Where are we now in CO2e , which pathway are we on?

[Tom_Mazanec]

So every square meter of the planet has the equivalent of a 3.2?watt bulb burning on it.
What is the wattage of a small penlight bulb?

[nanning]

Tom, I think that the 3.2W is from the extra GHG in the atmosphere since pre-industrial. It is not the total incoming power and it is not the same for all places on Earth. You could say that the cumulative radiative forcing is a force that changes the pre-industrial climate equilibrium. In our case to much higher temperatures because of a positive force (and a high climate sensitivity).
So the light bulb is much stronger than 3.2W and uses no batteries .

[Tom_Mazanec]

Yes, I know there is a lot of illumination. I meant the extra illumination.

[Hefaistos]

Tom, I think that the 3.2W is from the extra GHG in the atmosphere since pre-industrial. It is not the total incoming power and it is not the same for all places on Earth. You could say that the cumulative radiative forcing is a force that changes the pre-industrial climate equilibrium. In our case to much higher temperatures because of a positive force (and a high climate sensitivity).
So the light bulb is much stronger than 3.2W and uses no batteries .

The radiative forcing from the GHG is 3.2 W/sq.m, which corresponds to 1.2 K or so in average increased temperatures. The other effect you talk about is not a forcing per se, but are various feedback processes.

https://scienceofdoom.com/2014/06/26/the-greenhouse-effect-explained-in-simple-terms/#comment-153310

[kassy]

Losing the remaining Arctic sea ice and its ability to reflect incoming solar energy back to space would be equivalent to adding one trillion tons of CO2 to the atmosphere, on top of the 2.4 trillion tons emitted since the Industrial Age, according to current and former researchers from Scripps Institution of Oceanography at the University of California San Diego.

At current rates, this roughly equates to 25 years of global CO2 emissions.

https://scripps.ucsd.edu/news/research-highlight-loss-arctics-reflective-sea-ice-will-advance-global-warming-25-years

So this exactly the sort of thing we try to avoid. And the effect should build as we lose ice along the way.

Can we avert this at our current rate? With actual realized global reductions because that is how the planet counts? I doubt it.

Posted to wrong thread? Its an old story and a bad paper.

They've only looked at the summer and ignored the winter and generalised from the summer to a year round effect. Loss of ice in winter is cooling, not heating and its a dominant effect not a trivial one. This is a number for what would happen if the ice were removed in April, kept in a cold store in Svalbard over the summer, and then replaced at the end of September.

This is a common mistake and a common alarmist cherry pick. Ice insulates and when it goes missing the effects are opposite in winter to what they are in summer.

Lets start with another paper:

Summary
The Arctic Ocean will become ice free during summer before mid-century unless greenhouse gas emissions are rapidly reduced.

Notz and Stroeve 2018
https://link.springer.com/article/10.1007/s40641-018-0113-2

This is the abstract of the actual paper:

Abstract
During recent decades, there has been dramatic Arctic sea ice retreat. This has reduced the top‐of‐atmosphere albedo, adding more solar energy to the climate system. There is substantial uncertainty regarding how much ice retreat and associated solar heating will occur in the future. This is relevant to future climate projections, including the timescale for reaching global warming stabilization targets. Here we use satellite observations to estimate the amount of solar energy that would be added in the worst‐case scenario of a complete disappearance of Arctic sea ice throughout the sunlit part of the year. Assuming constant cloudiness, we calculate a global radiative heating of 0.71 W/m2 relative to the 1979 baseline state. This is equivalent to the effect of one trillion tons of CO2 emissions. These results suggest that the additional heating due to complete Arctic sea ice loss would hasten global warming by an estimated 25 years.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL082914

I don´t think they actually extrapolate. It is just the effect they calculate.

And that is why we should tried to avoid this although at our current rate that is going to be hard.

*

There is a bit of a problem with the pathways. They are not really useful.
This is also because they forgot to define dangerous.

We know that we want to avoid certain feedbacks like:
Loss of arctic sea ice (failing in the thirties)
Permafrost becoming a source (already done)
Triggering Iceland and Antarctica

So if we just take the Arctic ice as a safe point it is clear that collectively we should have done a lot more.

Combine this with the knowledge that we wont slow that fast because we are not planning to and the fact that the effect lingers even if we go zero overnight then saving the ice looks really iffy.

[Tom_Mazanec]

Triggering Iceland and Antarctica

And Greenland.

[kassy]

Yes Greenland not Iceland.

[Simon]

May not be the right thread but as Arctic summer sea ice is being referred to, the latest modelling indicates circa 2035 for its first disappearance.

https://www.sciencedaily.com/releases/2020/08/200810113216.htm

[mitch]

The Guarino et al (2020) study that gave 2035 for BOE used CMIP6 models, which tend to have higher equilibrium climate sensitivity, and added the melt pond physics.  While it appears that 2035 is plausible, I will wait for more confirmation.  Or, we can all wait 15 years and see for ourselves. 

[kassy]

Adding physics that actually happen will improve the forecast. 15 years is quite short climate wise.

I am quite happy to wait but i maintain that the planet does not have that luxury because when we know it happened it is too late. And we know it is happening although we much like to ignore it.

