Radiative forcing and CO2eq

[Ned W]

A couple of weeks ago I posted about this in another thread (Consequences / surface temperatures) but it was rather off-topic for that thread.  Since it's not really about "consequences" or "surface temperatures", I thought I'd move over here, and be a bit more precise.

First, let's take a look at radiative forcing from greenhouse gases and in particular the updated calculations of forcings from Etminan (2016).  Here are the recent trends in forcing from CO2, CH4, and N2O (the "big three" well-mixed greenhouse gases), with forcings relative to the pre-industrial baseline (basically the year 1765 CE):



The new calculations shift the forcing from CH4 slightly upward, and make smaller changes in CO2 and N2O.  The combined effect of all three sets of changes is shown in the following figure:



Note that in the above figure, the "greenhouse gases" line includes CO2/CH4/N2O plus all the other well-mixed greenhouse gases (halocarbons, etc.)  For the rest of this post, any reference to "greenhouse gases" means all such gases, not just the main three.

Overall, Etminan 2016 increased the total forcing since 1765 from well-mixed greenhouse gases (WMGHGs) by about 3.9%.  Looking ahead, over the next few decades, the updated calculations for forcing will have a slightly smaller effect (3.4% increase in WMGHGs, for forcing in 2050 relative to now):



Note 1: Radiative forcing (RF) represents a change in the Earth's radiation balance relative to some baseline condition (or time period). It is often expressed relative to the "pre-industrial" baseline, but for this "future change" figure it is handy to calculate the RF relative to current (2017) conditions.

Note 2: The orange line in those last two figures represents all anthropogenic forcings other than WMGHGs -- land use albedo, black carbon, tropospheric ozone, aerosols, etc.  In the past, the net sum of these non-GHG forcings has been net negative, relative to 1765.  However, as shown in the last figure above, the non-GHG forcings are now increasing rather than decreasing, i.e., on balance they are increasing warming rather than decreasing it.

Data source

[Ned W]

Another related topic that came up in the "surface temperatures" thread was CO2 Equivalence -- basically, converting the forcings from non-CO2 sources into a number that is "equivalent" to the forcing from CO2.  This is a confusing topic, made worse by the fact that the same term is used inconsistently.

One usage is based on mass of emissions (in metric tonnes).  Figures for non-CO2 emissions are converted to the equivalent mass of CO2 that would produce a similar warming over some time frame (e.g., 100 years) based on the relative "global warming potential" of the gases in question.  This metric is typically used for economic/accounting purposes, e.g. in regulating emissions.   This is not the usage of "CO2 equivalence" that is addressed in this post.

The other usage -- the one I am focused on here -- is based on atmospheric concentration (in parts per million by volume). The radiative forcings from non-CO2 greenhouse gases are summed, and then log-transformed using the inverse of the CO2 forcing model to back-calculate "CO2 equivalent (CO2e or CO2eq)". 

This is normally done, as noted in the previous paragraph, for the other well-mixed greenhouse gases (WMGHGs). I have also seen "CO2eq" calculated for the sum of all anthropogenic forcings (WMGHGs, other gases, aerosols, land use albedo, black carbon, etc.).  The latter number represents the net effect of all human interventions on the Earth's radiation balance, converted to an equivalent concentration of CO2.

The following figure shows CO2eq over time from RCP6 (blue lines are for WMGHGs only; red lines are for the total of all anthropogenic forcings). Both the AR5 version of the forcings calculation and the updated Etminan 2016 version are shown ("old" and "new" respectively).



As of 2016, the CO2eq from all WMGHGs was 490 ppmv under the "old" (AR5) calculations, or 500 ppmv under the "new" (Etminan 2016) calculations.

Using all anthropogenic forcings (from here) the CO2eq values are approximately 422 ppmv (old) and 432 ppmv (new).

It's important not to make too much of the specific numbers. For example, when a study says that we should endeavor to keep CO2 concentrations below some threshold to minimize climate disruption, that threshold is usually based on CO2 itself, and assumes that CO2eq will be some (unstated) higher number.  Adding more forcings into a calculated value of "CO2eq" doesn't actually bring us closer to the threshold; it raises the threshold because more is being included in it. Because of this, I think it's probably preferable to avoid using CO2eq as a method for integrating the effects of other greenhouse gases, and instead simply use the raw forcing values.

Nonetheless, here are the CO2eq values (based on WMGHGs) for 2016, from observations (NOAA ESRL) and from the CMIP5 RCP6 and RCP8.5 pathways. We appear to be between RCP6 and RCP8.5, but closer to the former.

[Archimid]

Good stuff Ned W.

[rboyd]

Ned, thanks for the great information.

For your "all anthropogenic forcings" are you including the negative forcing from aerosols?

[Ned W]

Good stuff Ned W.

Thanks!

Ned, thanks for the great information.

For your "all anthropogenic forcings" are you including the negative forcing from aerosols?

Yes, it's pretty much everything:
All greenhouse gases
Direct anthro aerosols (organic carbon, black carbon, sulfate, nitrate, etc.)
Stratospheric and tropospheric ozone
Stratospheric water-vapour from methane oxidisation
Landuse albedo
Black carbon on snow
and more.  It's from the Postdam Institute's files of forcings for CMIP5 model runs, at the link in the original post ... except I recalculated the forcings for CO2, CH4, and N2O myself using the Etminan equations.

That is why the "all anthro forcings" version of CO2eq is lower than the "greenhouse gases" version of CO2eq.

[Archimid]

When you say "Land use albedo" are changes in snow and ice albedo included?

[Ned W]

Depends what exactly you mean by that.

The data I'm plotting are for forcings not feedbacks.  So they include anthropogenic forcings that directly change the albedo of snow (e.g., the "black carbon on snow" forcing I listed above).  It's not part of the "land use albedo" forcing, it's a separate forcing of its own but it is included, yes.

But they don't include the albedo change from the reduction in snow and ice extent (which in turn is due to warming), because that's a feedback not a forcing.  Feedbacks are dealt with inside the models, not in the forcings that are used as input to the models. 

Given the same set of initial forcings (greenhouse gases, aerosols, black carbon, etc.) different models will handle the feedbacks (including the ice-albedo feedback and polar amplification) differently.  That's one of the reasons for variation in climate sensitivity as an emergent property from one model to the next.

[Archimid]

Such a clear answer, thanks. The distinction between forcings and feedbacks is very clear to me now.

[Ned W]

It was a good question. 

Mostly when people talk about albedo changes associated with less snow/ice, they are referring to the feedback (warming -> less snow extent -> lower albedo -> more warming).

Snow/ice extent as a forcing would involve humans somehow directly and artificially changing the area covered by snow/ice ... like snowmaking at ski areas (a negative forcing, reflects more light) or plowing snow off of roads etc. (a positive forcing, absorbs more light).

[jai mitchell]

Since Etminan 2016 states the 2011 differential value of forcing for CH4 to be +0.13, and you have previously stated that this value is too high, please post your "previous" and "new" values for CH4 for the year 2011.  If it is less (or more!) than 0.13 Watts per meter squared then your calculation is off.

Note that the relative values is not important here, only the differential, since you are using a different baseline than he does (1750).

I understand you are only looking at the "big three" (CO2, CH4 and NO2) so when you post your CO2eq values you need to note that you are excluding the additional forcing from O3 (0.4 W/m^2) and trace GHGs (0.339 W/m^2).  This additional forcing (using the pre-Etminan values produces a real CO2eq value of 526.6 ppmv The additional forcing of Etminan increases this value somewhat. 

http://cdiac.ess-dive.lbl.gov/pns/current_ghg.html

[Ned W]

Since Etminan 2016 states the 2011 differential value of forcing for CH4 to be +0.13, and you have previously stated that this value is too high, please post your "previous" and "new" values for CH4 for the year 2011.  If it is less (or more!) than 0.13 Watts per meter squared then your calculation is off.

Etminan 2016 uses the following values for concentrations:
Preindustrial: CO2 = 278 ppm, CH4 = 722 ppb, N2O = 270 ppb (last line of page 12620)
2011:  CO2 = 389 ppm, CH4 = 1800 ppb, N2O = 323 ppb (caption of Figure 2)

Using those concentrations, my calculated RF for CH4 is as follows:
Old version: 0.491 W m-2
New version: 0.606 W m-2
Difference: 0.114 W m-2

Etminan rounds off their results to two decimal places, thus turning 0.606 into 0.61 W m-2.

