Will rising carbon dioxide levels really boost plant growth?
Plants have become an unlikely subject of political debate. Many projections suggest that burning fossil fuels and the resulting climate change will make it harder to grow enough food for everyone in the coming decades. But some groups opposed to limiting our emissions claim that higher levels of carbon dioxide (CO₂) will boost plants' photosynthesis and so increase food production.
New research published in Science suggests that predicting the effects of increasing CO₂ levels on plant growth may actually be more complicated than anyone had expected.
To understand what the researchers have found out requires a bit of background information about photosynthesis. This is the process that uses light energy to power the conversion of CO₂ into the sugars that fuel plant growth and ultimately provide the food we depend on. Unfortunately, photosynthesis is flawed.
Molecules of CO₂ and oxygen are similar shapes and the key mechanism that harvests CO₂, an enzyme with the catchy name of RuBisCO, sometimes mistakes an oxygen molecule for one of CO₂. This wasn't a problem when RuBisCO first evolved. But about 30m years ago CO₂ levels in the atmosphere dropped to less than one-third of what they had been. With less CO₂ around, plants began mistakenly trying to harvest oxygen molecules more often. Today this is often a substantial drain upon a plant's energy and resources.
As it gets hotter, RuBisCO becomes even more prone to errors. Water also evaporates faster, forcing plants to take measures to avoid drying out. Unfortunately, stopping water getting out of their leaves also stops CO₂ getting in and, as RuBisCO becomes starved of CO₂, it wastes more and more of the plant's resources by using oxygen instead. At 25°C, this can consume one-quarter of what the plant produces – and the problem becomes more extreme as temperatures rise further.
However, some plants developed a way to avoid the problem by pumping CO₂ to the cells where the RuBisCO is located to turbocharge photosynthesis. These are known as C4 plants, as opposed to normal C3 plants which can't do this. C4 plants can be much more productive, especially under hot and dry conditions. They came to dominate Earth's tropical grasslands from 5m to 10m years ago, probably because the world became drier at this time and their water use is more efficient.
Maize (corn) and sugar cane are C4 plants but most crops are not, although a project initially funded by the Bill and Melinda Gates Foundation has been seeking to improve yields in rice by adding C4 machinery to it.
Most models of how plant growth and crop yields will be affected by the CO₂ released by burning fossil fuels have assumed that regular C3 plants may perform better. Meanwhile, the RuBisCO in C4 plants already gets enough CO₂ and so increases should have little effect on them. This has been supported by previous short-term studies.
The new Science paper reports data from a project that has been comparing C3 and C4 plants for the past 20 years. Their findings are surprising. As was expected, for the first ten years, C3 grasses grown under extra CO₂ did better – but their C4 equivalents did not. However, in the second decade of the experiment the situation reversed, with the C3 plants producing less biomass under higher levels of CO₂ and the C4 plants producing more.
It seems that this perplexing result may be because as time went by, less nitrogen was available to fertilise growth of plants in the C3 plots and more in the C4 plots. So the effect was not just due to the plants themselves but also to their interactions with the chemistry of the soil and its microbes.
These results suggest that the way that changes in CO₂ affect established ecosystems are likely to be complex and hard to predict. They may hint that, as CO₂ in the atmosphere increases, C4 tropical grasslands could perhaps absorb more carbon than expected, and forests, which are predominantly C3, might absorb less. But the exact picture is likely to depend on local conditions.
Impact on food
What this means for food production may be more straightforward and less comforting than at first glance. These results are from grasses that survive and continue to grow year on year. But current cereal crops are "annual plants" that die after one season and have to be replanted.
As a result, they don't have the opportunity to build up the soil interactions that seem to have boosted growth of the C4 plants in the experiment. We can't expect that our food security problems will be solved by C4 crop yields increasing in response to CO₂ as they did in the experiment. Similarly, the eventual fall in biomass seen in the C3 plots shouldn't happen in C3 annual crops.
But, as we know, C3 plants waste a lot more resources at higher temperatures, so any increase in photosynthesis from rising CO₂ levels seems likely to be at least cancelled out by the effects of the global warming it will cause. And that's without factoring in changes to rainfall patterns such as more frequent droughts. Solutions that seem to be too good to be true generally are – and, for the moment, that still seems to be the case for the idea that CO₂ enhanced crop yields will feed the world.