You can draw lines and extrapolate some time number in the future but we must also weigh that vs what is already locked in.

And think about the consequences that actually brings.

[ArcTickTock]

May not be the right thread but as Arctic summer sea ice is being referred to, the latest modelling indicates circa 2035 for its first disappearance.

https://www.sciencedaily.com/releases/2020/08/200810113216.htm

2035 seems about right, right around there is when the trend line for arctic sea ice volume at minimum reaches 0.

[Tom_Mazanec]

May not be the right thread but as Arctic summer sea ice is being referred to, the latest modelling indicates circa 2035 for its first disappearance.

https://www.sciencedaily.com/releases/2020/08/200810113216.htm

2035 seems about right, right around there is when the trend line for arctic sea ice volume at minimum reaches 0.

Of course that assumes we don't have a fluke event like 2012, which would bring it about sooner.

[kassy]

Warming Greenland Ice Sheet Passes Point of No Return
https://phys.org/news/2020-08-greenland-ice-sheet.html

Nearly 40 years of satellite data from Greenland shows that glaciers on the island have shrunk so much that even if global warming were to stop today, the ice sheet would continue shrinking.

See the link for the details but this is another one we can add. We are on overtime on this one too.

If you had asked me about 25 years ago what scenes i would imagine when this news broke i could not have come up with this.

Since this fact of Greenland melt is true today it also demonstrates that 1,5 C is not a safe goal.

[kassy]

May not be the right thread but as Arctic summer sea ice is being referred to, the latest modelling indicates circa 2035 for its first disappearance.

https://www.sciencedaily.com/releases/2020/08/200810113216.htm

2035 seems about right, right around there is when the trend line for arctic sea ice volume at minimum reaches 0.

Of course that assumes we don't have a fluke event like 2012, which would bring it about sooner.

If we go back through the historical record all the recent conditions are from icy conditions. ESAS has been melting for 12k years or so and it is only going to get worse.

We are heading into territory we know less well. Yes we have historical analogues but the data points are less scarce at that end. And you can combine that with the things we cannot model well.

We do not know where we are going to end up but we could have used some points of no return. Things we should have avoided. But those where glossed over for economic gains and bs discounting on those measures.

Even if we would hit the Paris goals we would still be in a world were the Arctic ice is doomed, Greenland too. And probably Antarctica is already in play too.

That is our world today.

[liefde]

Yes Greenland not Iceland.

Eeh.. remember the Ok glacier in Iceland? Declared "dead" in 2014..

[Stephan]

To finalize my update on greenhouse gases here is the summary of the four postings in the individual gas concentration threads.

More radiative forcing of the "NOAA gases" (CO₂, CH₄, N₂O, SF₆) in May 2020 than in Apr 2020 or in May 2019.

The values [W/m²], change to Apr 2020 and change to May 2019:
CO₂ 2.170   (+ 0.011)    (+ 0.031)   
CH₄ 0.520   (+ 0.000)    (+ 0.005)
N₂O 0.205   (+ 0.000)    (+ 0.004)
SF₆  0.0053 (+ 0.0000)  (+ 0.0002)
sum  2.900  (+ 0.011)   (+ 0.040)

The relative annual increase is 1.36 %.
It also means never before since we measure these gases has their radiative forcing been so strong.

[kassy]

Where does the heat go?

This study calculates that the amount of CO2 in the atmosphere must be reduced from the present concentration of nearly 410 ppm to approximately 350 ppm to bring the Earth back towards energy balance.

https://public.wmo.int/en/media/news/where-does-heat-go

See the article for details but hey look another piece of evidence that we are well into overshoot.

[nanning]

280 ppm is the pre-industrial level. Reaching that means returning to nature's original track. That should be the goal. To undo the damage we've done.

[wdmn]

280 ppm is the pre-industrial level. Reaching that means returning to nature's original track. That should be the goal. To undo the damage we've done.

Back on this old nonsense eh nanning? It would have been better had humans never evolved! But then that would mean blaming... nature?

At 280ppm we were heading into a glacial period.

[Stephan]

A short explanation of this plot would be helpful, wdmn, including the designation of x and y axes.
I guess it is worldwide temperature the last 10,000 years?

[wili]

wdmn, I know nanning can seem tiresomely simplistic and repetitive sometimes, but the fact of the matter is that somehow we have managed in quite a short time to turn the earth from a 'goldilocks' climate into something more and more resembling a fiery hell.

It is at least as important, and arguably much more, to try to figure out how we got here so we can figure out exactly what we have to stop doing (and thinking), as it is to understand the nuances of the science that tells us what is happening to sea ice on a day by day basis.

Humans 'evolved' to have thousands of different cultures around the world. Arguably, it is only one of those, modern industrial culture and society (at first Western, now global), that has pushed the world to and probably past the point that it will be readily habitable by future generations.

So questioning where we went wrong is not the same as being against all human evolution, lol.

Maybe we have to look further back than the industrial revolution. Maybe it was the particular way the industrial revolution developed that holds the key. In any case, the issue is not one that should, imo, be lightly tossed under the rug.

