PNNL

The Science

The oceans and the atmosphere are deeply connected and involved in a tangled network of two-way interactions. These connections influence how the Earth system responds to changes from external factors (like increasing CO₂ concentrations), but their complexity makes it difficult to disentangle the individual roles of the atmosphere and ocean. The method introduced here helps separate their contributions and allows for more accurate interpretations of climate model simulations and projections of environmental change in the Earth system.

The Impact

This method provides a more accurate isolation of the oceans’ and atmosphere’s roles than previous approaches. Improved isolation of their roles will also facilitate a better understanding of how errors in the individual ocean and atmosphere model components contribute to the biases of coupled Earth system models. It also helps clarify how ocean-atmosphere interactions affect features of the Earth system, such as ocean overturning circulation in the Atlantic and sea ice loss, that are very important responses to increasing CO₂.  

Summary

Forced changes and natural (yearly and decadal) variations in climate fields (like air temperature, winds, ocean currents, and sea ice amount) are produced by processes occurring in the atmosphere and ocean and their interactions. This study describes a method that helps untangle these interactions, separate the components of climate variations caused by the atmospheric and oceanic changes, and explore how the interactions between them explain climate variability and change. Two climate model experiments applied the method to understanding the planet’s response to quadrupled CO₂ concentrations. One experiment allowed all modeled interactions between the atmosphere and ocean to occur and the other (termed “partially coupled”) experiment excluded role of ocean circulation changes in the interactions, isolating the climatic changes caused by the atmospheric CO₂ increase alone. The difference between the two experiments revealed the climate changes attributable to ocean circulation changes. The researchers performed an additional, independent experiment to verify that the climate changes associated with the ocean circulation changes diagnosed from the partially coupled analysis were correct.  

PNNL Contact

Oluwayemi Garuba, Pacific Northwest National Laboratory, Oluwayemi.garuba@pnnl.gov

Philip Rasch, Pacific Northwest National Laboratory, philip.rasch@pnnl.gov

Funding

This study was supported by the Regional and Global Model Analysis (RGMA) component of the Earth and Environmental System Modeling program of the U.S. Department of Energy's Office of Science Biological and Environmental Research, as a contribution to the HiLAT-RASM project. This study used the research computing resources of the Pacific Northwest National Laboratory (PNNL) and the National Energy Research Scientific Computing Center, a U.S. Department of Energy Office of Science User Facility.