# Global warming and plant growth **URL:** \ **Category:** Factual Questions\ **Created:** [April 11, 2007, 9:45pm UTC](https://boards.straightdope.com/t/global-warming-and-plant-growth/399706 "2007-04-11T21:45:18Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![XT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/xt/32/456_2.png) [@XT](https://boards.straightdope.com/u/XT)\ **Post date:** [April 11, 2007, 9:45pm UTC](https://boards.straightdope.com/t/global-warming-and-plant-growth/399706/1 "2007-04-11T21:45:18Z")
One aspect of Global Warming I’m curious about is…assuming the GW is happening and is going to continue, what effect will this have on plant growth? I’ve seen a number of gloom and doom web sites saying crops will fail, the earth will dry up, etc etc…but is this really the case? Seems to me plants LIKE CO2…and won’t the extra heat have the effect of causing more water vapor to be put into the air, thus causing more rain? Can someone explain how this is likely to work in simple terms? It seems counter intuitive to me that plants will die and the earth will dry up considering the temperature changes I’ve read that are likely in the next century. -XT ---
**Author:** ![Kimstu](https://avatars.discourse-cdn.com/v4/letter/k/ecd19e/32.png) [@Kimstu](https://boards.straightdope.com/u/Kimstu)\ **Post date:** [April 12, 2007, 12:10am UTC](https://boards.straightdope.com/t/global-warming-and-plant-growth/399706/2 "2007-04-12T00:10:41Z")
I haven’t seen any climate scientist predicting that the earth as a whole will become a desert as a result of climate change as currently understood. According to the best estimates from the current models, some regions will get wetter and some drier. This will be good for agriculture in some areas and seasons and bad for it in others. As [this article](http://www.berkeley.edu/news/media/releases/2005/08/02_carbon.shtml) notes, > [@](#): > > Some scientists have suggested that the land and oceans will continue to absorb more and more CO2 as fossil fuel emissions increase, making plants flourish and the oceans bloom. > > [Berkeley prof. Inez Y.] Fung’s computer model, however, indicates that the “breathing biosphere” can absorb carbon only so fast. Beyond a certain point, the planet will not be able to keep up with carbon dioxide emissions. > > “The reason is very simple,” Fung said. “Plants are happy growing at a certain rate, and though they can accelerate to a certain extent with more CO2, the rate is limited by metabolic reactions in the plant, by water and nutrient availability, et cetera.” > > In addition, increasing temperatures and drought frequencies lower plant uptake of CO2 as plants breathe in less to conserve water. A second study she and colleagues published last week in PNAS report evidence for this temperature and drought effect. Since 1982, a greening of the Northern Hemisphere has occurred each spring and summer (except for 1992 and 1993, after Mt. Pinatubo erupted) as the climate has steadily warmed. As a result, there is a small but steady decline in atmospheric CO2 each growing season due to increasing photosynthesis at temperate latitudes in the northern hemisphere. When Fung and a team of her former and current post-doctoral fellows took a detailed look at this phenomenon, however, they discovered that since 1994, enhanced uptake of CO2 as photosynthesis revved up in the warm wet springs was offset by decreasing CO2 uptake during summers, which became increasingly hot and dry - an unsuspected browning in the past 10 years. > > “This negative effect of hot, dry summers completely wiped out the benefits of warm, wet springs,” Fung said. “A warming climate does not necessarily lead to higher CO2 growing-season uptake, even in temperate areas such as North America.” ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [April 12, 2007, 12:13am UTC](https://boards.straightdope.com/t/global-warming-and-plant-growth/399706/3 "2007-04-12T00:13:42Z")
