://www3.sympatico.ca/n.rieck/docs/world_population_limit.html I am now very worried that "climate change" combined with "the human population very close to 7 billion" places human culture in very grave danger. When food becomes less available, immune systems will become compromised resulting in pandemics of greater amplitude and frequency. Neil Rieck Kitchener / Waterloo / Cambridge, Ontario, Canada.
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  33. To add insult to injury, many people walk around reciting this grade-school explanation of photosynthesis: "CO2 is converted into O2". A college-level explanation of molecular biology tells us that "all the O2" liberated by plants comes from the photolysis of water (this was proved by radioactive tagging). In this model, hydrogen liberated by the photolysis of water is combined with CO2 to produce glucose. O2 is discarded as waste. Why should anyone care about this detail? Answer: Higher CO2 levels will drive up atmospheric temperature which will increase evaporation. This will cause less H2O to be available for photosynthesis, and it is H2O which will be the limiting factor, not CO2. Less photosynthesis will reduce our food supply while allowing CO2 levels to rise higher. Speculation: to avoid a CO2 run-away effect, humanity may need to engage in a world-wide terraforming of Earth just to get the CO2 problem under control.
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  34. Neil, Be careful with your argument. Much of the world's plant life is location in regions were the average temperature is well below 76F. Therefore, a temperature increase would move plant life closer to its optimal temperature for photosynthesis. Your water analysis is true wherever water is the limiting factor to plant growth. Other factors may be the limiter; temperature, sunlight, nutrients, even CO2. In areas where water is the limiting factor and evaporation outpaces precipitation photosynthesis will decrease.
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  35. EtR#184: "... a temperature increase would move plant life closer to its optimal temperature for photosynthesis" And yet we find the opposite: During the post Pinatubo cooling, the rate of increase of atmospheric CO2 dropped markedly due to enhanced photosynthesis -- clearly seen as the early 90s flat spot on the familiar CO2 graphs. From Robock 2003, Enhanced forward scattering of incoming solar radiation caused by the Pinatubo aerosols increased the diffuse radiation reaching the surface and decreased the direct flux. This allowed plants to photosynthesize more of the time, increasing the CO2 sink ... model experiments showed that the cool temperatures over land following volcanic eruptions produced reduced soil and plant respiration globally and enhanced gross primary productivity in the tropics, both of which would also reduce atmospheric CO2 concentrations. On a related note, temperature impacts maximum tree height, but not in a good way: The group used the same model to predict what would happen to tree height in the event of global temperature changes, and found that with an increase of 2 degrees Celsius across the country, the average height of the tallest trees would shrink by 11 percent. Conversely, a dip of 2 degrees Celsius would spur trees to sprout up by 13 percent.
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  36. Muon, Does that mean that 76F is not optimum for photosynthesis? I am not a biologist, so I was taking Neil's statements at face value.
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  37. EtR#186: No, it means that during an approximately 2 year volcanic aerosol induced 'global cooling' event, a higher percentage of CO2 was taken out of the atmosphere, apparently due to conditions conducive to enhanced plant growth. Hence the obvious flat spot. Your point in #184 refers to 'average temperature'; without further specification, that means annual average. Wouldn't it be more relevant to look at average temperature during the active growth season? DB -- see #182.
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    Moderator Response:

    [DB] My bad...buttinski response withdrawn (I picked a bad day to stop drinking bourbon).

  38. Neilrick @183, I'm no expert, but as glucose contains carbon, a source of carbon (CO2) must also be used in photosynthesis. Indeed, based on the generalized equation for photosynthesis, at least half of the oxygen released by the process must come from CO2: CO2 + 2H2A --light--> CH2O + 2A + H2O (where A is Oxygen in normal photosynthesis, and Sulfur in green sulfur bacteria) In essence the process could be understood as hydrogen being split from water by light, releasing oxygen as waste, and then the hydrogen reducing CO2, releasing half of the oxygen bound in the CO2 as waste. Moving to the essential point, regardless of the source of the oxygen, CO2 is still necessary for the formation of the sugar. Therefore higher concentrations of CO2 will make photosynthesis proceed faster, all else being equal. Of course, all else is definitely not equal in a warming world, as you point out.
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  39. Clarrifying my 188, an oxygen atom is split of the CO2 in the reduction process, releasing water as waste. So Neilrick's original statement about the source of the oxygen molecules is correct. The essential point still stands, however.
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  40. Actually, the process of photosynthisis is much more complicated than presented here, and requires interplay between more nutrients. The structural strength of cell walls etc are a huge component. This requires the micro nutrients at play. The optimum temp of optimum photosysnthis is plant dependant. As an example, wheat is what is called a cool season grass. Optimum growth is obtained at approx 76F. Corn is a warmer season type grass. Optimum temp is 81F. Rye grass is 71F. It is hard to pin an overall optimum temp for constructive vegetative growth as the window is in fact quit large.
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  41. It's also important to recognize that photosynthesis is a rate limiting system. The ingredients (light, temperature, water, carbon dioxide, and oxygen as an inhibitor) are all necessary in the right proportions for any particular plant. The system is only as good as the component that is in the lowest supply. You can have optimal levels of everything else, but it only produces according to the least available component. To make it analogous to a robot factory, you can have zillions of arms, legs, heads, and CPUs, but if you only have 100 bodies, you can only make 100 robots. Increasing any one component to an optimal value does little good, particularly if something else is already below or even changes away from its optimal value, or any one component moves into very unproductive territory. In particular, no matter what the level of CO2, many plants will shut down photosynthesis if they are losing too much moisture (due to elevated temperatures or dry conditions) and so are unable to productively keep their stomata open to take in the required CO2. So it is ridiculously simplistic to focus on one element like CO2 and to say that more is better without bothering to focus on other factors. And, in fact, because different plants have evolved for different conditions, even more CO2 may not be in our best interests. As one example, Corn is a C4 plant that has evolved to live with less water and lower CO2 levels. A change in CO2 or an accompanying change in temperature and moisture could easily make other plants more competitive, and reduce corn crop outputs. The same applies to any crop or plant you can think of. Yes, more CO2, under the right conditions may be good for plants in general... but not the same plants that enjoy dominance in today's climate.
