How Earth avoided global warming, last time around

Jun 11, 2014
Credit: NASA

Geochemists have calculated a huge rise in atmospheric CO2 was only avoided by the formation of a vast mountain range in the middle of the ancient supercontinent, Pangea. This work is being presented to the Goldschmidt geochemistry conference in Sacramento, California.

Around 300 million years ago, plate tectonics caused the continents to aggregate into a giant supercontinent, known as "Pangea". The sheer size of the continent meant that much of the land surface was far from the sea, and so the continent became increasingly arid due to lack of humidity. This aridity meant that rock weathering was reduced; normally, a reduction in rock weathering means that CO2 levels rise, yet in spite of this CO2 levels – which had been falling prior to the mountain formation- continued to drop, eventually undergoing the most significant drop in atmospheric CO2 of the last 500 million years. This phenomenon has remained unexplained, until now.

Now a group of French scientists from the CNRS in Toulouse have produced a model which seems to explain this contradiction. The period coincides with the rise of a vast series of in the interior of Pangea, the "Hercynian" mountains". These mountains arose in a wide belt, running from what is now the Appalachians, through to Ireland, South-Western England, through Paris and the Alps into Germany, and on further East.

According to team leader, Dr Yves Godderis (CNRS, Toulouse, France):

"The formation of these mountains meant that the rock weathering, which was threatening to slow to a walk through much of the supercontinent, was able to continue. The steep slopes of these Hercynian mountains produced physical erosion. Occurring in a humid equatorial environment, this physical erosion promoted rock weathering and removing CO2 from the atmosphere".

He continued, "We believe that it is this which led to the dramatic drop in atmospheric levels of CO2. We estimate that if it hadn't been for the formation of the Hercynian mountains, the atmospheric CO2 levels would have reached around 25 times the pre-industrial level, meaning that CO2 levels would have reached around 7000 ppm (parts per million). Let me put that into a present-day context; the current atmospheric CO2 levels are around 400 ppm, so this means that we would have seen CO2 rise to a level around 17 times current levels. This would obviously have had severe effects on the environment of that time. But the formation of the mountains in fact contributed to the greatest fall in atmospheric CO2 in the last 500 million years".

The team believes that even if the mountains had not formed and CO2 levels rose sharply, this would not have led to a runaway greenhouse effect as happened on Venus, because the increasing temperatures would have led to rocks being ultimately weathered, heat compensating for the scarcity of water. Rock weathering would have removed CO2 from the atmosphere, thus stopping the rising temperatures.

"So it would eventually have been self-correcting" said Dr Godderis, "but there's no doubt that this would have stalled Earth's temperature at a high level for a long, long time. The world would look very different today if these mountains had not developed when they did.

This is a new model which explains some of the events in the 80 million years following the start of the Carboniferous period, and of course the ideas need to be confirmed before we can be sure that the model is completely accurate. The take-home message is that the factors affecting atmospheric CO2 over geological periods of time are complex, and our understanding is still evolving".

Explore further: Ancient forests stabilized Earth's CO2 and climate

More information: The Goldschmidt Conference is the world's leading annual conference on geochemistry. It takes place in Sacramento, California from 8-13 June 2014. goldschmidt.info/2014/

Provided by European Association of Geochemistry

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User comments : 13

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Enviro Equipment Blog
1.7 / 5 (6) Jun 11, 2014
Naturally, climate change deniers will use undoubtedly twist this research conclusions to show that nature and man is the biggest engine of global warming.

Sigh.
Vietvet
3.5 / 5 (13) Jun 11, 2014
Naturally, climate change deniers will use undoubtedly twist this research conclusions to show that nature and man is the biggest engine of global warming.

Sigh.


Didn't you mean "nature, not man" instead of "nature and man"?