[wdmn]

@Stephen

My apologies.

The graph comes from: https://twitter.com/alxrdk/status/1295016785180270594

The time period (x-axis) is 12,000 years, 9980 BC - 2020 AD.
Baseline is 20th century mean. Minimum temperature shown = -1.37°C, Max T = 0.99°C (2020).

Sources for the data are provided in the above linked twitter thread.

The graph shows the end of the last glacial period, the Holocene and the Anthropocene (if you are so inclined to use the latter designation). The Holocene is the period in which agriculture and settled human civilization was born. Humans of course lived during the last glacial period, but were not present in large parts of currently inhabited land, as that land was under thick ice sheets.

I used this graph, because it very clearly shows the slow arc down from the Holocene maximum temperature. That arc had us on the trajectory to another glacial period, which would be -- one could argue -- at least as devastating to human civilization as global heating now threatens to be.

@wili

I of course agree that we are in a dire situation regarding climate change, as is unanimously stated by the most reputable climate scientists. The 350 ppm target was set by one of those same scientists, James Hansen.

While the consequences of industrialization are now threatening human civilization, I think it is ridiculous to dismiss the whole period as a cancer that should be done away with. I simply want to point out that the pre-industrial target would also condemn human civilization.

I also question the 280ppm target as arbitrary; it already includes human activity throughout the Holocene, so why is that "nature's track" as it was intended?. Why not "put it back as it was" before the Holocene? Before humans? What is "undoing the harm?" What is nature's track, if not the one that we're on? That of course includes the possibility that we address global heating before it does as much damage as it might (i.e. that we might completely overhaul our culture, including learning from those non-industrialized cultures that still exist).

Nanning's logic -- as has been discussed elsewhere ad nauseam -- presumes that humans have no right to take actions that affect nature's path, while at the same time declaring that we should make a decision to go back to one specific point in nature's path (i.e. making the human decision as to what nature's path should be; i.e. doing the same thing he condemns when we set the target at 350 ppm). He also seems to condemn human beings to either being passive animals that accept whatever fate is handed to us by "nature" (we should allow a glacial period or an astroid to hit us, even if we could avoid it, for example; which condemns nature for giving us a survival instinct and the ability to practice climate science or astronomy, etc.), or to eliminate us completely from nature (which, as pointed out, condemns nature, which gave rise to our species).

[nanning]

Back on this old nonsense eh nanning?
Nanning's logic -- as has been discussed elsewhere ad nauseam -- presumes

That's not my logic you describe wdmn. That's your logic projected onto me.
I won't react further to your unkind words and charges.
Main point is: high technology comes with high responsibility and we are not alone on this planet and this planet is not ours to spoil.

edit: added quotes

[wili]

I don't presume to speak for nanning.

But again I would point out that humans have devised thousands of different ways to live in the world without destroying it, and presumably there are countless more ways.

Global civilization seems to have hit on the one way to live in the world that destroys most other forms of life as well as disrupting the systems that support said life.

Our most desperate need is to rediscover a culture/way of life that fosters rather than obliterates the rest of the living community.

Any ideas?

[Tom_Mazanec]

I am sure mammoths, saber tooth tigers, mastodons, teratorns et al would dispute that global industrial civilization is the only one that exterminates other species.

[wili]

Yes, as humans left their original homelands in Africa, we probably wiped out a number of large species, being basically an invasive species ourselves. There is still some debate about which ones were wiped out by us and which failed to adapt to changing climates.

But those extinctions pale compared to the global mass extinctions and destruction of ecosystems going on today.

And once humans did settle in any particular area, they tended to fairly quickly develop a set of taboos to avoid wiping out crucial local and fauna. If they didn't they would generally not last very long.

[nanning]

Thank you wili. Beautiful.

[kassy]

And also off topic.

280 is moot if we cannot even get close to 350.
And extinctions belong in another thread.

Also to taboos:

I think that is wrong.

[nanning]

Thank you for letting it stand, moderator kassy.

"280 is moot if we cannot even get close to 350."
Indeed. It's completely academic.

[Sciguy]

I found the data for the RCP scenario assumptions on the IPCC website.

https://www.ipcc-data.org/observ/index.html

At that webpage, click on the top link, "Climate System Scenario Tables (Annex II of IPCC 5th Assessment Report, WG1 -- as Excel workbook"

This will open a large Excel spreadsheet with many tabs.  The tabs showing greenhouse gas concentrations by year are 4-1 (CO2), 4-2 (CH4), etc...

