Update On Jim Hansen’s Forecast Of Global Warming As Diagnosed By The Upper Ocean Heat Content Change

Jim Hansen responded in 2005 to a comment we made on ocean heat content with respect to a Science Express article he wrote in that year [Pielke and Christy, 2005; our Comment was (no surprise) rejected by Science]. Jim’s entire 2005 response can be read here.

“Contrary to the claim of Pielke and Christy, our simulated ocean heat storage (Hansen et al., 2005) agrees closely with the observational analysis of Willis et al. (2004). All matters raised by Pielke and Christy were considered in our analysis and none of them alters our conclusions.

The Willis et al. measured heat storage of 0.62 W/m2 refers to the decadal mean for the upper 750 m of the ocean. Our simulated 1993-2003 heat storage rate was 0.6 W/m2 in the upper 750 m of the ocean. The decadal mean planetary energy imbalance, 0.75 W/m2, includes heat storage in the deeper ocean and energy used to melt ice and warm the air and land. 0.85 W/m2 is the imbalance at the end of the decade.”

With the new 2010 paper

John M. Lyman, Simon A. Good, Viktor V. Gouretski, Masayoshi Ishii, Gregory C. Johnson, Matthew D. Palmer, Doug M. Smith, Josh K. Willis, 2010: Robust warming of the global upper ocean. Nature 465, 334-337 (20 May 2010) doi:10.1038/nature09043 Letter

we can update how well Jim Hansen’s prediction is comparing to observations. My last update was on February 9 2009 [I have a post on Keven Trenberth’s commentary on the Lyman et al paper on Monday].

The Lyman et al 2010 paper concludes that 

“Accounting for multiple sources of uncertainty, a composite of several OHCA curves using different XBT bias corrections still yields a statistically significant linear warming trend for 1993–2008 of 0.64W per meter squared (calculated for the Earth’s entire surface area), with a 90-per-cent confidence interval of 0.53–0.75 W per meter squared.”

The 1993 to 2008 value is close to the Hansen prediction despite the flattening of the heating of the upper ocean reported in the Lyman et al 2010 paper since 2003 [if we use Jim Hansen’s expected radiative imbalance at the end of the 1990s of 0.85 Watts per meter squared and use  80% of that to represent the upper ocean heat content change, his prediction of the heating rate of the upper ocean is 0.68 Watts per meter squared. This is within the uncertainty of the Lyman et al analysis].

However, there are important questions with respect to conclusion of Jim Hansen’s forecast as well as an opportunity.  First, since the heating rate is dominated by the time period prior to 2004, an assessment of whether the GISS model (which is the basis of Jim’s forecast) produces interruptions of the heating for this long needs to be made and reported. Also, over 40% of the heating occurred in just the time period 2002 and 2003 with about 30% more in 1999.  Does the GISS model predict such shorter term bursts of heating?

With respect tot the lack of recent heating, the Lyman et al 2010 paper write

“The individual OHCA curves all flatten out after around 2003, with some variability among curves in the year in which this levelling occurs. The causes of this flattening are unclear, but sea surface temperatures have been roughly constant since 2000. Although sea level has continued to rise steadily during this period, an increase in the amount of water added to the ocean by melting continental ice in recent years may account for most of this rise even with very little change in ocean heat content….The flattening of OHCA curves also occurs around the time (2004) that the Argo array of autonomous profiling floats first achieved near global coverage and became the primary source of OHCA data.”

A consequence of this absence of heating is that we should soon see a return to the radiative imbalance predicted by Jim Hansen, if he is correct. Indeed, this provides us the best opportunity we have over the next few years to test the robustness of the  multi-decadal global models to predict the climate system radiative imbalance (i.e. global warming).

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