[QUOTE=xtisme] Can someone explain how this is likely to work in simple terms? [/quote] No, because it isn’t a simple process. It’s a dman good question though. > [@](#): > > Seems to me plants LIKE CO2… They do, just like human like extra fat and extra salt. That doesn’t mean they are adapted to it. And because they aren’t adapated to it it tends to poison them just like excess fat and salt poisons humans. CO2 is essentially a fertiliser, but it’s naturally so stable that plants haven’t evolved any mechanism to cope with variation as they have with nitrogen or phosporus. Current research indicates that even moderate CO2 fertilisation reuslt i n malformation in most plants. They outgrow their own structural limitations. This uslally manifests itself as plants that lack robusteness. They grow so well when conditions are ideal that they lose all the structual defences against stress. As a result they can’t handle heat, they can’t handle cold, they can’t handle drought, they can’t handle rain, they cna;t handle disease and so forth. In short CO2 is a fertiliser in a sterile greenhouse, but it’s poison to any plant that has to be able to grow outside. Unfortunately as with many aspeects of this problem it’s going to be poor susbistence farmers who will be hit hardest. If you can afford irrigation, fertiliser, pesticide and so forth you can mitigate many of the worst effectsof CO2 fertilsiation by elimianting stress. If you can’t afford those things you’re up the proverbial. The next problem is that many tropical herbaceous plants, especially grasses, are what we call C4 and they have evolved to be competeive at low water and low CO2 levels. As CO2 levels increase they become less competitive with trees and broad leafed weeds. Thatmay not seem like a problem, but if you have to make aliving off your cattle and sheep then seeing your grasslands replaced with forests is a tragedy. Moroever a great many species depend on the existence of tropical grasslands. If they vanish you’ll see massive extinctions. And once again the people who will be suffering most will be those in tropical nations, which are the poorest. There are many other problems of CO2 fertilisation, but those are the two biggest worries. > [@](#): > > …and won’t the extra heat have the effect of causing more water vapor to be put into the air, thus causing more rain? Yes, and no. Yes we’ll see increased evpaoration. How that translates into precipitation is anyone’s guess. The big problem is that rainfall patterns will _change_. Areas that are currently arid will become moist, areas that are humid will become arid. That means massive starvation and huge expenses relocating populations and infrastructure to the new cerntresof productivity. In addition most of the world’s conservtation areas were conserved because they were unproductive. If the alteration in precipitation makes areas like the Serengeti or the Gobi productive then we end up with people moving into those areas. Where does the wildlife go? Neither we nor the wildlife can afford to wait 500 years to establish an laternatiev habitai in a newly arid zone since that would mean leaving an area twice the size fallow for that period. What we know will happen is that people will move into these newly productive zones and the wildlife will simply vanish. In addition precipitation is likely to become unreliable as the global systems try to find a new equilibrium. That means frequent droughts punctuated by floods. You only need to look at Australia to see what that does to productivity. Even areas of good rainfall are relatively unproductive because nobody can afford to invest in such a risky enterprise. At the end of the day you are looking at an unpredictable change, and that is never a good thing. It’s like playing Russian roulette. ---
**Author:** ![Kimstu](https://avatars.discourse-cdn.com/v4/letter/k/ecd19e/32.png) [@Kimstu](https://boards.straightdope.com/u/Kimstu)\ **Post date:** [April 12, 2007, 12:25am UTC](https://boards.straightdope.com/t/global-warming-and-plant-growth/399706/4 "2007-04-12T00:25:29Z")
> [@Blake](#): > > an laternatiev habitai Not being a typo nazi here, but this phrase actually stumped me so much that I had to feed it into Google before I figured out that it was probably intended to be “alternative habitat”, so I thought I’d pass along that info in case anybody else was confused by it. ---
