I want to thank Jos de Laat of the Royal Dutch Meteorological Institute (KNMI) for alerting me to a new peer reviewed paper on land surface heat storage. It is a very important research contribution as it adopts the appropriate unit of Joules to assess climate system heat changes.
The paper is
Stevens M. B., J. E. Smerdon, J. F. González-Rouco, M. Stieglitz, H. Beltrami (2007), Effects of bottom boundary placement on subsurface heat storage: Implications for climate model simulations, Geophys. Res. Lett., 34, L02702, doi:10.1029/2006GL028546.
The abstract reads,
“A one-dimensional soil model is used to estimate the influence of the position of the bottom boundary condition on heat storage calculations in land-surface components of General Circulation Models (GCMs). It is shown that shallow boundary conditions reduce the capacity of the global continental subsurface to store heat by as much as 1.0 × 10**23 Joules during a 110-year simulation with a 10 m bottom boundary. The calculations are relevant for GCM projections that employ land-surface components with shallow bottom boundary conditions, typically ranging between 3 to 10 m. These shallow boundary conditions preclude a large amount of heat from being stored in the terrestrial subsurface, possibly allocating heat to other parts of the simulated climate system. The results show that climate models of any complexity should consider the potential for subsurface heat storage whenever choosing a bottom boundary condition in simulations of future climate change.”
Important excerpts from the paper, as noted by Dr. de Laat include
“Most GCMs have shallow BBCPs [bottom boundary placements]; Figure 3 can serve as a guide to scale results from other models. For any soil model, if the BBCP is at a depth that is too shallow, the amount of energy stored in the ground may be underestimated. As shown in Figure 3, an increase in BBCP from 10 m to 100 m could result in a four- to five-fold increase in heat storage potential. Furthermore, if there is a feedback mechanism involved between land surface and atmosphere, this unabsorbed quantity of heat may partition to other model subsystems. This is potentially a very important issue for climate models since ascertaining the energy balance of the climate system and all its components is a fundamental requirement for proper evaluations of future climatic trends [Shin et al., 2006, and references therein].”
“As the simulation depth in the 1DSM increases, so too does the potential for subsurface heat storage. For example, for a BBCP at a depth of 10 m, the total heat stored in the subsurface (1.9 × 10**8 J) would be less than one-quarter of the asymptotic value (8.8 × 10**8 J). If scaled over the entire continental surface (1.5 × 10**14 m2), 1.0 × 10**23 J, or 75% of the corresponding asymptotic value (1.3 × 10**23 J) would not be stored in the terrestrial subsurface. This heat, absorbed over 110 years, is more than an order of magnitude greater than the heat absorbed by both the whole atmosphere and continental areas in the latter half of the 20th century [Beltrami et al., 2002; Levitus et al., 2005; Huang, 2006; Beltrami et al., 2006a].”
This is yet another example of why an assessment of heat storage changes in units of Joules should be the appropriate global warming and cooling currency (e.g. see), as well as further evidence of the complexity of the climate system which, unfortunately has been inaccurately discussed in the IPCC assessments. A significant consequence of such deeper land heat storage is that the GCM multi-decadal global climate predictions with shallow lower boundaries are overestimating the land surface temperature trends in response to a positive global radiative forcing.