Etminan's value of 0.48 W m-2 for the old version of CH4 in 2011 appears to be taken straight from the IPCC AR5 chapter 8,  but it should actually be 0.49 not 0.48.

Incidentally, as I mentioned in the other thread, Etminan's Table S1 in the Supplementary Materials gives their new-version values for lots of combinations of CO2, CH4, and N2O concentrations.  I ran through the first 20 rows of that table, and in every case my results matched theirs exactly.  So I had already verified that my calculations were correct before posting anything here.

Note that the relative values is not important here, only the differential, since you are using a different baseline than he does (1750).

Actually, all of my figures in this thread except for one are with the same pre-industrial baseline.  I have it labeled as "1765" on the graphs at the top of the thread, but it's the same actual concentrations as Etminan's "1750" baseline. 

And elsewhere (e.g., Table S1) Etminan uses a 2011 baseline.  It's really not a big deal.  You report forcings relative to whatever baseline makes sense for the question you're asking.

I understand you are only looking at the "big three" (CO2, CH4 and NO2) so when you post your CO2eq values you need to note that you are excluding the additional forcing from O3 (0.4 W/m^2) and trace GHGs (0.339 W/m^2).  This additional forcing (using the pre-Etminan values produces a real CO2eq value of 526.6 ppmv The additional forcing of Etminan increases this value somewhat. 

No.  The only place in this thread where I look at just the "big three" (CO2, CH4, and N2O) is in the very first graph of the first post.  In particular, in the CO2eq calculations (from the second post in this thread) I calculate CO2eq two ways:

(1) For all well-mixed greenhouse gases.  This includes CO2, CH4, N2O, plus all the halocarbons, etc. 

(2) For all anthropogenic forcings, including the above-mentioned greenhouse gases plus everything else -- black carbon, ozone, aerosols, land use albedo, etc. etc. etc.  The source for that is the Potsdam PIK website you yourself linked to in the other thread (here).  I just updated the CO2/CH4/N2O forcings using Etminan's equations.

I'll re-post this graph, from the top of this thread, because it provides what you're looking for.  The blue line is CO2eq from all well-mixed greenhouse gases (not just the big three).  The red line is GHGs plus all other anthropogenic forcings, including the ozone forcing you mention above.
 


As of 2016, the CO2eq from all WMGHGs was 490 ppmv under the "old" (AR5) calculations, or 500 ppmv under the "new" (Etminan 2016) calculations.

Using all anthropogenic forcings (from here) the CO2eq values are approximately 422 ppmv (old) and 432 ppmv (new).

[jai mitchell]

Using all anthropogenic forcings (from here) the CO2eq values are approximately 422 ppmv (old) and 432 ppmv (new).

Thanks for your response and your work this looks very interesting, The NOAA AGGI CO2eq for 2016 is calculated to be (see: https://www.esrl.noaa.gov/gmd/aggi/ ) 489 ppm. 

From their methodology paper here:  https://www.esrl.noaa.gov/gmd/aggi/aggi.html

See table 2, the values you have come up to theirs quite well 2016 CO2e

[AbruptSLR]

For what it is worth, Isaksen et al. (2011) ran a range of computer models to show that methane's atmospheric burden is greater when more methane is emitted to the atmosphere than assumed in AR4 (see the first image for Isaksen et al. (2011)'s emission rates input into computer models).  Isaksen et al (2011) found (see the first image) that as the assumed emission rate increased the chemistry of the atmosphere would change resulting in increased lifetime of methane, increased methane burden in the atmosphere and that the radiative forcing from the methane would increase (see the second image).

Isaksen, I. S. A., Gauss M., Myhre, G., Walter Anthony, K. M.  and Ruppel, C.,  (2011), "Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions", Global Biogeochem. Cycles, 25, GB2002, doi:10.1029/2010GB003845.

http://onlinelibrary.wiley.com/doi/10.1029/2010GB003845/abstract

[jai mitchell]

Isaksen also followed up the above 2011 paper with a 2014 paper that looked specifically at the impacts of increased emissions of CH4 from transportation and the Arctic in future years, as well as the climate feedbacks of increased Ozone production in a warming world.  see paper here: http://www.mdpi.com/2073-4433/5/3/518/htm

The chemistry balance shifts of Stratospheric water vapor and Ozone, and their increased forcing potentials are shown in table 2 and below.

Most concerning to me is the translation of the increased radiative forcing of Methane, and the resultant increase in tropopause heights as an additional warming feedback on the evaluation of Global Warming Potential of these short-lived climate pollutants.  If applied as an equal adjustment for both the GWP-100 and the GWP-20 then the adjusted multiplier of CO2e for methane under GWP-100 (35) and GWP-20 (105) increase to (37.4) and (112.1) respectively, and if emissions rates of CH4 are held constant over time.

However, since CH4 only exists in the upper atmosphere for 10-12 years, the relative impacts from this gas are front-loaded and since this front-loading results in a ~7% increased RF on the 100-year GWP then it stands to reason that under a shift to GWP-20 this effect would increase at a much higher rate than the GWP-100 value.

This very complex atmospheric chemistry issue, under varying climate conditions, requires updated inputs into complex chemistry transport models and GCMs to winnow out the total warming impacts.

note: an excellent reference describing these chemistry interactions from Daniel Jacobs' Introduction to Atmospheric Chemistry - 1999 Can be found here:  http://acmg.seas.harvard.edu/people/faculty/djj/book/bookchap11.html

full online book here: http://acmg.seas.harvard.edu/people/faculty/djj/book/

[jai mitchell]

It should also be noted that the NOAA AGGI value that matches yours also does not include increased water vapor or other feedbacks in their estimation of comparative total forcing. 

Did you include these values in your total anthropogenic CO2eq?

[AbruptSLR]

Readers should remain cautious of arbitrary redefinitions of CO2e (CO2eq) in terms of "total anthropogenic" radiative forcings, as the attached image illustrates that AR5 assigns relatively large uncertainties (compared to forcings from GHGs) to the negative forcing from both "Aerosol-Radiation Interac." and "Aerosol-Cloud Interac.".  Thus if future research indicates that the median values for these forcings are less negative than currently assumed, or if the aerosol concentrations decrease faster than assumed (e.g. due to rapid adoption of solar cells to replace fossil fuels), then the newly defined "total anthropogenic" radiative forcing CO2e would increase.

Furthermore, the first linked reference indicates that the climate models used for AR5 assumed incorrect distributions of atmospheric hydroxyl ion between the north and south hemispheres, meaning that they likely misinterpret the values of associated anthropogenic radiative forcings:

P. K. Patra, et al. (2014), "Observational evidence for interhemispheric hydroxyl parity", Nature 513, 219-223 DOI: 10.1038/nature13721

http://www.nature.com/nature/journal/v513/n7517/full/nature13721.html?foxtrotcallback=true


Also, see the associate article entitled: "Observational evidence for interhemispheric hydroxyl parity"

https://m.phys.org/news/2014-09-evidence-interhemispheric-hydroxyl-parity.html

Extract: "A new study published today in Nature based on observational data and modeling shows that surprisingly the self-cleansing power of the atmosphere does not differ substantially between the Northern and the Southern Hemisphere. Up to now model simulations generally showed higher levels of hydroxyl (the dominant "bleaching agent" of the atmosphere that oxidizes many pollutants) in the Northern Hemisphere (NH). This seemed logical in view of the massive amounts of nitrogen oxides emitted by traffic, domestic heating and industry in the NH. These nitrogen oxides act as catalysts that promote the formation of ozone (ozone smog) and subsequently hydroxyl.
…
Dr. Carl Brenninkmeijer of Max Planck Institute for Chemistry (Germany), who first estimated this ratio in 1992, says "this result puts a finger on a wound in our understanding or at least proper description of the oxidative capacity of the troposphere." This study suggests that top-down emission estimates of reactive species, such as methane and carbon monoxide, in key emitting countries in the NH that are based on a NH/SH OH ratio larger than 1 may have been overestimated. For example, inverse modeling studies with relatively high OH in the NH require unrealistically large CH4 emissions in the NH to counterbalance OH removal. The authors conclude "chemical reactions simulated by the models may be incomplete and further research is needed to investigate how global/hemispheric OH responds to the wide range of human influences and to improve our ability to predict Earth's environmental change.""