The trolls will try to spin this to favor their denier stupidity.
Floyd_Howard_Jr_
1.8 / 5 (15) Jun 11, 2014
Dems are trying to legislate a narrative change hurting the American people in the process! All Democrats and supporters here and abroad, are trying to flood the media with hysterical climate change & global warming alarms to take the heat off Dem candidates in the November 2014 and 2016 elections due to the train wreck of Obamacare! They shout, scream, cry, make outlandish claims and won't stop till after the elections! Poor Democrats! The tsunami cometh!
enviro414
2.3 / 5 (9) Jun 11, 2014
A graph showing CO2 and average global temperature for the last 550 million years is at http://www.geocra...ate.html

A simple equation, using only two drivers, calculates temperature anomalies since before 1900 with 90% accuracy (95% correlation) and credible estimates since the depths of the Little Ice Age. The analysis is described at http://agwunveile...pot.com/ and sub-links. CO2 change had no significant effect.
skills4u
5 / 5 (2) Jun 11, 2014
I am confused..
Quote "The sheer size of the continent meant that much of the land surface was far from the sea, and so the continent became increasingly arid due to lack of humidity. This aridity meant that rock weathering was reduced;"

Then quote..

"But Occurring in a humid equatorial environment, this physical erosion promoted rock weathering and removing CO2 from the atmosphere"."

Are they saying the mountains made an arid region humid ??

PinkElephant
4.4 / 5 (13) Jun 11, 2014
@skills4u,

1) The entire continent wasn't equatorial; hopefully you can see that easily enough in your mind's eye or here:

http://en.wikiped.../Pangaea

2) There are two kinds of humidity: absolute and relative. Absolute humidity is the mass fraction of water in the air, regardless of any other factor. Relative humidity is current water content as a percentage of maximum allowable content under a given temperature and pressure (warmer air can hold more water vapor without the latter precipitating out.) Even when absolute humidity drops, tall mountains can force incident air flow upward, driving relatively warmer (and therefore in absolute terms more humid) air higher where the temperature is colder, causing it to cool off past the dew point, and form clouds and precipitate out the excess moisture (landing it upon the mountain slopes.) So in that way, mountains can indeed "make an arid region humid". It's sometimes said that mountains make their own weather... ;-)
skills4u
4.9 / 5 (7) Jun 11, 2014
@pink
Thanks for your reply...your explanation sounds logical.
Shootist
2.2 / 5 (13) Jun 11, 2014
Medieval Climate Optimum
Roman Climate Optimum

The Hockey Stick was a hoax.

It was warmer then than now.
WatcherinLa
1.5 / 5 (8) Jun 11, 2014
Reid once said: 'You can go outside and spit and have the same effect as doubling carbon dioxide.'

Reid A. Bryson holds the 30th PhD in Meteorology granted in the history of American education. Emeritus Professor and founding chairman of the University of Wisconsin Department of Meteorology—now the Department of Oceanic and Atmospheric Sciences—in the 1970s he became the first director of what's now the UW's Gaylord Nelson Institute of Environmental Studies. He's a member of the United Nations Global 500 Roll of Honor—created, the U.N. says, to recognize "outstanding achievements in the protection and improvement of the environment." He has authored five books and more than 230 other publications and was identified by the British Institute of Geographers as the most frequently cited climatologist in the world.
Vietvet
3.5 / 5 (13) Jun 11, 2014
Medieval Climate Optimum
Roman Climate Optimum

The Hockey Stick was a hoax.

It was warmer then than now.


And you're still an idiot.
wob8t
1 / 5 (3) Jun 12, 2014
I'm hoping for "Focus Fusion" to help avoid it this time round. Guess we still have a 5 year wait if it's proven to work. Then I'm guessing if humans are to blame work can be done to reverse the damage.
katesisco
1 / 5 (5) Jun 12, 2014
Good explanation. Now, just where was this Hercynian strip of mountains? Pangea had only just come together and then blew apart quickly. And reconstructions show that the above Hercynians would have been exclusively in the 30 to 40 degree N Lat, I think.
I wonder if the sun's cycles of monopolarity and dipolarity controlled this pattern? I theorize that our magnetar sun had less and less energy each cycle and from 650,000 my the dipole aspect ruled increasingly. It appears that the amassed land surface ran N/S and would not this have precipitated a global tilt so that the land mass ran E/W on the Equator?
sirchick
5 / 5 (3) Jun 14, 2014
So those who are against global warming idea are happy for pollution to continue?

Whether climate change is occurring or not is no excuse to stop saving energy, and encourage a cleaner atmosphere.

So the debate is irrelevant, we still have to change our polluting ways either way..no one is dumb enough to believe pollution has no harmful effect on human health.

So theres no point in debating cos it doesn't change anything.

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