Developing a Carbon Observing System

There is a clear need to better understand and predict future climate change, so that science can more confidently inform climate policy, including adaptation planning and future mitigation strategies. Understanding carbon cycle feedbacks, and the relationship between emissions (fossil and land use) and the resulting atmospheric carbon dioxide (CO2) and methane (CH4) concentrations in a changing climate has been recognized as an important goal by the IPCC. To do this, the processes controling the carbon sources and natural land and ocean sinks must be better understood, and the behavior of anthropogenic carbon sources and natural land and ocean sinks must be quantified. There are also important uncertainties in current anthropogenic emissions, and these uncertainties will likely grow as the proportion of future anthropogenic emissions shifts to developing countries. The existing surface greenhouse gas observing networks provide (particularly for CO2) very accurate and precise measurements of background values, but they are not configured to target the extended, complex and dynamic regions of the carbon budget. One way to improve the coverage and resolution of these measurements is to collect high-resolution observations of CO2 and CH4 concentrations from space-based measurement platforms. Fortunately, Space Agencies around the globe are committed to carbon dioxide and methane observations: • GOSAT-2: Building upon the successful GOSAT mission, Japan is proceeding rapidly with the development of GOSAT-2; • OCO-2: NASA has successfully launched OCO-2 into the A-Train constellation; • MERLin: French-German Methane Remote Sensing Lidar Mission to be launched in 2016-17 • TanSat: The Chinese Carbon Dioxide Observing Satellite is currently under development by the Ministry of Science and Technology of China, Chinese Academy of Sciences and National Satellite Meteorological Center, and • CarbonSat: ESA has selected the CarbonSat mission as a candidate (with Fluorescence Explorer (FLEX)) for the 8th ESA Earth Explorer mission. In addition to these Low Earth Orbit (LEO) missions, a new mission in Geostationary Orbit (GEO), geoCARB, which would provide mapping-like measurements of carbon dioxide, methane, and carbon monoxide concentrations over major land areas, has been recently proposed to the NASA Venture Program. These pioneering missions, unfortunately, do not provide the spatial/temporal coverage to answer the key carbon-climate questions at process relevant scales nor do they address the distribution and quantification of anthropogenic sources at urban scales. They do demonstrate, however, that a well-planned future system of system integrating space-based LEO and GEO missions with extensive in situ observations and measurements could provide the accuracy, spatial resolution, and coverage needed to address critical open issues in the carbon-climate system. An integrated and coordinated approach is needed. Specification of the optimal, most cost-effective satellite observing configuration will require significant investments in analyses to determine the best mix of observing system vantage points, sensor technologies, in situ networks and analysis approaches. Addressing the critical uncertainties in the global carbon cycle will require a coordinated observation effort over the land, atmosphere, ocean and anthropogenic domains, together with coupled carbon-climate models and data assimilation systems. This paper will, in part, report on a recent NASA-funded community workshop in March 2015 at the University of Oklahoma that addressed these issues and prioritzed a set of research and observational needs.