Thursday, April 22, 2010

Where did the Heat Go?

By R.A. Pielke Sr.
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. Read more.

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