Furthermore, the linked reference indicates that it is easier to produce hydroxyl radicals in the atmosphere, than previously expected:

Fang Liu, Joseph M. Beames, Andrew S. Petit, Anne B. McCoy, and Marsha I. Lester, (26 September 2014) "Infrared-driven unimolecular reaction of CH3CHOO Criegee intermediates to OH radical products", Science, Vol. 345 no. 6204 pp. 1596-1598 DOI: 10.1126/science.1257158

http://www.sciencemag.org/content/345/6204/1596

Abstract: "Ozonolysis of alkenes, an important nonphotolytic source of hydroxyl (OH) radicals in the troposphere, proceeds through energized Criegee intermediates that undergo unimolecular decay to produce OH radicals. Here, we used infrared (IR) activation of cold CH3CHOO Criegee intermediates to drive hydrogen transfer from the methyl group to the terminal oxygen, followed by dissociation to OH radicals. State-selective excitation of CH3CHOO in the CH stretch overtone region combined with sensitive OH detection revealed the IR spectrum of CH3CHOO, effective barrier height for the critical hydrogen transfer step, and rapid decay dynamics to OH products. Complementary theory provides insights on the IR overtone spectrum, as well as vibrational excitations, structural changes, and energy required to move from the minimum-energy configuration of CH3CHOO to the transition state for the hydrogen transfer reaction."

See also:
http://www.reportingclimatescience.com/news-stories/article/key-atmospheric-detergent-reaction-seen-in-the-lab.html

&

See also:

"Ozone and methane changes and interactions Regional to global scales" by Ivar S.A. Isaksen

http://www.smhi.se/polopoly_fs/1.18855!/Ozone_Methane_Isaksen.pdf

[Ned W]

It should also be noted that the NOAA AGGI value that matches yours also does not include increased water vapor or other feedbacks in their estimation of comparative total forcing. 

Did you include these values in your total anthropogenic CO2eq?

Those are feedbacks, not forcings.  Forcings are used as inputs to the models, while feedbacks are represented by processes within the models.

[Ned W]

Readers should remain cautious of arbitrary redefinitions of CO2e (CO2eq) in terms of "total anthropogenic" radiative forcings

I agree that there's enough confusion over CO2eq already, and we should stick closely with the "traditional" definitions. 

Both of the versions of CO2eq I use in this thread come from the mainstream climate science literature and practice.  The version including only well-mixed greenhouse gases is in widespread use, e.g. (as Jai pointed out) in NOAA's AGGI.  This is the version that I personally prefer, and it's currently around 490 ppmv (using the AR5 forcings) or 500 ppmv (using the Etminan forcings).

The version based on the sum of all anthropogenic forcings is also used in the literature, e.g.,

Meinshausen, M. et al. 2011. The RCP greenhouse gas concentrations and their extensions from 1765 to 2300.  Climatic Change, November 2011, 109:213.

Values for CO2eq based on total anthropogenic forcings are provided at the Potsdam PIK RCP scenario data group website here -- see the spreadsheet for mixing ratios.  All I've done is update them to reflect the new forcing calculations from Etminan 2016.

That total-anthro version of CO2eq (now at 422 or 432 ppm) seems less practical to me, because it's more challenging to track all the obscure minor forcings in real-time.  But obviously people do use it. 

Again, though, I agree with your point that it's not a good idea to start modifying these generally accepted versions of CO2eq, say by idiosyncratically adding in some forcings but not others, or making other modifications.  But updating them to reflect the new calculations of radiative forcing from Etminan 2016 seems like a reasonable thing to do.  I'm not changing the composition of forcings used in CO2eq, just updating them.

[jai mitchell]

It should also be noted that the NOAA AGGI value that matches yours also does not include increased water vapor or other feedbacks in their estimation of comparative total forcing. 

Did you include these values in your total anthropogenic CO2eq?

Those are feedbacks, not forcings.  Forcings are used as inputs to the models, while feedbacks are represented by processes within the models.

To be clear, the models used to develop NOAA AGGI CO2eq forcing values do NOT include feedbacks that result from GCM model outputs.  However, we do have good satellite records of recent atmospheric water vapor increases and their additional forcing values can be extracted (with high uncertainty in comparison to 1750 values).

[morganism]

“This research shows that the warming effects of both methane and hydrogen have been underestimated by a significant amount,” said Wordsworth. “We discovered that methane and hydrogen, and their interaction with carbon dioxide, were much better at warming early Mars than had previously been believed.”

http://spaceindustrynews.com/bursts-of-methane-may-have-warmed-early-mars/#8217;s%20plenty%20of%20geographical%20evidence%20that%20rivers%20periodically%20flowed%20across%20the%20planet’s%20surface.%20Yet...

Researchers from the Harvard John A. Paulson School of Engineering and Applied Science (SEAS) suggest that early Mars may have been warmed intermittently by a powerful greenhouse effect. In a paper published in Geophysical Research Letters, researchers found that interactions between methane, carbon dioxide and hydrogen in the early Martian atmosphere may have created warm periods when the planet could support liquid water on the surface.

(i don't see link to the paper.)

[Ned W]

Jai, again, feedbacks like water vapor are handled differently than forcings.  They are not included in the calculated values for forcings because they aren't forcings. 

One could move a bunch of the net effects of feedbacks over onto the forcings side.  That would make the forcings larger, but climate sensitivity would then become smaller to compensate.  It would have no effect on future warming rates.

As ASLR said, it's better not to arbitrarily redefine terms and concepts that have existing meanings within the field.  The distinction between feedback and forcing isn't absolute, but at the level that ASIF operates at, the distinction is clear enough.

[Ned W]

One could move a bunch of the net effects of feedbacks over onto the forcings side.  That would make the forcings larger, but climate sensitivity would then become smaller to compensate.  It would have no effect on future warming rates.

I posted this in the other thread, but it's the perfect explanation of the above:



Kiehl, J. T. (1992) "Atmospheric General Circulation Modeling."  Chapter 10 in Trenberth, K. (ed), Climate System Modeling.  Cambridge University Press.

dT = lambda * G

G is the sum of forcings.  If you change the formalism to increase G and decrease lambda, it has no effect on dT.

[AbruptSLR]

Readers should remain cautious of arbitrary redefinitions of CO2e (CO2eq) in terms of "total anthropogenic" radiative forcings

I agree that there's enough confusion over CO2eq already, and we should stick closely with the "traditional" definitions. 

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. 

Martin Melles, Julie Brigham-Grette, Pavel S. Minyuk, Norbert R. Nowaczyk, Volker Wennrich, Robert M. DeConto, Patricia M. Anderson, Andrei A. Andreev, Anthony Coletti, Timothy L. Cook, Eeva Haltia-Hovi, Maaret Kukkonen, Anatoli V. Lozhkin, Peter Rosén, Pavel Tarasov, Hendrik Vogel & Bernd Wagner (20 July 2012), "2.8 Million Years of Arctic Climate Change from Lake El’gygytgyn, NE Russia", Science, Vol. 337 no. 6092 pp. 315-320, DOI: 10.1126/science.1222135

http://science.sciencemag.org/content/337/6092/315
&
https://www.geo.umass.edu/climate/papers2/Melles_Science2012.pdf


ABSTRACT: "The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El’gygytgyn in northeastern (NE) Russia provides a continuous, high-resolution record from the Arctic, spanning the past 2.8 million years. This core reveals numerous “super interglacials” during the Quaternary; for marine benthic isotope stages (MIS) 11c and 31, maximum summer temperatures and annual precipitation values are ~4° to 5°C and ~300 millimeters higher than those of MIS 1 and 5e. Climate simulations show that these extreme warm conditions are difficult to explain with greenhouse gas and astronomical forcing alone, implying the importance of amplifying feedbacks and far field influences. The timing of Arctic warming relative to West Antarctic Ice Sheet retreats implies strong interhemispheric climate connectivity."

Edit: I note that the attached plot is a Danish plot & uses Danish names, and also I note that to convert from the local temperature variations shown into GMSTA, one needs to divide the indicates temperatures by an Antarctica Amplification factor of from 2 to 3.

[Ned W]

As advanced Earth System Models, ESMs, do not need to use the concept of CO2e,

Well, nobody really needs the concept of CO2e -- one can just sum up the forcings and leave it at that, in W m-2, rather than fake CO2 ppmv. 

