Comments On Two Papers By Kevin Trenberth On The Global Climate Energy Budget

Kevin Trenberth (and Josh Willis) should be commended for providing us an open discussion of the issue of the energy budget of the climate system, as I posted yesterday with their permission; 

Further Feedback From Kevin Trenberth And Feedback From Josh Willis On The UCAR Press Release

We need more such collegiality. 

Today, I want to discuss two papers by Kevin. These are 

Trenberth, K. E., and J. T. Fasullo, 2010: Tracking Earth’s energy. Science, 328, 316-317 

Trenberth, K. E., 2009: An imperative for climate change planning: tracking Earth’s global energy. Current Opinion in Environmental Sustainability, 1, 19-27, doi:10.1016/j.cosust.2009.06.001. 

Since Kevin Trenberth is an internationally respected climate scientist, his views on this issue are worth discussing further. 

First, in terms of agreement, his goal of attempting to quantify the individual contributions to the climate system energy budget in terms of fluxes (watts per meter squared) is very much-needed.   I support Kevin on this effort. His various versions of Figure 2 in Trenberth (2009)  have been one of the most cited in global climate science.  

There are substantive issues with this figure, however, which include 

  • the uncertainties in the observational accuracy of each flux (in +/- Watts per meter squared) is not included.
  • the figure represents a long term average of these fluxes, but in the actual climate system these fluxes are never in equilibrium as solar irradiance varies through the year (e.g. see our paper for the resulting effect on the global average tropospheric temperatures as a function of the time of year).
  • the figure provides a global average of the fluxes, but in the actual climate system, these fluxes are spatially variable (e.g. see). 
  • the radiative imbalance is only about 0.26% of the global average incoming solar radiation and only about 0.31% of the global average outgoing long wave radiation so it is quite a challenge to diagnose a change in the resulting radiative imbalance (which is about 0.9 Watts per meter squared from Kevin’s paper).

The results of these complexities is that a global average, long-term mean of the fluxes (while valuable as a starting schematic) can obscure how the climate actually works. 

Figure 4 in his 2009 paper continues to focus on a global average, long-term mean perspective.  While here the uncertainty is included, the temporal variation with a year (even in the long-term multi-year average) in the radiative forcings and feedbacks is not included. 

As a result of these uncertainties, I recommend we start from the bottom row in Kevin’s figure 4. This is the total net imbalance which is given as about 0.9 Watts per meter squared (0.4 to 1.4 Watts per meter squared).  This is where Trenberth and Fasullo conclude in their 2010 paper that there is missing heat 

We have a way to estimate this imbalance independent of summing the climate forcings and feedbacks in figure 4. Despite Kevin’s 2009 conclusion that

“Many analyses before about 2008 of ocean heat content are now obsolete” 

as is discussed in yesterday’s post, all of the ocean analyses are in close agreement since 2005 and are concluded to be robust.  The net radiative imbalance (the bottom row in Kevin’s figure 4) is actually very close to zero over this time period.

In Table 1 of the 2009 paper, Kevin lists the column in the extreme right as the “Residual”.  This is the “missing heat” that he reports on in his Science Perspective. However, the analysis of the change in ocean heat content by Josh Willis and others shows that these is little if any unsampled heat in the climate system, at least since 2005 to last summer.  

My recommendations to resolve this disagreement with Kevin are as follows: 

  • start from the known radiative imbalance as documented by the ocean measurements (with estimates included, as Kevin has presented, for the other components of the climate system), and seek to diagnose the different contributions to the imbalance from each of the components in figure 2 in Trenberth (2009).  This approach starts from the imbalance, rather than seeking to determine the radiative imbalance (i.e. the residual) as a summation of a set of uncertain climate forcings and feedbacks.
  • in performing this analysis, the fluxes within the annual cycle also need to be presented (e.g. on a multi–year monthly average basis). This will permit a demonstrati0n as to whether we adequately understand the energy budget on this time scale. Since the annual average results from a summation through the 12 month annual cycle,  this will provide an improved opportunity to assess the extent we really understand this aspect of the climate system.
  • the spatial distribution of the fluxes on this time scale need to also assessed.

Finally, I am pleased that the Trenberth and Fasullo (2010) paper presented their figure with the “missing heat”. It is this heat that I presented as a test of the IPCC models in my post 

Update On A Comparison Of Upper Ocean Heat Content Changes With The GISS Model Predictions 

[see also my paper Pielke Sr., R.A., 2008: A broader view of the role of humans in the climate system. Physics Today, 61, Vol. 11, 54-55]. 

Apparently, unless the “missing heat” can be found, the conclusion would be that, at least for this relatively short time period, the models are not accurately replicating changes over time  in the energy budget of the real world climate system. Also, in order for the IPCC models to come back into conformity with the real world, they must have a substantially above average radiative imbalance in the next few years.

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