On past temperatures and anomalous late‐20th‐century warmth

Evidence from paleoclimatic sources and modeling studies support AGU's official position statement on climate change and greenhouse gases; namely that there is a compelling basis for concern over future climate changes, including increases in global‐mean surface temperatures, due to increased concentrations of greenhouse gases, primarily from fossil fuel burning. More specifically a number of reconstructions of large‐scale temperature changes over the past millennium support the conclusion that late‐20th century warmth was unprecedented over at least the past millennium. Modeling and statistical studies indicate that such anomalous warmth cannot be fully explained by natural factors, but instead, require a significant anthropogenic forcing of climate that emerged during the 19th and 20th centuries.