But insofar as people do choose to use the concept of CO2e, it's probably best to stick with the way it's used in the field.

[Ned W]

which did not include high negative forcings from anthropogenic aerosols that can leave the atmosphere within months of their emissions

If one wants a version of CO2eq that excludes short-lived forcings like aerosols and tropospheric ozone, one can use the standard greenhouse-gas definition of CO2eq.  But in the other thread you were arguing for the inclusion of tropospheric ozone, whose residence time is on the order of weeks to a month or so.  So I dug up the total-anthro version of CO2eq, which includes ozone (and everything else).

Either way is fine with me.  We can go with the definition of CO2eq that is narrowly focused on well-mixed greenhouse gases, or we can go with the definition that broadly includes all forcings.  But let's not make up a new version that includes all the positive forcings while excluding all the negative ones.

[AbruptSLR]

If one wants a version of CO2eq that excludes short-lived forcings like aerosols and tropospheric ozone, one can use the standard greenhouse-gas definition of CO2eq.  But in the other thread you were arguing for the inclusion of tropospheric ozone, whose residence time is on the order of weeks to a month or so.

Oversimplifying these issues can be counter productive as illustrated by the Sherwood (2015) presentation focuses on the influence of aerosols and tropospheric ozone on the radiative forcing over the Southern Ocean, which were not previously recognized.  The complexities of issues such as the interactions between forcing agents and the spatial distribution of impacts (including polar amplification) can lead both scientists and decision makers to err on the side of least drama and to downplay the typically high climate sensitivities identified by the most advanced ESMs:

Steven Sherwood (2015) "Radiosonde trends and a (perhaps) unexpected aerosol forcing mechanism", Ringberg workshop:

http://www.mpimet.mpg.de/fileadmin/atmosphaere/WCRP_Grand_Challenge_Workshop/Ringberg_2015/Talks/Sherwood_24032015.pdf


The first image shows that the cloud cover over the Southern Ocean is particularly susceptible to sulfate-induced changes in cloud radiative effect from a doubling of CO₂.

The second image shows a 7%/decade increase in Southern Ocean cloud condensation nuclei (CNN) from 1990 to 2005.

The third image shows observed data from the Southern Ocean comparing aerosol optical depth, AOD, to rainfall rates, cloud top pressure, cloud top temperature and cloud fraction and concludes that at low values of CNN that cloud fraction is proportional to CCN.

The fourth image summarizes Shewood Ringberg (2015) findings that since 1979 the Southern Ocean cloud fraction has increased by 10% per decade largely due to an increase in wind strength associated with the ozone hole over Antarctic; which has resulted in a zonal mean trend decrease of annual mean reflected shortwave forcing of about 1 W/m² per decade.

Extract:
"- We should not assume aerosol effects can only be in the northern hemisphere.

- Possible that greenhouse forcing in SH-extratropics has been negated by aerosol (or sea-ice) increases for some time. Deserves further attention?

- Would help to explain both (a) sluggish recent warming and (b) weird SH-NH contrast since 1979.

- Ozone depletion is the most likely culprit for the wind increase—would make this a rapid adjustment to ozone forcing."

[AbruptSLR]

Well, nobody really needs the concept of CO2e -- one can just sum up the forcings and leave it at that, in W m-2, rather than fake CO2 ppmv. 

Understanding effective radiative forcing is a good idea as expressed in the linked reference that provides a summary of the latest IPCC thinking on anthropogenic aerosols & their impact on global climate.  The reference states: "From 1850 to 2010, anthropogenic aerosols brought about a decrease of ∼2.53 K and ∼0.20 mm day−1 in global annual mean surface temperature and precipitation, respectively."  Therefore, as we are already over a +1C value of GMSTA, if we dropped back to 1850 levels of aerosols we might increase GMSTA to over +3.5C, even if we dropped to zero emissions of CO2 by switching 100% to solar & wind power today:

Hua Zhang, Shuyun Zhao, Zhili Wang, Xiaoye Zhang & Lianchun Song (25 January 2016), "The updated effective radiative forcing of major anthropogenic aerosols and their effects on global climate at present and in the future", International Journal of Climatology, DOI: 10.1002/joc.4613

http://onlinelibrary.wiley.com/doi/10.1002/joc.4613/abstract

Abstract: "The effective radiative forcing (ERF), as newly defined in the Intergovernmental Panel on Climate Change's Fifth Assessment Report (IPCC AR5), of three anthropogenic aerosols [sulphate (SF), black carbon (BC), and organic carbon (OC)] and their comprehensive climatic effects were simulated and discussed, using the updated aerosol-climate online model of BCC_AGCM2.0.1_CUACE/Aero. From 1850 to 2010, the total ERF of these anthropogenic aerosols was −2.49 W m−2, of which the aerosol–radiation interactive ERF (ERFari) and aerosol–cloud interactive ERF (ERFaci) were ∼ −0.30 and −2.19 W m−2, respectively. SF was the largest contributor to the total ERF, with an ERF of −2.37 W m−2. The ERF of BC and OC were 0.12 and −0.31 W m−2, respectively. From 1850 to 2010, anthropogenic aerosols brought about a decrease of ∼2.53 K and ∼0.20 mm day−1 in global annual mean surface temperature and precipitation, respectively. Surface cooling was most obvious over mid- and high latitudes in the northern hemisphere (NH). Precipitation change was most pronounced near the equator, with decreased and increased rainfall to the north and south of the equator, respectively; this might be largely related to the enhanced Hadley Cell in the NH. Relative humidity near surface was increased, especially over land, due to surface cooling induced by anthropogenic aerosols. Cloud cover and water path were increased, especially in or near the source regions of anthropogenic aerosols. Experiments based on the Representative Concentration Pathway (RCP) 4.5 given in IPCC AR5 shows the dramatic decrease in three anthropogenic aerosols in 2100 will lead to an increase of ∼2.06 K and 0.16 mm day−1 in global annual mean surface temperature and precipitation, respectively, compared with those in 2010."

[AbruptSLR]

I feel that it is premature to assume that we know the effective radiative forcings for different agents, when researchers like Myhre et al (2015) cann't even cut the uncertainty associated with TCR in half before 2030.

Gunnar Myhre, Olivier Boucher, François-Marie Bréon, Piers Forster & Drew Shindell, (2015), "Declining uncertainty in transient climate response as CO2 forcing dominates future climate change", Nature Geoscience, doi:10.1038/ngeo2371

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2371.html

Abstract: "Carbon dioxide has exerted the largest portion of radiative forcing and surface temperature change over the industrial era, but other anthropogenic influences have also contributed. However, large uncertainties in total forcing make it difficult to derive climate sensitivity from historical observations. Anthropogenic forcing has increased between the Fourth and Fifth Assessment Reports of the Intergovernmental Panel of Climate Change (IPCC) although its relative uncertainty has decreased. Here we show, based on data from the two reports, that this evolution towards lower uncertainty can be expected to continue into the future. Because it is easier to reduce air pollution than carbon dioxide emissions and because of the long lifetime of carbon dioxide, the less uncertain carbon dioxide forcing is expected to become increasingly dominant. Using a statistical model, we estimate that the relative uncertainty in anthropogenic forcing of more than 40% quoted in the latest IPCC report for 2011 will be almost halved by 2030, even without better scientific understanding. Absolute forcing uncertainty will also decline for the first time, provided projected decreases in aerosols occur. Other factors being equal, this stronger constraint on forcing will bring a significant reduction in the uncertainty of observation-based estimates of the transient climate response, with a 50% reduction in its uncertainty range expected by 2030."

