In April 2007 the US Interagency Research Policy Committee (IARPC) called for the development of an Arctic Observing Network (AON) to understand the causes and consequences of Arctic change. Under the joint leadership of NOAA and NSF, Committee staff prepared Arctic Observing Network (AON): Toward a US Contribution to Pan-Arctic Observing, a summary of ongoing and future Federal Arctic observing activities with a strategy for enhanced co-ordination and integration of these activities. This document constitutes the biennial update of the US Arctic Research Plan, focusing on observing needs. Enhanced co-ordination and integration of observing activities, and data and information management, will enable the agencies to respond with increased agility to the science questions posed by the Study of Environmental Arctic Change (SEARCH) program: m1 Is the Arctic system moving to a new state? 2 To what extent is the Arctic system predictable, i.e., what are the potential accuracies and/or uncertainties in predictions of relevant Arctic variables over different time scales? 3To what extent can recent and ongoing climate changes be attributed to anthropogenic forcing rather than to natural modes of variability? 4 What is the direction and relative importance of system feedbacks? 5 How are terrestrial and marine ecosystems and ecosystem services affected by environmental change and its interactions with human activities? 6 How do cultural and socio-economic systems interact with Arctic environmental change? 7 What are the most consequential links between the Arctic and Earth systems?