Earth system models include many interdependent components and processes to help us understand our planet.
Earth system models include many interdependent components and processes to help us understand our planet.
Image courtesy of Paul Ullrich, University of California, Davis

Earth system models and climate models are a complex integration of environmental variables used for understanding our planet. Earth system models simulate how chemistry, biology, and physical forces work together. These models are similar to but much more comprehensive than global climate models.

To understand Earth system models, it helps to first understand global climate models. Climate is the long-term pattern of weather variables. It includes temperature, rain and snowfall, humidity, sunlight, and wind and how they occur over many years. Climate models explain how these variables can change using mathematical analysis based on the physics of how energy, gases, and fluids move, combined with measurements taken from experiments, laboratories, and other observations in the real world.

Climate models include:

  • The atmosphere including clouds, aerosols, and gases.
  • The land surface and how it is covered by vegetation, snow and ice, lakes and rivers, and soil.
  • Sea ice and the oceans.
  • How all these components store and move the heat and carbon that warm the Earth’s atmosphere.

Global climate models treat the Earth as a giant grid. The size of each cell in the grid is determined by the power of the computer running the model. Just like a video game, higher resolution requires a much more powerful computer.

Earth system models include all the factors in climate models. But as complex as climate is, it is only one part of an even more complex Earth system. The goal of Earth system models is to understand how the Earth functions as a system of interdependent parts. These parts include the physical, chemical, and biological processes that all interact to shape our planet and the organisms on it. Earth system science is multidisciplinary, drawing on atmospheric science, oceanography, ecosystem ecology, soil microbiology, multi-sector analysis, and the core science disciplines of mathematics, chemistry, and physics.

Earth system models can help understand and provide critical information on water availability, drought, climate and temperature extremes, ice sheets and sea levels, and land-use change. They help scientists understand how plants, people, animals, and microbes all contribute to and are affected by the Earth’s climate. For example, different plants absorb carbon dioxide at different rates. Different landscapes—ice, oceans, natural vegetation, farmland, or cities—can change how the land absorbs or reflects sunlight. As temperatures and rainfall change, plants respond, changing the balance of carbon and atmospheric radiation. In the ocean, circulation patterns change the amount of plankton and seaweed.

These factors work on many time scales. The Sahara appears to have shifted back and forth from wet to dry over thousands to tens of thousands of years. Plants in a wet Sahara reflect sunlight and store carbon, while a dry Sahara absorbs sunlight and stores little carbon. These factors also work at very short time scales, such as the rapid expansion of cities in the 20th century into land formerly covered by plants, changing how the land reflects and stores heat and carbon. Chemical processes from the slow erosion of rock can release dust into the atmosphere, trapping more heat in the air. Short chemical processes such as pollution from industry and soot from forest fires can have similar effects.

Because Earth system models can include the effect of human decisions, they are useful tools for planning things like infrastructure, energy production and use, and landscape use. For example, an Earth system model could help a coastal city plan where to build a new highway to ensure that the new highway isn’t flooded if hurricanes become more severe in response to changes in the global climate.

Modeling the entire Earth or the Earth’s climate with sufficient accuracy is challenging for scientists. One solution is to create more powerful computers that can produce high resolution models with sophisticated ways of representing real-world variables. Another is reduced complexity models. These reduced complexity models provide lower resolution climate information but are easier and faster to run. This makes them perfect for research questions that do not require the detailed data provided by Earth system models. Researchers also use simplified models to quickly test narrow hypotheses about the planet. Researchers can also use focused multisector dynamic models to explore the interactions and interdependencies among specific human and natural systems.

DOE Office of Science: Contributions to Earth Systems and Climate Models

The Department of Energy (DOE) Office of Science Biological and Environmental Research (BER) program supports Earth systems and climate modeling through several related efforts. The Earth and Environmental Systems Modeling program (EESM) develops and applies models to increase scientific understanding of the factors in the integrated Earth system. It works on research as diverse as infrastructure planning and the development of advanced representations of the Earth. To build the computer codes needed to run complex Earth system and climate models on DOE’s fastest computers, DOE supports the Energy Exascale Earth System Model (E3SM) project through the BER Earth System Model Development (ESMD) program. The E3SM is a massive computer model of the planet designed to work on DOE’s Leadership Computing Facility supercomputers. E3SM will provide scientists and policymakers with predictions of the changing Earth system at the spatial resolutions necessary to make informed decisions. Finally, DOE’s Regional and Global Modeling Analysis (RGMA) program advances capabilities to design and analyze global and regional Earth system model simulations.

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