Box models
Box models are conceptual tools used to simplify and analyze complex systems by representing various components as interconnected boxes, which are linked by flows of materials or energy. In the context of environmental science, particularly the global carbon cycle, these models help to identify reservoirs—areas that can store or release substances, such as carbon in oceans, plants, and soils. A "pool" is often used interchangeably with "reservoir," though it may also include the atmosphere. Stocks refer to the actual quantities of substances, such as carbon dioxide and organic matter, within these reservoirs.
Box models are essential for understanding and predicting climate change, as they provide insights into how variations in carbon cycles influence global temperatures. They serve as a foundation for predictions made by organizations like the Intergovernmental Panel on Climate Change. Despite their utility, one significant challenge in developing accurate box models lies in estimating the sizes of reservoirs and the amounts of stock, particularly in less understood areas, such as gas hydrates on the seafloor. Overall, box models play a critical role in environmental science by allowing researchers to assess how stocks within reservoirs change due to various factors, informing strategies for mitigating climate change.
Subject Terms
Box models
Definition
Reservoirs, pools, and stocks are designations used in box models. A box model is a simplified version of a complex system, in which various parts of that system are reduced to boxes that are linked by fluxes. A reservoir is any box within that system that can accumulate, store, or release the substance of interest. In box models of the global carbon system, the oceans, terrestrial plants, soil, and rocks are examples of reservoirs. The atmosphere is typically not considered to be a reservoir. “Pool” is a term that is synonymous with “reservoir” but can include the atmosphere.
Stocks are the actual accumulations of the substance of interest. Thus, in a box model of the global carbon cycle, the stock is the mass or amount of carbon in various forms—including gas and dissolved species or solids, such as or inorganic minerals—in each reservoir. The stock in each reservoir is assumed to be well mixed, so that regardless of the size of the reservoir, the concentration of stock throughout the reservoir is uniform. The stock present in each reservoir can change over time, as the rate of input or output from each reservoir varies. In simple box models, reservoirs or pools are held to constant volumes. In more complicated models, the size of a reservoir can change. Numerical methods and computer programs are utilized with box models to solve equations to determine parameters such as the amount of stock in a given reservoir over time or the time needed for the amount of stock in a reservoir to change.
Significance for Climate Change
Box models, as simplified conceptual models of complex systems and processes, are of fundamental importance for predicting future climate conditions. Results from such models underlie the predictions that are published by the Intergovernmental Panel on Climate Change and other scientific and policymaking bodies. Such models can be applied to any complex system, regardless of scale, such as the global or the biochemical processes in a single cell. With regard to future global warming scenarios, variations in the global carbon cycle are among the fundamental drivers of climate change. Other topics of interest include the global cycles of water, nitrogen, oxygen, and sulfur.
In the development of a box model, the reservoirs and stocks of the species of interest are fundamental properties that must be defined in order to perform the necessary calculations. One of the largest sources of error in box models involves defining the size of reservoirs and pools and determining the amount of stock in each. For example, within the global carbon cycle, the stock of carbon present as gas hydrates in the seafloor is presently not well known. This value must be estimated from a relatively low number of measurements in specific regions and extrapolated to all other places on Earth where these compounds might be present. Gas hydrates have been a source of discussion in the scientific community as a trigger for rapid warming in the recent geologic past (as in the clathrate gun hypothesis of James Kennett).
A key question that is often addressed using box models is how the stock within a given reservoir might change in response to certain events. For example, to estimate the amount of global warming that has been caused by production of CO2, scientists must use box models to determine how the stock of CO2 in various pools (such as the atmosphere and oceans) has changed in response to the increased input of CO2 to the environment. Predictions of the length of time needed for atmospheric CO2 stocks to decline in response to future CO2 emissions are also based upon box models of the global carbon cycle.
Bibliography
Berner, Robert A. The Phanerozoic Carbon Cycle: CO2 and O2. New York: Oxford University Press, 2004.
Denman, Kenneth L., et al. “Couplings Between Changes in the Climate System and Biogeochemistry.” In Climate Change, 2007—The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, edited by Susan Solomon et al. New York: Cambridge University Press, 2007.
"How NASA Builds Resilience with Climate Models." NASA, 24 Aug. 2021, gpm.nasa.gov/applications/how-nasa-builds-resilience-climate-models. Accessed 21 Dec. 2024.
Kennett, James P., ed. Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis. Washington, D.C.: American Geophysical Union, 2003.
Roston, Eric. The Carbon Age: How Life’s Core Element Has Become Civilization’s Greatest Threat. New York: Walker, 2008.