IJIS

[jdallen]

IJIS:

9,338,262 km²（November 27, 2016）up 114,379 km² from previous and lowest measured for the date.

Hmmm.  Completely intuitive prediction - I'm thinking extent is going to rise at approximately this trajectory, closing with but not quite reaching 2006, until it reaches about 11 Million KM2.

At that point, I anticipate a plateau, as the freeze over of peripheral seas further south takes more time, eventually topping out around 13.5-14 Million KM2.  How much past 11 Million KM2 will depend highly on how much heat remains in the Kara, Barents, Bering, and Labrador seas, Baffin Bay (which retained some open water most of last season) and to a lesser possibility, the Hudson retaining open water.

[johnm33]

"Hudson retaining open water." Winters coming
 http://weather.gc.ca/city/pages/mb-42_metric_e.html

[jdallen]

"Hudson retaining open water." Winters coming
 http://weather.gc.ca/city/pages/mb-42_metric_e.html

This is good.  Now, lets hope temps start dipping consistently under -10C....

[charles_oil]

I think if the warm weather continues - Hudson will struggle to freeze properly any time soon.

http://cci-reanalyzer.org/wxrmaps/#forecast.GFS-025deg.ARC-LEA.T2
Still just above freezing on parts ...

http://cci-reanalyzer.org/wxrmaps/#forecast.GFS-025deg.ARC-LEA.T2_anom
10 - 15 degrees above "normal" for this time of year

[magnamentis]

IJIS:

9,338,262 km²（November 27, 2016）up 114,379 km² from previous and lowest measured for the date.

Hmmm.  Completely intuitive prediction - I'm thinking extent is going to rise at approximately this trajectory, closing with but not quite reaching 2006, until it reaches about 11 Million KM2.

At that point, I anticipate a plateau, as the freeze over of peripheral seas further south takes more time, eventually topping out around 13.5-14 Million KM2.  How much past 11 Million KM2 will depend highly on how much heat remains in the Kara, Barents, Bering, and Labrador seas, Baffin Bay (which retained some open water most of last season) and to a lesser possibility, the Hudson retaining open water.

i expect a flattening of this trajectory though with daily values of 100k +/- 10k soon, while outliers to both sides may always occur, let's see but finally this is very similar to your own expectations if i understood that right.

cheers

[Shared Humanity]

The emoji was intended to convey this comment to be snark. I have been pretty much terrified by AGW for a decade.

Dearest Shared Humanity,
My sincerest apologies. On my mobile it's hard to see emojis so I focus on the words. Of late I am angry which also causes blindness. I also don't understand all emojis. Sorry. Yours,

Please, don't worry. I could tell by your response that my short remark was misunderstood.

[Espen]

IJIS:

9,463,931 km²（November 28, 2016）up 125,669 km² from previous and lowest measured for the date.

[Espen]

IJIS:

9,570,761 km²（November 29, 2016）up 106,830  km² from previous and lowest measured for the date.

[Pmt111500]

When does the next compaction phase start? This is exciting!

[seaicesailor]

When does the next compaction phase start? This is exciting!

Well, not sure about how much compaction, but the ECMWF ensembles predict high pressure system becoming stronger and persistent over the Pacific side especially Beaufort, from day two to day ten, with low pressure system in Atlantic side and isobars crossing the Arctic in the Laptev->Greenland direction. The agreement of the prediction in the first days is pretty good.

[Espen]

IJIS:

9,673,021 km²（November 30, 2016）up 102,260 km² from previous and lowest measured for the date.

[Santiago]

Would it be possible to compare specific 2-year cycles?
For instance: 2006-2007, 2011-2012, 2016-(2017 not available yet obviously).

What I mean by 2-year cycle is that the graph is 2-years long in the graph's x-axis.
I just wonder whether this might help to see preconditioning trends.
I also wonder whether this could shed light on what to expect for 2017.

Santi

[Bill Fothergill]

@Santiago

I've set up a simple comparison as you asked, and have saved it in .pdf format.

However, when I select this using the "Attachments" button, and then try to Preview, nothing seems to happen.

Can someone please explain (using short words) what I am doing incorrectly.

[Bill Fothergill]

Oh, I see.

When I hit the "post" button, the attachment appears as a "paper-clip" which can then be downloaded.

What I was trying to do was to embed the diagram in my reply. Obviously I am too thick to do that correctly.

