Jump to content

Plant absorption of additional CO2?


Recommended Posts

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 by SH3RL0CK
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

  • 2 weeks later...
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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.