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Author Topic: How long does anthropogenic CO2 remain in the atmosphere?  (Read 7878 times)

Offline thedoc

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Kjell Arne Rekaa asked the Naked Scientists:
   
I'm so frustrated about all talking about what's going to happen in 86 years from now, when what we are emitting into our atmosphere now is going to influence the climate for virtually all time into the future.

Please read:
The Long Thaw: How Humans are Changing the Next 100,000 Years of Earth's Climate, or consult the author David Archer (Princeton University Press, 2009).

I've written some blogs about this most important topic of our future as well on:
http://les-kar.blogspot.com/

Thanks for a great podcast anyway!

Sincerely
Kjell Arne Rekaa

What do you think?
« Last Edit: 23/12/2013 18:17:53 by CliffordK »


 

Offline yor_on

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Re: How long does anthropogenic CO2 remain in the atmosphere?
« Reply #1 on: 23/12/2013 18:33:19 »
Ok.

A hundred to ?? two hundred years ?? for the main part. Up to thirty thousand years for its tail.
We don't have those numbers really. What we can do is to experiment and use what statistics we find.

The problem is that even if we would stop all anthropogenic CO2 today, putting all our cars etc into the 'garage'. We still have those numbers to look at, beginning from that day.

It sux terribly.
 

Offline CliffordK

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Re: How long does anthropogenic CO2 remain in the atmosphere?
« Reply #2 on: 23/12/2013 18:41:51 »
I agree that we are making changes to our atmosphere that we don't fully understand at this time.

Methane gets broken down in the atmosphere relatively quickly, and if the releases could be controlled, it should eventually reach a steady state, or possibly decline.

CO2, on the other hand is stable under oxygen and solar energy.  So, the question is what will become of the CO2 in the atmosphere.  A lot will depend on how long we continue to burn fossil fuels. 

Through wave action, the CO2 is quickly absorbed into the upper layers of the ocean.  However, it takes several years for the CO2 to diffuse through the entire several km depth of the ocean.   So, if fossil fuel emissions were to stop, over the next few decades, or perhaps centuries, a large portion of the excess CO2 would be absorbed and distributed through the ocean.  Not all, of course, but a significant amount. This may also be decreased somewhat if the oceans warm up.

Carbon Dioxide also acts like plant sugar. 
Plants are considered to be part of a carbon cycle.  However, apparently there is an excess that is being absorbed by the plants and not necessarily released.

Anyway, if we could stop CO2 emissions from fossil fuels, atmospheric levels would at least initially drop.  However, with all the climate change discussion, global emissions continue to rise every year.
 

Offline yor_on

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Re: How long does anthropogenic CO2 remain in the atmosphere?
« Reply #3 on: 23/12/2013 18:43:47 »
Another thing. We will always find people to admire, those 'keeping on' no matter what adversity they meet.
He**, that's what advertising is about. Giving you the feeling that you too is involved.

But you won't find one accepting that they choose this.
 

Offline evan_au

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Re: How long does anthropogenic CO2 remain in the atmosphere?
« Reply #4 on: 23/12/2013 19:31:44 »
Various estimates place the lifetime of CO2 in Earth's atmosphere at 30-100 years.

This is longer than most people want to think about or plan for.

Since it is so slow, it is easier to ignore it for now, leave it for the next generation - and then act surprised when historically unprecedented effects happen (like big storms hitting densely populated areas).
 

Offline yor_on

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Re: How long does anthropogenic CO2 remain in the atmosphere?
« Reply #5 on: 26/12/2013 00:22:20 »
I like this one from Lisa Moore. It is easy to read and quite straight forward.

