The largest climate mode shift over this time interval, the mid-Pleistocene transition, which occurred about 950,000 years ago, has previously been attributed to changes in the pattern and frequency of ice sheets. The new research suggests that this shift was caused by a change in the oscillation frequency of atmospheric carbon dioxide abundances. This hypothesis that can be directly tested by deep drilling on the Antarctic Ice Cap. If it is proved correct, it would suggest that relatively small, naturally occurring fluctuations in greenhouse gases are the master variable that has driven global climate change on time scales of ten thousand to one million years.

Modern observations of tropical sea surface temperature indicate a rise of one to two degrees Fahrenheit over the last 50 years. This trend is consistent with rising carbon dioxide in the atmosphere due to fossil fuel combustion.