Earth’s climate has fluctuated in the past at time scales from tens of millions of years to one or two decades. Ocean and continental sediments are excellent climate archives in a wide range of time scales. Ice cores, though limited in time to the last 800,000 years, are also excellent Earth climate records and have the additional advantage of providing a direct measure of fluctuations in atmospheric greenhouse gases.

Understanding the natural variability of the Earth’s climate and the external and internal causes of past climate fluctuations is essential to determine the anthropogenic influence on Earth global warming observed in last century and to limit the amount of uncertainty in future climate predictions. A firm statistical basis requires knowledge not only over the last several 100,000 years of glacial cycles but also further back in time to assess previous warm intervals. The talk will focus on past rapid climate changes and emphasize that the current atmospheric concentrations of carbon dioxide and methane have reached levels unobserved for at least the last 800,000 years according to the evidence preserved in ice records and most likely for the last 30 million years.

Keeling Curve. Monthly average atmospheric carbon dioxide concentration versus time at Mauna Loa Observatory, Hawaii (20°N, 156°W) where CO₂ concentration is in parts per million in the mole fraction (p.p.m.). http://scrippsco2.ucsd.edu/

Vostock and EPICA Dome C Ice records. Note the present day spike in methane and CO₂ above background. (Figure modified from ”Tiny Bubbles Tell All” Edward J. Brook Science 25 November 2005: Vol. 310. no. 5752, pp. 1285 – 1287)

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