Runaway global warming, what is the tipping point supposed to be?

[neutrino_cannon]

Could anyone fill me in on the model and explanation of runaway global warming? What are the positive feedback cycles that would cause increased temperature? Ice cap loss screwing with albedo, methane release from clathrate deposits, what else? How much difference would negative feedback factors like increased algal activity have? How hard a shove does the system need to go spiralling hard one way or another?


Simply, it occurs to me that at various points in the planet's history conditions have been substantially warmer. How big a metastable temperature range is there before Earth becomes Venus?

 

[DogB]

Oh boy, big question.

Firstly you can pretty much forget a Venus type situation. Earth is too far from the sun and our atmosphere is too thin. Other than that, IFAIK your question has no reliable answer.

Sorry I wasn’t more help but I really just wanted to give your thread a bump because I think it’s a good question and I’m interested in what answers you get.

 

[CapelDodger]

Could anyone fill me in on the model and explanation of runaway global warming? What are the positive feedback cycles that would cause increased temperature? Ice cap loss screwing with albedo, methane release from clathrate deposits, what else? How much difference would negative feedback factors like increased algal activity have? How hard a shove does the system need to go spiralling hard one way or another?


Simply, it occurs to me that at various points in the planet's history conditions have been substantially warmer. How big a metastable temperature range is there before Earth becomes Venus?

The planet won't become like Venus. The climate won't become anything that it hasn't already been in the past. Small comfort, perhaps, but there it is.

We won't know a tipping point for certain until it's happened. I think we've reached one already, but that's just my opinion, based primarily on what's been happening in the Arctic. Melting permafrost means it's game over, even if something was done to stop anthropogenic emissions (and nothing will be). Once the permafrost has gone that positive feedback will be over but there's a way to go before that happens. Arctic sea-ice will be gone much sooner, which will remove that positive feedback. The Greenland and Antarctic icecaps will take longer, but that's a minor positive feedback. Even deep-sea clathrates are finite.

Algae aren't only limited by temperature and CO2 they're also limited by nutrients, so I don't hold out much hope there. In fact I don't see any significant negative feedbacks on the horizon.

 

[CapelDodger]

Oh boy, big question.

Firstly you can pretty much forget a Venus type situation. Earth is too far from the sun and our atmosphere is too thin. Other than that, IFAIK your question has no reliable answer.

We'll know more after the event .

 

[Hindmost]

The tipping point will be when CapelDodger and Mhaze agree on anything

I think the tipping point on global warming has already occured...however, the "runaway" thing is the probably subject to interpretation. I don't think the methods we have to analyze global warming can predict how fast and how many issues will occur as we warm up. Of course we will find out.

glenn

 

[CapelDodger]

The tipping point will be when CapelDodger and Mhaze agree on anything

And we'll go skatin' with Satan .

 

[mhaze]

Could anyone fill me in on the model and explanation of runaway global warming? What are the positive feedback cycles that would cause increased temperature? Ice cap loss screwing with albedo, methane release from clathrate deposits, what else? How much difference would negative feedback factors like increased algal activity have? How hard a shove does the system need to go spiralling hard one way or another?


Simply, it occurs to me that at various points in the planet's history conditions have been substantially warmer. How big a metastable temperature range is there before Earth becomes Venus?

Yes, indeedy. The Y2k of the planet. Could CO2 do it in any concentration, given the log function response it has?

Venus, no similarity at all.

 

[lomiller]

Simply, it occurs to me that at various points in the planet's history conditions have been substantially warmer. How big a metastable temperature range is there before Earth becomes Venus?

Basically the oceans would need to boil away. After that temperature would still need to climb until carbonate rock broke down into CO2. This would release comparable amounts of CO2 to what we see on Venus and create similar conditions.

I think I’ve seen a number like a 50% increase in solar intensity would be required. There is simply no realistic scenario where it could occur. What is more threatening is a move to a different equilibrium then our economies and civilizations are built to withstand. A more realistic end of the world global catastrophe could come from ocean acidification killing off a good part of the oxygen producing bacteria in the oceans, and even that is unlikely.

 

[a_unique_person]

Could anyone fill me in on the model and explanation of runaway global warming? What are the positive feedback cycles that would cause increased temperature? Ice cap loss screwing with albedo, methane release from clathrate deposits, what else? How much difference would negative feedback factors like increased algal activity have? How hard a shove does the system need to go spiralling hard one way or another?


Simply, it occurs to me that at various points in the planet's history conditions have been substantially warmer. How big a metastable temperature range is there before Earth becomes Venus?

There is a difference between tipping point and runaway. You can have tipping point that takes us beyond the simple, first order, estimates of climate sensitivity. That doesn't mean runaway, it is the whole debate. Will get an 8C rise, or a 1C rise.