User comments
Half the Great Barrier Reef is gone now. Coastal areas are flooding. Droughts and wildfires are increasing.
CO2 may be a trace gas, but the fact there's enough of it that it can build every plant on earth shows that "trace gas" doesn't mean a thing in practical terms.
Stop destroying the planet for a bunch of oligarchs that couldn't care less about you
Hyper nonsense. this millenium is at the hot peak of the interglacial, which is due to axis and orbit oscillations. The temps would be expected to warm for the next 300-500 years and then cool down. So it's too early to warm the earth. millions of Africans and Arid climate people will be forced to flee away from their homelands into rich countries for food security, because people like this guy don't understand science or politics and they stab themselves in the back with their own confusion.
They are already fleeing in the millions due to the wars in the ME created by the One World Government deep state. Soros and the like are doing a great job of creating the world unrest needed to collapse western democracy.
https://www.natur...13254108
Yeah, right!! There were cooler periods! It actually was cooler this morning. And the 90s were definitely very cool! Hell, there even was a president who played sax, you tell me if this is not cool. And lets not forget taht my fridge is cool too!
Nah, forget it, I'll set you in the ignore list.
This has delayed plantings in many regions and will affect crop yields .
None of this is new. We know that increasing CO2 increases yields in the short term but after a point it can lead to reduced yields through plant toxicity - and even increase CO2 levels further as plant respiration rates change. That's before we take into account the impact of fast-changing seasons, rainfall and the shift of climatic zones. More importantly, higher CO2 levels don't necessarily benefit our food crops, even in the short term. There's no point in living in a lush, green world of inedible weeds growing in the wrong locations.
Not within the next century or more.
So what? What that has that got to do with us causing the recent warming?
It's a proven scientific fact that CO2 produced by human activity causes global warming because both well-tested basic physics tells us CO2 should cause warming and the empirical evidence has now confirmed it.
And there isn't any empirical evidence nor credible scientific theory to the contrary.
So you make a straw man and then blow it down.
Extremely few if any scientists have ever claimed that they have proven the world will starve in 10 years time.
You must be getting desperate; you cannot attack the scientific evidence that contradicts your twisted opinions and lies so you make up straw man crap to attack the scientists that collected or discovered that evidence you don't like.
One of the more important molecules plants need is CO2 without which the plants will die!
Plants need CO2, sunshine, nitrogen, oxygen and a long list of trace elements.
Take any element away and plants suffer.
So why has nature created the circumstances where plants are depleting the atmospheric CO2?
On a more insane level, why has nature evolved humans beings to remove large quantise of CO2 and bury them underground so plants cannot utilise the CO2, are there a species of human beings that have evolved suicidal tendencies!
"Many projections" claim that increasing CO2 will negatively impact agriculture in the future, while other studies show the increase in atmospheric CO2 has improved agricultural production. Which is right? Here's the fundamental difference in how they arrive at their conclusions: the projections of decreasing food production are entirely based on assumptions and computer models that have yet to be verified. The studies projecting increased crop yields from more CO2 are based on actual measurements and decades of studies and tests of CO2 on crops.
Worldwide agricultural production has been steadily improving over the last century largely due to technological improvements and there is no sign that will change anytime soon. The only people claiming it will are the climate alarmists.
No, because pumping CO2 into greenhouses don't cause droughts floods and hurricanes to destroy the same specific crops inside those greenhouses. That isn't specifically what this article argued but rather it suggested that how much plants benefit from more CO2 depends both on local conditions and whether they are C3 or C4, which is also correct because that is a proven scientific fact. That suggestion doesn't in anyway contradict or is in any way inconsistent with CO2 enrichment in greenhouses usually causing greater plant growth and yield.
Using your same moronic 'logic', burning fossil fuels to heat your home doesn't help you to travel so you would guess all those 'dumb' car drivers who pump fossil fuels into their car fuel tanks are wasting their time.
we obviously all already know this and it's irrelevance to the fact that too mush extra CO2 in the atmosphere will cause us some problems with global climate.