Here is the table for CO2:

Table AII.4.1 | CO2 abundance (ppm)                                 
Year   Observed   RCP2.6   RCP4.5   RCP6.0   RCP8.5   A2   B1   IS92a   Min   RCP8.5&   Max
PI   278 ± 2   278   278   278   278   278   278   278         
2011 obs   390.5 ± 0.3                              
2000      368.9   368.9   368.9   368.9   368   368   368         
2005      378.8   378.8   378.8   378.8               378.8   
2010      389.3   389.1   389.1   389.3   388   387   388   366   394   413
2020      412.1   411.1   409.4   415.8   416   411   414   386   425   449
2030      430.8   435.0   428.9   448.8   448   434   442   412   461   496
2040      440.2   460.8   450.7   489.4   486   460   472   443   504   555
2050      442.7   486.5   477.7   540.5   527   485   504   482   559   627
2060      441.7   508.9   510.6   603.5   574   506   538   530   625   713
2070      437.5   524.3   549.8   677.1   628   522   575   588   703   810
2080      431.6   531.1   594.3   758.2   690   534   615   651   790   914
2090      426.0   533.7   635.6   844.8   762   542   662   722   885   1026
2100      420.9   538.4   669.7   935.9   846   544   713   794   985 ± 97   1142

Here is the table for CH4:

Table AII.4.2 | CH4 abundance (ppb)                                                         
Year   RCP2.6   RCP4.5   RCP6.0   RCP8.5   A2   B1   IS92a      RCP2.6&         RCP4.5&         RCP6.0&         RCP8.5&   
PI   720   720   720   720            722   ±   25   722   ±   25   722   ±   25   722   ±   25
2011 obs                        1803   ±   4   1803   ±   4   1803   ±   4   1803   ±   4
2000   1751   1751   1751   1751   1760   1760   1760                                    
2010   1773   1767   1769   1779   1861   1827   1855   1795   ±   18   1795   ±   18   1795   ±   18   1795   ±   18
2020   1731   1801   1786   1924   1997   1891   1979   1716   ±   23   1847   ±   21   1811   ±   22   1915   ±   25
2030   1600   1830   1796   2132   2163   1927   2129   1562   ±   38   1886   ±   28   1827   ±   28   2121   ±   44
2040   1527   1842   1841   2399   2357   1919   2306   1463   ±   50   1903   ±   37   1880   ±   36   2412   ±   74
2050   1452   1833   1895   2740   2562   1881   2497   1353   ±   60   1899   ±   47   1941   ±   48   2784   ±   116
2060   1365   1801   1939   3076   2779   1836   2663   1230   ±   71   1872   ±   59   1994   ±   61   3152   ±   163
2070   1311   1745   1962   3322   3011   1797   2791   1153   ±   78   1824   ±   72   2035   ±   77   3428   ±   208
2080   1285   1672   1940   3490   3252   1741   2905   1137   ±   88   1756   ±   87   2033   ±   94   3624   ±   250
2090   1268   1614   1819   3639   3493   1663   3019   1135   ±   98   1690   ±   100   1908   ±   111   3805   ±   293
2100   1254   1576   1649   3751   3731   1574   3136   1127   ±   106   1633   ±   110   1734   ±   124   3938   ±   334

[SimonF92]

I plotted that data;

[Tor Bejnar]

From the 2020 Mauna Loa CO2 levels thread, Steven posted

Sunday evening [Sept. 27, 2020]- an update from Mauna Loa CO2:
Week beginning on September 20, 2020:     411.00 ppm

Now, are those IPCC numbers Ken just posted "Mauna Loa equivalent"? Or some other "average global number?  I looked it up (thanks for the guidance, Ken!): They are "global mean values".

So, what is the relationship between "global mean CO2" and Moana Loa values? 
(I guess we will have to wait for January 2021 to know the actual 2020 global mean CO2 value ...)

[SimonF92]

Methane too;

Oh my, i have just realised these plots have axes the wrong way round, please imagine the labels reversed- I havent used matplotlib for a while

[Sciguy]

From the 2020 Mauna Loa CO2 levels thread, Steven posted

Sunday evening [Sept. 27, 2020]- an update from Mauna Loa CO2:
Week beginning on September 20, 2020:     411.00 ppm

Now, are those IPCC numbers Ken just posted "Mauna Loa equivalent"? Or some other "average global number?  I looked it up (thanks for the guidance, Ken!): They are "global mean values".

So, what is the relationship between "global mean CO2" and Moana Loa values? 
(I guess we will have to wait for January 2021 to know the actual 2020 global mean CO2 value ...)

For 2019, NOAA reported an annual average of 411.43 ppm at Mauna Loa and 409.85 ppm for the global average.  So in 2019, Mauna Loa was about 1.6 ppm higher than the global average.  In 2018 Mauna Loa was 1.13 ppm higher and in 2017 Mauna Loa was 1.55 ppm higher. 

However, since this forum tracks Mauna Loa weekly averages, it's more complicated.

The NOAA Global Monitoring Laboratory publishes both the Mauna Loa and the Global values.  The Mauna Loa values are updated weekly but often change over time as the quality control process needs data from the other observatories that collect the same data.  The global value is updated monthly and lags by several months.  Currently, they are reporting the global measurement data from June 2020 (412.62 ppm) while Mauna Loa is reporting the August 2020 monthly average measurement (412.55 ppm).  While they're pretty close now, at other times of the year they differ.

To further complicate the issue, the RCPs are based on annual average concentrations.  These aren't available on the NOAA website until April or May of the next year, and they can be updated later in the year as more quality control is done. 

