To validate models pointing to a global climate that is increasing at a problematic rate, scientists have looked back millions of years.

According to BBC News, authors of a study published in the journal Nature examined ancient plankton fossils dug up from the ocean floor. The samples cover a time between 2.3 million and 3.3 million years ago known as the Pliocene and Pleistocene Epochs.

The researchers examined levels of carbon dioxide to measure their effect on the climate and their findings reportedly supported future projections from the Intergovernmental Panel on Climate Change (IPCC).

"Today the Earth is still adjusting to the recent rapid rise of CO2 caused by human activities, whereas the longer-term Pliocene records document the full response of CO2-related warming," study co-author Gavin Foster, of the University of Southampton, said in a press release. "Our estimates of climate sensitivity lie well within the range of 1.5 to 4.5 degrees Celsius increase per CO2 doubling summarized in the latest IPCC report. This suggests that the research community has a sound understanding of what the climate will be like as we move toward a Pliocene-like warmer future caused by human greenhouse gas emissions."

The study proves that the global climate has always been sensitive to CO2 emissions and validates why societies need to be mindful of them today.

"Our new records also reveal an important change at around 2.8 million years ago, when levels rapidly dropped to values of about 280 ppm, similar to those seen before the industrial revolution," study lead author Miguel Martínez-Botí, also of Southampton, said in the release. "This caused a dramatic global cooling that initiated the ice-age cycles that have dominated Earth's climate ever since."