Ancient forests stabilized Earth's CO2 and climate

Jan 23, 2014
These are digital images of trenches in a mineral made by networks of fungi. The circular feature in the picture on the right is a depression made by the formation of a terminal spore by a mycorrhizal fungus, which was linked to the roots of a maple tree under high CO2. Researcher Joe Quirk says: "These spores are characteristic of the ancient type of fungus that has associated with plant roots since plants first emerged onto the land over 400 million years ago. This is why the image is so exciting – it's good evidence this ancient fungus weathers minerals." Credit: Joe Quirk

UK researchers have identified a biological mechanism that could explain how the Earth's atmospheric carbon dioxide and climate were stabilised over the past 24 million years. When CO2 levels became too low for plants to grow properly, forests appear to have kept the climate in check by slowing down the removal of carbon dioxide from the atmosphere. The results are now published in Biogeosciences, an open access journal of the European Geosciences Union (EGU).

"As CO2 concentrations in the fall, the Earth loses its greenhouse effect, which can lead to glacial conditions," explains lead-author Joe Quirk from the University of Sheffield. "Over the last 24 million years, the geologic conditions were such that atmospheric CO2 could have fallen to very low levels – but it did not drop below a minimum concentration of about 180 to 200 parts per million. Why?"

Before fossil fuels, natural processes kept atmospheric in check. Volcanic eruptions, for example, release CO2, while weathering on the continents removes it from the atmosphere over millions of years. Weathering is the breakdown of minerals within rocks and soils, many of which include silicates. Silicate minerals weather in contact with carbonic acid (rain and atmospheric CO2) in a process that removes carbon dioxide from the atmosphere. Further, the products of these reactions are transported to the oceans in rivers where they ultimately form carbonate rocks like limestone that lock away carbon on the seafloor for millions of years, preventing it from forming carbon dioxide in the atmosphere.

Forests increase weathering rates because trees, and the fungi associated with their roots, break down rocks and minerals in the soil to get nutrients for growth. The Sheffield team found that when the CO2 concentration was low – at about 200 parts per million (ppm) – trees and fungi were far less effective at breaking down , which could have reduced the rate of CO2 removal from the atmosphere.

"We recreated past environmental conditions by growing trees at low, present-day and high levels of CO2 in controlled-environment growth chambers," says Quirk. "We used high-resolution digital imaging techniques to map the surfaces of mineral grains and assess how they were broken down and weathered by the fungi associated with the roots of the trees."

As reported in Biogeosciences, the researchers found that low atmospheric CO2 acts as a 'carbon starvation' brake. When the concentration of carbon dioxide falls from 1500 ppm to 200 ppm, weathering rates drop by a third, diminishing the capacity of forests to remove CO2 from the atmosphere.

The weathering rates by trees and fungi drop because low CO2 reduces plants' ability to perform photosynthesis, meaning less carbon-energy is supplied to the roots and their fungi. This, in turn, means there is less nutrient uptake from minerals in the soil, which slows down weathering rates over millions of years.

"The last 24 million years saw significant mountain building in the Andes and Himalayas, which increased the amount of silicate rocks and minerals on the land that could be weathered over time. This increased weathering of in certain parts of the world is likely to have caused global CO2 levels to fall," Quirk explains. But the concentration of CO2 never fell below 180-200 ppm because trees and fungi broke down minerals at low rates at those concentrations of .

"It is important that we understand the processes that affect and regulate climates of the past and our study makes an important step forward in understanding how Earth's complex plant life has regulated and modified the climate we know on Earth today," concludes Quirk.

Explore further: How does soil store CO2?

More information: The discussion paper (before peer review) and reviewers' comments are available at www.biogeosciences-discuss.net… d-10-15779-2013.html

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User comments : 12

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TechnoCreed
1.9 / 5 (7) Jan 23, 2014
This implies that we should regulate the CO2 cycle. Having good reserves of fossil fuel might be the best way to do that.
Maggnus
3.4 / 5 (8) Jan 23, 2014
This implies that we should regulate the CO2 cycle. Having good reserves of fossil fuel might be the best way to do that.


Can you clarify what you mean here?
goracle
4 / 5 (4) Jan 23, 2014
This implies that we should regulate the CO2 cycle. Having good reserves of fossil fuel might be the best way to do that.


Can you clarify what you mean here?