[AbruptSLR]

I provide the following linked passage from AR4, for those who do not understand the difference between radiative forcing and effective radiative forcing:

Title: "2.8.5 Efficacy and Effective Radiative Forcing"

https://ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-8-5.html

Extract: "Efficacy (E) is defined as the ratio of the climate sensitivity parameter for a given forcing agent (λi) to the climate sensitivity parameter for CO2 changes, that is, Ei = λi / λCO2 (Joshi et al., 2003; Hansen and Nazarenko, 2004). Efficacy can then be used to define an effective RF (= Ei RFi) (Joshi et al., 2003; Hansen et al., 2005). For the effective RF, the climate sensitivity parameter is independent of the mechanism, so comparing this forcing is equivalent to comparing the equilibrium global mean surface temperature change. That is, ΔTs = λCO2 x Ei x RFi Preliminary studies have found that efficacy values for a number of forcing agents show less model dependency than the climate sensitivity values (Joshi et al., 2003). Effective RFs have been used get one step closer to an estimator of the likely surface temperature response than can be achieved by using RF alone (Sausen and Schumann, 2000; Hansen et al., 2005; Lohmann and Feichter, 2005). Adopting the zero-surface-temperature-change RF, which has efficacies closer to unity, may be another way of achieving similar goals (see Section 2.8.3). This section assesses the efficacy associated with stratospherically adjusted RF, as this is the definition of RF adopted in this chapter (see Section 2.2). Therefore, cloud-aerosol interaction effects beyond the cloud albedo RF are included in the efficacy term. The findings presented in this section are from an assessment of all the studies referenced in the caption of Figure 2.19, which presents a synthesis of efficacy results. As space is limited not all these studies are explicitly discussed in the main text."

Caption for the attached image: "Figure 2.19. Efficacies as calculated by several GCM models for realistic changes in RF agents. Letters are centred on efficacy value and refer to the literature study that the value is taken from (see text of Section 2.8.5 for details and further discussion). In each RF category, only one result is taken per model or model formulation. Cloud-albedo efficacies are evaluated in two ways: the standard letters include cloud lifetime effects in the efficacy term and the letters with asterisks exclude these effects. Studies assessed in the figure are: a) Hansen et al. (2005); b) Wang et al. (1991); c) Wang et al. (1992); d) Govindasamy et al. (2001b); e) Lohmann and Feichter (2005); f) Forster et al. (2000); g) Joshi et al. (2003; see also Stuber et al., 2001a); h) Gregory et al. (2004); j) Sokolov (2006); k) Cook and Highwood (2004); m) Mickley et al. (2004); n) Rotstayn and Penner (2001); o) Roberts and Jones (2004) and p) Williams et al. (2001a)."

[Ned W]

to err on the side of least drama

There's already a thread for that over here:

Topic: Conservative Scientists & its Consequences

Let's not start down that same road in this one.

[Ned W]

There's a very nice history of the term "CO2e" and its usage here:

Gohar, LK and KP Shine.  2007.  Equivalent CO2 and its use in understanding the climate effects of increased greenhouse gas concentrations.  Weather 62(7): 307-311.

Gohar and Shine include a figure showing the evolution of CO2e over time.  It includes four different series: 

1. CO2 alone
2. the "Kyoto gases" (CO2, CH4, N2O, SF6, HFCs, and PFCs)
3. the "Kyoto + Montreal gases" (an expanded version that includes more gases regulated under the Montreal Protocol)
4. an early attempt to make a "total anthropogenic forcings" version of CO2e, which included all of the above plus aerosols and ozone. 

I've updated that figure by superimposing the more recent calculations of CO2e:



My lines for CO2 alone, Kyoto GHG, and Kyoto + Montreal GHG fall right on top of the equivalent lines from Gohar and Shine 2007.  The "sum of anthro forcings" line (dark orange) is significantly higher than the "GHGs + aerosols + ozone" line from Gohar and Shine 2007 (dashed gray).  I think this is mostly due to better understanding of the magnitude of the ozone and aerosol forcings since GS2007 was published, though the dark orange line does include some additional minor forcings that might have been omitted from GS2007.

Note that adding in the Etminan 2016 updates would raise the orange, yellow, and blue lines by about 10 ppm.

Anyway, the paper presents a nice history of CO2e and in particular the role of the Stern Review.

[Ned W]

Mostly I've been focusing on forcing from the so-called "well-mixed" greenhouse gases.  Here's a look at the net effects of the most important "other" (non-WMGHG) pollutants on radiative forcing.  This graph shows the forcing from aerosols (total direct effect) and tropospheric ozone, under RCP 6 and RCP 8.5:



In general, the two pollutants have been mostly counteracting each other.  Aerosols cool the planet while tropospheric ozone (from photochemical reactions with smog etc.) warm the planet.  The sum of the two (aerosols + ozone) is shown below:



RCP 6 assumes that the net effect right now is a slight cooling, while RCP 8.5 assumes that it's a slight warming.  Both assume that over the next few decades, aerosols will be cleaned up faster than tropospheric ozone pollution, contributing about 0.1 to 0.15 W m-2 of each scenario's anticipated warming by 2050.

There is a lot of uncertainty in these estimates.  Faster reduction in aerosols would increase the rate of warming, while faster reduction in ozone would decrease warming.

[AbruptSLR]

I note that the RCP scenarios do not consider the Trump Administration's rollback on HFC regulations; which per the linked article could cumulatively add 9.5 billion tons of HFC to the atmosphere by 2050:

Title: "Economy-Wide Gains, 9.5 Billion Tons HFC Emissions At Risk From U.S. Court of Appeals Ruling

https://www.forbes.com/sites/energyinnovation/2017/08/22/economy-wide-gains-9-5-billion-tons-hfc-emissions-at-risk-from-u-s-court-of-appeals-ruling/#eaf923e51227

[AbruptSLR]

The linked reference makes the following statement: "Our key finding based on the updated model simulations is that there is stronger positive radiative forcing of aerosols and ozone over the past 25 years than reported in IPCC AR5."

Gunnar Myhre et. al. (2017), "Multi-model simulations of aerosol and ozone radiative forcing due to anthropogenic emission changes during the period 1990–2015", Atmos. Chem. Phys., 17, 2709–2720, doi:10.5194/acp-17-2709-2017

https://www.atmos-chem-phys.net/17/2709/2017/acp-17-2709-2017.pdf

Abstract: "Over the past few decades, the geographical distribution of emissions of substances that alter the atmospheric energy balance has changed due to economic growth and air pollution regulations. Here, we show the resulting changes to aerosol and ozone abundances and their radiative forcing using recently updated emission data for the period 1990–2015, as simulated by seven global atmospheric composition models.  The models broadly reproduce large-scale changes in surface aerosol and ozone based on observations (e.g. -1 to -3%yr^-1 in aerosols over the USA and Europe). The global mean radiative forcing due to ozone and aerosol changes over the 1990–2015 period increased by +0.17+/-0.08Wm^-2, with approximately one-third due to ozone. This increase is more strongly positive than that reported in IPCC AR5. The main reasons for the increased positive radiative forcing of aerosols over this period are the substantial reduction of global mean SO₂ emissions, which is stronger in the new emission inventory compared to that used in the IPCC analysis, and higher black carbon emissions."

[jai mitchell]

There is a lot of uncertainty in these estimates.  Faster reduction in aerosols would increase the rate of warming, while faster reduction in ozone would decrease warming.

Those are great graphics. 

There is a lot of uncertainty in the emissions rates going forward but there is even MORE uncertainty in the total forcing impact of SO2, including impacts on cloud physics and on the ENSO and AMO. 

[jai mitchell]

Well, nobody really needs the concept of CO2e -- one can just sum up the forcings and leave it at that, in W m-2, rather than fake CO2 ppmv. 

Understanding effective radiative forcing is a good idea as expressed in the linked reference that provides a summary of the latest IPCC thinking on anthropogenic aerosols & their impact on global climate.  The reference states: "From 1850 to 2010, anthropogenic aerosols brought about a decrease of ∼2.53 K and ∼0.20 mm day−1 in global annual mean surface temperature and precipitation, respectively."  Therefore, as we are already over a +1C value of GMSTA, if we dropped back to 1850 levels of aerosols we might increase GMSTA to over +3.5C, even if we dropped to zero emissions of CO2 by switching 100% to solar & wind power today:

