Global warming and plant growth

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

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 notes,

No, because it isn’t a simple process. It’s a dman good question though.

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.

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.

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.

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 ?

:stuck_out_tongue:

Yikes, simulpost.

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.

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.

From Carbon limitation in trees 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].

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.