Indeed. Do you mean that we should have more coal, oil and gas ready to burn or that we should leave more of it there in case we need to induce warming in the future? Or something else?
Birger
4 / 5 (5) Jan 24, 2014
This self-regulating process -like other self-regulating climate processes- occur over very long time spans (from a human perspective).
Moebius
4.3 / 5 (3) Jan 24, 2014
As I've said before, one of our greatest enemies are the people cutting down the south american rain forest.
TechnoCreed
3 / 5 (2) Jan 24, 2014
This implies that we should regulate the CO2 cycle. Having good reserves of fossil fuel might be the best way to do that.


There is no need to clarify. Those who think that the only worthy time is 'here and now' have no respect for humanity.
Maggnus
2.3 / 5 (3) Jan 24, 2014
There is no need to clarify. Those who think that the only worthy time is 'here and now' have no respect for humanity.


Three people ask you for clarification, and your only response is there is no need to clarify. Alrighty then, a mysticism! And worthy of as much discussion.
TechnoCreed
2.3 / 5 (4) Jan 24, 2014
Magnus,

Obviously, you have no interest in the comment I made on a good article. The only thing you are looking for is where I stand. You want to make a political point at all cost, why? The world is not Republican and Democrat and I am not an American. So I will not not play this game, just like I will not trow one banana at your comment, like you did twice, because, for some reason, I did not enjoy what you had to say. There is no absolute truth just different points of view.

On this, have a nice day. Sincerely TC
Maggnus
3 / 5 (4) Jan 24, 2014
No Technocreed, I do not care where you stand politically. I thought you made an interesting observation, but I did not fully understand what you were trying to say. I asked you to clarify because I was interested, and 2 other people after me asked the same thing.

You can choose to clarify or not, I don't give a rat's behind. I am not American either, although it appears the rudeness they are often accused of resides elsewhere as well.

Sincerely, take your holier than thou attitude and place it firmly where it cannot see sunshine.
TechnoCreed
2 / 5 (4) Jan 25, 2014
Maggnus,

Although you seem to have some rhetorical abilities, you cannot hold your urge to resort to insults. That is the demonstration of your lack of character. I had to report your comment; one can always hope. I do not give high value to friendship in the cyber world, but I think respect and decency is still relevant. So I will quote your comment... just in case, but without the uncouthness.

No TechnoCreed, I do not care where you stand politically. I thought you made an interesting observation, but I did not fully understand what you were trying to say. I asked you to clarify because I was interested, and 2 other people after me asked the same thing.

You can choose to clarify or not, I don't give a rat's behind. I am not American either, although it appears the rudeness they are often accused of resides elsewhere as well.


Concerning your first paragraph, what can I say; I just threw a bone in the backyard and waited for the usual suspects to fight over it. It did not quite work as I expected; believe me I once sent this kind of curved ball on web page of enraged denialist 'The Reference Frame' and some of them fell for it.
I still believe that my original comment had enough consistency to stand on its own, but on your request, I added a subtlety that satisfied some other readers (considering the satisfaction meter), but somehow you were not!

There is no need to clarify. Those who think that the only worthy time is 'here and now' have no respect for humanity.


You were so frustrated by the 'There is no need to clarify.', that you dismissed the rest of my second comment. Had you not lost your temper and pieced the two comments together, you would had got some kind of answer:

This implies that we should regulate the CO2 cycle. Having good reserves of fossil fuel might be the best way to do that. Those who think that the only worthy time is 'here and now' have no respect for humanity.


I agree there is still some ambiguity here but god, you are not a school boy after all, what is so 'mystic' about this formulation.

Concerning the rest of your quoted comment. There is no insult in stating that I am not an American, and they know that the Republican, Democrat war is a laughable subject. So what is so rude about it?

I assure you that I hold no grudge; I consider that a lack of maturity. You will not receive any of my 'petulant' salutation either; since you do not appreciate them.

TC

Maggnus
3.4 / 5 (5) Jan 25, 2014
Interesting dissertation there technocreed., So your avowed purpose in coming to this science site is not to read the articles and offer insightful commentary, rather it is to ferment discord and hopefully bait argument? How droll.

Your passive/aggressive litany smacks of a desire to view yourself as above the cacophony you engender. Your sycophantic self congratulation is cloying.

Please do leave off, I'll have no truck with you.

Pkunk_
5 / 5 (2) Jan 26, 2014
As I've said before, one of our greatest enemies are the people cutting down the south american rain forest.

The fact is that rain forests don't take out as much CO2 from the atmosphere as temperate forests. And everyone else in the world has ruthlessly cut down their forests . In the last 1000 years we have chopped down very large temperate forests in Europe ,Asia and North America.

Instead of expecting the South Americans to play Angels , we should instead focus of reducing demand for wood in Europe and Asia so that there is less pressure to chop down forests in the Amazon basin.