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Bugalugs

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Has climate sensitivity been under-estimated?
« on: June 24, 2019, 09:31:37 AM »
Looking at the latest data and observations from the Arctic, it seems global warming is happening much faster than predicted.

Has climate sensitivity been severely under-estimated? Or is it tracking along as expected?

I saw a graph of the Greenland ice melt suggesting it was faster than even the "worst" IPCC model. Is this indicative of the state of progress of the planet?

I ask on this forum because I am hoping for science-based answer.

b_lumenkraft

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Re: Has climate sensitivity been under-estimated?
« Reply #1 on: June 24, 2019, 11:40:25 AM »
Hello and welcome Bugalugs to the forum.

First of all, some people here don't like it when new folks open new threads. There is a 'stupid question thread'. This is the right place for your question. And this is NOT because you are having a stupid question. :)

Actually, this is the big question, that is always discussed, even in this forum. There is absolutely no consensus on that.

There is an inherent flaw with all models: They don't see black swans.

For example, we don't know much about how and how much GHG (greenhouse gases) the thwarting permafrost will release.

And there are a lot of wild cards like this.

This is the reason why many believe that the models are too optimistic.

Bugalugs

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Re: Has climate sensitivity been under-estimated?
« Reply #2 on: June 24, 2019, 12:17:23 PM »
Thank you for taking the trouble to answer.

I am aware that the models don't take into account black swans.

I am curious if we are tracking faster than their swan-free models? The Greenland melting graph I saw would suggest so.

(I will have a look for the stupid questions thread, ty ...)

b_lumenkraft

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Re: Has climate sensitivity been under-estimated?
« Reply #3 on: June 24, 2019, 12:43:52 PM »

Quote
Model comparisons to data 1950-2050. Spaghetti are individual annual model results for each RCP. Solid curves are model ensemble annual averages.


Quote
Anomalies of annual, global-mean near-surface temperature from observations and the model (comprising SST over oceans, and near-surface air temperature over land). Solid lines show the ensemble mean, and shading shows the range of individual runs within each ensemble. Observations and the model both use their own 1850-1899 mean in the calculation of anomalies.


Quote
The recently published U.S. National Climate Assessment shows that we are currently on track for RCP8.5.

So no, we are not tracking faster than the worst case scenario so far.

Bugalugs

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Re: Has climate sensitivity been under-estimated?
« Reply #4 on: June 24, 2019, 01:09:25 PM »
Many thanks. I see the worst-case scenario plot may be our path if the current trend continues. The recent Arctic data is certainly worrying.

Time will tell.

Thank you again for your valuable time and knowledge.

b_lumenkraft

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Re: Has climate sensitivity been under-estimated?
« Reply #5 on: June 24, 2019, 01:16:39 PM »
Many thanks. I see the worst-case scenario plot may be our path if the current trend continues. The recent Arctic data is certainly worrying.

You are welcome and yes, it is worrying AF.

CO2 emissions need to radically come down. Fight for a $150/t carbon tax comrade. :)

kassy

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Re: Has climate sensitivity been under-estimated?
« Reply #6 on: June 24, 2019, 01:34:40 PM »
Here is a thread about some measures we use to predict/compare climate sensitivity.

https://forum.arctic-sea-ice.net/index.php/topic,2158.msg0.html

quoting from post 22 by ASLR, bolding mine:

Quote
As advanced Earth System Models, ESMs, do not need to use the concept of CO2e, to me the best reason for calculating this value is to compare with the paleo record (which did not include high negative forcings from anthropogenic aerosols that can leave the atmosphere within months of their emissions).  As currently the best ESMs cannot match the highly sensitive climate response during MIS 11c (the Holsteinian Peak), where MIS 11 extents from 424,000 to 374,000 years ago (see the attached image), I think it is important think about how feedback mechanism could make temperature variations of nearly 2C with CO2 concentrations around 285 ppmv.  This likely means that feedback mechanisms treated by current ESMs as noise may actual be important from a dynamical sensitivity point-of-view of such considerations as climatic state, climate attractors (such as PDO/AMO/ENSO interactions), and 'short-term' feedback mechanisms (such as the collapse of marine ice sheets and/or GHG emissions from permafrost, and/or methane hydrate, degradation).  In this regards, I note that the linked article indicates that the annual precipitation (PANN) in NE Siberia was much higher during MIS 11c than during MIS 5e (Eemian Peak) or MIS 1 (Holocene).  This higher annual precipitation likely fell as rainfall during MIS 11c; which may have contributed to a pulse of methane emissions from thermokarst lakes in the Arctic. 