"
Lisa Moore, Ph.D., scientist in the Climate and Air program at Environmental Defense.--

Here's a table showing a selection of greenhouse gases, their global warming potential (GWP), and their lifetimes:

Greenhouse Gas . . . . . . . .  .Lifetime years . . (100-Year GWP)
Carbon Dioxide (CO2) . . …. . . . hundreds .. .. . .1
Methane (CH4) . . . . . . …. . . .. . . 1 . . .  . . . .25
Nitrous Oxide (N2O) . . . . . . . . . .114 . . . . . . .298
Hydrofluorocarbon-23 (CHF3) . . . .264 . . . .. . .14,800
Sulphur hexafluoride (SF6) . . . . ..3,200.  . . . .22,800
PFC-14 (CF4) . . . . . . . .. . . . . .50,000 . . . . .7,390

Notice that the carbon dioxide lifetime is "hundreds of years", rather than a specific number. The IPCC ‘Third Assessment Report’ defines a gas's lifetime as the amount of the gas in the atmosphere divided by the rate at which it is removed from the atmosphere. That sounds simple enough, except that not all gases are removed by just one (or mainly one) process. Ironically, the gas that accounts for the greatest proportion of global warming, carbon dioxide (CO2), is the hardest to pin down. When CO2 is released into the atmosphere, about three-quarters of it dissolves into the ocean over a few decades (- Acidity -). The rest is neutralized by a variety of longer-term geological processes, which can take thousands of years.

From IPCC Fourth Assessment Report:  About 50% of a CO2 increase will be removed from the atmosphere within 30 years, and a further 30% will be removed within a few centuries. The remaining 20% may stay in the atmosphere for many thousands of years.

From U.S Greenhouse Gas Inventory Reports: (CO2) Atmospheric lifetime: 50-200 years. No single lifetime can be defined for CO2 because of the different rates of uptake by different removal processes.

From RealClimate: “My model indicates that about 7% of carbon released today will still be in the atmosphere in 100,000 years. I calculate a mean lifetime, from the sum of all the processes, of about 30,000 years. That's a deceptive number, because it is so strongly influenced by the immense longevity of that long tail. If one is forced to simplify reality into a single number for popular discussion, several hundred years is a sensible number to choose, because it tells three-quarters of the story, and the part of the story which applies to our own lifetimes.” ("How long will global warming last?")

For other gases, a meaningful lifetime is easier to calculate because one process dominates their removal from the atmosphere:

    * Methane is mostly scrubbed from the atmosphere by hydroxyl radicals (a chemical reaction).
    * Nitrous oxide is destroyed by photolytic reactions (chemical reactions involving photons or light) in the stratosphere.

As you can see from the chart, some gases have extraordinarily long lifetimes. Because emission rates are vastly higher than removal rates, greenhouse gases are accumulating in the atmosphere and will affect climate for generations to come."

Citing some more.

What happens when we add ‘man made’ CO2 (carbon dioxide)? Well the concentration/addition of molecules will get our atmosphere to become denser or thicker if you like, that in its turn will push that releasing ‘edge/surface’ where that heat finally leave our atmosphere, upwards to even colder layers, higher up. As those is colder they do not radiate heat as well as those layers that already is becoming ‘satiated’ by heat. And the whole time we have a constant creation of more manmade CO2 joining the atmosphere that we are ‘creating / transforming’ into CO2 from the Earth’s hidden/buried ‘sinks’ in form of coal and oil and natural gas (methane). Each ‘layer’ of air in our atmosphere will reach ever new equilibrium’s of heat, as they interact, that as molecules in each layer also will heat each other as they 'bump each other' and radiate.

Earth will slowly become a place where the radiation from those molecules, reflected in all directions, cause Earth to start conserving this energy, building up ‘heat’ in the air layers as it gets ‘trapped’ by our new molecules. And this ‘imbalance’ creating evermore warmer layers will keep on, until the highest level of our atmosphere is so ‘warmed up’ that it reflects as much heat in space as the planet is receiving from the sun and our digging up fossil fuels as oil and methane. - That as it is only in that highest layer Earth can regulate its temperature through radiating out in space -. Before the industrial revolution we were actually in a slowly cooling period on Earth, and should still be as I understands it? As for water-vapor it is well known that the higher up you come the ‘dryer’ the air will be, that means that most of the water-vapor falls out as rain further down.

