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AbruptSLR

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Re: Global Surface Air Temperatures
« Reply #1500 on: August 20, 2017, 08:05:41 PM »
Bloody hell.

Gistemp LOTI has just been updated, and the July value is (marginally, and subject to subsequent review) the highest July value thus far. That I wasn't expecting!

I suspect that the GISTEMP July 2017 is as warm as GISTEMP July 2016, because Antarctic Amplification is beginning to kick-in
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rboyd

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Re: Global Surface Air Temperatures
« Reply #1501 on: August 20, 2017, 08:20:09 PM »
Antarctic Amplification - Makes sense with so much less sea ice in the Antarctic last summer. Would it not also follow that the previous increase in Antarctic sea ice extent acted as a negative feedback, hiding some of the increase in atmospheric forcing? Now the opposite is happening.

Will be interesting to see if the Antarctic sea ice extent stays on the low side this southern summer, and a new trend may be in place. The 2016 loss is being blamed on "freak weather".

This Is Why Antarctic Sea Ice Crashed This Year

http://gizmodo.com/this-is-why-antarctic-sea-ice-crashed-this-year-1796604475

Storms caused massive Antarctic sea ice loss in 2016

"It is tempting to think that the 2016 low ice conditions may mark this turn toward decreasing ice, but that temptation is not warranted," Meier added. "It's too soon to tell whether the low ice conditions are an ephemeral downturn or the start of something more long-term."

https://phys.org/news/2017-06-storms-massive-antarctic-sea-ice.html




« Last Edit: August 20, 2017, 08:28:28 PM by rboyd »

miki

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Re: Global Surface Air Temperatures
« Reply #1502 on: August 20, 2017, 08:35:17 PM »
Antarctic daily temperature anomalies have been on the positive side almost everyday since July 23.

AbruptSLR

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Re: Global Surface Air Temperatures
« Reply #1503 on: August 20, 2017, 11:34:08 PM »
Antarctic Amplification is complex (and made more so by the freshwater hosing into the Southern Ocean (from glacial ice melting); however, the linked reference discusses the state of the at surface temperature at the West Antarctic Divide for the past ~ 40,000 years (see image bottom panel).  These findings indicate that current climate models are challenged to hind cast the observed findings and that models with low climate sensitivities can be eliminated from consideration.  Furthermore, they find that an Antarctic Amplification of 2 to 3 time GMSTA; which is higher than that observed over the satellite era:

Kurt M. Cuffey, Gary D. Clow, Eric J. Steig, Christo Buizert, T. J. Fudge, Michelle Koutnik, Edwin D. Waddington, Richard B. Alley, and Jeffrey P. Severinghaus (2016), "Deglacial temperature history of West Antarctica", PNAS, vol. 113 no. 50, 14249–14254, doi: 10.1073/pnas.1609132113

http://www.pnas.org/content/113/50/14249

Abstract: "The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth’s climate responds to various forcings, including a rise in atmospheric CO2. This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings. For Antarctica, the deglacial warming has previously been constrained only by the water isotopic composition in ice cores, without an absolute thermometric assessment of the isotopes’ sensitivity to temperature. To overcome this limitation, we measured temperatures in a deep borehole and analyzed them together with ice-core data to reconstruct the surface temperature history of West Antarctica. The deglacial warming was 11.3±1.8 ∘  11.3±1.8∘ C, approximately two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature. Although climate models perform well on average in this context, some recent syntheses of deglacial climate history have underestimated Antarctic warming and the models with lowest sensitivity can be discounted."

Extract: "Of greatest immediate interest, however, is our demonstration that the global deglacial temperature change was amplified by a factor of 2–3 in the Antarctic, that Antarctic warming was largely achieved by 15 ka in coherence with records from Southern Hemisphere mountain ranges, and that climate models of the deglaciation perform well on average, but that the ones with lowest sensitivity can be discounted. The early warming of the Southern Hemisphere, which our study helps to quantify, arose from combined effects of reduced northward oceanic heat transport, increased insolation, and increasing atmospheric CO2. Quantitative simulation of this phenomenon could provide an illuminating challenge for model studies."
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Ned W

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Re: Global Surface Air Temperatures
« Reply #1504 on: August 25, 2017, 01:30:53 PM »
In another thread there's been discussion of the possibility of temperatures hitting 2 C (above pre-industrial) by 2035.  Now, 2035 sounds far off, but it's only 18 years away. 

I thought I'd look at that question from an empirical angle:

(1) As I understand it, 2015 temperatures were around 1 C above pre-industrial, so 2 C would mean another +1 C above 2015 over the next 18 years.

(2) That works out to a trend of 0.56 C/decade, which is more than twice as steep as the fastest previous 18-year warming trend in GISTEMP (0.26 C/decade from 1927-1945).

(3) Here's a histogram of temperature trends over all 18-year periods in GISTEMP (blue line).  The orange point shows the trend that would be required to reach 2 C over the next 18 years:



That seems unlikely. 

----------------------------------
Methodological notes:
The x-axis values in the histogram are degrees C per year, not per decade.
The 18-year intervals used to compute the trend histogram are overlapping, and thus not independent. This autocorrelation, as well as the likelihood of non-stationarity, would need to be accounted for if one wanted to calculate a probability value for the hypothetical future trend.  Without doing that, we can at least say that the future trend is less improbable than it would appear visually in this representation. But it's still unlikely.

Archimid

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Re: Global Surface Air Temperatures
« Reply #1505 on: August 25, 2017, 01:51:06 PM »
There is now less global ice and warmer ocean than the last 18 year period. in the next 18 years there will be even less ice, an even warmer ocean and there might not be arctic sea ice in the summer. It seems unlikely only if everything else remains the same as it was before. That seems unlikely.
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Ned W

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Re: Global Surface Air Temperatures
« Reply #1506 on: August 25, 2017, 02:02:59 PM »
Yes, but the most recent 18-year period had less ice, warmer ocean, etc. than did the 18-year period before that, etc. etc.  Those things mean that the world is warmer than it was in previous 18-year periods, but they don't necessarily mean that the rate of warming is faster than it was in previous 18-year periods.

Having said that, though, the distribution of warming trend rates is clearly nonstationary, as I alluded to in the methodological footnote above.  Here's a better visualization of the histogram, where each 18-year trend is color-coded based on its end year:



Note that the shape of the histogram is different from the previous one because the bins are different.

While the fastest two 18-year warming trends were those ending in 1945 and 1944 (blue dots at far right), in general recent 18-year trends have been warming faster than older 18-year trends.

My quasi-informed guess is that this nonstationarity is still not enough to bring a rate of 0.56 C/decade into the range of reasonable likelihood for the next 18-year interval.  It's not impossible, but it does seem unlikely

Ned W

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Re: Global Surface Air Temperatures
« Reply #1507 on: August 25, 2017, 03:10:31 PM »
OK, just for fun let's carry this out a bit further.  Here's a simulation of what it would look like to reach +2 C pre-industrial by 2035:



Methodological notes are at the end of this post. 

My guess is that some people will look at that and say "Sure, that's totally plausible, why is Ned even questioning it?" Part of the reason it looks plausible is because we're just coming off of the 2016 El Nino, so temperatures rose very rapidly over the past couple of years.  Extrapolating the recent rise in temperatures naturally looks plausible.  But temperatures shouldn't be expected to continue to rise for two decades at the anomalously fast rate we saw in the transition from a La Nina to an El Nino. 

This can be seen more clearly in the histogram of trends:



This chart shows the same histogram as the previous post, but with the additional trends from the simulated data added as black circles.  The first couple are near the right edge of the "real" histogram, because 16 or 17 of their 18 years are based on "real" data.  As each 18-year trend loses a year of real data and gains a year of simulated data, the trend values zoom way out into historically unprecedented territory.

Personally, I find that unlikely.  If one asked me what I expect over the next 18 years, I would say that I expect continued warming with noise superimposed, at a rate that is mostly near the upper end of the observed historical rates of warming, with perhaps some modest acceleration.  From that point of view, the simulated histogram above looks very implausible.

But if one believes (as some here obviously do) that the climate will soon (or has already?) experienced some drastic nonlinear change, into a state quite different from the recent past, one might find this easily believable. 

In other words, YMMV.