[Seumas]

You can't embed a PDF. Try it as a .png or a .jpg instead.

[Jim Pettit]

Despite the entirely expected surge in sea ice extent growth the past few weeks, 2016 nonetheless held the first place spot every day of November. But of even greater note, 2016 is well ahead of all other years as far as year-to-date extent is concerned. Second place 2012 is far behind:

[Tigertown]

Bill Fothergill 2-year Comparison
Edit: tried downsizing to fit here.

[Bill Fothergill]

Thanks Tigertown & Seamus. 

Getting old is a pain in arse. Being old is worse. The alternative is even worse than that.

In Tigertown's rendition, the Legend appears to have been truncated.

2006/07 is in Blue. 2011/12 is in Red. 2016/17 is in Green.

[Bill Fothergill]

I forgot to mention that I have applied a trailing 10-day, equal-weighted smoothing to the diagram.

i.e. The very first data point in the 2006/07 series is the arithmetic mean for the JAXA/IJIS extent values ranging from Dec 23 2005 - Jan 1 2006. The final value in that series is the arithmetic mean taken over Dec 22 2007 - Dec 31 2007.

[Anne]

Bill, there's a slider underneath the graph, which reveals the key.

[Bill Fothergill]

Thanks Anne,

It's a toss-up which is going downhill fastest - the eyes or the brain.   

The slider simply failed to register on my consciousness (or what passes for it these days)

[magnamentis]

IJIS:

9,673,021 km²（November 30, 2016）up 102,260 km² from previous and lowest measured for the date.

the flattening of the curve i and other expected slowly seems to kick in, interesting weeks ahead but that infact applies to most of this year :-) let's see

[Santiago]

Bill Fothergill 2-year Comparison

Thanks Bill and Tigertown, much appreciated!

I know that this graph is the product of very complex phenomena which I don't really understand.
Having said that, there are some distinguishable relationships in the geometry of these curves:
1. The peak of a year 2 is subtly higher than that of its corresponding year 1.
2. The low in 2006 is somewhat flat or truncated. If it had a 'pointier' trajectory, similar to the other years, then there would be a repeated relationship between the lows of year 1 and 2 for each pair.
The relationship would be that year 2 is approx. 1 million km2 less than its corresponding year 1.

If this were to hold true in 2017, then would it be fair to expect a low of 3 million km2 for 2017?
I don't mean to oversimplify this, but I'm just wondering whether there is any merit in comparing 2-year periods.
I'm also a bit surprised to see how consistently close the curves are from one another at certain non-peak intervals.

Thanks again

[Espen]

IJIS:

9,761,201 km²（December 1, 2016）up 88,180 km² from previous and lowest measured for the date.

[oren]

Seems we are safely past the potential meeting point with 2006, and will now have to catch up to the main pack to get out of number one spot. Next target - the 2010 stall on Dec 18th.

[Bill Fothergill]

@ Oren

Yeah, and if you look at the IJIS/JAXA/ADS Antarctic display, you will see that the same thing is going on.

The "record low" Antarctic extent values between the 2nd to the 8th Dec (inc) are currently shared between 2002 and 2006, with 2005 in the basement from the 9th until the year end. Whatever happens over the forthcoming weeks, 2016 is certainly going to clock up more daily lows. It remains to be seen if 2017 will commence in a similar vein.

NSIDC's Charctic display for the Antarctic tells much the same story, but with the earlier years of 1979 and 1982 doing the propping up throughout most of December.
http://nsidc.org/arcticseaicenews/charctic-interactive-sea-ice-graph/

[Bill Fothergill]

...
I'm just wondering whether there is any merit in comparing 2-year periods.
...
I'm also a bit surprised to see how consistently close the curves are from one another at certain non-peak intervals.
...

There are many people on the Forum and on the ASIB who are quite sold on the idea of cyclicity, and the hypothesis that there is a recurring 5 year pattern has several vociferous advocates. Personally, I'm not convinced - either way.

Humans are great at seeing patterns, and that is why citizen-scientists (and the general public) are so useful in projects which require pattern recognition. See these two sites for example...
https://www.zooniverse.org/about
https://www.galaxyzoo.org/

Unfortunately, this propensity towards pattern recognition is so strong (an evolutionary imperative perhaps???) that we can sometimes see patterns that are mere chimeras.

As you know, 2007 and 2012 saw jaw-dropping losses near the annual mins, and, should the 5-year pattern manifest again next year, then 2017 will be something to behold.

