Demystifying Climate Models by Andrew Gettelman & Richard B. Rood

Author:Andrew Gettelman & Richard B. Rood
Language: eng
Format: epub, pdf
Publisher: Springer Berlin Heidelberg, Berlin, Heidelberg

7.10 Summary

Modeling the earth’s surface means modeling a complex set of coupled terrestrial systems. The surface fluxes that occur in the climate system are strongly affected by key properties of the surface: Water fluxes are affected by transpiration from plants. The presence of water is also important for moving energy around and releasing it as latent heat (analogous to the role of water in the atmosphere). This is very important in semiarid regions with dry soils. Transpiration of water from plants is an important part of surface processes. And since plants and ecosystems are dynamic and respond to climate, representing different plant types and the ecosystems that support them is critical. Furthermore, the growth and decay of plants in ecosystems depends on critical nutrients, such as carbon and nitrogen. Carbon is the common lifeblood of the earth system, changing forms from the solid earth and sediments, to biological tissue on land, in soils and in the ocean, to a greenhouse gas in the atmosphere. Understanding carbon couples terrestrial systems to climate as well. These systems include the cryosphere (snow and ice) and the anthroposphere (agricultural land, urban areas).

Modeling terrestrial systems involves several components. The biogeophysics of the system is described by a model of energy and water flows, including the absorption and emission of radiation. The hydrology of the land and the terrestrial water cycle is also simulated: Precipitation is input; evaporation, transpiration, and storage in soil moisture occur; and the remainder becomes runoff.

Terrestrial systems generally include a description of the type of ecosystems (plant types) on the surface and soil properties in the subsurface, often in detailed small-scale tiles. The descriptions of the plant types are typically based on climate effects and are not necessarily considered a “detailed” description by an ecologist. Descriptions of plant types represent the effects of ecosystems, or a population of plants, not individual plants. This is similar to parameterizations of clouds in the atmosphere designed to represent a distribution of clouds and their effects, not a single cloud. Different ecosystems have very different properties (height, leaf area, root depth, and transpiration) that affect surface fluxes. The ecosystem descriptions can be dynamic and evolve over time.

Key nutrient cycles, usually carbon and then nitrogen, are often added to land surface models to improve the ability to simulate changes in terrestrial carbon budgets. Changes to the land surface cycling of carbon can alter CO2 storage and emission.

Ice sheets and snow are an important land cover type for altering albedo and solar energy absorption at the surface. And ice sheets are important for storing water that affects global sea level. There are many complex and incompletely observed processes that determine the balance of ice sheets between accumulation, melting and flow. The Antarctic and Greenland ice sheets have different characteristics and critical uncertainties. The Antarctic ice sheet is sensitive to ocean processes beneath ice shelves and at the edges. The Greenland ice sheet is sensitive to melting on the surface and lubrication at the base.

Finally, many of these land

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