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Dharma Rupa

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Re: "Stupid" Questions :o
« Reply #1650 on: November 30, 2018, 10:22:16 PM »
I suspect the immense heat capacity of the oceans is simply dampening the time to equilibrium effects of the 50% increase in CO2 concentration from pre-industrial.  Give it a millenium or so.

The sudden swings in sea level tend to add doubt about that millennium estimate.

How so?  Sea level depends mostly on melting of ice on land masses.
If the mean temperature of the lower atmosphere goes up by 2 degrees C, how long does it take for the mass of the oceans to rise in temperature by a corresponding amount?

The accumulating heat of the earth at present won't be fully reflected in surface temperatures until heat stops going into the oceans and raising their heat content.  We know that total heat content of the oceans is increasing, so we know surface temperature increases don't fully reflect the current planetary radiation imbalance.

Actual evidence comes before theory.  That is how so.  Fact is that there have been numbers of large changes in sea level that have happened on time spans more like decades than millennia.

SteveMDFP

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Re: "Stupid" Questions :o
« Reply #1651 on: November 30, 2018, 10:39:39 PM »
I suspect the immense heat capacity of the oceans is simply dampening the time to equilibrium effects of the 50% increase in CO2 concentration from pre-industrial.  Give it a millenium or so.

The sudden swings in sea level tend to add doubt about that millennium estimate.

How so?  Sea level depends mostly on melting of ice on land masses.
If the mean temperature of the lower atmosphere goes up by 2 degrees C, how long does it take for the mass of the oceans to rise in temperature by a corresponding amount?

The accumulating heat of the earth at present won't be fully reflected in surface temperatures until heat stops going into the oceans and raising their heat content.  We know that total heat content of the oceans is increasing, so we know surface temperature increases don't fully reflect the current planetary radiation imbalance.

Actual evidence comes before theory.  That is how so.  Fact is that there have been numbers of large changes in sea level that have happened on time spans more like decades than millennia.

We may be talking past each other here.  In the face of warming of the planet, there can clearly be rather rapid melting of land-based ice, raising sea levels rather quickly.

It does not follow, however, that full themodynamic equilibrium with the mass of water in all the oceans has reached anywhere near equilibrium, even after all ice has been melted.  Surface temperatures won't fully reach such equilibrium until after the oceans have warmed.

gerontocrat

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Re: "Stupid" Questions :o
« Reply #1652 on: November 30, 2018, 11:37:02 PM »

 Sea level depends mostly on melting of ice on land masses.

Sort of yes and sort of no? Until a few years ago the increase in sea level was more down to thermal expansion of the oceans than land ice mass loss. Now it is more due to loss of land ice - but where does the energy come from to do it.

At the moment the majority of (increasing) ice loss is from Greenland calving. But that is accelerated  by ocean water melting glacial tongues and attacking glacial grounding lines and gravity does the rest. So a goodly part of the energy for that ice mass loss comes from the oceans. If not for that calving Greenland would be accumulating mass, not losing mass. (Greenland is a lot warmer than Antarctica)

If I have got Abrupt SLR's postings about the Antarctic right, due to bathymetry this is even more true for the Southern Continent. Ice shelves are being melted from underneath, as are glaciers and ice sheets resting on the sea floor at great depth. Even in winter, with land temperatures n degrees below zero, where n is large, ocean currents still bring in warmth at depth to gnaw away at the ice. If / when the Antarctic circumpolar current weakens, this will allow yet more ocean warmth to get down south. It is this that is most likely to cause abrupt sea level rise, and the principal energy source is from the warming oceans.

The attached map shows how much of Antarctica is below current sea level.
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Ned W

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Re: "Stupid" Questions :o
« Reply #1653 on: December 01, 2018, 02:50:48 AM »
Most / many ? IPCC scenarios envisage going over the +1.5 to +2 limit but then the miraculous (as yet non-existent) low-cost technology will exist to  directly capture many billion of tonnes of CO2 from the air which will gradually bring down the temperature increase to "reasonable" levels.

Some might say that this is cloud-cuckoo land but I am sure that those who presume to advise and govern us know what they are doing. (Looks for emoji for heavy sigh")

Of the four main CMIP5 pathways, only RCP 2.6 directly assumes net negative emissions and a decrease in atmospheric concentration.  The others (RCPs 4.5, 6.0, and 8.5) gradually stabilize the concentration but without actual decreases.

The main factor in that stabilization is probably ocean uptake -- as anthropogenic emissions are reduced later in this century, at some point the downward flux in the ocean is able to start eating away at the anthro CO2 pulse. Eventually most of it will end up in the ocean, but it takes a looooooong time.

This, incidentally, was why a lot of people in the first half of the 20th century assumed that Arrhenius was wrong and AGW would never be a problem -- they assumed ocean uptake would be sufficient to handle anthropogenic emissions.  They didn't understand the shallowness of the mixed layer and the low rate of mixing into the deep ocean.  Then (a) Keeling showed that actually the CO2 is in fact accumulating in the atmosphere, and (b) a bunch of oceanographers and geochemists (Takahashi et al.) explained why -- the ocean is too slow to absorb emissions at the rate we're generating them now. 

Ned W

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Re: "Stupid" Questions :o
« Reply #1654 on: December 01, 2018, 02:52:25 AM »
All the science I can find on 400+ppm CO2 in the atmosphere before present says the global average temp was 4-6c higher than today.