------------------------------
Methodological notes:
* To simulate future temperatures, I first set the 2035 value to 1.87 (equivalent to 2 C above pre-industrial for GISTEMP's baseline; see link from previous post for details).  I then interpolated between the 2017 and 2035 temperatures to fill in the intermediate years, and then perturbed each one with "noise" from the historical data.
* The "noise" was derived by detrending the 1970-1990 GISTEMP data using a LOESS model; the residuals from that detrending were added to the simulated data for 2018-2034.
* For 2017, I estimated the annual temperature by fitting a linear model that relates the Jan-July means to the annual mean; I then applied that model to the actual 2017 Jan-July mean to produce an expected value for the annual mean.

gerontocrat

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Re: Global Surface Air Temperatures
« Reply #1508 on: August 25, 2017, 03:33:00 PM »
Is it not the case that over 90 percent of excess energy trapped by higher CO2 concentrations goes into the oceans. CO2 concentrations will continue to increase for a good many years even in the best-case scenario. So even more excess energy will be trapped in the oceans.

Is there a thread where future ocean temperatures are discussed and modelled?
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AbruptSLR

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Re: Global Surface Air Temperatures
« Reply #1509 on: August 25, 2017, 05:20:14 PM »
There is now less global ice and warmer ocean than the last 18 year period. in the next 18 years there will be even less ice, an even warmer ocean and there might not be arctic sea ice in the summer. It seems unlikely only if everything else remains the same as it was before. That seems unlikely.

The linked SkS image shows high GMSTA values if ECS = 4.5C, and if the 'faux pause' was actually associated with temporary masking factors (like: aerosols (including anthropogenic, natural VOC's and volcanic), sequestering of heat in the ocean due to La Ninas, melting of both the key areas of permafrost and ice, and a temporary bloom of vegetation that then decays).  Thus GMSTA may rebound rapidly in the coming few years as these masking factors are eliminated or reversed.
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Archimid

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Re: Global Surface Air Temperatures
« Reply #1510 on: August 25, 2017, 06:02:39 PM »
I agree that if everything else remains the same for the next 18 years,  your analyses is likely correct. It is unlikely to hit 2C in 18 years.  I just don't think that everything will be the same. I doubt that in 18 years we will have summer sea ice in the Arctic. I think that after a BOE you can pretty much throw all the old models and data  away because it will be a different world.

I think  the warming we  experienced so far didnt change the climate much because "cold reserves" like the oceans, glaciers and ASI  buffered much of the extra heat.

I see oceans and glaciers as none renewable cold reserves. These reserves accumulated over thousands of years. They are being slowly saturated and depleted. These reserves are not likely to be depleted fast. However, as they are consumed they become less efficient at buffering heat, resulting in slightly faster warming. 

The ASI is different. I consider it a seasonal cold reserve. The Arctic accumulates cold during winter then that cold is used by the Northern hemisphere as a heat buffer during summer. That does not change the heat balance of the Earth  directly but it keeps  year to year temperatures within  a closer range.

  I believe that system is in danger of failure. If it fails, not only will there be abrupt climate change due to changes in seasonality,  changes in  albedo will increase the rate of warming . If that happens then 2C will be hit in no time.

I am an energy reservoir seemingly intent on lowering entropy for self preservation.

rboyd

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Re: Global Surface Air Temperatures
« Reply #1511 on: August 25, 2017, 06:46:13 PM »
On a CO2e basis, we are above RCP8.5. All UN IPCC scenarios use CO2e not just CO2.

If we are talking about the next 20 years, then we should be using the GWP20 number for methane, which puts CO2e even higher. So we already have an extreme level of forcing.

Add to that the probable reduction in aerosols (reduction in coal usage, more SO2 scrubbers, and lower sulphur bunker fuel) and decreasing Arctic sea ice, and the level of forcing jumps even further.

Short of some large-scale negative feedback I would be surprised if the temperature trend did not start to markedly accelerate during the next two decades.

oren

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Re: Global Surface Air Temperatures
« Reply #1512 on: August 26, 2017, 09:48:21 AM »
OK, just for fun let's carry this out a bit further.  Here's a simulation of what it would look like to reach +2 C pre-industrial by 2035:


Ned, your own chart shows 0 at about the 1940-1970 average. I know pre-industrial is not well defined but if you move your baseline by 0.25oc to the 1880-1930 average it will be much easier to imagine 2oc above baseline by 2035.

Csnavywx

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Re: Global Surface Air Temperatures
« Reply #1513 on: August 26, 2017, 04:33:14 PM »
Approaching this from a radiative forcing perspective:

Current eff. CO2 is about 430. Rate of CO2e increase is about 3.5ppm/yr. Assuming constant emissions and no net change in aerosols through 2035 yields 493ppm eff. CO2e.

Plugging this into the RF equation yields a radiative forcing of 0.73W/m2.

Using "vanilla" IPCC ECS of 3C yields a lambda of 0.8. Plugging this into the climate sensitivity equation yields a delta T of +0.58C or a TCR (70%) response of about +0.42C, and probably a little less over a period of just 18 years. So1.6-1.7C is the ballpark figure.

Using a Dressler back of the envelope "cloud feedback" sensitivity of 3.5C yields a lambda of about 0.93. That gives 0.67C or a TCR (70%) of 0.48C.

Using a Sherwood-type sensitivity (with subtropical cloud drying) of 4.0C yields a lambda of 1.06 and a delta T of 0.77C with TCR response of 0.54C. That would get us to about 1.7-1.8C in 2035.

So, to get 2C in 2035 requires something extra. A small decline in aerosol forcing (say 0.10W), a slow increase in emissions (an extra 0.10W), an ECS of 4C would get us there. A blue ocean event (which I expect in the early 2030s) and follow-on carbon cycle permafrost emission releases would help too.

Things that could temporarily retard the trend: a flip back to -PDO/-ENSO regime and the start of ice-melt feedback. This is a bit complicated though, as a -PDO/-ENSO in 15-20 years is likely to lead to a quick deterioration of remaining arctic sea ice as it favors summer ridging over the Arctic and Greenland.

At some point, GMST rise is going to start to become an increasingly irrelevant number as atmospheric and oceanic circulation changes are more seriously disrupted. The Nakamura paper published last year on a Blue Ocean Event is a good example of the disruptive potential, especially in fall and winter.
« Last Edit: August 26, 2017, 04:38:32 PM by Csnavywx »

gerontocrat

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Re: Global Surface Air Temperatures
« Reply #1514 on: August 26, 2017, 04:45:24 PM »
What about the capacity of the biosphere to absorb atmospheric CO2 ?
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jai mitchell

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Re: Global Surface Air Temperatures
« Reply #1515 on: August 26, 2017, 05:16:15 PM »
what are the implications of the recent 10-year trend of GMST toward future temperatures?

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AbruptSLR

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Re: Global Surface Air Temperatures
« Reply #1516 on: August 26, 2017, 05:33:27 PM »
Current eff. CO2 is about 430. Rate of CO2e increase is about 3.5ppm/yr. Assuming constant emissions and no net change in aerosols through 2035 yields 493ppm eff. CO2e.
Csnavywx,

Your assumptions need updating as per the following calculations CO2e at the end of 2016 was already at least 521 ppm; thus you need to redo your calculations using current values (also I note that your value of increase in CO2e per year of 3.5ppm also assumes NOAA's out of date value of GWP100 for methane of 25):

The linked NOAA website entitled: "THE NOAA ANNUAL GREENHOUSE GAS INDEX (AGGI)" was updated in Spring of 2017 with GHG data through the end of 2016 (see the attached images).  I note that if one assumes that the GWP100 for methane is 35 instead of 25 (per AR5), then NOAA's calculated value for the CO2-eq for 2016 would be 521ppm instead of 489ppm; which is a big difference, and one that NOAA should publically acknowledge.

https://www.esrl.noaa.gov/gmd/aggi/aggi.html

 Global Radiative Forcing, CO2-equivalent mixing ratio, and the AGGI
                         Global Radiative Forcing (W m-2)           CO2-eq
                                                                                     (ppm)        AGGI
Year     CO2     CH4    N2O   CFC12 CFC11 15-minor  Total Total   1990 = 1   %change

2013   1.882  0.496   0.184   0.167   0.059   0.114  2.901   478      1.340        2.0
2014   1.908  0.499   0.187   0.166   0.058   0.116  2.935   481      1.356        1.6
2015   1.939  0.504   0.190   0.165   0.058   0.118  2.974   485      1.374        1.8
2016   1.985  0.507   0.193   0.164   0.057   0.121  3.027   489      1.399        2.5

CH4   ΔF = β(M½ - Mo½) - [f(M,No) - f(Mo,No)]   β = 0.036

Furthermore, I note that industry is having a hard time finding replacement for the current generation of HFC's indicating that the atmospheric concentrations for these GHGs are likely to increase in the future.