Link to the global data:

https://www.esrl.noaa.gov/gmd/ccgg/trends/gl_data.html

Link to Mauna Loa data:

https://www.esrl.noaa.gov/gmd/ccgg/trends/data.html

[so_whats_happening]

I found the data for the RCP scenario assumptions on the IPCC website.

https://www.ipcc-data.org/observ/index.html

At that webpage, click on the top link, "Climate System Scenario Tables (Annex II of IPCC 5th Assessment Report, WG1 -- as Excel workbook"

This will open a large Excel spreadsheet with many tabs.  The tabs showing greenhouse gas concentrations by year are 4-1 (CO2), 4-2 (CH4), etc...

Here is the table for CO2:

Table AII.4.1 | CO2 abundance (ppm)                                 
Year   Observed   RCP2.6   RCP4.5   RCP6.0   RCP8.5   A2   B1   IS92a   Min   RCP8.5&   Max
PI   278 ± 2   278   278   278   278   278   278   278         
2011 obs   390.5 ± 0.3                              
2000      368.9   368.9   368.9   368.9   368   368   368         
2005      378.8   378.8   378.8   378.8               378.8   
2010      389.3   389.1   389.1   389.3   388   387   388   366   394   413
2020      412.1   411.1   409.4   415.8   416   411   414   386   425   449
2030      430.8   435.0   428.9   448.8   448   434   442   412   461   496
2040      440.2   460.8   450.7   489.4   486   460   472   443   504   555
2050      442.7   486.5   477.7   540.5   527   485   504   482   559   627
2060      441.7   508.9   510.6   603.5   574   506   538   530   625   713
2070      437.5   524.3   549.8   677.1   628   522   575   588   703   810
2080      431.6   531.1   594.3   758.2   690   534   615   651   790   914
2090      426.0   533.7   635.6   844.8   762   542   662   722   885   1026
2100      420.9   538.4   669.7   935.9   846   544   713   794   985 ± 97   1142

Here is the table for CH4:

Table AII.4.2 | CH4 abundance (ppb)                                                         
Year   RCP2.6   RCP4.5   RCP6.0   RCP8.5   A2   B1   IS92a      RCP2.6&         RCP4.5&         RCP6.0&         RCP8.5&   
PI   720   720   720   720            722   ±   25   722   ±   25   722   ±   25   722   ±   25
2011 obs                        1803   ±   4   1803   ±   4   1803   ±   4   1803   ±   4
2000   1751   1751   1751   1751   1760   1760   1760                                    
2010   1773   1767   1769   1779   1861   1827   1855   1795   ±   18   1795   ±   18   1795   ±   18   1795   ±   18
2020   1731   1801   1786   1924   1997   1891   1979   1716   ±   23   1847   ±   21   1811   ±   22   1915   ±   25
2030   1600   1830   1796   2132   2163   1927   2129   1562   ±   38   1886   ±   28   1827   ±   28   2121   ±   44
2040   1527   1842   1841   2399   2357   1919   2306   1463   ±   50   1903   ±   37   1880   ±   36   2412   ±   74
2050   1452   1833   1895   2740   2562   1881   2497   1353   ±   60   1899   ±   47   1941   ±   48   2784   ±   116
2060   1365   1801   1939   3076   2779   1836   2663   1230   ±   71   1872   ±   59   1994   ±   61   3152   ±   163
2070   1311   1745   1962   3322   3011   1797   2791   1153   ±   78   1824   ±   72   2035   ±   77   3428   ±   208
2080   1285   1672   1940   3490   3252   1741   2905   1137   ±   88   1756   ±   87   2033   ±   94   3624   ±   250
2090   1268   1614   1819   3639   3493   1663   3019   1135   ±   98   1690   ±   100   1908   ±   111   3805   ±   293
2100   1254   1576   1649   3751   3731   1574   3136   1127   ±   106   1633   ±   110   1734   ±   124   3938   ±   334

Hi sorry new to the forum. Long time lurker but had a question. The data presented in the 2.6 column it is as if we continued on the path of the current amount emissions of CO2 and Methane and then each sequential line to the right is if we were to increase in amounts being thrown into the atmosphere or is there some type of mitigation process in there i'm not seeing in 2.6 and 4.5? Clearly 8.5 is the most ambitious of them.

Thanks,
Tylor

[kassy]

Welcome Tylor.

Not sure if i would call 8.6 the most ambitious. It is the one where we emit most carbon.

You can read more in post #124 (and some below that):

Skepticalscience has a great article on the RCPs:

https://skepticalscience.com/rcp.php?t=3

[SimonF92]

If your ambition was to destroy the Arctic as it currently exists, then RCP 8.5 would be the best

[Sciguy]

Hi sorry new to the forum. Long time lurker but had a question. The data presented in the 2.6 column it is as if we continued on the path of the current amount emissions of CO2 and Methane and then each sequential line to the right is if we were to increase in amounts being thrown into the atmosphere or is there some type of mitigation process in there i'm not seeing in 2.6 and 4.5? Clearly 8.5 is the most ambitious of them.

Thanks,
Tylor

Tylor,

The RCPs are "representative concentration pathways" and each present a series of inputs for running climate simulations in models.  They're meant to represent a pattern of climate forcings, not really a forecast of future emissions.  So we'll never be entirely on one path or another.

