“The world’s oceans, atmosphere and glaciers have received a great deal of attention because of their sensitivity to warming, and also for the implications warming has on their respective abilities to store or release carbon dioxide,” Hugo Beltrami of St Francis Xavier University, Canada, told environmentalresearchweb. “Most general circulation models (GCMs), however, are not capable of storing realistic amounts of heat transferred from the atmosphere to the ground, because the bottom boundary of the model used to represent the subsurface is too shallow, usually 1 to 10 m.”
In this study Beltrami and colleagues of St Francis Xavier University and Complutense University of Madrid, Spain, calculated the amount of heat storage possible in the subsurface of the ECHO-G general-circulation model by using an offline soil model that simulates a deep bottom boundary that allows the subsurface to capture all the incoming energy from the atmosphere.
“This is the first time the subsurface component of a general circulation model has been examined for its realism,” said Beltrami. “We found that if the bottom boundary were placed deep enough [100 m] that all incoming energy was stored in the subsurface, the model could have accumulated 7.5 times as much heat. Increasing the subsurface depth in ECHO-G directly is not currently a viable option because of the huge computational demand.”
According to the team, the lack of ability of general circulation models to simulate storage of subsurface heat could affect the realism of their results. The underestimation of the heat stored may be particularly great for northern high latitudes.
“There are a number of important energy feedbacks that occur between land and atmosphere that could be affected over time by too small a subsurface heat storage reservoir,” said Beltrami. He believes that the next generation of global climate models should be designed with this in mind; advancements in computational resources may be sufficient to allow for deep subsurface components, or alternative types of bottom-boundary conditions.
“These results are also important because of the implications on the thermal regime of the ground in permafrost areas, and also on the long-term potential for carbon storage in soil,” added Beltrami. “Twice as much carbon as in the whole atmosphere is presently stored in the upper metre of the world’s soil. Proper assessment of the thermal regime of the ground would allow for assessment of the future stability of the old carbon currently stored in soils.”
The researchers, who reported their work in Geophysical Research Letters, now plan to examine other aspects of general circulation model performance “particularly those pertinent to high latitude climate – such as freeze/thaw, permafrost, and snow”.