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Let's say we invented a whizzy technology that took CO2 back to pre-industrial levels, say 280ppm, how long would it take for glaciation to resume ?

(I'm not angling for a denialist perspective here, I know warming is a problem)

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  • $\begingroup$ This addressed here : skepticalscience.com/heading-into-new-little-ice-age.htm $\endgroup$ – Tom Newton Oct 8 '17 at 11:44
  • $\begingroup$ Time would be in the order of magnitude of 10 000 years... $\endgroup$ – Communisty Oct 9 '17 at 6:44
  • $\begingroup$ Your second question is opinion-based (the question is geting flagged as such), so I have edited it out. $\endgroup$ – Jan Doggen Oct 9 '17 at 10:01
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This answer assumes 280 PPM CO2, at least until the ice age and oceans begin to draw CO2 from the atmosphere.

If we look at the Pleistocene and we measure how long glacial periods last and how long inter-glacial periods are, You could say, observing the Earth for the last 2.5 million years that being in an ice age is Earth's natural state, with only brief periods between ice ages.

Ice ages have also followed pretty regular patterns that makes them, in theory, somewhat predictable. Ice ages mostly followed a 40,000 year cycle, between about 2.5 million years ago to about 1 million years ago, then switched to roughly a 100,000 year cycle over the last million years.

It's not precisely known why the cycle switched from 40,000 to 100,000 years. That's known as the 100,000 year problem. But if we use the current 100,000 year cycle as a ballpark measuring stick or if we measure the length of interglacial periods (which are generally pretty short, 10,000 - 30,000 years), then the next ice age can be estimated at not too far off. Maybe 10,000 years.

But if we look closer at what actually triggers ice ages, which is (simplified version), colder summers in the Northern Hemisphere, driven by orbital variations. We can get a better estimate when ice ages should come by looking for when the Northern Hemisphere summers will get colder.

Milankovich cycles don't always neatly line up and the right conditions for the next ice age, based on orbital changes is a bit unclear. When the red line in this chart below is low ice ages are more likely to happen, and we're in a dip now, but coming out of a warmer summer period and relativly soon entering another one. There's a slightly bigger dip that peaks in about 60,000 years from now, another one 100,000 years from now and a bigger one, about 130,000 years from now.

enter image description here

Using this chart as a guideline, the next glaciation is more tricky to predict. Perhaps in 60,000 years. These predictions are hard to make though because ice ages are self sustaining.

So, short answer, perhaps the best answer. Nobody knows. The Milankovich cycles aren't lining up in the right way to make this prediction easy. We may be set for an unusually long inter-glacial period.

As for how catastrophic would it be. Well, for one, we'd see it coming and stopping an ice age would probably be easier than stopping ice from melting. Releasing CO2 and CH4 into the air for example. For a longer answer, how catastrophic would it be is a world-building question.

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    $\begingroup$ Well I'd heard it was next Tuesday, so this is quite a relief. Very nice answer btw +1! $\endgroup$ – uhoh Oct 9 '17 at 9:08
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    $\begingroup$ We are technically right near a minimum at present, so for years some people were predicting that we should be going into a glaciation now, but those people were not looking at the magnitude of the minimum. We do nto really know what magnitude is requires, but evidence show that this minimum is not low enough, and best guess if the next several will not be, and that is before any human caused factors are included. The lows 170,000 years out may do it, of it may be clear out there at 600,000+, of the tipping point may have already been reached to break the ice age cycle. $\endgroup$ – dlb Oct 10 '17 at 15:14
  • $\begingroup$ @dlb Nice comment. When you say 170,000 and maybe 600,000 plus, are you talking naturally or with human influence? I agree with you on the "soft minimum", that's an important point that makes this a tricky question to answer. I've also heard it argued that long before the industrial revolution, the agricultural revolution, and thousands of years of farming, progress and deforestation added some warming, even though the Earth has cooled over the last few thousand years, without human progress we might be in the beginnings of an ice age now. $\endgroup$ – userLTK Oct 10 '17 at 21:12
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    $\begingroup$ My understanding is that best guess is it takes Insolation minimums of roughly 460 Wm2 to kick start a glaciation period, but that is best guess from past data, and all of the data is indirect and being interpreted well after the fact. We did not get even close to that this minimum and will not again for several cycles. Past cycles have not 100% matched the Insolation pattern, but it has been fairly close. $\endgroup$ – dlb Oct 10 '17 at 21:51
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    $\begingroup$ @userLTK Ah, I know about this! What you have there is the Ruddiman early anthropocene hypothesis humansandnature.org/…. I first heard of that by watching this great lecture about climate and Milankovitch cycles etc youtu.be/Yze1YAz_LYM According to Ruddiman glaciation would be juuuust about starting by now if it wasn't for the GHG released by early farmers. So I thought I'd come and get a second take on that here. $\endgroup$ – Jimmy Widdle Oct 13 '17 at 13:07
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There are two factors determining when the next glacial cycle.

The first concerns the natural cycle that has been at play since the beginning of our present day Ice Age (about 2.6 million years ago). In this case the next glacial period ushers in as temperatures in the worlds oceans rise that in turn increases hurricane activity/force. As hurricane activity eventually extends into winter months they bring blizzard conditions the likes of which are the building blocks of a glacial period. The increase in ocean temperatures is primarily the result of the North American and Eurasian tectonic plate adjusting from the previous glacial period, namely at the ice free peripheries that had bowled upward as a result of the massive glacial weight that covered continents. These outer peripheries today lay mostly in the Oceans and so a resettling means “heat generated friction” as they grind along adjacent plates where the plate boundaries are convergent, and in the case where the boundaries are divergent, heat is generated as magma displaces into the ocean.

The second factor determining when the next glacial period is due, is as a result of man-made global warming. This will certainly change the “natural” game plan. In the past (without man-made global warming), interglacials lasted about 10,000–20,000 years, and so we can extrapolate from this that the next glacial period can begin any time in the near future and before 8,500 years.

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  • $\begingroup$ I haven't heard that rising ocean temperatures are a factor in glaciation - insolation and GHG loss from the atmosphere being the prime factors, I thought. Would you say ocean warming is included with those other processes ? $\endgroup$ – Jimmy Widdle Oct 1 '18 at 13:51

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