As the Co2 and H2O molecules drifts upward their mode of absorption changes. At a sea level the absorption is concentrated into discrete spikes with narrow gaps between the spikes and ‘shallow’ valleys. The ‘spikes’ we’re talking about is light (heat) absorbed in very specific wavelengths shown as dark lines in a spectrum. When the molecules are at the higher layers this absorption will change as the air-pressure goes down. Then their ‘spikes’ becomes much more defined and closer together (more heat absorbed per molecule) And CO2 won’t fall out as water vapor does (H2O-humidity-rain) at those lower altitudes, instead it will stay mixed no matter the height even though it will ‘thin out’ the higher we come just as our atmosphere. That’s why climate scientists talk about amount of heat conserved in different molecules and of global warming potential (GWP).

“Methane is a greenhouse gas that is 60-70 times more potent than carbon dioxide (CO2) over a twenty-year period (or 25 times over a hundred-year period). “ And that’s why methane is a ‘killer of life’ even in small quantities. Also you should know that CO2 when taken up by the oceans create acidity in them, creating a marine environment where our fishes, reefs, etc starts to die. And as I wrote earlier, they are already becoming saturated. "A study published in the journal Science revealed that since 1981, the Southern Ocean has been taking up less carbon dioxide - five to 30 per cent less per decade - than researchers had predicted previously. At the same time carbon dioxide emissions rose by 40 per cent, the study found. The reason for the slowdown is more winds over the Southern Ocean since 1958, caused by human-produced greenhouse gases and ozone depletion. " New global warming threat from Southern Ocean.

“Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3000 m and that the ocean has been absorbing more than 80% of the heat added to the climate system. Such warming causes seawater to expand, contributing to sea level rise. . Changes in precipitation and evaporation over the oceans are suggested by freshening of mid and high latitude waters together with increased salinity in low latitude waters. Mid-latitude westerly winds have strengthened in both hemispheres since the 1960s. More intense and longer droughts have been observed over wider areas since the 1970s, particularly in the tropics and subtropics. Increased drying linked with higher temperatures and decreased precipitation have contributed to changes in drought. Changes in sea surface temperatures (SST), wind patterns, and decreased snowpack and snow cover have also been linked to droughts. "
 

Offline yor_on

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Re: How long does anthropogenic CO2 remain in the atmosphere?
« Reply #6 on: 26/12/2013 01:06:16 »
You know, "New global warming threat from Southern Ocean." is an old one from 2007, Got curios reading it thinking what new might happen there and found this. http://inhabitat.com/new-york-city-sized-iceberg-breaks-free-of-antarctica-could-threaten-international-shipping-lanes/

Now "Pine Island Glacier is one of the largest ice streams in Antarctica. It flows, together with Thwaites Ice Stream, into the Amundsen Sea embayment in West Antarctica, and the two ice streams together drain ~5% of the Antarctic Ice Sheet. Pine Island Glacier flows at rates of up to 4000 m per year. It is of interest to scientists because it is changing rapidly; it is thinning, accelerating and receding, all of which contribute directly to sea level, and its future under a warming climate is uncertain. Pine Island Glacier is buttressed by a large, floating ice shelf, which helps to stabilise the glacier, but this ice shelf is itself thinning and recently calved a huge iceberg." http://www.antarcticglaciers.org/glaciers-and-climate/shrinking-ice-shelves/pine-island-glacier/

What is interesting, to me, is just that it is the west side of Antarctica where it all seems to happen. Hansen wrote, and warned, already in the 90:s if I remember right, about this possibility of Ice 'gliding down' the slope of west Antarctica, meeting the continental shelf, where the ocean gets really deep and so 'breaking loose'. Had the original text somewhere too, but can't find it now. Couldn't find any specific on if the original findings 2007 have changed for better or worse though. But this one is a good read, for those interesting in CO2 sequestering, on a marine basis. http://www.worldwatch.org/node/6323

(And that makes me think of tropical reefs, before, and after, acidity done its work. It's not just 25% food fish disappearing, is it? It's carbon sequestering too.)


We all live in interesting times, as the Chinese puts it.
« Last Edit: 26/12/2013 01:17:28 by yor_on »
 

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Re: How long does anthropogenic CO2 remain in the atmosphere?
« Reply #6 on: 26/12/2013 01:06:16 »

 

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