See that thread for the details.

Seeing how predictions shifted since the early nineties everything always arrives earlier then we predict so there is a systematic error and the bolded part might be the reason.

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crandles

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Re: Has climate sensitivity been under-estimated?
« Reply #7 on: June 24, 2019, 01:35:02 PM »
It is easy to try to suggest that from something like the first graph attached.

I think it is somewhat difficult to go from ice to co2 sensitivity or even from arctic temperature changes to global temperature changes. The arctic is expected to warm faster partly in response to less sea ice. How much faster is not entirely clear.

Also the ice may well behave somewhat unexpectedly, there is discussion in the literature that ice volume (particularly thick MYI) declined rapidly once it stopped making it all the way around beaufort gyre so there may well be a period of rapid decline circa 1998-2012. The models are all over the place and not good enough to capture this.

If the trend in ice is more like the second graph attached: no, I don't believe the horizontal extrapolation, the ice will still decline but perhaps more slowly now. If this happens then the trends may be more like the models and the arctic temperature trend may also be affected and slow down.

If that is what happens with the ice then the temperature trend may also move towards being more like the models.

Bugalugs

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Re: Has climate sensitivity been under-estimated?
« Reply #8 on: June 25, 2019, 05:39:11 AM »
Thanks again for your replies, all noted with interest.
« Last Edit: June 25, 2019, 12:22:26 PM by Bugalugs »

DrTskoul

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Re: Has climate sensitivity been under-estimated?
« Reply #9 on: July 31, 2019, 09:59:14 AM »
The latest from CMIP6:

The terrible truth of climate change

Quote
When the IPCC’s 5th Assessment Report was published in 2013, it estimated that such a doubling of CO2 was likely to produce warming within the range of 1.5 to 4.5 °C as the Earth reaches a new equilibrium. However, preliminary estimates calculated from the latest global climate models (being used in the current IPCC assessment, due out in 2021) are far higher than with the previous generation of models. Early reports are predicting that a doubling of CO2 may in fact produce between 2.8 and 5.8 °C of warming. Incredibly, at least 8 of the latest models produced by leading research centers in the United States, the United Kingdom, Canada and France are showing climate sensitivity of 5 °C or warmer.

Pmt111500

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Re: Has climate sensitivity been under-estimated?
« Reply #10 on: July 31, 2019, 01:25:37 PM »
The latest from CMIP6:

The terrible truth of climate change

Quote
When the IPCC’s 5th Assessment Report was published in 2013, it estimated that such a doubling of CO2 was likely to produce warming within the range of 1.5 to 4.5 °C as the Earth reaches a new equilibrium. However, preliminary estimates calculated from the latest global climate models (being used in the current IPCC assessment, due out in 2021) are far higher than with the previous generation of models. Early reports are predicting that a doubling of CO2 may in fact produce between 2.8 and 5.8 °C of warming. Incredibly, at least 8 of the latest models produced by leading research centers in the United States, the United Kingdom, Canada and France are showing climate sensitivity of 5 °C or warmer.
Note here the need for climate models to estimate the moisture and temperature levels of 40-50 years forward, in order for biologists and ecologist, gardeners and foresters to attempt to speed up the normal ecosystem response to higher temperatures and altered humidity. If done skillfully, this might create additional sinks of soil carbon. 5-6 degrees does sound like a reasonable estimate to me. So onwards moving plants, higher up and north, everyone, well exept southern hemispherers, of course. You can't plant a forest in ocean, well kelp maybe. Umm.
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Mozi

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Re: Has climate sensitivity been under-estimated?
« Reply #11 on: July 31, 2019, 02:09:44 PM »
So no, we are not tracking faster than the worst case scenario so far.