Tipping points would be the melting of the Arctic ice cap. Such an event could change the albedo of the earth, and lead to an end to much of the permanent ice in the area, for example. Another would be the melting of large amounts of permafrost, releasing large amounts of methane, that further contribute to AGW.

 

[spacediver]

can you explain more clearly what the difference between tipping point and runaway is?

I couldn't understand the difference based on your post, but I'm curious to know what it is!

 

[lomiller]

can you explain more clearly what the difference between tipping point and runaway is?

I couldn't understand the difference based on your post, but I'm curious to know what it is!

A tipping point is basically non-linearity rearing it’s head. A runanway condition is one possible consequence of that, but only one of several possibilities.

As an example of a tipping point, the long term climate sensitivity is probably about 3 deg C per doubling of CO2 but this is really just an approximation of a much more complex situation. There are vast stores of frozen methal hydrate underneath the artic ocean. They stay in a frozen state and even accumulate as long as the ocean stays below a certain temperature.

If your starting point is 4 deg below that threshold temperature, and you double CO2 levels you raise the temperature by 3 deg these deposits remain frozen and you get 3 deg of warming. If, however you start 1 degree below this threshold temperature these deposits turn to a very strong greenhouse gas that causes even more warming.

Because these deposits are finite, however, you don’t have a true runaway condition. There is enough greenhouse gases in the to raise the global temperate another 3 degrees or so if you are close to the tipping point climate sensitivity may be 9 deg for a doubling of CO2 (because you only need 1 deg before the deposits melt) but after a few extra degrees of warming this number drops back down to 3.

In a runaway condition you would never drop back, so basically what you had was a tipping point that did no lead to a runaway condition.

 

[bobdroege7]

can you explain more clearly what the difference between tipping point and runaway is?

I couldn't understand the difference based on your post, but I'm curious to know what it is!

They are essentially the same and differ only in magnitude.

A small step change in temperature or a large one.

After all, the runaway on Venus stopped.

 

[spacediver]

thanks lomiller.

So in the language of dynamical systems, I guess a runaway condition would be an attractor.

 

[lomiller]

thanks lomiller.

So in the language of dynamical systems, I guess a runaway condition would be an attractor.

That doesn’t really seem to fit. I’m not exactly an expert on dynamical systems theory (to say the least) but I view it like this: Lets say you have a multistable dynamical system. A tipping point would be the point at which you jump from one attractor to another, a runaway occurs when the attractor you tip over to is at infinity.

A true runaway is clearly not possible in a finite system , but in this case we are discussing a “Venus style runaway” in which the attractor is far beyond our norm but not truly infinite.

 

[a_unique_person]

can you explain more clearly what the difference between tipping point and runaway is?

I couldn't understand the difference based on your post, but I'm curious to know what it is!

My bad . There are better informed people here than me.

 

[mhaze]

....Simply, it occurs to me that at various points in the planet's history conditions have been substantially warmer. How big a metastable temperature range is there before Earth becomes Venus?

I note that although you have provoked some of the standard talking points from our resident Warmer community, none has directly answered your question (bolded by me). Let's leave out the exaggeration (Venus) which some of them jumped on and misdirected.

Let's ask the question once more:

How big a metastable temperature range is there before Earth moves to the alternate stable point that exists past the (tipping points, runaway, blah blah blah).

Either degrees C, K, F, or R may be used in the answer.

 

[CapelDodger]

How big a metastable temperature range is there before Earth moves to the alternate stable point that exists past the (tipping points, runaway, blah blah blah).

Either degrees C, K, F, or R may be used in the answer.

Nobody knows.

We know the kind of event that will constitute a tipping-point. That would include the self-reinforcing melting of permafrost. It may include the permanent loss of summer Arctic sea-ice.

Permafrost is already melting, and at an increasing rate, so that tipping-point has probably already been reached.

 

[mhaze]

Sorry, that's a bit too vague and speculative to rate as an explanation of the subject.

 

[CapelDodger]

Sorry, that's a bit too vague and speculative to rate as an explanation of the subject.

There's nothing vague about the words "melting" and "permafrost", nor is there anything speculative about the observed fact that permafrost is melting.

 

[BenBurch]

There's nothing vague about the words "melting" and "permafrost", nor is there anything speculative about the observed fact that permafrost is melting.

For example; http://www.sciencedaily.com/releases/2008/12/081210133814.htm

Much more methane gas is being emitted into the atmosphere from the tundra in northeast Greenland than previous studies have shown. New figures reveal that large amounts of greenhouse gases are being emitted into the atmosphere, not just during the warm summer months, but also during the colder autumn months.