It depends, in part, what you mean by a "runaway" greenhouse effect.
Do you mean an extremely rapid temperature rise, that continues (due to cascading feedback) for a while? That might happen if we manage to release enough methane clathrates and permafrost methane to melt the ice caps and so forth. That would likely trigger a lot more feedbacks (increased fires in now-dry forests, a lot of things dying, and so forth).
Do you mean a temperature rise that continues until we're almost as hot as Venus? That is... not at all likely, unless and until the sun is a *lot* hotter than it is now.
Runaway greenhouse effect: so much warming that the upper atmosphere contains water resulting in H/O dissociation resulting in hydrogen loss to space. End result is loss of all water on earth.
No one seems inclined to provide an earth average temperature where that would likely happen. David Archer gives an interesting description of what would need to happen for that to occur (see attached video starting at minute 21).
It seems clear to me that the expression. "oceans boil away" is an exaggeration of the temperature required. I'm sure that a runaway effect would get started at a temperature much lower than 100C.
Long live the tropopause!
At sea surface temperatures above 80 F (27 C), evaporation loads the atmosphere with a critical amount of water vapor, one of the most efficient greenhouse gases. Luckily for Earth, sea surface temperatures never reach more than about 87 F (30.5 C), and so the runaway phenomenon does not occur.
If you would like to know more about this you can alway go to my website at topicbug.ca and I would be happy to help you out.
450ppm of CO2 is considered the trigger point for rapid ATMOSPHERIC temperature rise. As long there's an abundance of ice to absorb the heat any actual ATMOSPHERIC heat rise will be delayed until as the ice melts* down to an X point...though nobody knows where the exact X point will be. At that point the refrigeration effect of the world's ice load will be gone and all excess atmospheric heat will be taken up by the world's oceans. On the plus side, the melt water will help cool the oceans to some degree so the exact takeoff point for a full on green house effect is any ones guess as to an exact day and date.
Currently the CO2 load is closing in on 400ppm and we add 15ppm per decade at the current rate. Let's just say by the early mid century something big WILL happen. Stand by for this to be a big issue in the 2040 presidential campaign.
Runaway Greenhouse Effect starts tomorrow.
A runaway greenhouse effect would occur if Earth were surrounded by an ocean of a liquid which has a climate sensitivity greater than the temperature change required to double its vapor pressure.
Noah is wrong. When all the ice melts, albedo positive feedback will no longer be a factor and warming will slow down.
When it warms, there will be more radiation heading out into space.
Just a guess but if CO2 levels jumped suddenly from 400 to 550, that might trigger runaway GW
For example the Greenland Ice Shelf and the Russian Permafrost melted in one day releasing tons of Methane it could happen methane is @ 23 times the strength of CO2 as a greenhouse gas
There is a lot of methane under that ice, millions of years worth
Much, much sooner than that. A 30 degree increase in (average) temperature would be a mass extinction event. We won't see that kind of temperature change until long after the runaway has started.
When will that be? My thinking is that the "trigger" will be the first summer of total Arctic ice melt. That's now forecast to be sometime between 2020 and 2060.
Runaway greenhouse effect can't happen. There is only so much energy coming into the atmosphere from the Sun. The greenhouse effect can't produce it's own heat, it only has the heat that is.
If the Earth was to ever overheat it wouldn't be due to the greenhouse effect, it could only happen if the Sun significantly increased it's output.
The slight warming we've experiences was due to increased SOLAR activity, NOT HUMAN ACTIVITY.
http://lasp.colorado.edu/lisird/tsi/hist...
Watch this and you will understand:
The Great Global Warming Swindle
When the Yellowstone Caldera blows it's top and spews ash into the atmosphere for years.
Im thinking at least a 30 degree F increase in temperature
The whole planet's temperature rose by one whole degree Celsius in 1997-1998 (on average) and the cause was supposedly El Nino produced. What makes you think a 0.75 Celsius Global temperature average rise since 1880 is runaway Global Warming? If you think 30 degrees F is runaway warming, then you could say it happens a lot on any given day. It started out 30 degrees F here this morning and the temperature rose to almost 60.
When the sun shifts millions of miles closer to our planet. Yikes!!
Anything you see here would be just a guess. There hasn't been proven any runaway point in CO2. If there was don't you think they would have simulated it in a laboratory by now?
It doesn't ever occur.
This has been PROVED by history. It's been much much warmer and co2 has been 20 times higher and Earth has gone into an ice age instead. Earth does it's own thing.