While this is true, it doesn't necessarily mean that climate sensitivity has not been underestimated. Obviously aerosols could be playing a huge part in restraining the temperature rise to date.

nanning

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Re: Has climate sensitivity been under-estimated?
« Reply #12 on: July 31, 2019, 06:56:19 PM »
climate sensitivity according to paleodata
glacial maximum: CO2 = 180 ppm
interglacial:    CO2 = 280 ppm
DeltaT = 4C
CO2 ppm fraction = (280/180) = 14/9
For a doubling of CO2: (2/(14/9))*4C = 9/7 * 4C = 36/7 = ~5.14C
I think I read this in Peter Wadhams's book.
Time for another joint.
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DrTskoul

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Re: Has climate sensitivity been under-estimated?
« Reply #13 on: July 31, 2019, 07:34:22 PM »
climate sensitivity according to paleodata
glacial maximum: CO2 = 180 ppm
interglacial:    CO2 = 280 ppm
DeltaT = 4C
CO2 ppm fraction = (280/180) = 14/9
For a doubling of CO2: (2/(14/9))*4C = 9/7 * 4C = 36/7 = ~5.14C
I think I read this in Peter Wadhams's book.
Time for another joint.

Pass it on please!!

Klondike Kat

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Re: Has climate sensitivity been under-estimated?
« Reply #14 on: July 31, 2019, 08:11:03 PM »
climate sensitivity according to paleodata
glacial maximum: CO2 = 180 ppm
interglacial:    CO2 = 280 ppm
DeltaT = 4C
CO2 ppm fraction = (280/180) = 14/9
For a doubling of CO2: (2/(14/9))*4C = 9/7 * 4C = 36/7 = ~5.14C
I think I read this in Peter Wadhams's book.
Time for another joint.

That assumes that the CO2 rise is the sole cause of the temperature rise.  Which begs the question of why the CO2 started rising.

jai mitchell

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Re: Has climate sensitivity been under-estimated?
« Reply #15 on: July 31, 2019, 08:19:33 PM »
If the trend in ice is more like the second graph attached: no, I don't believe the horizontal extrapolation, the ice will still decline but perhaps more slowly now. If this happens then the trends may be more like the models and the arctic temperature trend may also be affected and slow down.

If that is what happens with the ice then the temperature trend may also move towards being more like the models.


I seem to remember your 4X gompertz fit curve was originally crafted as an argument against curve fitting for a projection.  Is it now the case that you actually believe that this outcome is even slightly possible?
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jai mitchell

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Re: Has climate sensitivity been under-estimated?
« Reply #16 on: July 31, 2019, 08:21:58 PM »
The latest from CMIP6:

The terrible truth of climate change

Quote
When the IPCC’s 5th Assessment Report was published in 2013, it estimated that such a doubling of CO2 was likely to produce warming within the range of 1.5 to 4.5 °C as the Earth reaches a new equilibrium. However, preliminary estimates calculated from the latest global climate models (being used in the current IPCC assessment, due out in 2021) are far higher than with the previous generation of models. Early reports are predicting that a doubling of CO2 may in fact produce between 2.8 and 5.8 °C of warming. Incredibly, at least 8 of the latest models produced by leading research centers in the United States, the United Kingdom, Canada and France are showing climate sensitivity of 5 °C or warmer.

link found here:  https://www.themonthly.com.au/issue/2019/august/1566136800/jo-lle-gergis/terrible-truth-climate-change
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jai mitchell

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Re: Has climate sensitivity been under-estimated?
« Reply #17 on: July 31, 2019, 08:24:28 PM »
climate sensitivity according to paleodata
glacial maximum: CO2 = 180 ppm
interglacial:    CO2 = 280 ppm
DeltaT = 4C
CO2 ppm fraction = (280/180) = 14/9
For a doubling of CO2: (2/(14/9))*4C = 9/7 * 4C = 36/7 = ~5.14C
I think I read this in Peter Wadhams's book.
Time for another joint.

That assumes that the CO2 rise is the sole cause of the temperature rise.  Which begs the question of why the CO2 started rising.

KK

you really need to learn how to google before you continue to display your ignorance on this board.  Asking stupid questions like that caused us to open a whole new thread for the google challenged like yourself. 

