Can the Miocene climate inform the future?

Another climate reconstruction shows a correlation between temperature and CO 2 Atmospheric CO 2 concentrations are rapidly rising. To reliably predict the future, researchers have looked at past climates with comparable CO 2 concentrations, dating back millions of years. Although these past climates are not perfect analogs of the future, they still provide information about how the climate system functions under increased CO 2 concentrations. Because there are no direct observations of past climate states, climate variables need to be inferred from geological data, generally referred to as proxies. On page 116 of this issue, Herbert et al. ( 1 ) present a reconstruction of the evolution of atmospheric CO 2 concentration over the past 20 million years. Their data provide a consistent explanation for the long-term evolution of global temperature and ice sheets on Earth and give a glimpse into its climate future.