Plant absorption of additional CO2?

[SH3RL0CK]

This does bring up a question I have with regards to global warming. From John's post above:

So natural emissions are circa 770 Gt/year compared to human 26.4 Gt/year. Human emissions are far less than the natural ones.

It seems to me that the ppm atmospheric increase in CO2 (shown by various ice core data) is because of the cumulative addition of industry year after year. Without burning fossil fuels, nature is in a balance; 770Gt produced and 770Gt sequestered in plant material. So why is it that a mere 3% increase in CO2 emissions isn't all taken up by the environment? Why don't plants simply absorb this additional carbon? Is the ecosystem this finely balanced that some kind of limit is reached?

 

Mods: Upon reflection, this question is not relevant to the topic of this thread, please move to a new thread to avoid threadjacking. Thank you.

Edited July 27, 2009 by SH3RL0CK

[iNow]

It's about metabolism. Plants can only process so much CO₂ based on their size and structure (much like we can only breath a given volume of air... the processing of CO₂ is essentially a plant "breathing," and they can only "breath" a given volume). Further, their ability to process CO₂ DECREASES as temperatures increase and rain decreases (drought) since they are trying to slow their metabolism to maximize their available water (sipping instead of binge drinking).

 

 

 

http://earthobservatory.nasa.gov/Newsroom/view.php?id=27638

Currently, the land and oceans absorb about half of the carbon dioxide produced by human activity, most of it resulting from the burning of fossil fuels, Fung said. Some scientists have suggested that the land and oceans will continue to absorb more and more CO

₂

as fossil fuel emissions increase, making plants flourish and the oceans bloom.

 

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 CO

₂

, 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 CO

₂

as plants breathe in less to conserve water.

[Cap'n Refsmmat]

Split, as requested, from this thread.

[SH3RL0CK]

Thanks Cap'n!

 

iNow, it makes some sense. However, plant metabolism may slow down but nothing says there couldn't be more plants. Moreover, a lack of water certainly isn't present in the ocean which covers most of the surface of the earth (however, I can see a lack of nutrients being present in the ocean... ). Fung did this analysis by computer modeling, I will have to search to see if there is any actual testing which verifies this to be the case...perhaps more later...

 

Another thought, does this mean if people were to reduce the carbon output via fossil fuels to 50% of todays levels (which I think is possible), the plants would eventually return the atmospheric CO2 levels back to pre-industrial levels?

[iNow]

We'd really want to drop our contributions of CO₂ to zero, and even then it would still take millenia for plants to process everything we've input to the atmosphere already. Relative to human time scales, environmental equilibrium takes a very long time to achieve.

 

As for number of plants, I think they need fresh water, not sea (salt) water. The reason preventing them from absorbing more carbon dioxide is the same reason that you would likely not have as many total plants. If there's not enough water, I have a hard time imagining that plant density is going to increase by any significant number, but I'm guessing with that.

 

I also remember reading an article recently that suggested the pores on the leafs of plants get smaller as a result of higher CO₂. This seems related to my comment about metabolism above.

[Mokele]

Carbon isn't usually the limiting resource for plants - mostly it's nutrients and minerals from the soil, or water, or light (if they're in the understory). Adding more CO2 won't result in a given population of plants increasing in biomass if they're limited by the soil's phosphate concentration.

[bascule]

I think it's important to look at the CO₂ anomaly. CO₂ levels are in constant flux. Anthropogenic sources are almost completely responsible for 20th century increases in the CO₂ anomaly... almost all of the rest can be chalked up to feedbacks caused by a warming climate.

[Skye]

It's about metabolism. Plants can only process so much CO₂ based on their size and structure (much like we can only breath a given volume of air... the processing of CO₂ is essentially a plant "breathing," and they can only "breath" a given volume). Further, their ability to process CO₂ DECREASES as temperatures increase and rain decreases (drought) since they are trying to slow their metabolism to maximize their available water (sipping instead of binge drinking).

 

 

 

http://earthobservatory.nasa.gov/Newsroom/view.php?id=27638

Currently, the land and oceans absorb about half of the carbon dioxide produced by human activity, most of it resulting from the burning of fossil fuels, Fung said. Some scientists have suggested that the land and oceans will continue to absorb more and more CO

₂

as fossil fuel emissions increase, making plants flourish and the oceans bloom.

 

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 CO

₂

, 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 CO

₂

as plants breathe in less to conserve water.

That modeling ignores changes to the distribution of plants though, and plants that are better suited to hot dry conditions are likely to expand their ranges.

[coreview2]

That modeling ignores changes to the distribution of plants though, and plants that are better suited to hot dry conditions are likely to expand their ranges.

 

The modeling also ignores that "minor correlation" between warm climate and long growing season. Remember about 4,000 Vikings were farming on Greenland during the Medieval Warm Period.

 

There is a reason that we get fruits and vegetables from Florida and Calif all year 'round rather than Canada.

 

Presuming that plants don't respond to a broader range of warm weather (CO2 or not), is a gross error in presumption.