Please go here and don't come back until you get some understanding. 

https://forum.arctic-sea-ice.net/index.php/topic,143.0.html
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jai mitchell

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Re: Has climate sensitivity been under-estimated?
« Reply #18 on: July 31, 2019, 08:32:13 PM »
FYI we were discussing this back in 2014 on this thread.  I strongly suggest one goes back to see all of the references and indications that the ECS was much higher than the AR4 (at the time).  In our discussion we suggested that the ECS was most likely around 5C.  This is being borne out by the current CMIP6 models.  We also looked at the likely consequences of this underestimate (conservatism of scientists) throughout.  See:  https://forum.arctic-sea-ice.net/index.php/topic,1053.msg39360.html#msg39360

Tons of good references here by ASLR who has relegated himself to the Antarctica thread after not being allowed to post about U.S. politics for a bit.

Sure hope he comes back to visit on this thread.
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crandles

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Re: Has climate sensitivity been under-estimated?
« Reply #19 on: July 31, 2019, 11:47:08 PM »

KK

you really need to learn how to google before you continue to display your ignorance on this board.  Asking stupid questions like that caused us to open a whole new thread for the google challenged like yourself. 

Please go here and don't come back until you get some understanding. 

AFAICS, KK has shown good understanding of how that calculation works and yes it does ignore any forcings other than CO2.

Bugalugs

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Re: Has climate sensitivity been under-estimated?
« Reply #20 on: August 01, 2019, 01:06:01 AM »
Quote
climate sensitivity according to paleodata
glacial maximum: CO2 = 180 ppm
interglacial:    CO2 = 280 ppm
DeltaT = 4C
CO2 ppm fraction = (280/180) = 14/9
For a doubling of CO2: (2/(14/9))*4C = 9/7 * 4C = 36/7 = ~5.14C
I think I read this in Peter Wadhams's book.
Time for another joint.

I assume we can add some of mankind's special contributions to current sensitivity, methane feedback would have always been there but we now have a global livestock industry. Add also  the manmade gases, and ozone depletion.

Minus soot dimming.

The sun is also hotter now. Perhaps that is already factored in.

Just my layman thoughts, many thanks again for your considered answers.

Someone mentioned Southern Hemisphere kelp ... I can confirm the kelp has been disappearing around Tasmania for a few years now.

nanning

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Re: Has climate sensitivity been under-estimated?
« Reply #21 on: August 01, 2019, 03:45:39 AM »
@Bugalugs
What you call "soot" is called "aerosol"
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Archimid

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Re: Has climate sensitivity been under-estimated?
« Reply #22 on: August 01, 2019, 03:53:17 AM »
I think the climate state sensitivity to global warming and human sensitivity to climate state change have been underestimated.
I am an energy reservoir seemingly intent on lowering entropy for self preservation.

TerryM

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Re: Has climate sensitivity been under-estimated?
« Reply #23 on: August 01, 2019, 09:24:46 AM »
I think the climate state sensitivity to global warming and human sensitivity to climate state change have been underestimated.
I don't think you're wrong, but I certainly hope that you are.
Terry

Pmt111500

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Re: Has climate sensitivity been under-estimated?
« Reply #24 on: August 01, 2019, 11:08:09 AM »
climate sensitivity according to paleodata
glacial maximum: CO2 = 180 ppm
interglacial:    CO2 = 280 ppm
DeltaT = 4C
CO2 ppm fraction = (280/180) = 14/9
For a doubling of CO2: (2/(14/9))*4C = 9/7 * 4C = 36/7 = ~5.14C
I think I read this in Peter Wadhams's book.
Time for another joint.

That assumes that the CO2 rise is the sole cause of the temperature rise.  Which begs the question of why the CO2 started rising.
No, it just assumes CO2 is the most important of the greenhouse gases which it is at least in the long term. This does not prevent spikes of temperature generated by methane.
Cooling the outside by heat pump.

verytallguy

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Re: Has climate sensitivity been under-estimated?
« Reply #25 on: August 01, 2019, 12:08:47 PM »
climate sensitivity according to paleodata
glacial maximum: CO2 = 180 ppm
interglacial:    CO2 = 280 ppm
DeltaT = 4C
CO2 ppm fraction = (280/180) = 14/9
For a doubling of CO2: (2/(14/9))*4C = 9/7 * 4C = 36/7 = ~5.14C
I think I read this in Peter Wadhams's book.
Time for another joint.