Hua Zhang, Shuyun Zhao, Zhili Wang, Xiaoye Zhang & Lianchun Song (25 January 2016), "The updated effective radiative forcing of major anthropogenic aerosols and their effects on global climate at present and in the future", International Journal of Climatology, DOI: 10.1002/joc.4613

http://onlinelibrary.wiley.com/doi/10.1002/joc.4613/abstract

Abstract: "The effective radiative forcing (ERF), as newly defined in the Intergovernmental Panel on Climate Change's Fifth Assessment Report (IPCC AR5), of three anthropogenic aerosols [sulphate (SF), black carbon (BC), and organic carbon (OC)] and their comprehensive climatic effects were simulated and discussed, using the updated aerosol-climate online model of BCC_AGCM2.0.1_CUACE/Aero. From 1850 to 2010, the total ERF of these anthropogenic aerosols was −2.49 W m−2, of which the aerosol–radiation interactive ERF (ERFari) and aerosol–cloud interactive ERF (ERFaci) were ∼ −0.30 and −2.19 W m−2, respectively. SF was the largest contributor to the total ERF, with an ERF of −2.37 W m−2. The ERF of BC and OC were 0.12 and −0.31 W m−2, respectively. From 1850 to 2010, anthropogenic aerosols brought about a decrease of ∼2.53 K and ∼0.20 mm day−1 in global annual mean surface temperature and precipitation, respectively. Surface cooling was most obvious over mid- and high latitudes in the northern hemisphere (NH). Precipitation change was most pronounced near the equator, with decreased and increased rainfall to the north and south of the equator, respectively; this might be largely related to the enhanced Hadley Cell in the NH. Relative humidity near surface was increased, especially over land, due to surface cooling induced by anthropogenic aerosols. Cloud cover and water path were increased, especially in or near the source regions of anthropogenic aerosols. Experiments based on the Representative Concentration Pathway (RCP) 4.5 given in IPCC AR5 shows the dramatic decrease in three anthropogenic aerosols in 2100 will lead to an increase of ∼2.06 K and 0.16 mm day−1 in global annual mean surface temperature and precipitation, respectively, compared with those in 2010."

My god, I forgot about that.  Wasn't that paper somewhat challenged by the climate scientific body, I mean ascribing a 2C increase SOLELY to the removal of SO2 from our emission profile and adding that to the current warming ~1.1C AND locked-in warming from current GHG forcing ~0.6C AND future warming from carbon cycle feedbacks ~1.3C by 2100 (this is a very low estimate) would mean that we have already locked in a +5.0C world at today's GHG levels!

Talk me down ASLR!!!! IMA bout 2 jump. . .

[Ned W]

Well, this is a case where it helps to look at the big picture.  That Zhang et al. (2016) estimate of aerosol forcing was a fairly extreme outlier.  It's far outside the range of the vast majority of other studies, far outside the IPCC's range, and far outside the range of more recently published (and more comprehensive) work using GISS Model E2 (Nazarenko et al. 2017). 

Instead, I would recommend reading Ulrike Lohmann's (2017) discussion of the state of the science on aerosol forcing:

Lohmann, U. 2017. Why does knowledge of past aerosol forcing matter for future climate change?  Atmospheres 122(9): 5021-5023.

Lohmann's figure 1 gives a nice view of the results of 57 papers on aerosol forcing (including both Zhang et al. 2016 and Nazarenko et al. 2017).  I've updated it to show the mean of the 57 studies, and also the IPCC AR5 best estimate and credible range:



Only two other papers of the 57 (only one in the past decade) have reported as extreme an aerosol forcing as Zhang et al.  Meanwhile, here's what Nazarenko (2017) finds:

* In an atmosphere-only model, the sum of the direct and indirect radiative forcings (ERFari+aci) ranges between about −0.45 W m−2 and −1.1 W m−2, which is nicely inside the IPCC range and overlaps well with the IPCC's best estimate (0.8 )

* In a coupled ocean-atmosphere model, both the direct and indirect forcings are substantially reduced, ranging from −0.3 to −0.7 W m−2.  The authors explain this as follows:

Climate change has thus mitigated the indirect effect that the aerosol emissions would have produced, via its alteration in cloud properties. From the previous discussion, a likely candidate in this regard is the aerosol effect on tropical upper tropospheric clouds [...] associated with the increased relative humidity available in that region as climate warms.

[Daniel B.]

Well, this is a case where it helps to look at the big picture.  That Zhang et al. (2016) estimate of aerosol forcing was a fairly extreme outlier.  It's far outside the range of the vast majority of other studies, far outside the IPCC's range, and far outside the range of more recently published (and more comprehensive) work using GISS Model E2 (Nazarenko et al. 2017). 

Instead, I would recommend reading Ulrike Lohmann's (2017) discussion of the state of the science on aerosol forcing:

Lohmann, U. 2017. Why does knowledge of past aerosol forcing matter for future climate change?  Atmospheres 122(9): 5021-5023.

Lohmann's figure 1 gives a nice view of the results of 57 papers on aerosol forcing (including both Zhang et al. 2016 and Nazarenko et al. 2017).  I've updated it to show the mean of the 57 studies, and also the IPCC AR5 best estimate and credible range:



Only two other papers of the 57 (only one in the past decade) have reported as extreme an aerosol forcing as Zhang et al.  Meanwhile, here's what Nazarenko (2017) finds:

* In an atmosphere-only model, the sum of the direct and indirect radiative forcings (ERFari+aci) ranges between about −0.45 W m−2 and −1.1 W m−2, which is nicely inside the IPCC range and overlaps well with the IPCC's best estimate (0.8 )

* In a coupled ocean-atmosphere model, both the direct and indirect forcings are substantially reduced, ranging from −0.3 to −0.7 W m−2.  The authors explain this as follows:

Climate change has thus mitigated the indirect effect that the aerosol emissions would have produced, via its alteration in cloud properties. From the previous discussion, a likely candidate in this regard is the aerosol effect on tropical upper tropospheric clouds [...] associated with the increased relative humidity available in that region as climate warms.

What is interesting in the Zhang, et. al. paper is that their effective radiative forcing for aerosols alone is lower than most, but their aerosol-cloud interaction is higher (more negative).  This recetn paper by Unger, et. al. shows greater aerosol influences that the average, although not a much as Zhang, et. al.

http://pubs.rsc.org/en/content/articlelanding/2017/fd/c7fd00033b#!divAbstract

[AbruptSLR]

Talk me down ASLR!!!! IMA bout 2 jump. . .

jai,
What people really care about is how big will the climate impacts be and how fast will they occur.  Thus people are really interested in effective radiative forcing, ERF, rather than RF (see the following linked lecture visuals & attached image) due to the combination of forcings and feedbacks.

Title: "Forcing and feedbacks", from Climate Dynamics (Summer Semester 2017) by J. Mulmenstadt

https://home.uni-leipzig.de/~jmuelmen/lehre/cd/cd-2017/lec11.pdf

The link makes it clear that considering the fast response from CO₂ is relatively straight forward, but the impacts from slow response feedbacks, particularly from the ocean (note that OHC is higher than AR5 assumed, as the oceans have been absorbing extra heat since 1750) and ENSO can rapidly increase effective values of ECS up to the range of 4 to 5C.  If so then the Zhang et al (2016) values (which include feedbacks) are not 'outliers' but rather are an indication that the effective ECS this century is higher than other researchers are assuming.  Furthermore, the attached image illustrates how ERF can be determined but due to uncertainties accurate estimates of ERF will take decades, and by that time we may have crossed several tipping points if AR5 is erring on the side of least drama

Best,
ASLR

[AbruptSLR]

Further to the point in my last post that 267 years of ocean warming is triggering slow response feedbacks (particularly those associated with the ENSO and the Southern Ocean), per the following op/ed piece: "Earth’s energy imbalance (EEI): the difference between incoming solar radiation and outgoing longwave (thermal) radiation." Furthermore, ocean heat content, OHC, is the dominate measure of EEI, and therefore should be reported in the output of CMIP6 as per the second cited reference Cheng et al (2017) the measured OHC of the upper 2,000 m of ocean since 1960 is actually 13% higher than assumed in CMIP5 {& the increase in OHC (including ice melt) is 18% than that for the upper 2,000 m].

Given the vital importance of this OHC with regard to 'slow response' feedback mechanisms such as the ice-climate feedback mechanism, the ESLD assumptions of CMIP5 and AR5 will likely extract a heavy price from future generations.

Title: "Taking the Pulse of the Planet"

https://eos.org/opinions/taking-the-pulse-of-the-planet?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz091517

Extract: "Ocean heat content and sea level rise measurements may provide a more reliable answer than atmospheric measurements
…
Since 2006, the Argo program of autonomous profiling floats has provided near-global coverage of the upper 2,000 meters of the ocean over all seasons [Riser et al., 2016]. In addition, climate scientists have been able to quantify the ocean temperature changes back to 1960 on the basis of the much sparser historical instrument record [Cheng et al., 2017].