Edit: The third image of Table 8.7 of AR5 has this footnote for methane: "These values do not include CO2 from methane oxidation. Values for fossil methane are higher by 1 and 2 for the 20 and 100 year metrics, respectively (Table 8.A.1)"  Thus, when you consider methane from fossil fuel and when you consider the GWP from the CO2 from methane oxidation, the resulting GWP values are higher than in Table 8.7 (i.e. the GWP100 for fossil fuel methane is 36 so when averaged with natural methane I use 35.

Also AR5 asserts a -50 and +75% uncertainty in their GWP values for CH4 (on the 100 year timeline); which means that this confidence range has a fat right-tail.
« Last Edit: August 26, 2017, 05:41:27 PM by AbruptSLR »
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AbruptSLR

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Re: Global Surface Air Temperatures
« Reply #1517 on: August 26, 2017, 05:57:12 PM »
Csnavywx,

Your assumptions need updating as per the following calculations CO2e at the end of 2016 was already at least 521 ppm; thus you need to redo your calculations using current values (also I note that your value of increase in CO2e per year of 3.5ppm also assumes NOAA's out of date value of GWP100 for methane of 25):

Csnavywx,

If you do choose to update your calculations, please note that per Etminan et. al. (2016), AR5 erred on the side of least drama with regards to the GHG radiative forcing equations, particularly methane but also for NO2 and CO2:

M. Etminan, G. Myhre, E. J. Highwood & K. P. Shine (27 December 2016), "Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing", Geophysical Research Letters, DOI: 10.1002/2016GL071930

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071930/full

Abstract: "New calculations of the radiative forcing (RF) are presented for the three main well-mixed greenhouse gases, methane, nitrous oxide, and carbon dioxide. Methane's RF is particularly impacted because of the inclusion of the shortwave forcing; the 1750–2011 RF is about 25% higher (increasing from 0.48 W m−2 to 0.61 W m−2) compared to the value in the Intergovernmental Panel on Climate Change (IPCC) 2013 assessment; the 100 year global warming potential is 14% higher than the IPCC value. We present new simplified expressions to calculate RF. Unlike previous expressions used by IPCC, the new ones include the overlap between CO2 and N2O; for N2O forcing, the CO2 overlap can be as important as the CH4 overlap. The 1750–2011 CO2 RF is within 1% of IPCC's value but is about 10% higher when CO2 amounts reach 2000 ppm, a value projected to be possible under the extended RCP8.5 scenario."
« Last Edit: August 26, 2017, 06:38:10 PM by AbruptSLR »
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oren

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Re: Global Surface Air Temperatures
« Reply #1518 on: August 26, 2017, 06:29:54 PM »
The linked NOAA website entitled: "THE NOAA ANNUAL GREENHOUSE GAS INDEX (AGGI)" was updated in Spring of 2017 with GHG data through the end of 2016 (see the attached images).  I note that if one assumes that the GWP100 for methane is 35 instead of 25 (per AR5), then NOAA's calculated value for the CO2-eq for 2016 would be 521ppm instead of 489ppm; which is a big difference, and one that NOAA should publically acknowledge.

https://www.esrl.noaa.gov/gmd/aggi/aggi.html

CH4   ΔF = β(M½ - Mo½) - [f(M,No) - f(Mo,No)]   β = 0.036

Edit: The third image of Table 8.7 of AR5 has this footnote for methane: "These values do not include CO2 from methane oxidation. Values for fossil methane are higher by 1 and 2 for the 20 and 100 year metrics, respectively (Table 8.A.1)"  Thus, when you consider methane from fossil fuel and when you consider the GWP from the CO2 from methane oxidation, the resulting GWP values are higher than in Table 8.7 (i.e. the GWP100 for fossil fuel methane is 36 so when averaged with natural methane I use 35.

Also AR5 asserts a -50 and +75% uncertainty in their GWP values for CH4 (on the 100 year timeline); which means that this confidence range has a fat right-tail.
ASLR, maybe you could shed some light on this stupid question of mine: seeing as methane concentrations are on an ever-upward trend, despite the fact that methane is constantly removed from the atmosphere - why not use the actual forcing of current methane in the atmosphere, "instantaneous GWP", which I would guess is much higher than even the GWP20 value? I mean, if we totally stopped emitting now and all natural sources would oblige to do the same, then all jolly good, use GPW20 or whatever, but as that is not happening the actual radiative forcing of methane is much higher than these numbers suggest.

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Re: Global Surface Air Temperatures
« Reply #1519 on: August 26, 2017, 06:40:59 PM »
Csnavywx,

Your assumptions need updating as per the following calculations CO2e at the end of 2016 was already at least 521 ppm; thus you need to redo your calculations using current values (also I note that your value of increase in CO2e per year of 3.5ppm also assumes NOAA's out of date value of GWP100 for methane of 25):

Csnavywx,

If you do choose to update your calculations, please note that per Etminan et. al. (2016), AR5 erred on the side of least drama with regards to the GHG radiative forcing equations, particularly methane but also for NO2 and CO2:

Csnavywx,

If you decide to update your values for CO₂e and the current radiative forcing equations [per Etminan et. al. (2016)], you might as well update what you use as a canonical value for ECS.  To this end, I provide the first attached image from the linked Real Climate article about climate sensitivity which per Proistosescu and Huybers (2017), indicates that ECS is higher than the canonical AR5 value, due to the accumulation of heat in the Pacific, and Southern, Oceans since the beginning of the Industrial Revolution:

Title: "Sensible Questions on Climate Sensitivity"

http://www.realclimate.org/index.php/archives/2017/08/sensible-questions-on-climate-sensitivity/

Please note that in the first attached image [where PH 17 means Proistosescu and Huybers (2017), and ICS means 'instantaneous climate sensitivity] that the bar for observational ICS values entitled "Marvel et al 2016; Otto et. al. accounting for efficacy" has a median value for ICS of about 3.25C (and an upper value close to 8C); which is close to the median value on the bar entitled "PH17 (w/Lewis Comments)" for the modeled value of ICS.  However, the median value of the modeled ECS value for the bar entitled "PH 17" is close to 3.7C (with an upper value close to 6C).

See also

Cristian Proistosescu and Peter J. Huybers (05 Jul 2017), "Slow climate mode reconciles historical and model-based estimates of climate sensitivity", Science Advances, Vol. 3, no. 7, e1602821, DOI: 10.1126/sciadv.1602821

http://advances.sciencemag.org/content/3/7/e1602821

Extract: "The latest Intergovernmental Panel on Climate Change Assessment Report widened the equilibrium climate sensitivity (ECS) range from 2° to 4.5°C to an updated range of 1.5° to 4.5°C in order to account for the lack of consensus between estimates based on models and historical observations. The historical ECS estimates range from 1.5° to 3°C and are derived assuming a linear radiative response to warming. A Bayesian methodology applied to 24 models, however, documents curvature in the radiative response to warming from an evolving contribution of interannual to centennial modes of radiative response. Centennial modes display stronger amplifying feedbacks and ultimately contribute 28 to 68% (90% credible interval) of equilibrium warming, yet they comprise only 1 to 7% of current warming. Accounting for these unresolved centennial contributions brings historical records into agreement with model-derived ECS estimates."

Note that in the second attached image from PH 17, Panel A of the attached image includes the activated slow feedback mode while the Panel B show data not corrected for Lewis's comments for ICS.
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Re: Global Surface Air Temperatures
« Reply #1520 on: August 26, 2017, 08:16:54 PM »
Using a Sherwood-type sensitivity (with subtropical cloud drying) of 4.0C yields a lambda of 1.06 and a delta T of 0.77C with TCR response of 0.54C. That would get us to about 1.7-1.8C in 2035.

