Is a runaway greenhouse effect underway?

[Lancer]

Yes, I'm not replying until it sinks some.

[Zkribbler]

Originally posted by Vince278
The most counterintuitive thing I've heard about that is that global warming could cause another ice age.

Ice caps start to melt (as is beginning to happen now ) >> Fresh water flows into the Atlantic Ocean changing its salinity (which is also beginning to happen now) >> The drop in the salt level causes the lamination of warm and cold currents--which is usually found in the Altlantic--to erode >> When the warm and cold waters of the Atlantic mix together, the surface temperture of the Atlantic drops >> The Atlantic Ocean forms a huge heat sink and presto >> ICE AGE

[Kuciwalker]

Re: Is a runaway greenhouse effect underway?

Originally posted by techumseh
Scientists believe a "runaway greenhouse effect", similar to the one which gave Venus teperatures of 900 degrees Celsius, is possible on earth. It seems that water vapour is a much more efficent greenhouse gas than CO2 and if the oceans warm up enough, increased evaporation will produce a "positive feedback loop" which would continue until the oceans literally boil away. One study (linked below) found that this may already have begun.

Except that increased cloud cover will reflect a lot of light from the sun.

[Zkribbler]

Re: Re: Is a runaway greenhouse effect underway?

Originally posted by Kuciwalker
Except that increased cloud cover will reflect a lot of light from the sun.

Yeah, that's what the said about Venus...and looked what happened there. 800 degrees in the shade and there's no shade!

[Kuciwalker]

It has a bunch of other stuff in its atmosphere too.

[Odin]

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.

[techumseh]

Apparently, the critical ocean surface temperature for the runaway wet greenhouse effect is ~80F. This is only happening now in a small area of the Pacific, NE of Australia. The average surface temp of the worlds oceans is now in the high 50's. By the end of this century, it may reach ~70F. The polar ice caps play a huge role in moderating ocean temperatures. If they were to melt completely, things would heat up very fast. So no immediate threat. It's just that we don't know where the point of no return is.

[Odin]

Originally posted by techumseh
Apparently, the critical ocean surface temperature for the runaway wet greenhouse effect is ~80F. This is only happening now in a small area of the Pacific, NE of Australia. The average surface temp of the worlds oceans is now in the high 50's. By the end of this century, it may reach ~70F. The polar ice caps play a huge role in moderating ocean temperatures. If they were to melt completely, things would heat up very fast. So no immediate threat. It's just that we don't know where the point of no return is.

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.

[Lancer]

http://en.wikipedia.org/wiki/Snowball_Earth

[Jon Miller]

Re: Is a runaway greenhouse effect underway?

Originally posted by techumseh
Scientists believe a "runaway greenhouse effect", similar to the one which gave Venus teperatures of 900 degrees Celsius, is possible on earth. It seems that water vapour is a much more efficent greenhouse gas than CO2 and if the oceans warm up enough, increased evaporation will produce a "positive feedback loop" which would continue until the oceans literally boil away. One study (linked below) found that this may already have begun.

http://csep10.phys.utk.edu/astr161/lect/venus/greenhouse.html

http://www.nasa.gov/centers/ames/news/releases/2002/02_60AR.html

http://www.greenleft.org.au/back/2004/605/605p13.htm

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

[Lancer]

"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/faculty/hoffman/snowball_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."

[Ben Kenobi]

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.

So higher CO2 concentrations are saving the planet? Cool.

[Geronimo]

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.

[MrFun]

Originally posted by Az
yes. We're all going to die.

[Geronimo]

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.