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  42. 189, Tom, It should be pointed out that overall photosynthesis needs and uses H2O to create complex carbon chains. It does not, in aggregate, generate H2O as a "waste" product, as it does with O2.
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  43. Sphaerica @192 - agreed. But the entire process can be understood as two steps: 1) Takes two water molecules, and produces four hydrogen ions and leaves an Oxygen molecule as waste. 2) Takes a CO2 molecule and those four hydrogen ions and produces a sugar, and a water molecule as waste. The net process consumes CO2 and water to produce sugar and oxygen.
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  44. I agree with Tom and Sphaerica, Plants growth will be determined by the limiting factor. If that factor is CO2, then plants will experience mroe growth in a CO2 rich environment. If that factor is anything else (as mentioned previously), then increased levels of CO2 will be immaterial.
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  45. Eric: Yes and no. An increase in co2 results in a plant becomeing more efficient as a rule. The increase in co2 will overcome some of the other limiting factors becauase of improved root mass and less respiration.
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  46. Eric, it isn't as simple as that. In general plant life is adapted to an environmental niche; climate change may well make conditions more optimal for photosynthesis in some location, but not for the species of plants that are currently growing there. If you are a tree living at the edge of your environmental niche, it will be of little consolation that your death will provide a useful habitat for some other species (forgive the anthropomorpisation). As with human civilisation, it is the change that is the problem, rather than the eventual environmental conditions. We (and especially our agricultural practices) are adapted to a particular climate. Any change means that our practices are suddenly sub-optimal. This is a problem if you can't adapt (for instance because you are a tree ;o).
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  47. Was not aware of that Camburn. As I mentioned earlier, I am not a biologist. Are there other processes that might be affected by rising CO2 levels? Dikran, I think your environmental changes may fall under Sphaerica's list (191). If temperature, water, or some other factor is the limiter, then unfavorable changes in that factor would make conditions worse. Baring an unfavorable change, increases in atmospheric CO2 will enhance plant growth. See Tom's post @193. Change is not necessarily bad. It all depends on what change occurs.
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  48. 197, Eric the Red, I think you misunderstand. All of those factors are limiters. Which ever is in the least supply is the one that governs production. CO2 increase is meaningless if it is accompanied by temperature, light (clouds) or moisture changes which push things away from the optimums for those factors. Or, in other cases where other changes are needed but don't arise (like a desert, where moisture is already low) the increase in CO2 is meaningless. And all of these factors (precipitation patterns, temperatures, etc.) are going to change virtually everywhere with climate change. It doesn't even help if the change in temperature is better for most of the year, but out of the range for a particular crop for just three weeks (during the growing season). That will kill any benefits that might have been realized by CO2. My point is that hanging your hat on "more CO2 is good" is almost certainly so simplistic as to be beyond rational consideration. Your rephrasing to say "barring an unfavorable change" is trying to dismiss the importance of those other factors by implying that changes in them are unlikely, so we can all cheer for more CO2. That is, quite simply, absolutely not the case.
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  49. Sphaerica @198, I think Camburn's point at 195 is a valid one. In an enhanced CO2, moisture restricted environment a plant can divert more of its resources from harvesting sunlight to harvesting water (increased root mass), thus partially compensating for the lack of the primary limiting factor (moisture) because of a superabundance of another factor (CO2). Therefore, if soil moisture remained constant, the plant could have enhanced growth as a result of enhanced CO2, even where water was the primary limiting factor. Another adaption of this type which is a common feature of high CO2 environments in the past is reduced stomata, evidenced in the fossil record. The reduction in stomata means the plant does not gain as much growth advantage from the elevated CO2, but does conserve water better. The problem glossed over by deniers is that: 1) The changes stimulated by higher CO2 content are not all advantageous under normal environmental conditions. For example, trees grown in enhanced CO2 atmospheres show reduced ability to close stomata in dry conditions, thus making them more, not less vulnerable to drought. 2) The environmental conditions themselves will also change, thus potentially overwhelming any gain made by the plants. Thus if increased temperatures result in a 10% loss of soil moisture, a 5% increase in root mass due to enhanced CO2 still leaves the plant stressed and possibly dying due to lack of water (where water was the limiting factor). 3) Large scale and rapid changes in climate, which are likely in the coming centuries will overwhelm the ability of plants, particularly native species, to adapt in the short term, as you point out. Most of the biology I have learnt comes from the study of evolution. Consequently I have no doubt that a warmer world will be a more productive world, ie, sustain a greater biomass in the long term. But the long term is 10 thousand to 10 million years, depending on the scale and pace of the initial perturbation. A ten thousand year recovery will be little consolation to our descendants in the next few centuries.
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  50. Thank you Tom, By itself, it appears that increased level of CO2 will only benefit plant growth. However, if environmental conditions change for the worse as a result, then those changes could overwhelm the gains made by CO2 increases. Do we know how readily plantlife could adapt to changes in temperature and/or precipitation? Obviously, different plant species will respond differently.
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