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.
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