A multinational team of researchers has examined conditions during Earth’s most recent warm period, the Pliocene, and determined that recent climate change predications from the Intergovernmental Panel on Climate Change (IPCC) are correct.

During the Pliocene, roughly 2.3 to 3.3 million years ago the Co2 in the Earth’s atmosphere was 350-400 PPM, a level that was reached last year. The Earth at that time was warmer by about 3.5 degrees Fahrenheit (2 degrees Celsius) than it is right now.

By studying the Earth’s climate during that period, the researchers were able to estimate how the Earth’s climate will respond to increasing levels of Co2 levels now, or the “climate sensitivity”. The research, published in the journal Nature, also examines how climate sensitivity can vary over the long term.

So, for example, Co2 doesn’t immediately correlate to temperature. Last year atmospheric Co2 hit 400 ppm but it will take some time for the warming to occur. Greenhouse gasses warm the planet by trapping heat. Heat from the sun causes warmth but with low Co2 a greater percentage of that warmth is lost to space. As greenhouse gasses increase less heat is lost to space and the planet gradually develops warmer average temperatures.

“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. Our estimates of climate sensitivity lie well within the range of 1.5 to 4.5ºC increase per CO2 doubling summarised 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,” said Gavin Foster, in a statement.

Foster, of the University of Southampton is co-author of the study.

“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. This caused a dramatic global cooling that initiated the ice-age cycles that have dominated Earth’s climate ever since,” said lead author Dr Miguel Martínez-Botí, also from Southampton.

The researchers stated that the impact of current Co2 levels could continue to be felt for centuries, with sea levels rising anywhere from 30 to 100 feet.

“Over the next several centuries, ice sheets could be expected to return to Pliocene levels,” said Professor Eelco Rohling from the Research School of Earth Sciences at Australian National University, a co-author of the paper told the Australian.

While temperatures and sea levels are only starting to change, according to Rohling, ice cover has already begun to adjust to the new climate.

“It is West Antarctica and Greenland that are most important and they can be responsible for 12m of sea level. Processes are just getting going,”

The team also examined the question of whether or not climate sensitivity varied over time. For example was it different in warmer times than in colder times such as the ice age?

“We find that climate change in response to CO2 change in the warmer period was around half that of the colder period. We determine that this difference is driven by the growth and retreat of large continental ice sheets that are present in the cold ice-age climates; these ice sheets reflect a lot of sunlight and their growth consequently amplifies the impact of CO2 changes,” Professor Eelco Rohling of The Australian National University in Canberra

“When we account for the influence of the ice sheets, we confirm that the Earth’s climate changed with a similar sensitivity to overall forcing during both warmer and colder climates,” added Professor Richard Pancost from the University of Bristol Cabot Institute.

Recent volcanic activity is also thought to have minimized the recent impacts of climate change. A recent study published in Nature Geoscience shows that volcanos are at least partially responsible for the so-called “global warming hiatus”. Volcanos add to climate change over the long term by sending large amounts of Co2 into the air.

However, in the short term they can have a cooling effect. In addition to greenhouse gasses, volcanos also eject sulfur dioxide gas into the stratosphere. The gas forms tiny droplets of sulfuric acid, the cause of acid rain, which reflects incoming light back into space. With less light reaching the Earth the temperature cools, temporarily.

The latest IPCC report, as well as reports from past years, can be found at Ipcc.ch.