That assumes that the CO2 rise is the sole cause of the temperature rise.  Which begs the question of why the CO2 started rising.
No, it just assumes CO2 is the most important of the greenhouse gases which it is at least in the long term. This does not prevent spikes of temperature generated by methane.

The standard way of calculating sensitivity, the "Equilibrium Climate Sensitivity" or "Charney Sensitivity" specifically *excludes* albedo effects of ice sheet changes.  In order to generate a comparable number from interglacials, you need to include for the changing albedo.

If you include the effects of ice sheet and other slow changes, then you're looking at "Earth System Sensitivity".

Brief explainer:

http://hannahlab.org/understanding-earth-system-sensitivity-ess/

Hansen and Sato concluded ECS ~3, ESS ~4.5

http://www.columbia.edu/~jeh1/mailings/2012/20120508_ClimateSensitivity.pdf

 

nanning

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Re: Has climate sensitivity been under-estimated?
« Reply #26 on: August 01, 2019, 05:15:36 PM »
<snippage>
Welcome to the forum verytallguy and thank you for the information and links.
Can you explain please what is wrong with my paleo assumption concerning the strong interdependence/correlation of CO2/temperature in all paleorecords?

edit: I havent't read any of the links yet, sorry if the information is there. Can you give it in lay(wo)mans terms please?
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crandles

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Re: Has climate sensitivity been under-estimated?
« Reply #27 on: August 01, 2019, 05:32:38 PM »
<snippage>
Welcome to the forum verytallguy and thank you for the information and links.
Can you explain please what is wrong with my paleo assumption concerning the strong interdependence/correlation of CO2/temperature in all paleorecords?

edit: I havent't read any of the links yet, sorry if the information is there. Can you give it in lay(wo)mans terms please?

You are taking 4K as the temperature change that occurred. This is the change from all forcings including CO2 other GHGs, aerosols, albedo from ice sheets.

Then the calculation you produced assumes all of that change come from just CO2 change.

>"my paleo assumption concerning the strong interdependence/correlation of CO2/temperature in all paleorecords"

CO2 is a strong driver of temperature changes and gives quite reasonable correlations between CO2 and temperature. However, it isn't perfect correlation and over long periods of time other effects can build up over time. That build up over time is likely to be particularly true with albedo affected by ice sheets.

I think this shows that you do need to take other effects into account;
http://julesandjames.blogspot.com/2006/03/climate-sensitivity-is-3c.html

Quote
We can also look to the paleoclimate record for evidence from our planet's past climate. During the last ice age, the total radiative forcing was roughly 8Wm-2 lower than today (mostly due to lower CO2 and large ice sheets, with dust and vegetation changes also contributing). 8Wm-2 is roughly twice the forcing of doubled CO2 (although in the opposite direction), so with the global temperature at that time being about 6C cooler than at present, a climate sensitivity of about 3C looks pretty good again. However, again there are significant uncertainties in all of these values I've quoted, and it's also not clear that one value of climate sensitivity will necessarily apply both to doubled CO2 and to this rather different forcing. In fact model results (such as our own) show a fair amount of uncertainty in the response to these different scenarios.

Your 4K may well be a better estimate than the 6C quoted here. (I think there have been some revisions making LGM warmer.)

nanning

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Re: Has climate sensitivity been under-estimated?
« Reply #28 on: August 01, 2019, 06:02:47 PM »
<snippage>
Thanks crandles, I understand that our current situation is quite different because of it being anthropogenic.
The question of climate sensitivity with regard to a doubling of CO2 will therefore (more other GHG and effects from the extreme rate of change) likely be more than the ~5.14C from my calculation using paleo data.
Do you agree with this reasoning?
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crandles

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Re: Has climate sensitivity been under-estimated?
« Reply #29 on: August 01, 2019, 07:35:04 PM »
<snippage>
Thanks crandles, I understand that our current situation is quite different because of it being anthropogenic.
The question of climate sensitivity with regard to a doubling of CO2 will therefore (more other GHG and effects from the extreme rate of change) likely be more than the ~5.14C from my calculation using paleo data.
Do you agree with this reasoning?

