evidence: The magnitude of climate change beyond the next few decades will depend primarily on the amount of greenhouse gases (especially carbon dioxide) emitted globally. Without major reductions in emissions, the increase in annual average global temperature relative to preindustrial times could reach 9°F (5°C) or more by the end of this century. With significant reductions in emissions, the increase in annual average global temperature could be limited to 3.6°F (2°C) or less. [...] Warming and associated climate effects from CO2 emissions persist for decades to millennia. In the near-term, changes in climate are determined by past and present greenhouse gas emissions modified by natural variability. Reducing net emissions of CO2 is necessary to limit near-term climate change and long-term warming. Other greenhouse gases (e.g., methane) and black carbon aerosols exert stronger warming effects than CO2 on a per ton basis, but they do not persist as long in the atmosphere (Ch. 2); therefore, mitigation of non-CO2 species contributes substantially to near-term cooling benefits but cannot be relied upon for ultimate stabilization goals. (Very high confidence) (Ch. 14)