Reply By Josh Willis To Climate Science Questions Of August 19 2008

Josh Willis graciously has answered the questions that were asked in the Climate Science weblog of August 19 2008.

 Question by Roger A. Pielke Sr.

“In terms of global warming, there is not a ‘bigger picture’ than the diagnosis and monitoring of ocean heat content changes.”

Reply by Josh Willis

I agree.  However, there is a 50 year record of ocean heat content that, despite it’s recent problems, still shows 50 years of ocean warming and implies a net positive radiative imbalance over that period.  Furthermore,the 100 year records of sea surface temperature:

and global sea level rise:

strongly suggest that the net imbalance goes back even further.  Of course, I agree with you that other forcings besides CO2 are also important.  And I believe you that the relative strength of the different forcings is still uncertain.  But I think it would be very surpising to learn that CO2 doesn’t matter at all.  So, given its residence time and the likelihood that humans will continue to increase the amount in the atmosphere over the next century, it seems like a no-brainer that we are in for at least some addition anthropogenic warming from CO2 over the next 100 years.

Question by Roger A. Pielke Sr.

“A question for you is when will you be posting upper ocean heat content anomaly maps and long term trends in near real time? This would substantially elevate the scientific discussion of global warming.”

Reply by Josh Willis

Yes, I know I’m behind on this.  Issues with data biases continue to come up.  Although I don’t think there will be any problems as large as those with the XBT probes or the small group of bad Argo floats, researchers at CSIRO are continuing to make refinements to the pressure measurements returned by Argo floats.  And, if they discover problems that affect large numbers of floats in the same way, it could have an impact on estimates of globally-integrated ocean heat content.  Again, I think these problems will end up being small, but they are slowing progress on making real-time estimates of ocean heat content.

Question by Roger A. Pielke Sr.

“My question to you is what would have to occur in terms of the accumulation of upper ocean heat content for you to reject the IPCC climate model predictions of global warming? For instance, what accumulation in Joules must the upper ocean have for the 10 year period starting in 2004 for you to not reject the model predictions of this quantity?”

Reply by Josh Willis

I don’t think “when should we reject the model” is quite the right question to ask.  I think we should back up a bit and ask “what should we expect the model to get right?”  The problem is that we really don’t have a good idea of what the interannual to decadal variability in ocean heat content and radiative imbalance looks like.  That’s because until recently, the accuracy of ocean heat content estimates has not been adequate to resolve year-to-year fluctuations. Estimates like those from Levitus are good enough to say that the Earth has been out of radiative balance for much of the last 50 years, but they are not accurate enough to get the interannual flucatuations right, and the decadal variations were plagued by data problems.  As we fix these problems, we will get a better idea of what these interannual to decadal changes look like and we can begin to ask if the models are getting it right.

But suppose we find that there is internal ocean variabiltiy that causes year-to-year and decade-to-decade fluctuations in the radiative imbalance, and that the IPCC models don’t simulate this variability.  That doesn’t necessarily mean that the IPCC estimates of net heat content change after 50 to 100 years will be way off base, only that the envelope of possible future heat content changes is broader than expected because there is natural variability we didn’t now about.  In other words, we may find out that the radiative balance fluctuates naturally over periods of years to decades, but that the IPCC models are still getting the magnitude of the external forcing approximately right.  I’m not saying that’s definitely the case.  Only that we can’t rule it out solely on the basis of a few years of zero radiative imbalance.

I do agree with you that several years of zero or little radiative imbalance poses some very difficult questions for the modeling community. But I do not think it is grounds for outright rejection of all model results.

Roger A. Pielke Response  

With respect to anthropogenic CO2, I agree it is (and will continue to be) a warming forcing. However, it does not mean that the total radiative imbalance due to human activities will be positive over multi-decadal time scales, since a number of the forcings are negative. These negative effects include several of the aerosol forcings that we identified in the 2005 NRC report (e.g. see), as well as possible negative radiative effects from circulation changes (both from natural and human caused effects; e.g. see).

 In terms of rejecting the global  climate models as having forecast skill, if they cannot quantitatively simulate decadal global heat accumulation, they certainly should not be used for decadal regional climate predictions (which they are being used for; e.g see).

The current lack of global warming for four years is too short to convincingly reject the models with respect to the prediction of the decadal radiative imbalance but, I agree with you that it certainly raises difficult questions for the modeling community. The tracking of the ocean heat content in the coming years should be among the highest priorities in climate science.

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