Reconciling Topdown and Bottomup Approaches Anna M Michalak

Reconciling Top-down and Bottom-up Approaches Anna M. Michalak Department of Civil and Environmental Engineering Department of Atmospheric, Oceanic and Space Sciences University of Michigan

Questions to Address n What are the critical knowledge gaps? n What synthesis and integration activities can help address knowledge gaps? Some suggestions of kinds of activities to consider: q Treatment of uncertainty in measurements and models q Components of the N. Am. carbon budget: current status and potential improvements (e. g. urban/suburban flux estimates, fossil fuel fluxes). This topic would take SOCCR as a point of departure. q Integration of short-term and long-term measurements (e. g. flux sites compared to biometrics). q Formal intercomparisons of inverse modeling methods. q Formal intercomparisons of forward modeling methods. q Comparison of forward and inverse modeling methods. q Carbon-nitrogen cycle interactions. n What are the next steps to move forward?

What are the main challenges to collaboration between (primarily) top-down and (primarily) bottom-up researchers? n n n n Scale (resolution, time span, domain) Data limitations Attribution (i. e. process-based) vs. Diagnosis (i. e. magnitude) Use of biospheric models as priors in top-down modeling Uncertainty analysis (both bottom-up and top-down) Terminology Need better understanding of feedbacks Common goals / data products / scientific questions

NACP Questions 1. What is the carbon balance of North America and adjacent oceans? What are the geographic patterns of fluxes of CO 2, CH 4, and CO? How is the balance changing over time? (“Diagnosis”) 2. What processes control the sources and sinks of CO 2, CH 4, and CO, and how do the controls change with time? (“Attribution/Processes”) 3. Are there potential surprises (could sources increase or sinks disappear)? (“Prediction”) 4. How can we enhance and manage long-lived carbon sinks ("sequestration"), and provide resources to support decision makers? (“Decision support”) Source: Scott Denning, Monday AM presentation

Synthesis Framework Atmospheric measurements WITHIN THE CONTEXT OF MOVING TOWARDS PREDICTION Top-down models Transport models n n n Bottom-up models n n n Scale Data limitations Attribution vs. Diagnosis vs. Prediction Use of biospheric models as priors Uncertainty analysis Terminology Feedbacks Common goals / data products / scientific questions

What are the next steps to move forward? n Organizing committee to propose goals and structure of synthesis q Two step process with general committee with representatives from different communities and sub-committees from individual components n “Wash dirtiest laundry first” q Sharing strengths and weaknesses of both sets of approaches q Being explicit about assumptions n Take steps towards resolving terminology differences n Make better use of “surprises” in our top-down analyses to inform bottom-up studies n Do more event-based and hypothesis based analysis n CAUTION: The types of models that will disagree about future carbon fluxes are not necessarily going to disagree about current fluxes n Remaining questions: q How do you see long-term change from short-term fluxes? q Need to coordinate with MCI q What role should flux towers play?