The First State of the Carbon Cycle Report The North American Carbon Budget and Implications for the Global Carbon Cycle

Interagency Committee relies on Department of Commerce and NOAA certifications regarding compliance with Section 515 and Department guidelines as the basis for determining that this product conforms with Section 515. For purposes of compliance with Section 515, this CCSP Synthesis and Assessment Product is an " interpreted product " as that term is used in NOAA guidelines and is classified as " highly influential. " This document does not express any regulatory policies of the United States or any of its agencies, or provide recommendations for regulatory action. The influence of greenhouse gases and particulate pollution on our present and future climate has been widely examined and most recently reported in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. While both long-lived (e.g. carbon dioxide) and short-lived (e.g., soot) gases and particles affect the climate, previous projections of future climate, such as the IPCC reports, have focused largely on the long-lived gases. This U.S. Climate Change Science Program Synthesis and Assessment Product provides a different emphasis. We first examine the effect of long-lived greenhouse gases on the global climate based on updated emissions scenarios produced by another CCSP Synthesis and Assessment Product (SAP 2.1a). In these scenarios, atmospheric concentrations of the long-lived greenhouse gases leveled off, or stabilized, at predetermined levels by the end of the 21st century (unlike in the IPCC scenarios). However, the projected future temperature changes, based on these stabilization emissions scenarios, fall within the same range as those projected for the latest IPCC report. We confirm the robust future warming signature and other associated changes in the climate. We next explicitly assess the effects of short-lived gases and aerosols. Their influence is found to be global in nature, substantial when compared with long-lived greenhouse gases, and potentially extending to the end of this century. They can significantly change the regional surface temperature, and by the year 2100 they may be responsible for a significant increase in surface temperature and decrease in rainfall over the summertime continental United States. It is noteworthy that the simulated climate response to these pollutants is not confined to the area where they occur. This implies a strong linkage between regional air quality control strategies and global climate change. We identify specific emissions reductions that would lead to benefits for both air quality and climate change mitigation, including North American surface transportation and Asian domestic fuel burning. The results reveal …