From these temperature measurements, scientists extract OHC. These analyses show that during 2015 and 2016, the heat stored in the upper 2,000 meters of the world ocean reached a new 57-year record high (Figure 1). This heat storage amounts to an increase of 30.4 × 1022 Joules (J) since 1960 [Cheng et al., 2017], equal to a heating rate of 0.33 Watts per square meter (W m−2) averaged over Earth’s entire surface—0.61 W m−2 after 1992. Improved measurements have revised these values upward by 13% compared with the results of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Rhein et al., 2013].

Studies show that taking the full ocean depth, ice melt, and other factors into account, Earth is estimated to have gained 0.40 ± 0.09 W m−2 since 1960 and 0.72 W m−2 since 1992 [Cheng et al., 2017]—18% higher than for the top 2,000-meter OHC alone.
…
The EEI has implications for the future and should be fundamental in guiding future energy policy and decisions; it is the heartbeat of the planet. Changes in OHC, the dominant measure of EEI, should be a fundamental metric along with SLR.

As we continue to scrutinize the fidelity of specific climate models, it is critical to validate their energetic imbalances as well as their depiction of GMST. The fact that the Coupled Model Intercomparison Project Phase 5 (CMIP5) ensemble mean accurately represents observed global OHC changes [Cheng et al., 2016] is critical for establishing the reliability of climate models for long-term climate change projections.

Consequently, we recommend that both the EEI and OHC be listed as output variables in the CMIP6 models, in addition to SLR and GMST. This vital sign informs societal decisions about adaptation to and mitigation of climate change [Trenberth et al., 2016]."

See also the associated reference:

Lijing Cheng, Kevin E. Trenberth, John Fasullo, Tim Boyer, John Abraham & Jiang Zhu (10 Mar 2017), "Improved estimates of ocean heat content from 1960 to 2015", Science Advances, Vol. 3, no. 3, e1601545, DOI: 10.1126/sciadv.1601545

http://advances.sciencemag.org/content/3/3/e1601545

Abstract: "Earth’s energy imbalance (EEI) drives the ongoing global warming and can best be assessed across the historical record (that is, since 1960) from ocean heat content (OHC) changes. An accurate assessment of OHC is a challenge, mainly because of insufficient and irregular data coverage. We provide updated OHC estimates with the goal of minimizing associated sampling error. We performed a subsample test, in which subsets of data during the data-rich Argo era are colocated with locations of earlier ocean observations, to quantify this error. Our results provide a new OHC estimate with an unbiased mean sampling error and with variability on decadal and multidecadal time scales (signal) that can be reliably distinguished from sampling error (noise) with signal-to-noise ratios higher than 3. The inferred integrated EEI is greater than that reported in previous assessments and is consistent with a reconstruction of the radiative imbalance at the top of atmosphere starting in 1985. We found that changes in OHC are relatively small before about 1980; since then, OHC has increased fairly steadily and, since 1990, has increasingly involved deeper layers of the ocean. In addition, OHC changes in six major oceans are reliable on decadal time scales. All ocean basins examined have experienced significant warming since 1998, with the greatest warming in the southern oceans, the tropical/subtropical Pacific Ocean, and the tropical/subtropical Atlantic Ocean. This new look at OHC and EEI changes over time provides greater confidence than previously possible, and the data sets produced are a valuable resource for further study."

[jai mitchell]

RE: Aerosols

*cough*

http://iopscience.iop.org/article/10.1088/1748-9326/aa5dd8

Here we show evidence from observations and climate models that external forcing largely governs decadal GMST variations in the historical record with internally generated variations playing a secondary role, except during those periods of IPO extremes. . . The most recent warming hiatus apparent in observations occurred largely through cooling from a negative IPO extreme that overwhelmed the warming from external forcing.

and

http://www.nature.com/nclimate/journal/v6/n10/full/nclimate3058.html

The prevailing view is that this negative PDO occurred through internal variability.  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. . . 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.

note:  This is also directly related to ASLR's post above as negative IPO absorbs much more forcing in the ocean and +IPO returns this heat energy to the atmosphere.

[Ned W]

What people really care about is how big will the climate impacts be and how fast will they occur.  Thus people are really interested in effective radiative forcing, ERF, rather than RF

If you read Lohmann, all of the reported forcings in Figure 1 (reposted below) are ERFs. 

Likewise, the reported aerosol forcings from Nazarenko (2017) are ERF = -0.3 to -0.74.

Hope that helps.

Well, this is a case where it helps to look at the big picture.  That Zhang et al. (2016) estimate of aerosol forcing was a fairly extreme outlier.  It's far outside the range of the vast majority of other studies, far outside the IPCC's range, and far outside the range of more recently published (and more comprehensive) work using GISS Model E2 (Nazarenko et al. 2017). 

Instead, I would recommend reading Ulrike Lohmann's (2017) discussion of the state of the science on aerosol forcing:

Lohmann, U. 2017. Why does knowledge of past aerosol forcing matter for future climate change?  Atmospheres 122(9): 5021-5023.

Lohmann's figure 1 gives a nice view of the results of 57 papers on aerosol forcing (including both Zhang et al. 2016 and Nazarenko et al. 2017).  I've updated it to show the mean of the 57 studies, and also the IPCC AR5 best estimate and credible range:



Only two other papers of the 57 (only one in the past decade) have reported as extreme an aerosol forcing as Zhang et al.  Meanwhile, here's what Nazarenko (2017) finds:

* In an atmosphere-only model, the sum of the direct and indirect radiative forcings (ERFari+aci) ranges between about −0.45 W m−2 and −1.1 W m−2, which is nicely inside the IPCC range and overlaps well with the IPCC's best estimate (0.8 )

* In a coupled ocean-atmosphere model, both the direct and indirect forcings are substantially reduced, ranging from −0.3 to −0.7 W m−2.  The authors explain this as follows:

Climate change has thus mitigated the indirect effect that the aerosol emissions would have produced, via its alteration in cloud properties. From the previous discussion, a likely candidate in this regard is the aerosol effect on tropical upper tropospheric clouds [...] associated with the increased relative humidity available in that region as climate warms.

[Ned W]

erring on the side of least drama

I'd once again like to politely request that you leave that shtick in one of the many other threads where it's already commonplace, e.g.,

Topic: Conservative Scientists & its Consequences

Part of the reason I started this thread was to get away from the sneering and insults that have been proliferating elsewhere.  In my experience scientists generally try to err on the side of least ERROR, and it is polite to assume that everyone, even those with whom we disagree, are following that in good faith. 

Obviously I can't enforce decorum and assumption of good faith here; this is just a polite request.

[AbruptSLR]

Obviously I can't enforce decorum and assumption of good faith here; this is just a polite request.

While Hayhoe and Kopp take no offense at the use of the phase 'erring on the side of least drama' (see below) to characterize a systematic tendency in consensus climate science to underestimate potential future climate impacts of global warming; I have no problem with complying with your polite request:

Katharine Hayhoe and Robert E Kopp (2016), "What surprises lurk within the climate system?", Environ. Res. Lett. 11 120202, https://doi.org/10.1088/1748-9326/11/12/120202

http://iopscience.iop.org/article/10.1088/1748-9326/11/12/120202
http://iopscience.iop.org/article/10.1088/1748-9326/11/12/120202/pdf

Extract: "… global climate models have a tendency to underestimate—both in the global mean and especially at the poles—the magnitude of warming in response to higher CO2 levels. This underestimation hints at potential shifts in the state of the climate system that could increase climate sensitivity in a warmer world.  A bias towards under-estimation is evident in predicting more recent rates of sea level rise, and other physical changes in the climate system, while scientific assessments over the past few decades have demonstrated a systematic tendency towards 'erring on the side of least drama'. Together, these limitations emphasize the need to stress-test ESMs against the paleoclimate record, and to build models and conduct simulations that explore potential catastrophic events and states of the world with low or unknown probability but profound consequences."

[jai mitchell]

erring on the side of least drama

I'd once again like to politely request that you leave that shtick in one of the many other threads where it's already commonplace, e.g.,

Topic: Conservative Scientists & its Consequences

Part of the reason I started this thread was to get away from the sneering and insults that have been proliferating elsewhere.  In my experience scientists generally try to err on the side of least ERROR, and it is polite to assume that everyone, even those with whom we disagree, are following that in good faith. 

Obviously I can't enforce decorum and assumption of good faith here; this is just a polite request.