Csnavywx,

While I will not pretend that I know what ECS will be for the rest of this century, but if per PH 17, CMIP5 gives a median value near 3.7C; and as many positive feedbacks have been identified since CMIP5 was run; you might want to consider evaluating an ECS of 4.5C as that is near the median value (the mid-range is 4.85C) of the linked reference that cites findings from an improved version of CESM that increases ECS from 4.1C to 5.6C (I note also that only the most advances ESM projections seem to be able to come close to paleo values of polar amplification):

William R. Frey & Jennifer E. Kay (2017), "The influence of extratropical cloud phase and amount feedbacks on climate sensitivity", Climate Dynamics; pp 1–20, doi:10.1007/s00382-017-3796-5

https://link.springer.com/article/10.1007%2Fs00382-017-3796-5?utm_content=bufferfdbc0&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Global coupled climate models have large long-standing cloud and radiation biases, calling into question their ability to simulate climate and climate change. This study assesses the impact of reducing shortwave radiation biases on climate sensitivity within the Community Earth System Model (CESM). The model is modified by increasing supercooled cloud liquid to better match absorbed shortwave radiation observations over the Southern Ocean while tuning to reduce a compensating tropical shortwave bias. With a thermodynamic mixed-layer ocean, equilibrium warming in response to doubled CO2 increases from 4.1 K in the control to 5.6 K in the modified model. This 1.5 K increase in equilibrium climate sensitivity is caused by changes in two extratropical shortwave cloud feedbacks. First, reduced conversion of cloud ice to liquid at high southern latitudes decreases the magnitude of a negative cloud phase feedback. Second, warming is amplified in the mid-latitudes by a larger positive shortwave cloud feedback. The positive cloud feedback, usually associated with the subtropics, arises when sea surface warming increases the moisture gradient between the boundary layer and free troposphere. The increased moisture gradient enhances the effectiveness of mixing to dry the boundary layer, which decreases cloud amount and optical depth. When a full-depth ocean with dynamics and thermodynamics is included, ocean heat uptake preferentially cools the mid-latitude Southern Ocean, partially inhibiting the positive cloud feedback and slowing warming. Overall, the results highlight strong connections between Southern Ocean mixed-phase cloud partitioning, cloud feedbacks, and ocean heat uptake in a climate forced by greenhouse gas changes."

Best,
ASLR
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AbruptSLR

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Re: Global Surface Air Temperatures
« Reply #1521 on: August 26, 2017, 08:20:07 PM »
ASLR, maybe you could shed some light on this stupid question of mine: seeing as methane concentrations are on an ever-upward trend, despite the fact that methane is constantly removed from the atmosphere - why not use the actual forcing of current methane in the atmosphere, "instantaneous GWP", which I would guess is much higher than even the GWP20 value? I mean, if we totally stopped emitting now and all natural sources would oblige to do the same, then all jolly good, use GPW20 or whatever, but as that is not happening the actual radiative forcing of methane is much higher than these numbers suggest.

oren,

I am an engineer and not a scientist, so I am not qualified to determine CO2e values based on GWP20 values; but I do not dispute your logic.

Best,
ASLR
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Re: Global Surface Air Temperatures
« Reply #1522 on: August 26, 2017, 08:28:37 PM »
OK, just for fun let's carry this out a bit further.  Here's a simulation of what it would look like to reach +2 C pre-industrial by 2035:


Ned, your own chart shows 0 at about the 1940-1970 average. I know pre-industrial is not well defined but if you move your baseline by 0.25oc to the 1880-1930 average it will be much easier to imagine 2oc above baseline by 2035.
The chart is from GISTEMP, so 0 corresponds to GIS's 1951-1980 baseline.  The -0.25 level early in the GISTEMP record is representative of the late LIA, and thus was slightly cooler than what is generally meant by pre-industrial (from the 1700s, before the LIA minimum).  I am using the definition of pre-industrial from here, which works out to about -0.13 on the GISTEMP baseline.

One could lower the baseline to -0.25, and yes, that would make it easier to reach.  But it would also mean that we've already seen most of the 2 C increase by now.  In essence, you're making us cross the threshold sooner but it's a lower and less meaningful threshold. 

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Re: Global Surface Air Temperatures
« Reply #1523 on: August 26, 2017, 08:32:22 PM »
Approaching this from a radiative forcing perspective:

Current eff. CO2 is about 430. Rate of CO2e increase is about 3.5ppm/yr. Assuming constant emissions and no net change in aerosols through 2035 yields 493ppm eff. CO2e.

Plugging this into the RF equation yields a radiative forcing of 0.73W/m2.

Using "vanilla" IPCC ECS of 3C yields a lambda of 0.8. Plugging this into the climate sensitivity equation yields a delta T of +0.58C or a TCR (70%) response of about +0.42C, and probably a little less over a period of just 18 years. So1.6-1.7C is the ballpark figure.

Using a Dressler back of the envelope "cloud feedback" sensitivity of 3.5C yields a lambda of about 0.93. That gives 0.67C or a TCR (70%) of 0.48C.

Using a Sherwood-type sensitivity (with subtropical cloud drying) of 4.0C yields a lambda of 1.06 and a delta T of 0.77C with TCR response of 0.54C. That would get us to about 1.7-1.8C in 2035.
Very nicely done.  Thanks.

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Re: Global Surface Air Temperatures
« Reply #1524 on: August 26, 2017, 08:37:50 PM »
what are the implications of the recent 10-year trend of GMST toward future temperatures?
Sure, one could extrapolate that.  It's an approach that was popular at WUWT a few years ago -- take a decadal trend that happened to start with the 1998 El Nino and extend it into the 2008 La Nina cool phase.  By focusing on carefully chosen short-term temperature trends, a lot of people convinced themselves that "global warming has stopped".

Now the 10-year trend starts with that 2008 La Nina cooling and ends with the 2016 El Nino.  So, yes, you could follow WUWT's approach and make productive use of unrealistic short-term temperature trends.  Not what I would recommend, though.

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Re: Global Surface Air Temperatures
« Reply #1525 on: August 26, 2017, 09:32:48 PM »
That would be true in a vacuum of information, I was able to determine quite early on that the 'pause' was a result of shifts (and increases) of SO2 emissions away from U.S. and Europe and into China.

I also recognize now that shifts toward cleaner fuel and coal burning efficiency as well as renewables and air quality measures will rapidly engage a large portion of warming potential that, so far, has been hidden in the signal.

Not just that of increased prevalence of El Ninos.

http://www.nature.com/nclimate/journal/v6/n10/full/nclimate3058.html
Nature Climate Change 6, 936–940 (2016)

Quote
The prevailing view is that this negative PDO occurred through internal variability7, 8, 9, 10, 11. However, here we show that coupled models from the Fifth Coupled Model Intercomparison Project robustly simulate a negative PDO in response to anthropogenic aerosols implying a potentially important role for external human influences. The recovery from the eruption of Mount Pinatubo in 1991 also contributed to the slowdown in GMST trends. Our results suggest that a slowdown in GMST trends could have been predicted in advance, and that future reduction of anthropogenic aerosol emissions, particularly from China, would promote a positive PDO and increased GMST trends over the coming years.
Haiku of Futures Passed
My "burning embers"
are not tri-color bar graphs
+3C today

Csnavywx

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Re: Global Surface Air Temperatures
« Reply #1526 on: August 26, 2017, 09:43:40 PM »
Using a Sherwood-type sensitivity (with subtropical cloud drying) of 4.0C yields a lambda of 1.06 and a delta T of 0.77C with TCR response of 0.54C. That would get us to about 1.7-1.8C in 2035.

Csnavywx,

While I will not pretend that I know what ECS will be for the rest of this century, but if per PH 17, CMIP5 gives a median value near 3.7C; and as many positive feedbacks have been identified since CMIP5 was run; you might want to consider evaluating an ECS of 4.5C as that is near the median value (the mid-range is 4.85C) of the linked reference that cites findings from an improved version of CESM that increases ECS from 4.1C to 5.6C (I note also that only the most advances ESM projections seem to be able to come close to paleo values of polar amplification):

William R. Frey & Jennifer E. Kay (2017), "The influence of extratropical cloud phase and amount feedbacks on climate sensitivity", Climate Dynamics; pp 1–20, doi:10.1007/s00382-017-3796-5

https://link.springer.com/article/10.1007%2Fs00382-017-3796-5?utm_content=bufferfdbc0&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Global coupled climate models have large long-standing cloud and radiation biases, calling into question their ability to simulate climate and climate change. This study assesses the impact of reducing shortwave radiation biases on climate sensitivity within the Community Earth System Model (CESM). The model is modified by increasing supercooled cloud liquid to better match absorbed shortwave radiation observations over the Southern Ocean while tuning to reduce a compensating tropical shortwave bias. With a thermodynamic mixed-layer ocean, equilibrium warming in response to doubled CO2 increases from 4.1 K in the control to 5.6 K in the modified model. This 1.5 K increase in equilibrium climate sensitivity is caused by changes in two extratropical shortwave cloud feedbacks. First, reduced conversion of cloud ice to liquid at high southern latitudes decreases the magnitude of a negative cloud phase feedback. Second, warming is amplified in the mid-latitudes by a larger positive shortwave cloud feedback. The positive cloud feedback, usually associated with the subtropics, arises when sea surface warming increases the moisture gradient between the boundary layer and free troposphere. The increased moisture gradient enhances the effectiveness of mixing to dry the boundary layer, which decreases cloud amount and optical depth. When a full-depth ocean with dynamics and thermodynamics is included, ocean heat uptake preferentially cools the mid-latitude Southern Ocean, partially inhibiting the positive cloud feedback and slowing warming. Overall, the results highlight strong connections between Southern Ocean mixed-phase cloud partitioning, cloud feedbacks, and ocean heat uptake in a climate forced by greenhouse gas changes."