No, you are missing the significance of albedo from ice sheets.

Much of the cooling will be due to albedo increasing reflecting sunlight. If (guessing) 2k of the 4k cooling was due to this and other GHGs, aerosols etc, that would leave 2k cooling due to CO2. Then you could plug that 2K into your calculation. That gives climate sensitivity of 2.6C.

I am very uncertain about that 2K guess, experts would be able to put together a better estimate. Even with that done, this is still only a single method and our best estimate of climate sensitivity will take account of what other methods also find.

https://www.researchgate.net/publication/237132619_Using_multiple_observationally-based_constraints_to_estimate_climate_sensitivity

Suggests from LGM the likelihood function for climate sensitivity

Quote
This near-symmetric shape is well described by the Gaussian distribution with mean 2.7◦C and standard deviation 1.7◦C (see Figure).

(Yes I fixed my guess to get close to this.)

jai mitchell

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Re: Has climate sensitivity been under-estimated?
« Reply #30 on: August 01, 2019, 10:35:32 PM »
Quote
Incredibly, at least eight of the latest models produced by leading research centres in the United States, the United Kingdom, Canada and France are showing climate sensitivity of 5°C or warmer.

The terrible truth about climate change

https://www.themonthly.com.au/issue/2019/august/1566136800/jo-lle-gergis/terrible-truth-climate-change
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crandles

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Re: Has climate sensitivity been under-estimated?
« Reply #31 on: August 01, 2019, 11:56:13 PM »
Interesting timeline of published ecs estimates at
https://www.carbonbrief.org/guest-post-why-results-from-the-next-generation-of-climate-models-matter

Perhaps worth noting that what the models show isn't necessarily what the final best estimate range is.

Quote
Early results suggest ECS values from some of the new CMIP6 climate models are higher than previous estimates, with early numbers being reported between 2.8C (pdf) and 5.8C. This compares with the previous coupled model intercomparison project (CMIP5), which reported values between 2.1C to 4.7C. The IPCC’s fifth assessment report (AR5) assessed ECS to be “likely” in the range 1.5C to 4.5C and “very unlikely” greater than 6C.

2.8-5.8 is certainly up from 2.1 to 4.7. More work needed before we know how much that pushes up the 1.5-4.5C likely range.

jai mitchell

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Re: Has climate sensitivity been under-estimated?
« Reply #32 on: August 08, 2019, 05:55:32 PM »
Interesting timeline of published ecs estimates at
https://www.carbonbrief.org/guest-post-why-results-from-the-next-generation-of-climate-models-matter

Perhaps worth noting that what the models show isn't necessarily what the final best estimate range is.

Quote
Early results suggest ECS values from some of the new CMIP6 climate models are higher than previous estimates, with early numbers being reported between 2.8C (pdf) and 5.8C. This compares with the previous coupled model intercomparison project (CMIP5), which reported values between 2.1C to 4.7C. The IPCC’s fifth assessment report (AR5) assessed ECS to be “likely” in the range 1.5C to 4.5C and “very unlikely” greater than 6C.

2.8-5.8 is certainly up from 2.1 to 4.7. More work needed before we know how much that pushes up the 1.5-4.5C likely range.


Perhaps it is worth noting that the range of ECS provided by the IPCC ARs that includes estimations from historic data (due to incomplete understanding of aerosol forcing parameters) and the rejection of known but not well understood future tipping points (like sea ice) fundamentally bias low their final estimation and that their final range estimation is not 'best.'
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Simon

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Re: Has climate sensitivity been under-estimated?
« Reply #33 on: August 08, 2019, 08:08:36 PM »
Water vapour has an amplifying feedback of 2.7 based upon its temperature dependent radiative forcing value of 2.2W/m2. RF at 2xco2 preindustrial value is 3.7W/m2. Add the effect of the other well mixed greenhouse gases eg methane, n2o, SF6 and an approximate total could be as high as 5.5W/m2. Times this by the H2O amplifier to get about 15W/m2. This this RF value by the well known 0.31 to get temperature rise and we have an increase in temperature of about 4.6K. However, there are a number of feedbacks which could alter this value, albedo, change in land use, aerosols, clouds so nobody really knows what will happen.