However, as I said, I'm unconvinced that there is any "casus belli" to support the hypothesis. Basically, I think the noise level is still too great to expect any accuracy in short-term prediction.

A few years ago, both Rob Dekker and myself wrote articles on Neven's blog on the subject...
http://neven1.typepad.com/blog/2013/06/problematic-predictions.html#more
http://neven1.typepad.com/blog/2013/07/problematic-predictions-2.html

Should 2017 follow a similar pattern to 2007 and 2012, then it might start to show up quite quickly on a 2-year chart of the type provided above.

...

Regarding your comment about how those curves looked close except near the min/max turning points, I suspect that is more to do with the ways our eyes interpret such curves.

I've tried to demonstrate this effect in the attached chart. This shows a full two cycles of three distinct sine waves. The sine waves are identical in frequency, amplitude and phase, but there is a constant offset of +0.05 applied to the red, and a similar offset of +0.1 applied to the green.

I suspect that most people "see" the separation as being biggest near the turning points - even although it is identical throughout.

[DoomInTheUK]

A beautiful example Bill, your marbles haven't completely gone.

[John_The_Elder]

I beg to differ on the "same phase" . If they were in phase they would cross the zero degree line at the same time. The green sine wave is leading,followed by red with blue at zero degrees, zero amplitude.

John

[oren]

I beg to differ on the "same phase" . If they were in phase they would cross the zero degree line at the same time.

Read again. They are offset, each one has its "zero line" at a different height.

[Bill Fothergill]

I beg to differ on the "same phase" . If they were in phase they would cross the zero degree line at the same time.

Read again. They are offset, each one has its "zero line" at a different height.

John, as Oren has already stated, your assertion is in error, but it's an understandable mistake that you are making.

The blue sine wave was generated using the RAD and SIN functionality in Excel, with the values (in degrees) shown along the X-axis as the seed. (Actually, to generate a reasonably smooth curve, 5 degree steps were employed, but, for clarity, the display has been set to show 20 degree steps.) To this, a constant offset of 0.05 was added to generate the red sine wave, and an offset of 0.1 used to generate the green sine wave.

Such an action does NOT, and CANNOT produce any phase shift. (Or, for that matter, any frequency or amplitude shift.)

If you were to look at the 90 and 450 degree markings, you would see that this is where the maximum values occur for each of the three curves. Similarly, the minimum values for each curve appear at the 270 and 630 degree marks.

At the 0, 180, 360, 540 and 720 degree marks, each of the curves is at precisely the halfway point between the min and max - for the appropriate curve. The red curve therefore has an offset of 0.05 above the nominal Zero value on the Y-axis at each of these positions along the X-axis. Similarly, the green curve shows a value of 0.1 on the Y-axis at the identical position along the X-axis.

If one were to expand the graphic, it could be seen that the "Zero crossing" for the red curve occurs just under 3 degrees "late" on the down slope, and the same amount "early" on the upward slope. The green curve however occurs just under 6 degrees "late" on the down slope, and just under 6 degrees "early" on its upward trajectory.

These values of just under 3 and just under 6 degrees (closer to 2.87 and 5.74) equate to a mathematical quantity known as the Arcsin (or Inverse Sine) of, respectively, the 0.05 and 0.10 offsets.

[mmghosh]

There is a physical basis to the 5/6 year cycle, it is related to a possible 2 year lag for El Nino heat to transfer to the Arctic.

[Bill Fothergill]

There is a physical basis to the 5/6 year cycle, it is related to a possible 2 year lag for El Nino heat to transfer to the Arctic.

Whilst ENSO undoubtedly has planetary scale implications, I don't really buy in to that argument. El Nino is a quasi-periodic phenomenon, with a periodicity which is in the 2-7 year range.

Attached is a subset of the NOAA data from 1990 onward. Prior to the 2015/16 event, the last seriously big El Nino was the corker in which happened in 1997/98. (Doctors Christy & Spencer are still fixing their colours to that particular mast, and the effect of the latent heat transfer from ocean >> atmosphere which ensued.)

Full NOAA data set is here...
http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

The 97/98 monster was far bigger than anything preceding the 2007 and 2012 Arctic sea ice "collapses", so one would have to answer the question "why did that have no really apparent effect on sea ice extent/area in 1999, 2000 or 2001?".

