Based on research such as the seminal 1976 article reviewed here, it is assumed that the timing of glacial-interglacial cycles is triggered by cycles in the amount of sunlight reaching the earth. But the variation in the amount sunlight reaching the Earth is so weak that the observed magnitude of warming and cooling, during glacials and interglacials, cannot be explained by the solar variations alone.

The Vostok ice core record shows that over about 400,000 years there is a close, positive correlation between temperature and atmospheric carbon dioxide and methane. This article argues that the observed temperature change leading to glacials and interglacials is explained by the strong variation in atmospheric carbon dioxide and methane concentrations.

The article suggests that there is a positive feedback in the earth climate system: a small initial warming caused by a change in solar input causes carbon dioxide and methane concentrations to rise, which in turn causes more warming. The feedback works in the opposite way leading to cooling when solar-input decreases.

Applied to our current climate, it is suggested that the feedback mechanism amplifies the warming caused by anthropogenic GHG emissions. It is estimated that if doubling CO2 concentrations would cause 1.5–4.5°C warming, the feedback mechanism would actually result in 1.6–6.0°C warming or up to 1.5°C warmer temperatures than currently predicted by the IPCC.

Margaret S. Torn and John Harte, Missing feedbacks, asymmetric uncertainties, and the underestimation of future warming, GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L10703, doi:10.1029/2005GL025540, 2006

Bertram M. Schwarzschild, Carbon dioxide drove the ending of the last glacial epoch,Physics Today, June 2012, page 16

C. Lorius, J. Jouzel, D. Raynaud, J. Hansen, and h. Le Treut, The ice-core record:climate sensitivity and future greenhouse warming, Nature, Vol 347, 13 September 1990

Ice-driven CO2 feedback on ice volume, W. F. Ruddiman, Clim. Past, 2, 43–55, 2006

Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation, Jeremy D. Shakun, Peter U. Clark,F eng He, Shaun A. Marcott, Alan C. Mix, Zhengyu Liu, Bette Otto-Bliesner, Andreas Schmittner & Edouard Bard, Nature, 484, 49–54 (05 April 2012) doi:10.1038/nature10915