3 ms·

Then why would an ice age ever happen?

by xyzzy4 10y ago

eximius 10y ago
Presumably global cooling accelerates cooling. I think the point is that deviation from some 'normal' global temperature catalyzes or inhibits greenhouse gas proliferation. (At least in the positive direction, I haven't read it so I don't know if their proposal supports this.)
arcadius 10y ago
A very interesting topic is how the details of Earth's orbit at any one time affect the change in global temperature. You can read more about it here: https://en.wikipedia.org/wiki/Milankovitch_cycles https://en.wikipedia.org/wiki/Milankovitch_cycles
- cossatot 10y ago
  Milankovitch cycles are thought to be a major factor, by everyone from climate scientists to oil companies (who have refined the history of these cycles exquisitely to help identify petroleum in particular rock units deposited during rising or falling sea levels). Another, much longer term factor (tens to hundreds of millions of years) has to do with the positions of the continents on earth, which affects how well ice can be stored. If there is considerable landmass near the poles and it's cold, then ice sheets can form, which increase the amount of reflected solar radiation (albedo) and decrease the amount of heat stored in the oceans (which have less volume due to ice sheet storage, and because sea level falls, the warm shallow seas that hold a lot of heat are much smaller). This can help cooling feedbacks. When the continents are arranged such that there is little polar landmass, these situations are reversed which leads to heating.
- JshWright 10y ago
  PBS Space Time did a great video on this topic. https://www.youtube.com/watch?v=ztninkgZ0ws https://www.youtube.com/watch?v=ztninkgZ0ws
ChuckMcM 10y ago
And that is a really good question. The interesting thing about this paper is it points out that prior to a glacial period there is a rise in temperature. The onset of ice ages appears to be much more rapid than the onset of warming. This was one of the ideas used in the "Day After Tomorrow" movie, although soundly criticized for presenting a very short time frame change into an ice age, that an overly warm earth can trigger a transition into an ice age is not unheard of. Lots of time questions about time frame and mechanism. I lost the paper I read that was suggesting the mechanism was water vapor (a pretty important green house gas) which as the planet warmed the air carried more vapor which hits critical mass, turns into a nearly permanent covering layer of clouds in the upper atmosphere, which then causes water at lower altitudes to precipitate out as snow. Sort of a self induced nuclear winter type scenario. The key conclusion of the paper is that the system responds in a non-linear way. That makes predicting its behavior with models like the one IPCC uses very challenging.
milesvp 10y ago
The best models that predict surface temperatures that I've seen have to do with the deep sea ocean conveyors (https://en.wikipedia.org/wiki/Thermohaline_circulation https://en.wikipedia.org/wiki/Thermohaline_circulation). There's something like 3 major currents with periods measured in years, and their phase greatly influences global temperatures. One of the current theories that I find very convincing is that ice ages happen when one or more of these currents gets disrupted. If the heat from the equator stopped making it to the poles, you could start seeing massive glaciation start to happen. http://science.nasa.gov/science-news/science-at-nasa/2004/05mar_arctic/ http://science.nasa.gov/science-news/science-at-nasa/2004/05...
snowwrestler 10y ago
Feedbacks still need a forcing. Other comments below name a couple of forcings: orbital variations and continental distribution. These are forcings because nothing in the Earth's climate causes them--they are essentially external inputs that change the fundamental limit of energy available the climate: insolation. If the amount of solar energy available to the climate changes, then the temperature equilibrium of the climate must change. As things change, the changes can themselves cause further changes, producing nonlinear effects. That's what this paper is addressing: the idea that warming itself can cause additional warming. But it all starts with a forcing. If the forcing is removed or reversed, then the equilbrium must shift back. Regardless of how strong a feedback might be, it can't overcome a forcing. (That's the essential distinction between the two.) So: regardless of how much the temperature is run up by various feedbacks when the Earth gets closer to the sun, once the Earth moves away from the sun again, the temperature must go down again. And another ice age begins.

