Ocean Variability in the Models

Posted by on

A group of climate modelers at Lawrence Livermore and elsewhere has taken issue (in the peer-reviewed literature) with an argument made by Roger Pielke Sr. and others that the models cannot adequately explain variability in ocean temperatures:

Using simulations of 20th century climate performed with 13 numerical models, we demonstrate that the apparent discrepancy between modeled and observed variability is largely explained by accounting for changes in observational coverage and instrumentation and by including the effects of volcanic eruptions. Our work casts doubt on two recent claims: (i) that the 0- to 700-m layer of the global ocean experienced a substantial OHC decrease over the 2003 to 2005 time period and (ii) that models cannot replicate such changes. Our analysis shows that the 2003–2005 cooling is largely an artifact of a systematic change in the observing system, with the deployment of Argo floats reducing a warm bias in the original observing system.

Simulated and observed variability in ocean temperature and heat content, AchutaRao et al., Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0611375104

4 Comments

  1. John – Their peer reviewed paper is a significant addition to the evaluation of multi-decadal global climate prediction as I agree ocean heat content change is the most appropriate climate metric to use to diagnose global warming or cooling.

    The challenge for them now is to show they can skillfully predict the recent (last few years) lack of global average ocean warming, as well as the changes over the next few years. As I posted on Climate Science in the weblog

    A Litmus Test For Global Warming – A Much Overdue Requirement [http://climatesci.colorado.edu/2007/04/04/a-litmus-test-for-global-warming-a-much-overdue-requirement/]

    this real time comparison between models and observations is an essential test that is required to accept their model predictions as skillful.

    In my weblog, I posed the following question,

    “What is the magnitude ocean heat storage changes each year?”

    and added

    “For global warming to occur, the heat, as measured in Joules, needs to increase each year.

    The heat accumulation for the period from 2002 to the present and into the future needs to be a high priority. For example to sustain a global warming rate of 1 Watt per meter squared since 2002 for the following ten years requires the accumulation of 1.6 *10**23 Joules within the climate system.”

    The 2007 IPCC Statement for Policymakers [http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_SPM-v2.pdf] gives a mean value of 1.78 Watts per meter squared (see Figure SPM.2) for the “Global average radiative forcing (RF) estimates and ranges in 2005”, so that the actual ocean heat accumulation, without even considering positive radiative feedbacks (such as water vapor), should make the total positive radiative forcing even larger.

    Unfortunately, the AchutaRao et al paper is silent on this issue. See also

    “The Net Climate Feedbacks Must Be A Negative Effect On The Global Average Radiative Imbalance If The IPCC Conclusion Of Net Anthropogenic Radiative Forcings Is Correct” [http://climatesci.colorado.edu/2007/03/19/climate-feedbacks-must-be-a-negative-effect-on-the-global-average-radiative-imbalance-if-the-ipcc-conclusion-of-anthropogenic-radiative-forcings-are-correct/].

  2. “The challenge for them now is to show they can skillfully predict the recent (last few years) lack of global average ocean warming, as well as the changes over the next few years.”

    I don’t think anyone has ever claimed that ocean-atmosphere climate models can predict (hindcast or forecast) year-to-year variations in ocean heat content. What AchutaRao et al are arguing (apparently, I’m downloading the paper right now) is that the models have realistic levels of interannual variability. I believe you were arguing recently, Roger, that they don’t.

    BTW, thanks very much for the link, John.

  3. “I’m downloading the paper right now”

    Oops, no I’m not. It appears our library has a PNAS full-text subscription only for material 6 months older or earlier, thus ensuring we are right at the forefront of 6-month-old science. On second thoughts, maybe that’s not a bad idea, as recent experience in this area has shown us not to get too excited about results that are hot off the presses.

Comments are closed.