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Author Topic: Has climate sensitivity been under-estimated?  (Read 475 times)

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.


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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.


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 »