Comment On The Article “Recovery Of Upper Ocean Heat From Major Volcanic Eruptions” By Heckendorn Et Al 2010

There is quite an informative article in the January 2010 issue of the SPARC [stratospheric processes and their role in climate] Newsletter. The article is

P. Heckendorn, F. Arfeuille, D. Weisenstein, S. Brönnimann, T. Peter, 2010 “SPARC Volcano Workshop 8-9 July 2009, Zurich, Switzerland” SPARC 2010 Newsletter no34 January.

I have two comments on this informative meeting summary

In  Section “Part IV: Radiative, chemical and dynamical response to volcanic eruptions”, there is the text

“G.Stenchikov showed with CM2.1, the recent GFDL coupled climate model (Delworth et al., 2006), that the accumulated averaged volcanic ocean heat content anomaly reaches about 1023 J, and offsets about 1/3 of the anthropogenic warming. After the Tambora and Mt. Pinatubo eruptions, the heat content below 300 m was reduced for decades (see Figure 5). Deep ocean temperature, sea level, salinity, and MOC (meridional overturning circulation) have a relaxation time of several decades to a century. This suggests that the Tambora subsurface temperature and sea level perturbations could have lasted well into the 20th century.”

This multi-decadal climate system memory to the radiative forcing of a volcanic eruption is quite an important conclusion. This would, of course, also apply to all other types of radiative forcing.  Climate prediction is clearly an initial value problem as I wrote about in

Pielke, R.A., 1998: Climate prediction as an initial value problem. Bull. Amer. Meteor. Soc., 79, 2743-2746. 

My second comment is with respect to the clear evidence of a negative radiative feedback (i.e. an adjustment back to a zero anomaly) when the volcanic eruptions produce a cooling radiative forcing (see the two figures below). This is clearly seen in the two figures below from the Stenchikov et al study reported on above. The obvious question is whether this negative feedback, for example, is due to changes in cloud cover in response to the volcanic emissions, and if such a feedback also operates when there is a warming radiative forcing. 

   
 
 

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