One could, of course, claim that this was merely part of the pre-conditioning which enabled subsequent dramatic retreats, but that smacks somewhat of straw-clutching.

[John_The_Elder]

I beg to differ on the "same phase" . If they were in phase they would cross the zero degree line at the same time.

Read again. They are offset, each one has its "zero line" at a different height.

John, as Oren has already stated, your assertion is in error, but it's an understandable mistake that you are making.

The blue sine wave was generated using the RAD and SIN functionality in Excel, with the values (in degrees) shown along the X-axis as the seed. (Actually, to generate a reasonably smooth curve, 5 degree steps were employed, but, for clarity, the display has been set to show 20 degree steps.) To this, a constant offset of 0.05 was added to generate the red sine wave, and an offset of 0.1 used to generate the green sine wave.

Such an action does NOT, and CANNOT produce any phase shift. (Or, for that matter, any frequency or amplitude shift.)

If you were to look at the 90 and 450 degree markings, you would see that this is where the maximum values occur for each of the three curves. Similarly, the minimum values for each curve appear at the 270 and 630 degree marks.

At the 0, 180, 360, 540 and 720 degree marks, each of the curves is at precisely the halfway point between the min and max - for the appropriate curve. The red curve therefore has an offset of 0.05 above the nominal Zero value on the Y-axis at each of these positions along the X-axis. Similarly, the green curve shows a value of 0.1 on the Y-axis at the identical position along the X-axis.

If one were to expand the graphic, it could be seen that the "Zero crossing" for the red curve occurs just under 3 degrees "late" on the down slope, and the same amount "early" on the upward slope. The green curve however occurs just under 6 degrees "late" on the down slope, and just under 6 degrees "early" on its upward trajectory.

These values of just under 3 and just under 6 degrees (closer to 2.87 and 5.74) equate to a mathematical quantity known as the Arcsin (or Inverse Sine) of, respectively, the 0.05 and 0.10 offsets.

Thanks for the clarification, these old eyes are not as sharp as they once were.
 

[RoxTheGeologist]

I've tried to demonstrate this effect in the attached chart. This shows a full two cycles of three distinct sine waves. The sine waves are identical in frequency, amplitude and phase, but there is a constant offset of +0.05 applied to the red, and a similar offset of +0.1 applied to the green.

I suspect that most people "see" the separation as being biggest near the turning points - even although it is identical throughout.

Humans are very good at ascribing value to random data, trying to identify patterns. It's a sales pitch that is often use to sell market models despite the strong evidence that the data is a random walk.

[Ice Shieldz]

The 97/98 monster was far bigger than anything preceding the 2007 and 2012 Arctic sea ice "collapses", so one would have to answer the question "why did that have no really apparent effect on sea ice extent/area in 1999, 2000 or 2001?".

One reason why 97/98 had no apparent impact could be related to the fact that the polar jet, esp down to 500hpa, didn't have the degree of meridional amplitude (waviness) and persistent blocking that we've seen in more recent years building up to and including 2015-2016.  This waviness or sinuosity has enabled nino-boosted atmospheric Rosby waves to advect heat and moisture into the arctic during and after our latest nino.
https://www.carbonbrief.org/scientists-discuss-how-strongly-a-warming-arctic-is-implicated-in-extreme-weather

[DavidR]

It is also worth considering that after the 1982/3 El Nino, 1984 was a record low year for the Arctic Sea Ice; after the 1997/8 El Nino 1999 was a record low year; and after the 2015/16 El Nino?

It already looks bad for next year!

[Santiago]

However, as I said, I'm unconvinced that there is any "casus belli" to support the hypothesis. Basically, I think the noise level is still too great to expect any accuracy in short-term prediction.

This makes sense to me. There is no evidence to support such a pattern.
Thanks for helping me realize this.

If I may be a bit candid: perhaps we'd have to see the presumed 5-year cycle repeat at least another 10 times before we'd begin to give it any serious consideration. By then, many of us will be deceased. So even if it were real, it may not even be ours to discuss.

[Espen]

IJIS:

9,893,102 km²（December 2, 2016）up 131,901 km² from previous and lowest measured for the date.

[etienne]

To come back on the cycle discussion, I made a graph with the NSIDC Sea Ice Extend data with just yearly averages and trend. I didn't find IJIS data for such a long time.

On this graph, the value of May 9th, 2012  (12-05-09, or yy-mm-dd date format) is the Sea Ice Extend average between May 10th 2011 and May 9th, 2012.