Best,
ASLR

Hi ASLR,

I was simply giving a back of the envelope calculation based on some of the more recent mainstream ECS values (where most of the uncertainty is in cloud response). It could indeed be faster (or slower). Paleo-evidence from the Arctic is one reason I lean above 3C for ECS, as very high rates of AA aren't likely to be captured fully by current models.

The CO2e value I gave was accounting for median aerosol forcing, so it's really a CO2e-aerosol calculation. The higher GWP of methane wasn't really as much of a factor because of uncertainty in methane increases going forward. We still don't truly understand why the slowdown through 2007 (or the follow-on speed up) occurred. I do expect increased methane emission from permafrost melt, but the onset of more serious emissions is probably going to be tied more closely to sea-ice free summers, which is likely around or after the 2035 timeframe discussed here.

I do think we need to be careful though. You can have high climate sensitivity and still have strong natural variability and/or response to slow the "would-be" trend for years at a time. The Pacific just got done demonstrating that over the last 15 years. The North Atlantic subpolar gyre and Southern Ocean can also act as spoilers (the former is doing just that right now) as could ice melt/increasing freshwater intrusions.

In fact, the authors of PH17/A17 mention this:

Quote
An important core finding of A17 and PH17 is that values of ICS drawn from the historical record are not sufficient to constrain values of ECS. Indeed, within models, ICS and ECS differ as the strength of radiative feedbacks change over time as patterns of surface temperature evolve with warming. PH17 demonstrated that portions of the climate system that respond over centennial timescales (such as the southern oceans) are important amplifiers of climate sensitivity in the models – a slow-mode response leading to values of ECS that are higher than the values of ICS that reflect more transient warming. Increasing sensitivity over time seems to be associated with a low-cloud feedback excited by warming in the Eastern Equatorial Pacific and Southern Ocean. This slow-mode response (and thus ECS) is essentially unconstrained by global energy budget observations because warming in these regions has been small, possibly held back by upwelling water from the ocean interior.

Note the reiteration of the importance of the SST surface warming pattern too. Something that has been brought up before (I believe by Dressler?).

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Re: Global Surface Air Temperatures
« Reply #1527 on: August 26, 2017, 09:58:23 PM »
I was simply giving a back of the envelope calculation based on some of the more recent mainstream ECS values (where most of the uncertainty is in cloud response).

I hope that using mainstream assumptions for both ECS and future methane emissions (including from: fossil fuel, agriculture and natural sources like tropical peat-lands), benefits society; however, as Mother Nature does not care what the mainstream assumes; I am concerned that being too optimistic may soon result in numerous Earth Systems (not just the Arctic, but such systems as: WAIS cliff failures & hydrofracturing; thermokarst lake formation in permafrost regions; tropical rain forest degradation; and positive ENSO feedbacks) to move beyond their tipping points by 2050.
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Csnavywx

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Re: Global Surface Air Temperatures
« Reply #1528 on: August 26, 2017, 10:16:31 PM »
I was simply giving a back of the envelope calculation based on some of the more recent mainstream ECS values (where most of the uncertainty is in cloud response).

I hope that using mainstream assumptions for both ECS and future methane emissions (including from: fossil fuel, agriculture and natural sources like tropical peat-lands), benefits society; however, as Mother Nature does not care what the mainstream assumes; I am concerned that being too optimistic may soon result in numerous Earth Systems (not just the Arctic, but such systems as: WAIS cliff failures & hydrofracturing; thermokarst lake formation in permafrost regions; tropical rain forest degradation; and positive ENSO feedbacks) to move beyond their tipping points by 2050.

You're right, it doesn't. I'm going for what I see is the "most likely answer" to the question of temperature in 2035. There's a solid case for at least 1.6C (as I calculated above). It could very well be higher. You might use it as a lower bound.

I'm in the camp that GMST becomes (gradually) increasingly worth less as a measure of change as we go forward due to aforementioned changes in atmospheric and oceanic circulation as the climate system increasingly tries to balance an increasingly imbalanced system. Unpredictable transient phenomenon become more likely to occur. The unprecedented increase in trade wind strength in the tropical Pacific from 2001-2014 is an example. The sudden loss of Arctic MYI is another.

In particular, I'm interested to see how Northern Hemispheric atmospheric circulation continues to change over time (especially in the fall and winter). I think either that or a collapse/severe weakening of the SPG is the next flash point, the latter of which would have the effect of slowing GMST increases down again (though with repercussions).

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Re: Global Surface Air Temperatures
« Reply #1529 on: August 26, 2017, 10:52:02 PM »
Quote
Northern Hemispheric atmospheric circulation ... either that or a collapse/severe weakening of the SPG is the next flash point, the latter effect of slowing GMST increases (though with repercussions).
Along the lines of these two articles?

An abrupt weakening of the subpolar gyre as trigger of Little Ice Age-type episodes
E Chamarro et al
https://link.springer.com/article/10.1007%2Fs00382-016-3106-7 free full text

We investigate the mechanism of a decadal-scale weakening shift in the strength of the subpolar gyre (SPG) that is found in one among three last millennium simulations with a state-of-the-art Earth system model.

The SPG shift triggers multicentennial anomalies in the North Atlantic climate driven by long-lasting internal feedbacks relating anomalous oceanic and atmospheric circulation, sea ice extent, and upper-ocean salinity in the Labrador Sea.

Yet changes throughout or after the shift are not associated with a persistent weakening of the Atlantic Meridional Overturning Circulation or shifts in the North Atlantic Oscillation...  climate reconstructions describe a transition between a stronger and weaker SPG during the relatively warm medieval climate and the cold Little Ice Age respectively.

The simulated SPG shift is caused by a rapid increase in the freshwater export from the Arctic and associated freshening in the upper Labrador Sea. Such freshwater anomaly relates to prominent thickening of the Arctic sea ice, following the cluster of relatively small-magnitude volcanic eruptions by 1600 CE.

The subpolar gyre (SPG) influences the North Atlantic climate by modulating the transport of heat and salt between the North Atlantic and the Arctic oceans and, particularly, into the Nordic and Labrador seas, where deep water formation takes place.

Variations in the strength and shape of the SPG can lead to major changes in, for example, the intensity of the AMOC or the distribution of sea ice in the Arctic). A recent paleoceanographic reconstruction of the Atlantic mid-depth gyre circulation over the past 1500 years suggested that the SPG weakened between the Medieval Climate Anomaly 950–1250 CE and the Little Ice Age 1450–1850...

Freshening of the Labrador Sea as a trigger forLittle Ice Age development
M Alonso-Garcia ... WS Broecker ... et al
https://www.clim-past.net/13/317/2017/cp-13-317-2017.pdf free full text

The comparison of our Labrador Sea IRD records with other climate proxies from the subpolar North Atlantic allowed us to propose a sequence of processes that led to the cooling that occurred during the LIA, particularly in the Northern Hemisphere.

This study reveals that the warm climate of the MCA may have enhanced iceberg calving along the SE Greenland coast and, as a result, freshened the subpolar gyre (SPG). Consequently, SPG circulation switched to a weaker mode and reduced convection in the Labrador Sea, decreasing its contribution to the North Atlantic deep water formation and, thus, reducing the amount of heat transported to high latitudes.

This situation of weak SPG circulation may have made the North Atlantic climate more unstable, inducing a state in which external forcings (e.g. reduced solar irradiance and volcanic eruptions) could easily drive periods of severe cold conditions in Europe and the North Atlantic like the LIA. This analysis indicates that a freshening of the SPG may play a crucial role in the development of cold events during the Holocene, which may be of key importance for predictions about future climate.

Csnavywx

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Re: Global Surface Air Temperatures
« Reply #1530 on: August 26, 2017, 11:20:27 PM »
https://www.nature.com/articles/ncomms14375?WT.feed_name=subjects_earth-and-environmental-sciences

Abrupt cooling over the North Atlantic in modern climate models

Quote
Observations over the 20th century evidence no long-term warming in the subpolar North Atlantic (SPG). This region even experienced a rapid cooling around 1970, raising a debate over its potential reoccurrence. Here we assess the risk of future abrupt SPG cooling in 40 climate models from the fifth Coupled Model Intercomparison Project (CMIP5). Contrary to the long-term SPG warming trend evidenced by most of the models, 17.5% of the models (7/40) project a rapid SPG cooling, consistent with a collapse of the local deep-ocean convection. Uncertainty in projections is associated with the models’ varying capability in simulating the present-day SPG stratification, whose realistic reproduction appears a necessary condition for the onset of a convection collapse. This event occurs in 45.5% of the 11 models best able to simulate the observed SPG stratification. Thus, due to systematic model biases, the CMIP5 ensemble as a whole underestimates the chance of future abrupt SPG cooling, entailing crucial implications for observation and adaptation policy.