**Author:** ![elelle](https://avatars.discourse-cdn.com/v4/letter/e/f0a364/32.png) [@elelle](https://boards.straightdope.com/u/elelle)\ **Post date:** [April 12, 2007, 12:34am UTC](https://boards.straightdope.com/t/global-warming-and-plant-growth/399706/5 "2007-04-12T00:34:42Z")
**Blake** , A fine reply to a good question. Can you add any commentary on large trees/forests being cut, and health of sustainable soil ecosystems, particularly mycorhizzal systems ? ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [April 12, 2007, 12:34am UTC](https://boards.straightdope.com/t/global-warming-and-plant-growth/399706/6 "2007-04-12T00:34:43Z")
😛 ---
**Author:** ![elelle](https://avatars.discourse-cdn.com/v4/letter/e/f0a364/32.png) [@elelle](https://boards.straightdope.com/u/elelle)\ **Post date:** [April 12, 2007, 12:35am UTC](https://boards.straightdope.com/t/global-warming-and-plant-growth/399706/7 "2007-04-12T00:35:48Z")
Yikes, simulpost. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [April 12, 2007, 12:47am UTC](https://boards.straightdope.com/t/global-warming-and-plant-growth/399706/8 "2007-04-12T00:47:03Z")
[QUOTE=elelle] **Blake** , A fine reply to a good question. Can you add any commentary on large trees/forests being cut, and health of sustainable soil ecosystems, particularly mycorhizzal systems ? [/QUOTE] I’m not sure I understand. It’s not immediately obvious that those factors will have any influence on the influence of increased CO2 levels on plant growth. ---
**Author:** ![wevets](https://avatars.discourse-cdn.com/v4/letter/w/e9a140/32.png) [@wevets](https://boards.straightdope.com/u/wevets)\ **Post date:** [April 12, 2007, 12:49am UTC](https://boards.straightdope.com/t/global-warming-and-plant-growth/399706/9 "2007-04-12T00:49:29Z")
**Blake** and **Kimstu** have provided some good information, but I just wanted to add to what they’ve said - that yes, CO[sub]2[/sub] is a necessary resource for plants, but no - just adding CO[sub]2[/sub] to the atmosphere is unlikely to universally boost plant growth. It’s not clear that large portions of the biosphere have CO[sub]2[/sub] as their limiting nutrients. Nitrogen, Phosphorous, and other nutrients are much more likely to be limiting in many cases, and not all plants uniformly benefit from an increase in CO[sub]2[/sub]. Recently I came across a paper that addressed exactly this question for forests, and it attempted to answer the question of whether increased CO[sub]2[/sub] in the atmosphere would increase tree biomass across four different climatic zones. > [@Christian Körner](#): > > It is concluded that, irrespective of the reason for its periodic cessation, growth does not seem to be limited by carbon supply. Instead, in all the cases examined, sink activity and its direct control by the environment or developmental constraints, restricts biomass production of trees under current ambient CO2 concentrations. From [Carbon limitation in trees](http://www.blackwell-synergy.com/links/doi/10.1046%2Fj.1365-2745.2003.00742.x) _Journal of Ecology_ It turns out that better than trying to fertilize the biosphere by adding carbon dioxide would be to use, well, fertilizer. Carbon limitation is probably much more common in systems that don’t have direct contact with the atmosphere - aquatic and subterranean ecosystems. While it’s true that some plants can increase growth in experiments where CO[sub]2[/sub] is artifically increased, these experiments are usually done in greenhouses and without other nutrient limitation. I am not aware of any _in situ_ experiments that suggest increases in growth across the flora of an entire ecosystem can be caused by increases in CO[sub]2[/sub]. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [April 12, 2007, 1:04am UTC](https://boards.straightdope.com/t/global-warming-and-plant-growth/399706/10 "2007-04-12T01:04:21Z")
[QUOTE=wevets] I am not aware of any _in situ_ experiments that suggest increases in growth across the flora of an entire ecosystem can be caused by increases in CO[sub]2[/sub]. [/QUOTE] I’ve seen quite a few field experiments and they all suggest just the opposite: CO2 fertilisation reduces productivity. It does that in a number of ways but essentially plants just aren’t adapted to variations in CO2 levels. Either it has no effect or, more usually, it has a negative effect.