I don't see any pattern, excepted that we are more below the trend at the begining and at the end of the graph, with might mean that we don't have a linear trend.

What is sure is that after 2005, we are often below the trend, but check at the CO2 emission curve : http://data.worldbank.org/indicator/EN.ATM.CO2E.KT

There is a NSIDC and Max Planck Institute stating "3 square meters of summer sea ice disappear in the Arctic for every metric ton of carbon dioxide (CO2) that a person directly or indirectly produces"
http://nsidc.org/news/newsroom/us-and-german-researchers-calculate-individual-contribution-climate-change

The other interesting point is that the increase of the CO2 emission probably started with the increase of the oil price.
https://en.wikipedia.org/wiki/Price_of_oil#/media/File:Brent_Spot_monthly.svg

But I couldn't see any easy correlation with the economical growth
http://data.worldbank.org/indicator/NY.GDP.MKTP.KD.ZG

Looks like CO2 emission once up don't come easely down. The good news is that it doesn't seem to increase so much anymore.
https://www.theguardian.com/environment/2016/nov/14/fossil-fuel-co2-emissions-nearly-stable-for-third-year-in-row
But I always wonder how such datas can be calculated with so many areas with war or unrests.

Best regards,

Etienne

[be cause]

Hi Etienne ..

when banks were given the freedom to lend many times the amount of security they actually had ; the money became available to pour into destroying the future . Any returns are free money to the 1% , as the loans made to the 'little people' have to be repaid . Our planet has become a casino and the rich cannot lose (at this stage) . This is where the funding of Climate catastrophe has come from .

[shmengie]

What is sure is that after 2005, we are often below the trend, but check at the CO2 emission curve :

Studied it for a while and then it hit me. It's hard to see, IMO. CO₂ isn't the cause of warming, even tho it helps, it's also one of the symptoms. If you look closely, methane (CH₄ small increases of PPB) is precursor larger CO₂ increases at PPM.

Presently we're Fracking CH₄ (CH₄ell) out of the Earth at an unprecedented rates internationally. CO₂ production was marginally lower in 2016 compared to 2015, but CH₄ production is at an all time high.

The unprecedented recede of Antartic sea ice and now global sea ice coincides as a consequence of the Aliso Canyon blowout, which vented around 100,000 tons of methane into the atmosphere before it was plugged.

I don't know how accurate my calculation of 100k tons == 8.6GT  CO₂  but I fear it's close.  There's not much data floating about, w/regard to methane floating about...

I don't believe  CO₂ is the LARGEST contributor.

[Tigertown]

CO² lasts so much longer.

"While CO2 persists in the atmosphere for centuries, or even millennia, methane warms the planet on steroids for a decade or two before decaying to CO2.
In those short decades, methane warms the planet by 86 times as much as CO2, according to the Intergovernmental Panel on Climate Change."   
https://www.scientificamerican.com/article/how-bad-of-a-greenhouse-gas-is-methane/

Lately it appears that H²O vapor has been the most powerful gas to influence the Arctic, though it took the other gases to  boost it to that position.

[jdallen]

What is sure is that after 2005, we are often below the trend, but check at the CO2 emission curve :

Studied it for a while and then it hit me. It's hard to see, IMO. CO₂ isn't the cause of warming, even tho it helps, it's also one of the symptoms.

Careful, shmengie;

You need to evaluate the relative forcing of each of the major GHG's - CO2, CH4 and CO2.  You also have to place each in context. 

I think Tigertown has also put thing pretty well in context; short term, CO2 is the fuse, H2O is the bomb.  CH4 will have some prompt effects as we see out-gassing from clathrates and biomass as things heat up, but none of that would be happening if we hadn't pushed CO2 concentration to over 400PPM.

The effect of CH4 is also very quick - it rapidly oxidizes in the atmosphere, and can't persist long enough to really have a serious impact - it's half life is measured in years, not decades.  Even if we have a massive CH4 spike, 50 years out, 98% of it will be gone.  Even with a spike, while it may affect very short term weather, it won't have as much long term effect on climate as CO2 (and in association with that, increased humidity) will have.

Now, increased CH4 is still a problem - don't get me wrong.  However, it isn't the long term problem posed by CO2 increases.

[Espen]

IJIS:

9,997,606 km²（December 3, 2016）up 104,504 km² from previous and lowest measured for the date.