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Re: Global Surface Air Temperatures
« Reply #1531 on: August 26, 2017, 11:30:06 PM »
http://onlinelibrary.wiley.com/doi/10.1002/2016GL070526/full

On the atmospheric response experiment to a Blue Arctic Ocean

Quote
We demonstrated atmospheric responses to a reduction in Arctic sea ice via simulations in which Arctic sea ice decreased stepwise from the present-day range to an ice-free range. In all cases, the tropospheric response exhibited a negative Arctic Oscillation (AO)-like pattern. An intensification of the climatological planetary-scale wave due to the present-day sea ice reduction on the Atlantic side of the Arctic Ocean induced stratospheric polar vortex weakening and the subsequent negative AO. Conversely, strong Arctic warming due to ice-free conditions across the entire Arctic Ocean induced a weakening of the tropospheric westerlies corresponding to a negative AO without troposphere-stratosphere coupling, for which the planetary-scale wave response to a surface heat source extending to the Pacific side of the Arctic Ocean was responsible. Because the resultant negative AO-like response was accompanied by secondary circulation in the meridional plane, atmospheric heat transport into the Arctic increased, accelerating the Arctic amplification.

Particularly interesting is the transient response in this experiment (which alludes to my point above about surprise transient responses). Initially, the stratosphere is an important directly coupled component. However, after that, the "permanent" response to fully ice free conditions in the autumn causes a complete decoupling with the stratosphere.

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Re: Global Surface Air Temperatures
« Reply #1532 on: August 26, 2017, 11:35:06 PM »
Quote
Northern Hemispheric atmospheric circulation ... either that or a collapse/severe weakening of the SPG is the next flash point, the latter effect of slowing GMST increases (though with repercussions).
Along the lines of these two articles?

An abrupt weakening of the subpolar gyre as trigger of Little Ice Age-type episodes
E Chamarro et al
https://link.springer.com/article/10.1007%2Fs00382-016-3106-7 free full text

We investigate the mechanism of a decadal-scale weakening shift in the strength of the subpolar gyre (SPG) that is found in one among three last millennium simulations with a state-of-the-art Earth system model.

The SPG shift triggers multicentennial anomalies in the North Atlantic climate driven by long-lasting internal feedbacks relating anomalous oceanic and atmospheric circulation, sea ice extent, and upper-ocean salinity in the Labrador Sea.

Yet changes throughout or after the shift are not associated with a persistent weakening of the Atlantic Meridional Overturning Circulation or shifts in the North Atlantic Oscillation...  climate reconstructions describe a transition between a stronger and weaker SPG during the relatively warm medieval climate and the cold Little Ice Age respectively.

The simulated SPG shift is caused by a rapid increase in the freshwater export from the Arctic and associated freshening in the upper Labrador Sea. Such freshwater anomaly relates to prominent thickening of the Arctic sea ice, following the cluster of relatively small-magnitude volcanic eruptions by 1600 CE.

The subpolar gyre (SPG) influences the North Atlantic climate by modulating the transport of heat and salt between the North Atlantic and the Arctic oceans and, particularly, into the Nordic and Labrador seas, where deep water formation takes place.

Variations in the strength and shape of the SPG can lead to major changes in, for example, the intensity of the AMOC or the distribution of sea ice in the Arctic). A recent paleoceanographic reconstruction of the Atlantic mid-depth gyre circulation over the past 1500 years suggested that the SPG weakened between the Medieval Climate Anomaly 950–1250 CE and the Little Ice Age 1450–1850...

Freshening of the Labrador Sea as a trigger forLittle Ice Age development
M Alonso-Garcia ... WS Broecker ... et al
https://www.clim-past.net/13/317/2017/cp-13-317-2017.pdf free full text

The comparison of our Labrador Sea IRD records with other climate proxies from the subpolar North Atlantic allowed us to propose a sequence of processes that led to the cooling that occurred during the LIA, particularly in the Northern Hemisphere.

This study reveals that the warm climate of the MCA may have enhanced iceberg calving along the SE Greenland coast and, as a result, freshened the subpolar gyre (SPG). Consequently, SPG circulation switched to a weaker mode and reduced convection in the Labrador Sea, decreasing its contribution to the North Atlantic deep water formation and, thus, reducing the amount of heat transported to high latitudes.

This situation of weak SPG circulation may have made the North Atlantic climate more unstable, inducing a state in which external forcings (e.g. reduced solar irradiance and volcanic eruptions) could easily drive periods of severe cold conditions in Europe and the North Atlantic like the LIA. This analysis indicates that a freshening of the SPG may play a crucial role in the development of cold events during the Holocene, which may be of key importance for predictions about future climate.

Along those lines -- at least to a degree. There's some fresh doubt over the stability of the entire AMOC as well. I'll find that paper.

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Re: Global Surface Air Temperatures
« Reply #1533 on: August 26, 2017, 11:36:31 PM »
This analysis indicates that a freshening of the SPG may play a crucial role in the development of cold events during the Holocene, which may be of key importance for predictions about future climate.

While I fully appreciate all of these points about the importance of the freshening of the SPG w.r.t. to potentially slowing of the rate of increase in the GMSTA, I still have concerns including:

- Due to the bi-hemispheric seesaw, a cooling of the North Atlantic historically has resulted in a warming of the deep water in the Southern Ocean; which may increase the risk that WAIS will collapse sooner rather than later.
- Hansen has warned that a slow-down of the MOC will likely lead to decades of extreme weather events (The storms of his grandchildren), as there were during the LIA.
- Associated shifts in precipitation patterns could result in widespread crop losses (as occurred during the LIA) and/or stress to the tropical rainforests.
- The slow response positive feedback mechanisms identified by PH17 have already been triggered by GHG emitted since the beginning of the industrial age and it will take over 150 years to eliminate these slow response positive feedbacks (regardless of what the SPG does).
- Finally, I note that we are currently at a CO2e of over 521ppm which can/will cause a lot of climate impacts over the next few decades no matter what optimistic assumptions one makes about future methane emission, gradual freshening of the SPG, or the cleverness of mankind.
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Re: Global Surface Air Temperatures
« Reply #1534 on: August 27, 2017, 02:17:38 AM »
The linked reference indicates that AR5 meaningfully underestimates future global warming from land use and land cover change (LULCC).  This is an example of a mechanisms that may result in more rapid warming in the coming decades than projected by CMIP5:

Natalie M Mahowald, Daniel Ward, Scott Doney, Peter Hess and James T Randerson (2017), "Are the impacts of land use on warming underestimated in climate policy?", Environmental Research Letters, https://doi.org/10.1088/1748-9326/aa836d

http://iopscience.iop.org/article/10.1088/1748-9326/aa836d
&
http://iopscience.iop.org/article/10.1088/1748-9326/aa836d/pdf

Abstract: "While carbon dioxide emissions from energy use must be the primary target of climate change mitigation efforts, land use and land cover change (LULCC) also represent an important source of climate forcing. In this study we compute time series of global surface temperature change separately for LULCC and non-LULCC sources (primarily fossil fuel burning), and show that because of the extra warming associated with the co-emission of methane and nitrous oxide with LULCC carbon dioxide emissions, and a co-emission of cooling aerosols with non-LULCC emissions of carbon dioxide, the linear relationship between cumulative carbon dioxide emissions and temperature has a two-fold higher slope for LULCC than for non-LULCC activities. Moreover, projections used in the Intergovernmental Panel on Climate Change (IPCC) for the rate of tropical land conversion in the future are relatively low compared to contemporary observations, suggesting that the future projections of land conversion used in the IPCC may underestimate potential impacts of LULCC. By including a "business as usual" future LULCC scenario for tropical deforestation, we find that even if all non-LULCC emissions are switched off in 2015, it is likely that 1.5°C of warming relative to the preindustrial era will occur by 2100. Thus, policies to reduce LULCC emissions must remain a high priority if we are to achieve the low to medium temperature change targets proposed as a part of the Paris Agreement. Future studies using integrated assessment models and other climate simulations should include more realistic deforestation rates and the integration of policy that would reduce LULCC emissions."
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Re: Global Surface Air Temperatures
« Reply #1535 on: August 27, 2017, 09:51:05 AM »
Figure 5 of the reference on findings of the CloudSat & CALIPSO within the A-Train, shows a dramatic increase (more positive) in observed net cloud feedback as compared to prior assumptions.  This of course means that ECS is higher than previously assumed.

