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Author Topic: Ice-age inception?  (Read 4013 times)

nukefix

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Ice-age inception?
« on: June 02, 2014, 10:27:48 AM »
What do you think about the idea that greenhouse gases might stop the Earth from going into the next ice-age? This climate-skeptic blog links to a couple of interesting scientific papers:

http://wattsupwiththat.com/2014/05/29/glacial-inception/

What do you think about the idea, is there a consensus about these matters between scientists?

ktonine

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Re: Ice-age inception?
« Reply #1 on: June 02, 2014, 10:53:30 AM »
nukefix - MIT Technology Review pretty much pooh-poohs the idea.  Orbital forcing lasts for quite awhile and is very hard to defeat.  This is in accord with most of what I've read on the subject.

icefest

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Re: Ice-age inception?
« Reply #2 on: June 02, 2014, 02:18:58 PM »
nukefix - MIT Technology Review pretty much pooh-poohs the idea.  Orbital forcing lasts for quite awhile and is very hard to defeat.  This is in accord with most of what I've read on the subject.

I'd disagree. That article states that the current GHG released will not hang around long enough to have an effect - I'll agree with that.

The basic premise of "greenhouse gases might stop the Earth from going into the next ice-age" is a reasonable one, and if we manage to avert the coming calamity, a continuous controlled release of methane might eventually be needed to stabilise the earths temperature.
Open other end.

nukefix

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Re: Ice-age inception?
« Reply #3 on: June 02, 2014, 03:00:01 PM »
It seems some people are speculating that without the extra GHGs we might be sliding into the next ice-age already by now. I guess climate modelling can shed some light into this but I wonder if it's really possible to predict when an ice-age "should" begin. An error of a mere 500 years is huge in the human timescale.

crandles

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Re: Ice-age inception?
« Reply #4 on: June 02, 2014, 04:10:35 PM »
http://www.realclimate.org/index.php/archives/2005/03/how-long-will-global-warming-last/

suggests

Quote
When you release a slug of new CO2 into the atmosphere, dissolution in the ocean gets rid of about three quarters of it, more or less, depending on how much is released. The rest has to await neutralization by reaction with CaCO3 or igneous rocks on land and in the ocean [2-6]. These rock reactions also restore the pH of the ocean from the CO2 acid spike. My model indicates that about 7% of carbon released today will still be in the atmosphere in 100,000 years [7]

If we stop emitting after releasing enough to get the peak up to 560ppm and half of it having been absorbed by oceans then if I am doing calculations correctly rather than falling back to 280 it tends to fall towards 280+1/4*2*(560-280)=420ppm by 1000 years and then takes a further 99,000 years to fall to 320ppm.

At 1,000 years where the GW effect could remain at over 3C for global average temperature (perhaps more if ice sheets collapse?). Calculated from 420ppm being over half a doubling and Earth system sensitivity at 6C. Temperature at the poles rise twice as fast as average so there could be around 6 or 7C temperature increase at the poles even after 1000 years. This might be enough to prevent an ice age starting?

At 100,000 years though, the GW effect at poles looks more like a 1C increase and that seems much less likely to be enough to stop an ice age starting.


So if there is no intelligent life, the Milankovitch cycles with periods of 21K 41k and 100k years will eventually come around to causing an ice age again. If the next is due in 2000 years then it could well be prevented even if we stop all our emissions at the 560ppm level and the delay to the next ice age could be a considerable length of time (41,000 years?). However if intelligent life is around, we seem quite capable of producing sufficient strong GHGs to ward off an ice age.

These calculations seem a bit woolly to me. There seems some disagreement perhaps because of lack of agreement on how long the CO2 lasts. I suspect the correct expert on this are CO2 cycle scientists. Someone that has just looked up a CO2 e-folding time of maybe 100 years or so without further research is likely to be wrong on this. I doubt scientists debate this much.

I have no idea but suspect there is room for disagreement on whether next ice age is delayed until next 41k year cycle or whether in 10k years further into 41k cycle the conditions could still be sufficient to initiate an ice age. Of course there is also room for discussion of the scenario of whether we stop burning fossil fuels at 560ppm or some other level or reduce the level but continue to produce some emissions or ....

