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Vince278
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I believe your explanation is the one I've heard.
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Geronimo
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st cloud USA
Jan 1970
time: 05:21
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quote:
Originally posted by Odin
Sensationalist BS. there is no way we are going to turn into Venus. It is crap from like this that gives conservatives an excuse to ignore the legitimate data. Most scientists expect an increase of about 2 to 4 degrees Celsius by the end of the century. |
AFAIK the scenario described is possible, scientists just don't yet know why earlier warmer periods with a more pronounced greenhouse effect did not spiral into this sort of destructive feedback loop. I'm not aware of any scientist who would claim that there is no way to convert earth into a venus like inferno. If venus were magically transported to earths orbit it wouldn't cool very much at all. Earth has erything it would need to become a brutally hot venus twin. We just don't yet know why that has never happened here.
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Odin
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Biology Nerd at Minnesota State University Moorhead
Sep 2000
time: 23:21
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quote:
Originally posted by Geronimo
We just don't yet know why that has never happened here. |
The explaination I heard is called the carbonate cycle. Carbon dioxide reacts with calcium ions from eroded rock to make calcium carbonate. The calcium carbonate is carried to the ocean by rivers, and is deposited as limestone. some of the limestone is subducted and the carbon dioxides is released by the heat of the mantle and is released back into the atmosphere by volcanos. the system has a built in negative feedback, if things warm up the increase in moisture increases the erosion rate, which removes more CO2, cooling things back down again and decreasing the erosion rate.
An important thing to mention is that the sun has slowly brighted over the last 4.5 billion years, it is 20% brighter now than it was then. Also, our atmosphere resembled Venus, but the weaker sun made it so the temperatue was "only" 90C at the formation of the oceans 4.4 billion years ago. very quicly most of that CO2 was converted into limestone, and by 4 billion years ago the Earth was left with an atmosphere no much thicker than now dominated by Nitrogen and CO2 and lower temeratures (but still quite hot). as the sun warmed up the carbonate cycle reduced the amount of CO2 in the air to compansate. Unfortunately, we are running out of CO2, plants are already strained for CO2 at today's 360ppm (or 280ppm before industrialization), and some grasses and herbs have evolved the C4 cycle to extract CO2 as efficiently as possible. in 400 million years the level of CO2 will have become so low that all terrestrial vegetation will begin to die, and the runaway greenhouse will begin. 
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Jon Miller
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sure...
except that earth has had periods in it's history when it was a LOT more greenhousy then it is now
so even if we are affecting the environment... it is not going to do anything venus like to the earth
at worse.. there will be a massive climate change and some extinctions (and life will get a lot harder for humans)
outside of nuclear bombs and toxic waste.. humans can't really negatively effect the earth (when considered as a whole and under geologic timescales)
Jon Miller
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Lancer
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Oregon Coast, USA! or Bohol, Philippines!
Apr 1999
time: 05:21
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"except that earth has had periods in it's history when it was a LOT more greenhousy then it is now"
http://www-eps.harvard.edu/people/f...ball_paper.html
"Ken Caldeira and Jim Kasting at The Pennsylvania State University estimated that roughly 0.12 bar of carbon dioxide (about 350 times the present concentration) would have been required to overcome the albedo of a snowball Earth. Assuming current rates of volcanic carbon dioxide emissions, a Neoproterozoic "snowball" Earth would have lasted for millions to tens of million of years before the sea ice would begin to melt at the Equator. A "snowball" Earth would not only be the most severe glaciation conceivable, it would be the most prolonged."
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Geronimo
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st cloud USA
Jan 1970
time: 05:21
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quote:
Originally posted by Odin
The explaination I heard is called the carbonate cycle. Carbon dioxide reacts with calcium ions from eroded rock to make calcium carbonate. The calcium carbonate is carried to the ocean by rivers, and is deposited as limestone. some of the limestone is subducted and the carbon dioxides is released by the heat of the mantle and is released back into the atmosphere by volcanos. the system has a built in negative feedback, if things warm up the increase in moisture increases the erosion rate, which removes more CO2, cooling things back down again and decreasing the erosion rate.
An important thing to mention is that the sun has slowly brighted over the last 4.5 billion years, it is 20% brighter now than it was then. Also, our atmosphere resembled Venus, but the weaker sun made it so the temperatue was "only" 90C at the formation of the oceans 4.4 billion years ago. very quicly most of that CO2 was converted into limestone, and by 4 billion years ago the Earth was left with an atmosphere no much thicker than now dominated by Nitrogen and CO2 and lower temeratures (but still quite hot). as the sun warmed up the carbonate cycle reduced the amount of CO2 in the air to compansate. Unfortunately, we are running out of CO2, plants are already strained for CO2 at today's 360ppm (or 280ppm before industrialization), and some grasses and herbs have evolved the C4 cycle to extract CO2 as efficiently as possible. in 400 million years the level of CO2 will have become so low that all terrestrial vegetation will begin to die, and the runaway greenhouse will begin. |
I guess I should say we aren't certain as to why that hasn't happened here. There are a variety of mechanisms that may have been influenced by the intrinsic differences between earth and Venus. I suppose my point is that nobody should claim that there is 'no way' that earth could experience a runaway greenhouse effect like venus did.
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Geronimo
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st cloud USA
Jan 1970
time: 05:21
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quote:
Originally posted by Odin
80F seems much too low for a runaway greenhouse, the Earth is usually much warmer than it is right now, we live in an unusually cold period. Usually there are no continental glaciers and the oceans are relatively warm and stagnant. Only when you have lots of mountain building coupled with lots of land near the poles do you get an "Ice House" configuration like today. The carbonate cycle gives the necissary negitive feedback to prevent a runaway greenhouse effect. the temoerature might rise 4C, and will cause a lot of climatic distruption, but one we run out of fossil fuels the oceans will slowly absorb the CO2, and the glacial-interglacial cycle of our curent ice age will return. |
we essentially 'short circuit' the carbonate cycle when we burn fossile fuels.
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22-05-2005 12:24
800 degrees in the shade and there's no shade!
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