The number at the end of the RCP is the radiative forcing in the year 2100.  So RCP 2.6 would see 2.6 watts per meter of forcing while RCP would have 8.5 watts per meter in 2100.

The pattern of forcings over the years is broadly described in each of the scenario descriptions.  RCP 8.5 assumes continued growth in fossil fuel emissions, including burning coal at an increasing rate, for the rest of the century.  RCP 2.6 assumes we began reducing non-CO2 greenhouse gas emissions, especially methane, in 2011 (which we haven't), we reach a peak in CO2 emissions around 2040 and then decline and use Negative Emissions Technologies to reduce CO2 concentrations from 2050 through 2100.  RCPs 4.5 and 6.0 assume a peak of CO2 emissions in the second half of the century and then stabilization of concentrations toward the end of the century.

A good summary in easy to read format is available at skepticalscience.org at this link:

https://www.skepticalscience.com/rcp.php

That website has some very useful graphics that show the assumed emission trajectories in each of the scenarios:



The assumed atmospheric concentrations:



One of the interesting features of all of the RCPs, which were developed about 15 years ago, is that they assumed that renewable energy would be too expensive to deploy extensively.  This is shown in another image at the skeptical science article:



Of course, wind and solar are now cheaper than coal and competitive with natural gas, so these assumptions are way too pessimistic.  By 2030, almost all new energy investment will be wind and solar (about 67% is now, with coal seeing almost no new investment the past two years), so by 2050, almost no fossil fuel power plants will be operating. 

[so_whats_happening]

Hi sorry new to the forum. Long time lurker but had a question. The data presented in the 2.6 column it is as if we continued on the path of the current amount emissions of CO2 and Methane and then each sequential line to the right is if we were to increase in amounts being thrown into the atmosphere or is there some type of mitigation process in there i'm not seeing in 2.6 and 4.5? Clearly 8.5 is the most ambitious of them.

Thanks,
Tylor

Tylor,

The RCPs are "representative concentration pathways" and each present a series of inputs for running climate simulations in models.  They're meant to represent a pattern of climate forcings, not really a forecast of future emissions.  So we'll never be entirely on one path or another.

The number at the end of the RCP is the radiative forcing in the year 2100.  So RCP 2.6 would see 2.6 watts per meter of forcing while RCP would have 8.5 watts per meter in 2100.

The pattern of forcings over the years is broadly described in each of the scenario descriptions.  RCP 8.5 assumes continued growth in fossil fuel emissions, including burning coal at an increasing rate, for the rest of the century.  RCP 2.6 assumes we began reducing non-CO2 greenhouse gas emissions, especially methane, in 2011 (which we haven't), we reach a peak in CO2 emissions around 2040 and then decline and use Negative Emissions Technologies to reduce CO2 concentrations from 2050 through 2100.  RCPs 4.5 and 6.0 assume a peak of CO2 emissions in the second half of the century and then stabilization of concentrations toward the end of the century.

A good summary in easy to read format is available at skepticalscience.org at this link:

https://www.skepticalscience.com/rcp.php

That website has some very useful graphics that show the assumed emission trajectories in each of the scenarios:



The assumed atmospheric concentrations:



One of the interesting features of all of the RCPs, which were developed about 15 years ago, is that they assumed that renewable energy would be too expensive to deploy extensively.  This is shown in another image at the skeptical science article:



Of course, wind and solar are now cheaper than coal and competitive with natural gas, so these assumptions are way too pessimistic.  By 2030, almost all new energy investment will be wind and solar (about 67% is now, with coal seeing almost no new investment the past two years), so by 2050, almost no fossil fuel power plants will be operating.

I appreciate the amazing response to this my wording may not have been the best to use but this truly helped me understand and I thank you for that. I see there may be a few who may dislike my approach to speaking about these things, unfortunately that is on them. Ill remove myself at this point from the conversation and going back to lurking.

[Stephan]

To finalize my update on greenhouse gases here is the summary of the four postings in the individual gas concentration threads.

More radiative forcing of the "NOAA gases" (CO₂, CH₄, N₂O, SF₆) in June 2020 than in June 2019, but less than in May 2020, because CO₂ and CH₄ reach their seasonal maximum in May.

The values [W/m²], change to May 2020 and change to June 2019:
CO₂ 2.161    (- 0.009)    (+ 0.031)   
CH₄ 0.519    (- 0.001)    (+ 0.005)
N₂O 0.205   (+ 0.000)    (+ 0.003)
SF₆  0.0053 (+ 0.0000)  (+ 0.0001)
sum  2.891  (- 0.009)   (+ 0.040) (rounding differences)

The relative annual increase is 1.43 %, a little bit higher than May 2020.

[Juan C. García]

To finalize my update on greenhouse gases here is the summary of the four postings in the individual gas concentration threads.

More radiative forcing of the "NOAA gases" (CO₂, CH₄, N₂O, SF₆) in June 2020 than in June 2019, but less than in May 2020, because CO₂ and CH₄ reach their seasonal maximum in May.