There are two basic categories of error in science.

The tendency to have one kind of error is much more likely than the other in science.

To state that the reason that this well documented error bias is cultural (among scientists) is within the auspices of sociologists who study science.

To find and state that the guiding cultural driver that causes scientists to have an overwhelming prevalence of Type II errors (see: http://sciencepolicy.colorado.edu/admin/publication_files/2014.34.pdf ) is due to an aversion of the 'drama' (really: a risk to credibility) caused by having a Type I error is not an insult or 'dig', it is a function of the studies of social sciences.

[AbruptSLR]

Obviously, the issues raised in this thread do not represent 'settled science' as indicated by the linked reference about CMIP6's efforts to better quantify these effects:

Collins et al (2017), "AerChemMIP: quantifying the effects of chemistry and aerosols in CMIP6", Geosci. Model Dev., 10, 585–607, doi:10.5194/gmd-10-585-2017

https://www.geosci-model-dev.net/10/585/2017/gmd-10-585-2017.pdf

Abstract: "Abstract. The Aerosol Chemistry Model Intercomparison Project (AerChemMIP) is endorsed by the Coupled-Model Intercomparison Project 6 (CMIP6) and is designed to quantify the climate and air quality impacts of aerosols and chemically reactive gases. These are specifically near-term climate forcers (NTCFs: methane, tropospheric ozone and aerosols, and their precursors), nitrous oxide and ozone depleting halocarbons. The aim of AerChemMIP is to answer four scientific questions.

1. How have anthropogenic emissions contributed to global radiative forcing and affected regional climate over the historical period?

2. How might future policies (on climate, air quality and land use) affect the abundances of NTCFs and their climate impacts?

3. How do uncertainties in historical NTCF emissions affect radiative forcing estimates?

4. How important are climate feedbacks to natural NTCF emissions, atmospheric composition, and radiative effects?

These questions will be addressed through targeted simulations with CMIP6 climate models that include an interactive representation of tropospheric aerosols and atmospheric chemistry. These simulations build on the CMIP6 Diagnostic, Evaluation and Characterization of Klima (DECK) experiments, the CMIP6 historical simulations, and future projections performed elsewhere in CMIP6, allowing the contributions from aerosols and/or chemistry to be quantified.  Specific diagnostics are requested as part of the CMIP6 data request to highlight the chemical composition of the atmosphere, to evaluate the performance of the models, and to understand differences in behaviour between them."

[AbruptSLR]

To reiterate the point of my last post, the linked reference concludes that there is a lot of uncertainty associated with model projections of the impacts of aerosols and chemically reactive gases:

Heyn, I., K. Block, J. Mülmenstädt, E. Gryspeerdt, P. Kühne, M. Salzmann, and J. Quaas (2017), Assessment of simulated aerosol effective radiative forcings in the terrestrial spectrum, Geophys. Res. Lett., 44, doi:10.1002/2016GL071975.

https://spiral.imperial.ac.uk/bitstream/10044/1/43885/7/Heyn_et_al-2017-Geophysical_Research_Letters.pdf

Extract: "The analysis in this paper relies on global climate models. Beyond climate model results, very little is known quantitatively about the global forcing due to the reaction of ice-phase, mixed-phase, and deep convective clouds to aerosol perturbations. A truly realistic estimate, or even just reliable uncertainty interval, thus requires substantial further research, especially for effects in the terrestrial spectrum. Observational estimates are urgently needed. The current state of the art, however, suggests that the effective forcing in the terrestrial spectrum is either small, or, for models where it is large, is accompanied by a large negative effective forcing in the solar spectrum."

[AbruptSLR]

The first linked reference studies dynamical cloud response to aerosol forcing and concludes: "The dynamical cloud response is closely linked to the meridional displacement of the Hadley Cell that, in turn, is driven by changes in the cross-equatorial energy transport. In this way, the dynamical cloud changes act as a positive feedback on the meridional displacement of the Hadley Cell, roughly doubling the projected changes in cross-equatorial energy transport compared to that from the microphysical changes alone." 

The dynamical cloud changes that Soden & Chung (2017) document is directly relevant findings of the second reference Robert J. Allen & Osinachi Ajoku (2016), which finds that the reduction in aerosol emissions from China is rapidly expanding the NH tropical belt (especially in the Pacific); which contributes directly to higher climate impacts than assumed by CMIP5/AR5:

Brian Soden and Eui-Seok Chung (2017), "The Large Scale Dynamical Response of Clouds to Aerosol Forcing" Journal of Climate", https://doi.org/10.1175/JCLI-D-17-0050.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0050.1?utm_content=bufferaa6b0&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "We use radiative kernels to quantify the instantaneous radiative forcing of aerosols and the aerosol-mediated cloud response in coupled ocean-atmosphere model simulations under both historical and future emission scenarios. The method is evaluated using matching pairs of historical climate change experiments with and without aerosol forcing and accurately captures the spatial pattern and global mean effects of aerosol forcing. We show that aerosol-driven changes in the atmospheric circulation induce additional cloud changes. Thus, the total aerosol-mediated cloud response consists of both local microphysical changes and non-local dynamical changes that are driven by hemispheric asymmetries in aerosol forcing. By comparing coupled and fixed-SST (sea surface temperature) simulations with identical aerosol forcing we isolate the relative contributions of these two components, exploiting the ability of prescribed SSTs to also suppress changes in the atmospheric circulation. The radiative impact of the dynamical cloud changes are found to be comparable in magnitude to that of the microphysical cloud changes, and act to further amplify the inter-hemispheric asymmetry of the aerosol radiative forcing. The dynamical cloud response is closely linked to the meridional displacement of the Hadley Cell that, in turn, is driven by changes in the cross-equatorial energy transport. In this way, the dynamical cloud changes act as a positive feedback on the meridional displacement of the Hadley Cell, roughly doubling the projected changes in cross-equatorial energy transport compared to that from the microphysical changes alone."

&

Robert J. Allen & Osinachi Ajoku (2016), "Future aerosol reductions and widening of the northern tropical belt", Journal of Geophysical Research Atmospheres, DOI: 10.1002/2016JD024803

http://onlinelibrary.wiley.com/doi/10.1002/2016JD024803/abstract;jsessionid=F22142969E1033CAF1DFF0C651FCFEC5.f02t01

Abstract: "Observations show that the tropical belt has widened over the past few decades, a phenomenon associated with poleward migration of subtropical dry zones and large-scale atmospheric circulation. Although part of this signal is related to natural climate variability, studies have identified an externally forced contribution primarily associated with greenhouse gases (GHGs) and stratospheric ozone loss. Here we show that the increase in aerosols over the twentieth century has led to contraction of the northern tropical belt, thereby offsetting part of the widening associated with the increase in GHGs. Over the 21st century, however, when aerosol emissions are projected to decrease, the effects of aerosols and GHGs reinforce one another, both contributing to widening of the northern tropical belt. Models that have larger aerosol forcing, by including aerosol indirect effects on cloud albedo and lifetime, yield significantly larger Northern Hemisphere (NH) tropical widening than models with direct aerosol effects only. More targeted simulations show that future reductions in aerosols can drive NH tropical widening as large as greenhouse gases, and idealized simulations show the importance of NH midlatitude aerosol forcing. Mechanistically, the 21st century reduction in aerosols peaks near 40°N, which results in a corresponding maximum increase in surface solar radiation, NH midlatitude tropospheric warming amplification, and a poleward shift in the latitude of maximum baroclinicity, implying a corresponding shift in atmospheric circulation. If models with aerosol indirect effects better represent the real world, then future aerosol changes are likely to be an important—if not dominant—driver of NH tropical belt widening."

[jai mitchell]

The radiative impact of the dynamical cloud changes are found to be comparable in magnitude to that of the microphysical cloud changes, and act to further amplify the inter-hemispheric asymmetry of the aerosol radiative forcing.

Is this a major deviation from what has currently been assumed? if so, this is pretty cutting-edge stuff!

[Daniel B.]

The radiative impact of the dynamical cloud changes are found to be comparable in magnitude to that of the microphysical cloud changes, and act to further amplify the inter-hemispheric asymmetry of the aerosol radiative forcing.

Is this a major deviation from what has currently been assumed? if so, this is pretty cutting-edge stuff!

Not really.  Many have claimed that the radiative impact is quite high.  Others not so much.  This is still a highly debated topic.