each of the six major past ice ages began when the atmospheric carbon dioxide content was far higher than at present.
each of the six major past ice ages began when the atmospheric carbon dioxide content was far higher than at present.
geologic temperature record:10
the gradual intensification of this ice age over the last 3 million years has been associated with declining concentrations of the greenhouse gas carbon dioxide, though it remains unclear if this change is sufficiently large to have caused the changes in temperatures.