• Water Cycle: How do the hydrological cycle and water resources interact with the climate system on local to global scales? How will more realistic portrayals of features important to the water cycle (resolution, clouds, aerosols, snowpack, river routing, land use) affect river flow and associated freshwater supplies at the watershed scale?

  To address the water cycle, the project plan hypothesized that: 1) changes in river flow over the last 40 years have been dominated primarily by land management, water management and climate change associated with aerosol forcing; 2) during the next 40 years, greenhouse gas (GHG) emissions in a business as usual scenario may drive changes to river flow.

  A goal of ACME is to simulate the changes in the hydrological cycle, with a specific focus on precipitation and surface water in orographically (associated with or induced by the presence of mountains) complex regions such as the western United States and the headwaters of the Amazon.

• Biogeochemistry: How do biogeochemical cycles interact with global climate change? How do carbon, nitrogen and phosphorus cycles regulate climate system feedbacks, and how sensitive are these feedbacks to model structural uncertainty?

  To address biogeochemistry, ACME researchers will examine how more complete treatments of nutrient cycles affect carbon-climate system feedbacks, with a focus on tropical systems, and investigate the influence of alternative model structures for below-ground reaction networks on global-scale biogeochemistry-climate feedbacks.

• Cryosphere Systems: How do rapid changes in cryospheric systems, or areas of the earth where water exists as ice or snow, interact with the climate system? Could a dynamical instability in the Antarctic Ice Sheet be triggered within the next 40 years?

  For cryosphere, the team will examine the near-term risks of initiating the dynamic instability and onset of the collapse of the Antarctic Ice Sheet due to rapid melting by warming waters adjacent to the ice sheet grounding lines.

  The experiment would be the first fully-coupled global simulation to include dynamic ice shelf-ocean interactions for addressing the potential instability associated with grounding line dynamics in marine ice sheets around Antarctica.

ACME is the only major national modeling project designed to address US Department of Energy (DOE) mission needs and efficiently utilize DOE Leadership Computing resources now and in the future.

Over a planned 10-year span, the project aim is to conduct simulations and modeling on the most sophisticated HPC machines as they become available, i.e., 100-plus petaflop machines and eventually exascale supercomputers. The team initially will use US Department of Energy (DOE) Office of Science Leadership Computing Facilities at Oak Ridge and Argonne national laboratories.

The grand challenge simulations are not yet possible with current model and computing capabilities, but we developed a set of achievable experiments that make major advances toward answering the grand challenge questions using a modeling system, which we can construct to run on leading computing architectures over the next three years.

—David Bader, LLNL atmospheric scientist and chair of the ACME council

ACME intends to achieve its goal through four intersecting project elements:

1. A series of prediction and simulation experiments addressing scientific questions and mission needs. ACME envisions simulation campaigns of three to four years each with successive versions of the modeling system. Every campaign will inform the next, and the partners envision four to five campaigns with successive versions of the modeling system leading to the grand challenge simulations in approximately 10 years.

2. A well-documented and tested, continuously advancing, evolving, and improving system of model codes that comprise the ACME Earth system model. The core of the ACME project is model development. The ACME model development path currently envisions five development cycles for its modeling system over the next 10 years, although only three will be both started and completed over the time span.

3. The ability to use effectively leading (and “bleeding”) edge computational facilities soon after their deployment at DOE national laboratories. The project envisions that versions v2 and beyond will include elements of the co-design process developed by DOE. Co-design refers to a computer system design process where scientific problem requirements influence architecture design and technology constraints inform formulation and design of algorithms and software. While the ACME project is not a co-design center, it aims to have an impact on the facility roadmap through a close partnership with LCF scientists and engineers.

4. An infrastructure to support code development, hypothesis testing, simulation execution, and analysis of results.

Initial funding for the effort has been provided by DOE’s Office of Science.

Resources

• Bader D, W Collins, R Jacob, P Jones, P Rasch, M Taylor, P Thornton, and D Williams (2014) “Accelerated Climate Modeling for Energy (ACME) Project Strategy and Initial Implementation Plan.”