Graeme Stephens et. al. (2017), "CloudSat and CALIPSO within the A-Train: Ten years of actively observing the Earth system", BAMS, https://doi.org/10.1175/BAMS-D-16-0324.1

http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-16-0324.1?utm_content=bufferebbb9&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer
or
http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-16-0324.1

Abstract: "The more than 10 years of observations jointly collected by CloudSat and CALIPSO satellites has resulted in new ways of looking at aerosol, clouds, and precipitation and new discoveries about processes that connect them.

One of the most successful demonstrations of an integrated approach to observe Earth from multiple perspectives is the A-Train satellite constellation (e.g. Stephens et al., 2002). The science enabled by this constellation flourished with the introduction of the two active sensors carried by the NASA CloudSat and the NASA/CNES Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellites that were launched together on April 28th, 2006. These two missions have provided a 10-year demonstration of coordinated formation flying that made it possible to develop integrated products and that offered new insights on key atmospheric processes. The progress achieved over this decade of observations, summarized in this paper, clearly demonstrate the fundamental importance of the vertical structure of clouds and aerosol for understanding the influences of the larger scale atmospheric circulation on aerosol, the hydrological cycle, the cloud-scale physics and on the formation of the major storm systems of Earth. The research also underscored inherent ambiguities in radiance data in describing cloud properties and how these active systems have greatly enhanced passive observation. It is now clear that monitoring the vertical structure of clouds and aerosol is essential and a climate data record is now being constructed. These pioneering efforts are to be continued with EarthCARE mission planned for launch in 2019."

Caption: "Figure 5 Upper three panels are from Hartmann et al (1992) who estimate the contribution to the cloud radiative effects (CRE) of five classes of clouds as defined according to the ISCCP radiance classification (upper left). The bottom panels are the equivalent analysis but with classification determined by the radar-lidar data of CloudSat and CALIPSO where true cloud heights establish the types and cloud thickness (x axis) are from water and ice path information which is proportional to cloud optical depth. The differences in CRE between this latter analysis and that of Hartmann et al underscores the effects of misclassification of clouds on the interpretation of their radiative effects. Ci=cirrus, D.C.=Deep Convection, M.L.=multi-layer, AS=Altostratus, AC-Alto-cumulus, NS=Nimbostratus, St=stratus, SC=stratocumulus and Cu=cumulus."
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AbruptSLR

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Re: Global Surface Air Temperatures
« Reply #1536 on: August 27, 2017, 05:04:38 PM »
Here is a comparison of between recent GMSTA and solar irradiance.  During the LIA solar irradiance was relatively low, volcanic activity was relatively high and the AMOC was relatively low; thus without anthropogenic radiative forcing we might be in a cooling mode now.
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Ned W

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Re: Global Surface Air Temperatures
« Reply #1537 on: August 27, 2017, 05:22:22 PM »
I get the impression that some people here, who have not done the calculations, may not fully realize how small an impact various news items have on the near-term outlook.

Consider the revisions to the radiative forcings for CO2, CH4, and N2O from Etminan et al (2016).  These revisions got a lot of attention here on ASIF, and people sometimes talk as if they are some kind of game-changer for the climate.

In reality, the net effect of all three sets of revisions is to increase the total forcing (relative to preindustrial) from CO2, CH4, and N2O by 4.4%.  But most of that change is in long past, and they actually become less and less significant over time.  For the forcing change relative to 2000, the revisions only raise it by 0.5%

Here's a graph showing the total of CO2, CH4, and N2O for the old RF calculations vs the new ones.  Can you spot the difference?  You need to squint very hard at the upper right hand corner:



If the rate of increase in atmospheric CH4 concentration accelerates dramatically, the revisions will have a larger effect.  Over an 18-year time frame, that might increase the total radiative forcing by 1%, instead of the 0.5% we saw from 2000-2017.  In terms of projecting short term temperature change (e.g., to 2035) it will be lost in the noise.

----------------------------
Methodological notes:
Original versions of radiative forcing calculations here.
Revised versions from Etminan et al. (2016) here.
Atmospheric concentrations of CO2, CH4, and N2O here.

AbruptSLR

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Re: Global Surface Air Temperatures
« Reply #1538 on: August 27, 2017, 05:51:48 PM »
I get the impression that some people here, who have not done the calculations, may not fully realize how small an impact various news items have on the near-term outlook.

Picking one feedback at a time and discounting it to the point of ignoring it is counterproductive. There are a large number of incremental positive feedbacks that can work synergistically to increase GMSTA, and the only way to correctly do the calculations is using a high end ESM analysis like the following linked CESM analysis that shows that ECS is currently likely somewhere from 4.1C to 5.6C (I note also that only the most advances ESM projections seem to be able to come close to paleo values of polar amplification):

William R. Frey & Jennifer E. Kay (2017), "The influence of extratropical cloud phase and amount feedbacks on climate sensitivity", Climate Dynamics; pp 1–20, doi:10.1007/s00382-017-3796-5

https://link.springer.com/article/10.1007%2Fs00382-017-3796-5?utm_content=bufferfdbc0&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Global coupled climate models have large long-standing cloud and radiation biases, calling into question their ability to simulate climate and climate change. This study assesses the impact of reducing shortwave radiation biases on climate sensitivity within the Community Earth System Model (CESM). The model is modified by increasing supercooled cloud liquid to better match absorbed shortwave radiation observations over the Southern Ocean while tuning to reduce a compensating tropical shortwave bias. With a thermodynamic mixed-layer ocean, equilibrium warming in response to doubled CO2 increases from 4.1 K in the control to 5.6 K in the modified model. This 1.5 K increase in equilibrium climate sensitivity is caused by changes in two extratropical shortwave cloud feedbacks. First, reduced conversion of cloud ice to liquid at high southern latitudes decreases the magnitude of a negative cloud phase feedback. Second, warming is amplified in the mid-latitudes by a larger positive shortwave cloud feedback. The positive cloud feedback, usually associated with the subtropics, arises when sea surface warming increases the moisture gradient between the boundary layer and free troposphere. The increased moisture gradient enhances the effectiveness of mixing to dry the boundary layer, which decreases cloud amount and optical depth. When a full-depth ocean with dynamics and thermodynamics is included, ocean heat uptake preferentially cools the mid-latitude Southern Ocean, partially inhibiting the positive cloud feedback and slowing warming. Overall, the results highlight strong connections between Southern Ocean mixed-phase cloud partitioning, cloud feedbacks, and ocean heat uptake in a climate forced by greenhouse gas changes."
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Ned W

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Re: Global Surface Air Temperatures
« Reply #1539 on: August 27, 2017, 06:43:48 PM »
Huh.  I wrote: 

Quote
If the rate of increase in atmospheric CH4 concentration accelerates dramatically, the revisions will have a larger effect.  Over an 18-year time frame, that might increase the total radiative forcing by 1%, instead of the 0.5% we saw from 2000-2017.

I did the calculations in a hurry, and need to check them over.  But it seems to be possible that over the next couple of decades, the new methods for calculating radiative forcing could well lead to a result that is actually lower than the old methods. 

In other words, if you extrapolate the growth of CO2, CH4, and N2O to 2035, and calculate the total forcing in 2035 relative to 2017, it will literally be lower under the methods of Etminan (2016) than under the methods used previously (which come from Myhre et al 1998, I believe).

I don't have my spreadsheet handy but will try to confirm that later.  Good news, if true. 

jai mitchell

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Re: Global Surface Air Temperatures
« Reply #1540 on: August 27, 2017, 07:47:48 PM »
I get the impression that some people here, who have not done the calculations, may not fully realize how small an impact various news items have on the near-term outlook.


Ned,

This is an interesting discussion.

A question about your calculation,  You are developing a value for total irradiative forcing using CO2e for the value.

So, first question, What multiplier did you use for CH4 was it the 21 value used by SAR? was it the 28 value for AR5, is it the 35 value derived from longer atmospheric residency times? and then did you multiply (whichever value you used by the 14% increase developed by Etminan (2016)?

second question,

What if you instead looked at the 20-year forcing potentials?  using an 85 times multiplier, or the 105 times multiplier more recently developed.   Knowing that the CH4 shortwave function derived in Etminan (2016) is only applied to CH4, and that CH4 has an atmospheric residency of about 12 years and the additional forcing of this CH4 applied during these 12 years produces a 14% increase on a 100-year timeline, what is the appropriate adjustment to, say the 105 times multiplier (I am figuring it is close to 35% higher for the 20-year timeline).