DrTskoul

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Re: Has climate sensitivity been under-estimated?
« Reply #34 on: August 09, 2019, 12:36:41 AM »
H2O is at equilibrium ... only the excess water is added to the forcing calcs

Tom_Mazanec

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Re: Has climate sensitivity been under-estimated?
« Reply #35 on: September 10, 2019, 04:04:06 AM »
Here is an interesting calculation if you think climate sensitivity is underestimated:
http://www.trillionthtonne.org/
For How much warming should we expect per tonne of carbon released into the atmosphere? click 3 C per trillion tons, pessimistic
For At what level do you want global temperatures to peak? click on 2 C moderate warming
Then we will exceed the carbon budget on Saturday October 5.
LESS THAN A MONTH FROM NOW
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vox_mundi

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Re: Has climate sensitivity been under-estimated?
« Reply #36 on: September 17, 2019, 12:25:21 PM »
Earth to Warm More Quickly, New Climate Models Show
https://phys.org/news/2019-09-earth-quickly-climate.html

By 2100, average temperatures could rise 6.5 to 7.0 degrees Celsius above pre-industrial levels if carbon emissions continue unabated, separate models from two leading research centres in France showed.

... "With our two models, we see that the scenario known as SSP1 2.6—which normally allows us to stay under 2C—doesn't quite get us there," Olivier Boucher, head of the Institute Pierre Simon Laplace Climate Modelling Centre in Paris, told AFP.

A new generation of 30-odd climate models known collectively as CMIP6—including the two unveiled Tuesday—will underpin the IPCC's next major report in 2021.

A core finding of the new models is that increased levels of CO2 in the atmosphere will warm Earth's surface more easily than earlier calculations had suggested.

If confirmed, this higher "equilibrium climate sensitivity", or ECS, means humanity's carbon budget—our total emissions allowance—is likely to shrink.

Quote
... "Higher warming would allow less time to adapt and mean a greater likelihood of passing climate 'tipping points' such as thawing of permafrost, which would further accelerate warming."

The French models are among the first to be released, but others developed independently have come to the same unsettling conclusion, Boucher confirmed.

"The most respected ones—from the United States, and Britain's Met Office—also show a higher ECS" than the previous generation of models, he said.

-----------------------

2050 Is Too Late – We Must Drastically Cut Emissions Much Sooner
https://phys.org/news/2019-09-late-drastically-emissions-sooner.amp



Four UK emissions pathways. (a) is based on our current rate of reduction, and (b) shows that linearly reducing emissions to net zero by 2050 means we’ll exhaust our carbon budget in four years. (c) shows that 2025 is the latest date we could linearly reduce our emissions to net zero, and (d) shows that for a 2050 target to stay within our budget, we’d need a 24% annual reduction in emissions.

The UK footprint has been falling slowly (at around 1.5% a year) since 2010. But if it continued to fall this slowly, the carbon budget would be exhausted by 2023, in just four years' time (Scenario a).

... What is notable about the 'Scenario c' pathway is that, within little more than a decade, carbon emissions must already have fallen to a very low level. With a 24% annual rate of reduction, UK emissions in 2030 would only be 22m tonnes—less than 5% of the current level of emissions. Only a small programme of negative emissions technologies would be needed to achieve net zero at this point.

Clearly the challenge is still colossal. A 24% reduction in emissions amounts to a cut of 140 million tonnes in the very first year alone. The UK has never achieved anything close to this since its carbon footprint was first measured in 1990. In 2009, when the economy was in recession, the carbon footprint fell by 80m tonnes, while its best post-crisis reduction saw a fall of only 38m tonnes in 2016.
« Last Edit: September 17, 2019, 12:30:59 PM by vox_mundi »
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vox_mundi

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Re: Has climate sensitivity been under-estimated?
« Reply #37 on: September 18, 2019, 10:19:53 PM »
Uh-Oh ...

