GFDL has constructed NOAA’s first Earth System Models (ESMs) to advance our understanding of how the Earth's biogeochemical cycles, including human actions, interact with the climate system. Like GFDL's physical climate models, these simulation tools are based on an atmospheric circulation model coupled with an oceanic circulation model, with representations of land, sea ice and iceberg dynamics. ESMs incorporate interactive biogeochemistry, including the carbon cycle. Building the ESMs has been a large collaborative effort involving scientists from GFDL, Princeton University, Department of Interior and other institutions, to study climate and ecosystem interactions and their potential changes, from both natural and anthropogenic causes.
The atmospheric component of the ESMs includes physical features such as aerosols (both natural and anthropogenic), cloud physics, and precipitation. The land component includes precipitation and evaporation, streams, lakes, rivers, and runoff as well as a terrestrial ecology component to simulate dynamic reservoirs of carbon and other tracers. The oceanic component includes features such as free surface to capture wave processes; water fluxes, or flow; currents; sea ice dynamics; iceberg transport of freshwater; and a state-of-the-art representation of ocean mixing as well as marine biogeochemistry and ecology.
While carbon is necessarily included as the basic building block of ecosystems undergoing terrestrial and oceanic chemistry, associated chemical and ecological tracers which control nutrient limitation, plant biomass, productivity, and functional composition are also included. Chemical tracers are also tracked in the atmosphere. ESMs capture numerous types of emissions, variations of land surface albedo due to both natural vegetation changes and land use history such as agriculture and forestry, and aerosol chemistry. Adding these different components to the ESM represents a major step forward in simulating the Earth's ecological systems in a comprehensive and internally consistent context.
ESM2M and ESM2G:
Our first prototype model, ESM2.1, evolved directly from GFDL’s successful CM2.1 climate model. Building on this, we produced two new models representing ocean physics with alternative numerical frameworks to explore the implications of some of the fundamental assumptions embedded in these models. In one model, ESM2M, pressure-based vertical coordinates are used along the developmental path of GFDL’s Modular Ocean Model version 4.1. In the other, ESM2G, an independently developed isopycnal model using the Generalized Ocean Layer Dynamics (GOLD) code base was used.
Both ESM2M and ESM2G utilize a more advanced land model, LM3, than was available in ESM2.1 including a variety of enhancements (Milly et al., in prep; Dunne et al., accepted).