The Earth’s climate is changing, and without action by the world’s nations the planet will get warmer, sea level will rise, and patterns of rainfall will change. Will the changes be gradual, allowing natural systems and societal infrastructure to adjust in a timely fashion? Or will they come faster than expected, planned, or budgeted for, forcing reactive, rather than proactive, behaviors? This report focuses on abrupt climate changes and impacts that could severely affect the physical climate system, natural systems, and/or human systems. It summarizes current knowledge about potential abrupt climate changes and abrupt changes to the ocean, atmosphere, ecosystems, and high-latitude areas, and identifies key research and monitoring needs. It also recommends development of an abrupt change early warning system to enable the prediction and possible mitigation of such changes before their impacts are severe. Identifying vulnerabilities can help efforts to increase resiliency, avoid significant damage, and inform decisions on the balance between mitigation and adaptation. There is still much to learn about abrupt climate change and its impacts, but to willfully ignore the threat of such change could lead to higher costs, loss of life, suffering, and environmental degradation. This report makes the case that it is time now to anticipate and prepare for the inevitable changes.