Study of Ancient Climate Suggests Future Warming Could Accelerate
https://phys.org/news/2019-09-ancient-climate-future.html
 
Researchers at the University of Michigan and the University of Arizona used a state-of-the-art climate model to successfully simulate—for the first time—the extreme warming of the Early Eocene Period, which is considered an analog for Earth's future climate.

They found that the rate of warming increased dramatically as carbon dioxide levels rose, a finding with far-reaching implications for Earth's future climate, the researchers report in a paper scheduled for publication Sept. 18 in the journal Science Advances.

Another way of stating this result is that the climate of the Early Eocene became increasingly sensitive to additional carbon dioxide as the planet warmed.

Quote
... "It is a scary finding because it indicates that the temperature response to an increase in carbon dioxide in the future might be larger than the response to the same increase in CO2 now. This is not good news for us."

The researchers determined that the large increase in climate sensitivity they observed—which had not been seen in previous attempts to simulate the Early Eocene using similar amounts of carbon dioxide—is likely due to an improved representation of cloud processes in the climate model they used, the Community Earth System Model version 1.2, or CESM1.2.

The same cloud processes responsible for increased climate sensitivity in the Eocene simulations are active today, according to the researchers.

... "For the first time, a climate model matches the geological evidence out of the box—that is, without deliberate tweaks made to the model. It's a breakthrough for our understanding of past warm climates," Tierney said.

... The current consensus among climate scientists is that the equilibrium climate sensitivity (ECS) is likely to be between 1.5 C and 4.5 C (2.7 F-8.1 F).

The equilibrium climate sensitivity in CESM1.2 is near the upper end of that consensus range at 4.2 C (7.7 F). The U-M-led study's Early Eocene simulations exhibited increasing equilibrium climate sensitivity with warming, suggesting an Eocene sensitivity of more than 6.6 C (11.9 F), much greater than the present-day value.

Open Access: J.Zhu, C.Poulsen, et.al. "Simulation of Eocene extreme warmth and high climate sensitivity through cloud feedbacks" Science Advances (2019).
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

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jai mitchell

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Re: Has climate sensitivity been under-estimated?
« Reply #38 on: September 30, 2019, 08:27:37 PM »
the paleosens work from 2012 also showed this non-linearity of ECS  Though they simply checked over the last 800,000 years. see:  https://forum.arctic-sea-ice.net/index.php?topic=1053.1550

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Klondike Kat

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Re: Has climate sensitivity been under-estimated?
« Reply #39 on: October 01, 2019, 01:43:17 PM »
the paleosens work from 2012 also showed this non-linearity of ECS  Though they simply checked over the last 800,000 years. see:  https://forum.arctic-sea-ice.net/index.php?topic=1053.1550

There is no compelling reason for ECS to be linear.  As in most chemical and physical equilibria, it should decrease with increasing concentrations.

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Re: Has climate sensitivity been under-estimated?
« Reply #40 on: October 01, 2019, 04:15:57 PM »
the paleosens work from 2012 also showed this non-linearity of ECS  Though they simply checked over the last 800,000 years. see:  https://forum.arctic-sea-ice.net/index.php?topic=1053.1550

There is no compelling reason for ECS to be linear.  As in most chemical and physical equilibria, it should decrease with increasing concentrations.

But doesn't ECS take that into account? Being the change of a doubling of CO2, instead of an addition of N trillion tons. Each increment will then be larger.
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Klondike Kat

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Re: Has climate sensitivity been under-estimated?
« Reply #41 on: October 01, 2019, 05:11:40 PM »
the paleosens work from 2012 also showed this non-linearity of ECS  Though they simply checked over the last 800,000 years. see:  https://forum.arctic-sea-ice.net/index.php?topic=1053.1550

There is no compelling reason for ECS to be linear.  As in most chemical and physical equilibria, it should decrease with increasing concentrations.

But doesn't ECS take that into account? Being the change of a doubling of CO2, instead of an addition of N trillion tons. Each increment will then be larger.

ECS is related to the log of CO2 concentration.  The issue is whether that is truly linear.

jai mitchell

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Re: Has climate sensitivity been under-estimated?
« Reply #42 on: October 09, 2019, 02:53:13 AM »
ECS vs Temperature not ECS vs CO2 concentration. 

The Paleosens paper showed that ECS increased with temperature non-linearly.
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