[6roucho]

I don't know how accurate my calculation of 100k tons == 8.6GT  CO₂  but I fear it's close.  There's not much data floating about, w/regard to methane floating about...

One kilogram of methane is 21x as effective at trapping heat in the earth's atmosphere as a kilogram of carbon dioxide within 100 years, so 100 Kt methane ~ 2.1 Mt C02 in terms of its warming potential. Far short of 8.6 Gt but nonetheless a significant contributor to warming.

The current yearly emissions of methane from all sources (natural and anthropogenic) is ~500 Mt. During the last two hundred years, atmospheric methane concentrations have more than doubled to ~1800 ppbv.

http://icp.giss.nasa.gov/education/methane/intro/cycle.html

[Bill Fothergill]

It is also worth considering that after the 1982/3 El Nino, 1984 was a record low year for the Arctic Sea Ice; after the 1997/8 El Nino 1999 was a record low year; and after the 2015/16 El Nino?

It already looks bad for next year!

David, the Nimbus 7 mission launched in Oct 1978, and part of its payload was the Scanning Multi-channel Microwave Radiometer, or SMMR. The multi-channel nature of this passive sensor enabled differentiation between new ice and multi-year ice, something that was not possible with its 1972 precursor, the Electrically Scanning Microwave Radiometer (ESMR). As a consequence, the NSIDC usually starts its ice data sets at 1979. (Although the ESMR data set is available to download as an FTP.)

The September average extent in 1984 was 7.11 million sq kms, but this was just 140k below the 1981 value. However, given that there was only 6 years of data in the can by that stage, I think it's stretching things a bit to draw any conclusions about the ENSO state acting as a meaningful predictor. Anyway, that "record" lasted just 12 months and was then pushed back to 3rd lowest in 1989, before being absolutely stuffed in 1990.

I'm not sure which data you are looking at when you state that 1999 was a record low year. In the NSIDC monthlies, the September average extent for 1999 was 6.29 million sq kms. However, the equivalent value in 1995 had been 6.18 millions sq kms, with 1990 also having registered as 6.27 million sq kms.

The years in which record low September average extents have appeared in the NSIDC database are...

1984, 1985, 1990, 1995, 2002, 2005, 2007, 2012

That's 8 in 38 years of data, so it's pretty damn close to about once every 5 years. However, that pattern absolutely fails to convince me that there is some underlying driver which has a 5-year period.
 
On the other hand, I completely agree that it looks bad for next year! 

[Bill Fothergill]

... 
There's not much data floating about, w/regard to methane floating about...

I don't believe  CO₂ is the LARGEST contributor.

Regarding CH₄ atmospheric variations over time, you might want to have a dekko at some of the material offered on the Carbon Dioxide Information Analysis Centre...
http://cdiac.ornl.gov/trends/atm_meth/modern_methane.html

Tigertown & Jdallen have already responded regarding the relative size of different forcing agents. I don't know if you are familiar with the material presented on this subject in the various IPCC reports. The relevant section from the 5th Assessment Report can be seen here...
https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf

In particular, you might want to check out Table 8.2 on page 678. Don't worry! The pagination number refers to the document in its entirety, not to Chapter 8 from Working Group 1.

As gets discussed from time to time on the ASIB, the trajectory of future atmospheric CH₄ loading is very problematic. The Arctic Methane Emergency Group feel that methane release from clathrates is an imminent disaster waiting in the wings, whilst others feel that their concerns are unnecessarily alarmist. (I'm fence-sitting.)

[Bill Fothergill]

... Bill, your marbles haven't completely gone.

Thank you. At the most recent census, the count was down to a single remaining marble.

I'm too scared to ask for a recount. 

[Bill Fothergill]

... One kilogram of methane is 21x as effective at trapping heat in the earth's atmosphere as a kilogram of carbon dioxide within 100 years ...

My understanding (always very limited) is that a more recent estimate puts the GWP100 value for methane at either 28 or 34, depending whether or not climate carbon feedbacks are considered.

Please see Table 8.7 on Page 714 of...
https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf

As mentioned in an earlier post, the Page number referes to the entire 5th Assessment Report, not to the link provided.

Until about 2 weeks ago, I was still thinking in terms of a value very similar to you, but was brought up to date on the Mauna Loa CO₂ thread...
http://forum.arctic-sea-ice.net/index.php/topic,1546.50.html

The relevant stuff starts at about Comment #63