Then why would an ice age ever happen?

by xyzzy4 10y ago

Then why would an ice age ever happen?

Presumably global cooling accelerates cooling. I think the point is that deviation from some 'normal' global temperature catalyzes or inhibits greenhouse gas proliferation. (At least in the positive direction, I haven't read it so I don't know if their proposal supports this.)

arcadius 10y ago

A very interesting topic is how the details of Earth's orbit at any one time affect the change in global temperature. You can read more about it here: https://en.wikipedia.org/wiki/Milankovitch_cycles https://en.wikipedia.org/wiki/Milankovitch_cycles

cossatot 10y ago
Milankovitch cycles are thought to be a major factor, by everyone from climate scientists to oil companies (who have refined the history of these cycles exquisitely to help identify petroleum in particular rock units deposited during rising or falling sea levels). Another, much longer term factor (tens to hundreds of millions of years) has to do with the positions of the continents on earth, which affects how well ice can be stored. If there is considerable landmass near the poles and it's cold, then ice sheets can form, which increase the amount of reflected solar radiation (albedo) and decrease the amount of heat stored in the oceans (which have less volume due to ice sheet storage, and because sea level falls, the warm shallow seas that hold a lot of heat are much smaller). This can help cooling feedbacks. When the continents are arranged such that there is little polar landmass, these situations are reversed which leads to heating.
JshWright 10y ago
PBS Space Time did a great video on this topic. https://www.youtube.com/watch?v=ztninkgZ0ws https://www.youtube.com/watch?v=ztninkgZ0ws

ChuckMcM 10y ago

And that is a really good question. The interesting thing about this paper is it points out that prior to a glacial period there is a rise in temperature. The onset of ice ages appears to be much more rapid than the onset of warming. This was one of the ideas used in the "Day After Tomorrow" movie, although soundly criticized for presenting a very short time frame change into an ice age, that an overly warm earth can trigger a transition into an ice age is not unheard of. Lots of time questions about time frame and mechanism. I lost the paper I read that was suggesting the mechanism was water vapor (a pretty important green house gas) which as the planet warmed the air carried more vapor which hits critical mass, turns into a nearly permanent covering layer of clouds in the upper atmosphere, which then causes water at lower altitudes to precipitate out as snow. Sort of a self induced nuclear winter type scenario. The key conclusion of the paper is that the system responds in a non-linear way. That makes predicting its behavior with models like the one IPCC uses very challenging.

milesvp 10y ago

The best models that predict surface temperatures that I've seen have to do with the deep sea ocean conveyors (https://en.wikipedia.org/wiki/Thermohaline_circulation https://en.wikipedia.org/wiki/Thermohaline_circulation). There's something like 3 major currents with periods measured in years, and their phase greatly influences global temperatures. One of the current theories that I find very convincing is that ice ages happen when one or more of these currents gets disrupted. If the heat from the equator stopped making it to the poles, you could start seeing massive glaciation start to happen. http://science.nasa.gov/science-news/science-at-nasa/2004/05mar_arctic/ http://science.nasa.gov/science-news/science-at-nasa/2004/05...

snowwrestler 10y ago

Feedbacks still need a forcing. Other comments below name a couple of forcings: orbital variations and continental distribution. These are forcings because nothing in the Earth's climate causes them--they are essentially external inputs that change the fundamental limit of energy available the climate: insolation. If the amount of solar energy available to the climate changes, then the temperature equilibrium of the climate must change. As things change, the changes can themselves cause further changes, producing nonlinear effects. That's what this paper is addressing: the idea that warming itself can cause additional warming. But it all starts with a forcing. If the forcing is removed or reversed, then the equilbrium must shift back. Regardless of how strong a feedback might be, it can't overcome a forcing. (That's the essential distinction between the two.) So: regardless of how much the temperature is run up by various feedbacks when the Earth gets closer to the sun, once the Earth moves away from the sun again, the temperature must go down again. And another ice age begins.