It is critically important to understand what actual forcing potential we will be facing over the next 20 years.
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jai mitchell

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Re: Global Surface Air Temperatures
« Reply #1541 on: August 27, 2017, 07:52:52 PM »
Ned,

Follow up question:

how does your RF graph show such a small change in the radiative forcing when Etminan (2016) abstract says the following:

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071930/pdf

Quote
Abstract New calculations of the radiative forcing (RF) are presented for the three main well‐mixed greenhouse gases, methane, nitrous oxide, and carbon dioxide. Methane’s RF is particularly impacted because of the inclusion of the shortwave forcing; the 1750–2011 RF is about 25% higher (increasing from 0.48Wm−2 to 0.61Wm−2) compared to the value in the Intergovernmental Panel on Climate Change (IPCC) 2013 assessment;

according to this work, the increase in total RF due to this revision of the CH4 shortwave effect is +0.13 W/m^2  Why doesn't your graph show this size of a difference?
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jai mitchell

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Re: Global Surface Air Temperatures
« Reply #1542 on: August 27, 2017, 08:44:12 PM »
See Graph of the Actual Forcing Series with Etminan Revision, The same historic forcing values were used for AR4 and AR5 (as far as I remember).
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Ned W

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Re: Global Surface Air Temperatures
« Reply #1543 on: August 27, 2017, 09:44:28 PM »
I get the impression that some people here, who have not done the calculations, may not fully realize how small an impact various news items have on the near-term outlook.


Ned,

This is an interesting discussion.

A question about your calculation,  You are developing a value for total irradiative forcing using CO2e for the value.

So, first question, What multiplier did you use for CH4 was it the 21 value used by SAR? was it the 28 value for AR5, is it the 35 value derived from longer atmospheric residency times? and then did you multiply (whichever value you used by the 14% increase developed by Etminan (2016)?

I calculated the radiative forcings for each molecule directly from their concentrations, using the equations given in the sources linked to under "methodological notes" in my post above. I then compared the total forcing (CO2 + CH4 + N2O) for the two methods, old (IPCC) and new (Etminan).

The wording of your questions suggests you haven't actually looked at either of the sources.  If you care about this stuff and want to understand it, I highly recommend doing the actual calculations yourslef and experimenting with different values of CO2, CH4, etc. 

Ned W

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Re: Global Surface Air Temperatures
« Reply #1544 on: August 27, 2017, 09:58:59 PM »
Ned,

Follow up question:

how does your RF graph show such a small change in the radiative forcing when Etminan (2016) abstract says the following:

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071930/pdf

Quote
Abstract New calculations of the radiative forcing (RF) are presented for the three main well‐mixed greenhouse gases, methane, nitrous oxide, and carbon dioxide. Methane’s RF is particularly impacted because of the inclusion of the shortwave forcing; the 1750–2011 RF is about 25% higher (increasing from 0.48Wm−2 to 0.61Wm−2) compared to the value in the Intergovernmental Panel on Climate Change (IPCC) 2013 assessment;

according to this work, the increase in total RF due to this revision of the CH4 shortwave effect is +0.13 W/m^2  Why doesn't your graph show this size of a difference?

This is where it helps to be comfortable doing the calculations directly, because a lot of things become clear when one does that.

Radiative forcing, as the term is used here, refers to a change in radiative flux over some specific time period (or, alternatively, relative to some baseline condition).  Your quote is referring to the forcings relative to 1750.  The radiative forcing from CH4 was larger over that time period, so the difference between new vs old methods of calculation is larger.

In this thread, we've been talking about short-term changes in temperature, e.g. 2000-2017 or 2018-2035.  The RF for CH4 at present is a much smaller portion of the total RF, so using the old vs new method makes less of a difference.  In addition, the (small) increase in RF for methane under the new system is partially negated by (small) decreases in the RF for CO2 and N2O. 

Ned W

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Re: Global Surface Air Temperatures
« Reply #1545 on: August 27, 2017, 10:10:48 PM »
See Graph of the Actual Forcing Series with Etminan Revision, The same historic forcing values were used for AR4 and AR5 (as far as I remember).
This is the same issue as your previous post, so see my previous answer.

Notice how each pair of lines in your graph is so closely parallel?  There is a gap between the old and new methods, but that gap is not growing much in recent years.  That means the difference between old and new methods arose earlier in the time series. 

So the radiative forcing in 2017 relative to 1750 is a bit higher under the new method.  And the radiative forcing in 2035 relative to 1750 will still be a bit higher under the new method.  But the radiative forcing in 2035 relative to 2017 will be only trivially different between the old vs new methods.

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Re: Global Surface Air Temperatures
« Reply #1546 on: August 27, 2017, 10:37:04 PM »
ASLR, maybe you could shed some light on this stupid question of mine: seeing as methane concentrations are on an ever-upward trend, despite the fact that methane is constantly removed from the atmosphere - why not use the actual forcing of current methane in the atmosphere, "instantaneous GWP", which I would guess is much higher than even the GWP20 value? I mean, if we totally stopped emitting now and all natural sources would oblige to do the same, then all jolly good, use GPW20 or whatever, but as that is not happening the actual radiative forcing of methane is much higher than these numbers suggest.

oren,

I am an engineer and not a scientist, so I am not qualified to determine CO2e values based on GWP20 values; but I do not dispute your logic.

Best,
ASLR

Makes absolute sense to me. The very high CO2e numbers that result from using realistic methane gwp amounts does make me think that the masking factors, such as SO2 aerosols, are having a much greater impact than currently assumed. As they are reduced, the level of net forcing will then pick up strongly. Add in albedo reductions and I see the possibility of 2oC in the 2030's. A really aggressive move away from coal may definitely bring that date forward.

jai mitchell

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Re: Global Surface Air Temperatures
« Reply #1547 on: August 27, 2017, 11:01:14 PM »
See Graph of the Actual Forcing Series with Etminan Revision, The same historic forcing values were used for AR4 and AR5 (as far as I remember).
This is the same issue as your previous post, so see my previous answer.

Notice how each pair of lines in your graph is so closely parallel?  There is a gap between the old and new methods, but that gap is not growing much in recent years.  That means the difference between old and new methods arose earlier in the time series. 

So the radiative forcing in 2017 relative to 1750 is a bit higher under the new method.  And the radiative forcing in 2035 relative to 1750 will still be a bit higher under the new method.  But the radiative forcing in 2035 relative to 2017 will be only trivially different between the old vs new methods.

No,

You are completely misunderstanding what the upward revision to CH4 forcing means.  It is an upward revision to the previous calculation of forcing from that source.  That means that, no matter what the baseline, the CH4 forcing values are raised by that much (about 25%)  Redo your calculations and forget about the increase in forcing since a certain time, by not adjusting the baseline value UPWARDS you are underestimating the impact of this revision.

In other words, the 2017 value must be revised upwards (compared to the AR5 value) by at least +0.16 W/m^2
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Re: Global Surface Air Temperatures
« Reply #1548 on: August 27, 2017, 11:21:08 PM »
No, Jai.  I'm sorry, but you're wrong.  The question I'm trying to answer is "what effect do the revised calculations for RF have on expected future temperature change". 

The answer to that is "very little". 


jai mitchell

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Re: Global Surface Air Temperatures
« Reply #1549 on: August 28, 2017, 12:42:03 AM »
future temperature change is a function of total forcing, not additional forcing between now and some future date.  Measured in top of atmosphere radiation imbalance (TOA).  What this revision means is that the TOTAL forcing is higher than previously calculated.  Hansen and Sato (2012) determined a median value of TOA at +0.6 W/m^2. 

Calculations of Global Warming Potential are measured on 20, 100 and 500 year timelines and comparative values are assessed over these time frames of contributions to future warming.  by raising the total forcing at TOA by 0.13 you are effectively adding an additional ~100,000 Hiroshima bombs per day to the total energy accumulation of planet earth.

In addition, Ricke & Caldiera (2014) showed that full warming impact from emissions does not reach full forcing potential (with water vapor feedbacks) for ~8 years.  This means that there is a whole hell of a lot of warming still locked in at current forcing levels.

CH4, measured on a 100-year timeline is approximately 23% of the total forcing profile of GHGs if calculated on a 20-year timeline with Etminan (2016) upward revision, this value goes up to closer to 60% of total warming contribution.

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