The values [W/m²], change to May 2020 and change to June 2019:
CO₂ 2.161    (- 0.009)    (+ 0.031)   
CH₄ 0.519    (- 0.001)    (+ 0.005)
N₂O 0.205   (+ 0.000)    (+ 0.003)
SF₆  0.0053 (+ 0.0000)  (+ 0.0001)
sum  2.891  (- 0.009)   (+ 0.040) (rounding differences)

The relative annual increase is 1.43 %, a little bit higher than May 2020.

Thanks for your posts, Stephan. 
Is there a way to change the final value to CO2e, in ppm?
And a way to compare the sum of them with what we have, by example, versus 1980?

[wolfpack513]

Using ESRL AGGI you can extrapolate the annual CO2 equivalent down to a monthly value.
With the seasonal cycle in GHGs, I would only use year over year monthly changes.

A radiative forcing increase of 0.05 Watts/m2 is worth ~5 ppm of CO2 equivalent.
https://www.esrl.noaa.gov/gmd/aggi/aggi.html

[nanning]

Thanks wolfpack513.
Do you know what methane CO₂e factor is used? It can differ hugely (ca. 20-100) and is therefore a bit arbitrary. It would be good to post that number also for clarity.
Aerosols are not included because they are spatially heterogeneous and short-lived. But it's constantly being replenished with new aerosols. I understand that a global figure is impossible, but it sure is part of integrated radiative forcing. Can a global map be made?
At what height in the atmosphere is the radiative forcing valid? Top of troposphere or at sea level?
Perhaps I've misunderstood.

[Sciguy]

Thanks wolfpack513.
Do you know what methane CO₂e factor is used? It can differ hugely (ca. 20-100) and is therefore a bit arbitrary. It would be good to post that number also for clarity.
Aerosols are not included because they are spatially heterogeneous and short-lived. But it's constantly being replenished with new aerosols. I understand that a global figure is impossible, but it sure is part of integrated radiative forcing. Can a global map be made?
At what height in the atmosphere is the radiative forcing valid? Top of troposphere or at sea level?
Perhaps I've misunderstood.

 

Since the RCPs show the concentrations of greenhouse gases that were used to define the forcings, we can directly compare measured concentrations to the concentrations used to build the RCPs.  We can ignore the global warming potentials and assumed timeframes.

[nanning]

Thanks Ken (I am not very familiar with RCP), but where do they measure the radiative forcing? Does it include aerosols (especially in the NH)?
Furthermore you seem to say that knowing the CO₂e is not important? I think actually it is for defining GHG budgets for certain climate/GMST outcomes.
And I don't understand "concentrations of greenhouse gases that were used to define the forcings". The forcings are defined?

[oren]

Nanning, if you wish to learn more about Radiative Forcing, Global Warming Potential and other related issues, you will be smarter (and much more confused) if you read this old thread here.
You will discover the difference between concentration-based calculations (=Radiative Forcing) and emission-based calculations (=GWP). But the confusion will stem from the big argument between Ned W and ASLR. Ned W was out to prove at all costs that methane is not important using narrowly defined science (I think he was wrong and tried to explain why, as you'll see if you read to the end). ASLR was out to prove the opposite at all costs but used very widely defined science and thus they talked past each other to no avail. Still I learned a lot from that thread.

In essence:
* RF is derived from a given concentration compared to a baseline concentration. For example CO2 today vs. CO2 one year ago.
* GWP is derived by assessing what would happen given an x amount of emissions, some of which would be absorbed or decayed over time. For example, a pulse of 1GT of methane.
* And my position was that to discuss RF properly one must calculate a baseline RF - concentration now compared to concentration if humanity ceased all emissions, thus taking into account the emission and decay rates separately, rather than lumping them together.

[nanning]

Thanks oren. I haven't read anything I didn't know (RF can be expressed in other units as well imo). Perhaps I have problems in connecting them to my questions.
Am I right in thinking that GWP is not only from emissions but also from loss of albedo?
I have read many times about the multiple of radiative forcing effect that methane gives compared to carbon dioxide. I've read numbers from 20-100 depending on the time-frame.
I have no 'agenda'.

[Sciguy]

Nanning,

I was responding in the context of this thread, which uses the weekly or monthly observations of greenhouse gas concentrations and then tries to determine which of the RCPs we are closest too.

The thread got a bit confusing because they refer to CO2e in the title.  As Oren pointed out, CO2e is a way to compare the global warming potential of different greenhouse gases as they are emitted.  It doesn't really work for concentrations, because of the different lifetimes of the greenhouse gases.

As you note, methane has a short lifetime compared to CO2 (11 to 12 years versus 100+).  So the calculation for it's CO2e can range from 25 (which I think is implied by the calculations used in NOAA's greenhouse gas index) if you're looking at climate change over a century, to 80 for it's warming over 20 years.  The long term global warming for methane has been revised up to 34 in the past few years because of the feedbacks methane causes in atmospheric chemistry as it decays.

