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Sunday, January 11, 2015

Are all forcings created equal?

Crowley and Untermann's 1200 year Global and Hemispheric Volcanic Forcing Estimate 2013 appears to be the most comprehensive reconstruction of Volcanic activity available.  The link embedded is to the data archived on the NCDC website.  I tend to have issues with the whole "global" forcing thing.  Averaging volcanic forcing should be a bit more challenging.  C & W break down the volcanic events by hemisphere and tropics.  Tropical activity should reflect the most energy and SH activity should have more impact on ocean heat capacity variation than NH activity.  Time of year due to the shift in solar forcing is another factor along with thermal inertia due to ocean circulation which doesn't seem to have an easily predictable pattern.  So determining the "global" forcing impact of sporatic volcanic activity should be a bitch squared.

A typical way to look at volcanic forcing is a rapid impact that quickly goes to zero.  This is probably a good way if you are looking for short term impacts in the lower troposphere which some consider to be the "global" "surface".  

A more realistic way in my opinion would to be looking for the more gradual but longer lived impact on ocean heat content.  For this chart I used an 11 year moving average to spread the forcing out.  If you know the time constants needed, you could determine an "average" forcing for some period and then a cumulative forcing based on that average.  With that approach, a period with less than "average" forcing would appear to be a period with positive solar forcing.  If the cumulative forcing from some prior period is large enough or the time constant long enough, you may not be able to find any reasonable fit.  Add to that the large uncertainties in paleo climate reconstructions and you have a can of worms.

Based on current estimates of ocean heat uptake and the Oppo et l. 2009 Indo-Pacific Warm Pool temperature reconstruction, it looks like around 300 years of initial forcing information would be required to have any confidence in a fit.  That is not something that is going to wow the overly confident crowd that publish things like this.

 In the background is a recent chart published by Micheal Mann of hockey stick fame with the titile 1000 years of "GLOBAL" temperature and CO2 Change.  It is a bit hard to see but from 1902 back is one of his old tree ring circus based NH temperature reconstructions with 1902 to present (~1998) being the instrumental period data deftly spliced.  Overlain is the Oppo et al. 2009 IPWP reconstruction which seems to indicate Mikey might be fudging his "GLOBAL" interpretation a touch.  Steve McIntyre has a post on Mikey's latest called More Mann Grafting over at Climate Audit.

If you happen to think Mikey is a gifted statistical genius, Volcanic forcing has virtually zero impact on climate, so Crowley and Untermann wasted taxpayer dollars on a futile effort.  I don't personally know any of the players, but I do tend to have my doubts about Mann's Mathematical prowess.

In the overlay I included the 50 year smoothed and monthly data for the East Indian Ocean with Oppo 2009 sans a real "splice" for perspective.  The Oppo et al. 2009 data ends in 1955 and is actually close to 50 year smoothed data "binned" or interpolated to decade resolution.  Because of that, a 50 year smooth comparison, not a decadal smooth should be a more reasonable comparison but I will leave that up to anyone wanting to play with the data.  The monthly data I included should provide a rough picture of what uncertainty might be appropriate.

As I said, if Mikey is right, this is just another waste of time.  Everyone should stop what they are doing and start kissing their asses good bye.  Working under the assumption that Mikey may not be the sharpest tack in the box, the Oppo et al. 2009 reconstruction of the IPWP, which happens to have an extremely high correlation with "global" temperatures, plus the Crowley and Untermann 2013 volcanic forcing reconstruction provide some interesting opportunities to reduce some to the volcanic forcing uncertainty.

In the world of solar forcing there are also plenty of opportunities.  It turns out that sun spot numbers leave a bit to be desired as a solar forcing proxy.  There are other solar energy proxies like 10Be and 14C which should provide some indication in the variation in solar but thanks to volcanic emissions having a possible impact on high energy solar emissions that produce the 10Be and C14, solar and volcanic may be inextricable linked in paleo forcing reconstructions.  Some time ago I used the Steinhilber TSI reconstruction combined with Crowley and Untermann to create a "global" Sol y Vol forcing estimate.  This time I went for the more tropical combination.

 I don't have units for the forcing thanks to the solar kerfuffle, but this should be a ballpark visualization of the potential forcing variation.  As you can see ~1230 should have been the minimum temperature period if the oceans and atmosphere both respond rapidly.  According to Oppo et al. 2009, ~1700 was the minimum temperature period in the IPWP and likely tropics.  That would indicate that there is a considerable, ~350 year lag in ocean response to the numerous volcanic events with some solar influence.

That multiple century lag is not something I have seen considered in most of the Climate Science literature.  It is something that I have considered and using the limited current Ocean Heat Uptake data and the Oppo et al. 2009 reconstruction from 1700, there is an indication of just such a lag.

Not a perfect fit by any means but a hint of something more that needs to be considered.

Using a cumulative forcing estimate you can end up with something like this.  This is not particularly robust but it is encouraging to get a rough fit, especially the ~1700 AD minimum just by assuming the cumulative forcing would result in about the same shape as the Oppo et al. 2009 reconstruction.  I don't have units since this there is no indication of initial values meaning this whole effort could be a waste of time, but there it is if someone can think of a more "scientific" method of determining what correlation there should be.

Of course this could be adjusted to match the Mann reconstruction/splice by simply tuning down the volume so to speak making solar and volcanic insignificant.  In any case, some slow weekend I may come back to this in search of an epiphany.

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