 

wili

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Re: Ice-age inception?
« Reply #5 on: June 02, 2014, 04:32:36 PM »
CO2 cycle, indeed. MacDougall (2013) calculated that just part of the permafrost melt will now be enough to offset the ocean uptake enough that, even with total cessation of all further emissions starting immediately, atmospheric CO2 levels would not go down for at least two centuries. And that's just figuring in one part of one carbon feedback.

We can't and should not try to micro-manage the earth systems. We have pretty well buggered about every earth system that there is, so fantasies about fine tuning the plane to suit our whims is just gas at this point. As Lovelock used to say, leaving humans to manage the earth's systems is like leaving a goal to manage a garden.
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

crandles

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Re: Ice-age inception?
« Reply #6 on: June 02, 2014, 05:45:59 PM »
CO2 cycle, indeed. MacDougall (2013) calculated that just part of the permafrost melt will now be enough to offset the ocean uptake enough that, even with total cessation of all further emissions starting immediately, atmospheric CO2 levels would not go down for at least two centuries. And that's just figuring in one part of one carbon feedback.

We can't and should not try to micro-manage the earth systems. We have pretty well buggered about every earth system that there is, so fantasies about fine tuning the plane to suit our whims is just gas at this point. As Lovelock used to say, leaving humans to manage the earth's systems is like leaving a goal to manage a garden.

Hmm. if we cease all emissions, is ocean uptake in next 200 years a huge amount?

From McDougall 2013:
Reversing climate warming by artificial atmospheric carbon-dioxide
removal: Can a Holocene-like climate be restored?
Quote
However, long-term model simulations also indicate that most of the temperature anomaly created by burning of fossil fuels will persist even 10000 years into the future. The simulations of Eby et al. [2009], for example, suggest that 70–80% of the peak surface temperature anomaly would remain by the year 12000 CE, for a large range of cumulative carbon emissions (160–5120 Pg C).

From McDougall et al 2012
Significant contribution to climate warming from the permafrost carbon feedback

Quote
According to our simulations, permafrost soils will release between 68 and 508 Pg carbon by 2100. We show that the additional surface warming generated by the feedback between permafrost carbon and climate is independent of the pathway of anthropogenic emissions followed in the twenty-first century. We estimate that this feedback could result in an additional warming of 0.13–1.69 °C by 2300.

508Pg carbon is certainly larger than I thought, even 68Pg is more than the roughly 1/16 of our total emissions that I was expecting.

Quote
We can't and should not try to micro-manage the earth systems.

Even if we shouldn't try, can you imagine the world with falling temperatures and heading for an ice age and humans not trying to stop it?

Before starting to 'micro-manage', we should stop and think what happens if we have to stop. In the case of sulphur injection to stratosphere to mitigate GW this leads to a no we shouldn't start doing this. However in other situations there may not be such scope for disaster. If approaching an ice age and satisfactory testing suggested it fell into that less dangerous class then I am much less sure about whether or not we should start trying. Perhaps I would even tend to favour starting such preventative action.

wili

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Re: Ice-age inception?
« Reply #7 on: June 03, 2014, 04:42:27 PM »
Crandles, thanks for tracking down the McDougall papers. It was actually the 2012 one I was thinking of.

"can you imagine the world with falling temperatures and heading for an ice age"

No, not for millions of years, if then.
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

Lennart van der Linde

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Re: Ice-age inception?
« Reply #8 on: June 04, 2014, 04:59:03 PM »
In this presentation David Archer says we'll make an ice-age impossible for half a million years (at around 50 minutes):


But I guess it could be millions of years as well...

nukefix

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Re: Ice-age inception?
« Reply #9 on: June 04, 2014, 05:35:08 PM »
In this presentation David Archer says we'll make an ice-age impossible for half a million years (at around 50 minutes):


But I guess it could be millions of years as well...
Great presentation - thanks!