When we propose to stop putting extra CO2 in the atmosphere, we are obviously not proposing to remove all the CO2 that is already in the atmosphere and you are a moron for making the straw man that we propose to remove all CO2.
Take a look at some of the results of this ongoing mutidecadal study.
http://www.biocon.umn.edu/
http://www.biocon.umn.edu/sites/g/files/pua2906/f/media/reichhobbiencc2013.pdf
http://www.biocon.umn.edu/sites/g/files/pua2906/f/media/reich.nature.2006a.pdf
http://www.biocon.umn.edu/sites/g/files/pua2906/f/media/lauoecol2009.pdf
http://www.biocon.umn.edu/sites/g/files/pua2906/f/media/bassiri.gcb_.2003.pdf
Obviously not entirely based on assumptions and computer models that have yet to be verified.
or vice versa
https://www.ideal...quence=2
There are currently no scientifically creditable alternative explanations of the main cause of the recent global warming for us to 'ignore' because the alternatives have already been examined and proven false and scientists are no more 'greedy' than you are and any 'greed' won't debunk empirical evidence or proof.
Lets say Newton and Einstein were greedy; so the law of gravity must be wrong?
you cannot ever validly attack science by attacking the character of the scientists.
No, its the truth. And your moronic link there tells plain lies for that machine mentioned in that link proves nothing it says it proves. What that centrifuge machine does is entirely irrelevant to what greenhouse gasses do; what a load of morons they are.
Higher levels of CO2 are harmful eh?
yes
1- your link is from 2012. if you want to learn about the detrimental effects, see SteveS post above: http://www.biocon.umn.edu/
2- since you have repeatedly ignored my multiple links to studies in the past, I am just going to post this link which directly refutes your claims with additional links/references you will also ignore: https://skeptical...nced.htm
deniers have claimed every year that the science is wrong for as long as I can remember, and the reality is that it keeps getting validated proving the deniers wrong
At some point the story of the boy who cried wolf becomes relevant
Trying to feed your dog twice as he can use much will not give you a dog that is twice as big. He will not only fail, he will have serious health issues.
For most C3 plants, growth can be increased almost 80% with enhanced CO2. This however assumes absolutely optimum amounts of water, other nutrients and sunshine (double natural light). Plants grown like this are also much weaker and susceptible to natural pathogens.
Interactions with individual micro-environments is the reason its so hard to tell benefits/detriments.
Outside, growth is limited by whatever thing the plant needs is most limited. In natural sunlight, optimal water and nutes, you can get a modest increase in growth with additional CO2, all other things being equal. But increasing temperature usually impacts water availability, and has detrimental effects on the amount of light convertible to plant mass.
Taking greenhouse results using enhanced lights as evidence climate change is beneficial is just plain stupid.
I am guessing they don't get the "real world" part of that.
C3. beans, rice, wheat, potatoes. most temperate crops. all woody trees.
C4. corn, sugarcane, amaranth. hot, dry. mostly grasses but some shrubs (cold-tolerant)
CAM. cactus, euphorbia, some orchids (epiphytic) short of water, not too hot.
Corn had record high yields per acre in 2017.
https://www.agweb...aa-usda/
It is all to easy to predict disaster and the high priests have been making a living doing so for 1000s of years.
Climate change also impacts weather variability. What good is 1% more plant growth if the chance of dying off due to extreme frost or extreme heat is upped by 50%?
Exactly backwards!! What do you think that fossil coal oil and gas is??? It is carbon that the PLANTS sequestered millions of years ago during a period when the Earth was a giant greenhouse! Now we stupid humans are digging up and releasing the stored CO2 of an entire geological era in mere decades. The problem isn't any particular CO2 level or change, it is the fast rate of change we are causing. Things are changing faster than nature and our infrastructure can adapt. The CO2 causes weather pattern shifts which are very disruptive. Have you noticed the link between crop failures and civil war in Africa?
" as the climate may be a moving target for centuries to come." So what else is new, climate changes.
MR166
Before making idiotic baseless assertions against the known scientific facts about climate like you did above, you could at least bother study what those known facts are which you clearly haven't above.
