The continual cycling of carbon through the atmosphere, oceans, soil, and living organisms is an essential function of the Earth system. The U.S. Carbon Cycle Science Program (under the auspices of USGCRP; carboncyclescience.us) and USGCRP agencies are working to understand how climate change and human activities are altering this foundational component of the environment, and how these alterations feed back to affect climate change. Some examples are highlighted below:

• At least two thirds of the world’s land-based organic carbon is stored in soil, but potentially major feedbacks between climate change and the release of soil carbon into the atmosphere are not well understood yet. To address this knowledge gap, the International Soil Carbon Network (ISCN) has been established to characterize the distribution and stability of soil carbon; forecast the vulnerability of soil carbon to changing climate, land use, and other disturbances; and distribute this information in formats that are useful to land managers, modelers, and policy makers. To learn more, visit: http://goo.gl/oWXqiJ

• The Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) experiment, a unique collaboration between DOE and the U.S. Forest Service (USDA-FS), will explore the vulnerability of peatland forests to changing climate. The loss of these ecosystems could lead to the release of ten thousand years of stored soil carbon into the atmosphere as greenhouse gases, further exacerbating climate change. The experiment, held in the Marcell Experimental Forest in Minnesota, provides a platform for testing mechanisms that control the vulnerability of peatland organisms and ecosystems to climate change, and will enable more accurate representations of these processes in Earth system models. Initial sampling and infrastructure development began in 2012, and experiments are slated to begin in 2015. To learn more, visit: http://go.usa.gov/8VV9

• The Carbon Monitoring System (CMS), a NASA-led effort also involving USDA-FS, NOAA, USGS, and non-governmental scientists, focuses on improving the monitoring of carbon stocks and fluxes. Key outcomes of this effort include biomass maps and other data products covering spatial scales ranging from local to global; demonstrations of carbon monitoring and accounting in support of local- and regional-scale management projects; and engagement with stakeholders to better understand their needs for carbon data products. New CMS studies are using airborne measurements to support national and international carbon management efforts, such as SilvaCarbon and the United Nations Reducing Emissions from Deforestation and Forest Degradation Programme (UN-REDD). To learn more, visit: http://go.usa.gov/NYze

• A full understanding of the carbon cycle requires research not only in natural systems but also in human-managed systems, and especially urban environments, which account for between 60 and 80 percent of global energy consumption and carbon emissions. As a first step in building an interdisciplinary community of social and natural scientists studying human–carbon interactions in urban systems, the U.S. Carbon Cycle Science Program sponsored a workshop in late 2013 with participants from government and academia. Participants delved into the challenges and opportunities involved in building a holistic research program on urbanization and the carbon cycle. To inform related efforts in the broader scientific community, workshop outcomes will be shared through several reports, two of which have been released.6 Urban– carbon research not only has the potential to advance carbon cycle science, but also to inform the management of urban green spaces and support climate resilience in heavily populated urban settings. To learn more, visit: http://goo.gl/IJyvbs