Paleoclimate
Scientists analyzing ancient ice from Antarctica have found that ocean temperatures dropped by 2 to 2.5 degrees Celsius over the past 3 million years, while carbon dioxide and methane levels changed only modestly. The studies, led by researchers from Oregon State University and others, suggest factors beyond greenhouse gases drove much of Earth's long-term cooling. The findings come from ice cores at Allan Hills in East Antarctica.
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Researchers have analysed a 3-million-year-old ice core from Allan Hills in Antarctica, measuring atmospheric CO2 at 250 parts per million and methane at 507 parts per billion during the late Pliocene. This epoch featured global temperatures about 1°C warmer than today and sea levels up to 25 metres higher. The levels are lower than previous indirect estimates.