It is and has been long known that global warming means warmer oceans thus more evaporation from oceans that will cause more average global rainfall; and NO climate scientists are claiming the contrary, idiot.
Obviously, warmer global temperatures would have complex local climatic effects making some areas drier and others wetter while increasing the overall annual average global rainfall. The greater local variably of monthly rainfall caused by warmer global temperature mains greater frequency of droughts (and floods) despite the overall yearly average global rainfall being higher.
Yes and all of that is predicted by the illustrious climate models and nothing else. As I said, NO REAL PROOF!
Cival wars cause death and destruction and famine, no hands to till the fields!
Nothing to do with global warming.
Nope; we are already seeing greater variability in weather across the globe; exactly as the models predicted.
That is a subjective statement with no mathematical proof to back it up. Any "change" at all qualifies as proof in your world.
there is experimental and observational proof - but you choose not to see it
considering your refusal to even consider historical evidence and modern validation (like Francis, Vavrus) then exactly how would anyone actually convince you of anything at all?
you've actively chosen to ignore not only experimental data but observed data - that is, by definition, delusional and fanatical behaviour
just because you refuse to see it and believe in reality doesn't mean it's not real and that you can fly with a black feather in your nose...
https://www.clima...ary-2016 El Nino seems to be a big suspect as a factor in this one.
http://www.opusa....esponse/
"mathematical proof"? You mean you think we need a "mathematical" proof rather an observational one to scientifically prove a model correctly predicts something in the real world? No, we require observational proof, which we do indeed have. And that proof isn't "subjective" as it comes out the readouts of our measuring instruments. Are you a flateather?
Yes we need mathematical proof that the data is not random noise in the system. This has nothing to do with models. There will be plenty of papers "Proving" that this years cold in the US and Europe was caused by CO2 just as there would have been plenty of papers "Proving" that the warmth was caused by CO2 if it was warmer than usual. You see the models prove that there is no such thing as a natural change.
What are you talking about?
So all those, say, temperature measurements made independently around the world consistently showing, say, a clear annual average ocean surface temperature increase within the known error of measurement, could be, according to you, so called "random noise in the system" thus false? Please don't talk bullocks. And what would, according to you, such a "mathematical proof" look like for that? Can you give a specific example of such a "mathematical proof" that "the data is not random noise in the system" and explain why it is required? You have absolutely no idea what you are talking about.
There is nothing wrong with our measurements of temperature and rainfall amount and wind speed. Try again.
I see one glaring problem with that comment: you've historically ignored any and all scientific data presented in those areas, be it statistical analysis or probability of occurrence due to CO2
FrancisVavrus comes to mind here as it's directly related:
It was hypothesized and modelled, then studied, then it was predicted to do [x] which was subsequently validated, and it currently demonstrates the situation with you perfectly
so tell me, if you were to be given this data, what would it do to your beliefs?
would you accept AGW? or would you deny it and give your many varied excuses you've historically used to ignore it already?
No, it depends on the evidence and the actual validity of its proposed interpretation irrespective of what people including scientists think accept or believe.
I agree and that is why I specified non partial scientists to review the findings. Accepted was a poor choice of word and validated would have been better.
a validated study *is* and *must be* reviewed by non-partial scientists - usually, scientists working to compete with the other scientists to prove them wrong
a study cannot be validated by the same people
so your statement essentially says that you will not accept any science that doesn't meet your preconcieved notions or is unacceptable to your political beliefs
a study cannot be validated by the same people"
Show what you are saying Capt. is, since all papers are "Reviewed" before being published, every published paper should be accepted without question.
Should be:
So what you are saying Capt. is, since all papers are "Reviewed" before being published, every published paper should be accepted without question.
My typos are getting absurd.
more to the point: it is reviewed by impartial scientistsexcept pseudoscience
in order to eliminate the more blatant pseudoscience, there has to be a process of review to ensure the worst of it is stopped - that is what peer review is
if deniers had the ability to produce factual science that refuted AGW, it would be published as that is the whole purpose of science
this is one of the most powerful indicators that denier bullsh*t is fanatical adherence to political rhetoric and not to science
Please sign in to add a comment. Registration is free, and takes less than a minute. Read more