The planet earth is 4.5 billion years old and has undergone many geologial and climatic changes. Geologists know: Earth history demonstrates continuous dynamic evolution. The above figure shows climate change over the last 65 million years. The data has been gained from oxygen isotope measurements (δ18O) on benthic foraminifera by Zachos et al. (2001) and reflect a combination of local temperature changes in their environment and changes in the isotopic composition of sea water associated with the growth and retreat of continental ice sheets. Figure and citation from wikipedia.com.Ancient climate records provide clear evidence of abrupt episodes of greenhouse warming in the past. Understanding cause and effect for these events continues to remain a major challenge. For the best-documented example, a burst of warming some 55 million year ago termed the Palaeocene–Eocene thermal maximum (PETM), known increases in greenhouse gases fail to explain even half of the observed warming. Read more..nature.com
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