One of the shortcomings of converting a short term greenhouse gas to a CO2e is that it doesn't accurately portray the warming effects of the short term gas over time.  So a new method to calculate global warming potential, GWP*, has been proposed.  This article explains it better.

https://www.carbonbrief.org/guest-post-a-new-way-to-assess-global-warming-potential-of-short-lived-pollutants

7 June 2018
Guest post: A new way to assess ‘global warming potential’ of short-lived pollutants
Dr Michelle Cain

At the moment, it is not obvious how this will be done. In a new paper published in npj Climate and Atmospheric Science, my co-authors and I address one of the stocktake’s key stumbling blocks – the treatment of all greenhouse gases as “CO2-equivalent”, using a metric known as “global warming potential” (GWP). This misrepresents the impact of short-lived climate pollutants, such as methane, on future warming.

We show that modifying the use of GWP, so that it accounts for the differences between short- and long-lived gases, can better link emissions to warming. This means that the true impact of an emission pathway on global temperature can be easily assessed. For countries with high methane emissions – due to, say, agriculture – this can make a huge difference to how their progress in emission reductions is judged.

Greenhouse gas emissions are commonly presented in units of billion tonnes of carbon dioxide equivalent (Gt CO2e). The de facto way of converting non-CO2 emissions to CO2e is to multiply the gas by its GWP100 (global warming potential over 100 years). The value of GWP100 for methane (CH4) from the last IPCC assessment report is 28. This means that methane has 28 times as much “global warming potential” as CO2, so 1Gt CH4 equates to 28 GtCO2e.

This masks the fact that 1 GtCH4 has a strong warming influence when it is first emitted, which then diminishes rapidly over a few decades. This is because chemical reactions cause it to be removed from the atmosphere, with a half life of about a decade. So, at the end of that 100 years, that methane is no longer causing strong warming, because it has almost all been destroyed.

By comparison, a 28Gt “equivalent” emission of CO2 would effectively persist in the atmosphere for centuries or longer, continuing to cause warming at almost the same rate as when it was first released. This shows how the two emissions are not really equivalent, which has important consequences if GWP100 is applied to future emissions scenarios inappropriately.

For example, the figure below shows some simplified emissions scenarios for CO2 and methane, with the resulting temperature responses. If methane is held constant (middle panel), temperature will remain constant. This is because the short lifetime of methane means atmospheric concentrations will remain constant with constant sources, assuming constant sinks. (Note that this is a simplification to demonstrate the direct warming from methane. Secondary effects from carbon cycle feedbacks following a methane emission can also cause smaller amounts of additional warming.)

However, a stable CO2 emission pathway leads to year-on-year increases in warming, because the CO2 accumulates in the atmosphere. If methane emissions are simply multiplied by GWP100 to generate CO2e, this would look like a warming pathway, when it should lead to stable temperatures.

Even more pronounced is the impact when emissions are falling (right panel). For methane, falling emissions leads to cooling. Converting to CO2e would imply warming until the emissions hit zero. Ambitious mitigation scenarios could, therefore, give the impression of giving rise to warming instead of cooling from methane, if expressed using GWP100.

By using GWP*, emissions of methane expressed as CO2e relate much more closely to temperature response. This can be seen in the figure below. The top panels use GWP100, while the lower panels use GWP*. The left panels show annual emissions of CO2e (upper left) and CO2e* (lower left). In the right panels, temperature is shown in the dashed lines alongside the cumulative CO2e/CO2e* emissions in the solid lines.

Consider a power station and a herd of cows. A power station emits CO2 by burning fossil fuels. This CO2 is taxed. When it shuts down permanently, it emits no more CO2, so is no longer taxed. However, the CO2 already emitted continues to affect the climate for hundreds, or potentially, thousands of years. So even after closing down, that power station still contributes to holding up global temperatures because of the CO2 that remains in the atmosphere.

Now to the cows. A herd of cows emits methane, so the farmer is taxed for those emissions. If the herd remains the same size with the same methane emissions every year, it will maintain the same amount of additional methane in the atmosphere year on year. In terms of its contribution to warming, this is equivalent to the closed power station.

The power station pushed up global temperatures when it was running in the past, just as the farmer’s great-grandparent pushed up global temperatures when they were building up the herd of cattle. But neither a steady herd of cattle nor a defunct power station is pushing up global temperatures any more.

[nanning]

Thank you Ken for explaining and providing the linked article. I understand better now .

[oren]

The only problem is that the planet is not in energy balance, and the herd of cows helps maintain methane levels that lead to further warming until the new balance is reached.
While the GWP of methane assume a pulse of methane being absorbed and decayed rather quickly, in truth the level of methane has been stable or rising. As humanity's problem is short-term and not just long-term, it should be realized that methane will help push the planet above 2C and into huge positive feedbacks, and then it will not help much that the methane decayed at some point when we stopped maintaining (and even increasing) its atmospheric level.
Thus the downplaying of methane using RF and GWP justifications is IMHO very wrong. IMHO Co2eq of methane should be calculated by the short-term warming it induces. I think this is what Stephan does.
However, emission of methane should be evaluated in comparison not to the resulting growth in methane concentrations over a year, but compared to the baseline where methane should have decayed from a year ago. I think this is where some posters are missing the issue. However the emission part is probably off-topic here, so I'll avoid further discussion.