This report focuses on the Climate Projections Based on Emissions Scenarios. The influence of greenhouse gases and particle pollution on our present and future climate has been widely examined. While both long-lived (e.g., carbon dioxide) and short-lived (e.g., soot) gases and particles affect the climate, other projections of future climate, such as the IPCC reports focus largely on the long-lived gases. This U.S. Climate Change Science Program Synthesis and Assessment Product provides a different emphasis. The authors 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 twenty-first century (unlike in the IPCC scenarios). However, the projected future temperature changes fall within the same range as those projected for the latest IPCC report. The authors confirm the robust future warming signature and other associated changes in the climate.

This document is part of the Synthesis and Assessment Products (SAP) described in the U.S. Climate Change Science Program (CCSP) Strategic Plan. This report is meant to synthesize and communicate the current state of understanding about the characteristics and implications of uncertainty related to climate change and variability to an audience of policymakers, decision makers, and members of the media and general public with an interest in developing a fundamental understanding of the issue.

Long-term, high-accuracy, stable environmental observations are essential to define the state of the global integrated Earth system, its history and its future variability and change. Observations for climate include: (1) operational weather observations, when appropriate care has been exercised to establish high accuracy; (2) limited-duration observations collected as part of research investigations to elucidate chemical, dynamical, biological, or radiative processes that contribute to maintaining climate patterns or to their variability; (3) high accuracy, high precision observations to document decadal-to-centennial changes; and (4) observations of climate proxies, collected to extend the instrumental climate record to remote regions and back in time to provide information on climate change at millennial and longer time scales. This report was requested by the United Nations Framework Convention on Climate Change (UNFCCC) in order to serve as input to see how progress has been made with respect to the Global Climate Observing System (GCOS) Implementation Plan developed in 2004 In accordance with the UNFCCC guidelines, the sections of the report delineate specific U.S. climate monitoring activities in several distinct yet integrated areas as follows: (1) common issues; (2) non-satellite atmospheric observations; (3) non-satellite oceanic observations; (4) non-satellite terrestrial observations; (5) satellite global atmospheric, oceanic, and terrestrial …