I'm not sure where that is coming from.

According to the IPCC fifth assessment report, Chapter 5:

Quote
During the mid-Pliocene (3.3 to 3.0 million years ago), atmospheric
CO2 concentrations between 350 ppm and 450 ppm (medium confidence)
occurred when global mean surface temperatures were 1.9°C
to 3.6°C (medium confidence) higher than for pre-industrial climate.

Thanks, Steven.  You beat me to it.

wdmn

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Re: "Stupid" Questions :o
« Reply #1655 on: December 01, 2018, 07:23:43 AM »
“The last time the Earth experienced a comparable concentration of CO2 was 3-5 million years ago, when the temperature was 2-3°C warmer and sea level was 10-20 meters higher than now,” said WMO Secretary-General Petteri Taalas.

https://www.forbes.com/sites/michaelmarshalleurope/2018/11/29/a-simple-guide-to-all-the-scary-and-depressing-climate-change-news-at-the-moment/#1dad09a3776a

Not sure what Petteri's source is, but he make it sounds as though it was 3-4C above pre-industrial.

El Cid

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Re: "Stupid" Questions :o
« Reply #1656 on: December 01, 2018, 11:41:04 AM »
As for climate sensitivity and paleoclimate comparisons I strongly advise everyone to read these two short studies:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140001039.pdf

https://www.skepticalscience.com/Why_the_Miocene_Matters.html

The first one gives a very wide range of 2-5 degrees (Centigrade or Kelvin) sensitivity for doubling of Co2 based on a metaanalysis of paleoclimate studies

The second says that the mid Miocene climatic optimum is probably (sort of) a good comparison to today's rapid Co2 emissions (and levels).

"Going further back into the Miocene, tropical sea surface temperatures were as much as 12°C warmer at 12 million years ago, with CO2 levels similar to today, estimated at around 400ppm. Ice was minimal in high northern latitudes and ice was restricted to inland portions of East Antarctica, while the rest of the continent supported temperate forests"

"The MMCO was ushered in by CO2 levels jumping abruptly from around 400ppm to 500ppm, with global temperatures warming by about 4°C  and sea levels rising about 40m (130 feet) as the Antarctic ice sheet declined substantially and suddenly. "

"Even allowing for that, the fact that models need a sensitivity of 4°C per CO2 doubling to recreate Mid-Miocene warmth suggests that the modern value is more likely towards the upper end of the IPCC range of 1.5-4.5°C than the lower end"


So all in all, it seems that a doubling of Co2 is more likely to lead to 4-5 degrees of warming and we are likely to get there by 2100. Of course this also means that NH midlatitude land areas (USA,Canada,Europe,Russia) are likely to get warmer by more than that, possibly 6-8 degrees...

Klondike Kat

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Re: "Stupid" Questions :o
« Reply #1657 on: December 01, 2018, 02:45:09 PM »

"Even allowing for that, the fact that models need a sensitivity of 4°C per CO2 doubling to recreate Mid-Miocene warmth suggests that the modern value is more likely towards the upper end of the IPCC range of 1.5-4.5°C than the lower end"


So all in all, it seems that a doubling of Co2 is more likely to lead to 4-5 degrees of warming and we are likely to get there by 2100. Of course this also means that NH midlatitude land areas (USA,Canada,Europe,Russia) are likely to get warmer by more than that, possibly 6-8 degrees...

The alternative is that there more involved than a simple temperature-CO2 correlation.  There were most likely other factors involved back then.

AmbiValent

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Re: "Stupid" Questions :o
« Reply #1658 on: December 03, 2018, 09:10:09 AM »
Has the current back-and-forth between periods of rapid ice growth and near standstill always been there (just with more ice), or is it a result of climate change, maybe via weakening the jet stream allowing warmer air to get to the polar region easier?
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gerontocrat

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Re: "Stupid" Questions :o
« Reply #1659 on: December 03, 2018, 02:14:14 PM »
Has the current back-and-forth between periods of rapid ice growth and near standstill always been there (just with more ice), or is it a result of climate change, maybe via weakening the jet stream allowing warmer air to get to the polar region easier?
There was a discussion last year about how there are waves of above/below average melt/gain, and I think that has always been so, and probably due to temporary changes in wind, waves and temperatures. But the weather people hypothesise that global warming has weakened the polar jet stream and with big fat lazy Rossby waves weather patterns can stick around a lot longer.

Perhaps this is showing up in longer waves of above/below average freeze/melt?
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
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FredBear

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Re: "Stupid" Questions :o
« Reply #1660 on: December 08, 2018, 01:52:05 AM »
Goodbye Waves - I take these as the wispy ice patterns on the fringes of patches of melting ice floes, with open sea outside, seen on satellite pictures. Does anyone know what causes them, has anyone physically seen them? (I wondered if it was fresh water floating away from the ice being cooled by surrounding colder [below 0oC] salty water??)

johnm33

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Re: "Stupid" Questions :o
« Reply #1661 on: December 08, 2018, 01:24:32 PM »
"goodbye waves" Iirc W.D. coined the phrase, https://eh2r.blogspot.com/search?q=goodbye+waves
added, probably best to load just a couple of those posts, lots of images and animations.
« Last Edit: December 08, 2018, 01:33:27 PM by johnm33 »