Ancient global warming puzzle solved

During this period, known as the middle Miocene Climate Optimum, global temperatures were as much as 3 to 4 degrees warmer than today’s average temperatures, similar to estimates for 2100. The position of the continents were similar to today and the seas were flourishing with life. This period, which occurred between 15 and 17 million years ago, has puzzled geologists for decades.

Professor Carrie Lear, the senior scientist on the study and based at Cardiff University’s School of Earth and Ocean Sciences, said: “Our planet has been warm before. We can use ancient fossils to help understand how the climate system works during these times.”

In their study, published in Nature Communications, the team used the chemistry of marine fossils taken from long sediment cores from the Pacific, Atlantic and Indian oceans to fingerprint the temperature and carbon levels of the seawater in which the ancient creatures once lived during the middle Miocene Climate Optimum.

Their results showed that the massive volcanic eruptions of the Columbia River flood basalts released CO₂ into the atmosphere and triggered a decline in ocean pH. With global temperatures rising as a consequence of this, sea-levels also rose, flooding large areas of the continents. This created the ideal conditions to bury large amounts of carbon from the accumulations of marine organisms in sediments, and to transfer volcanic carbon from the atmosphere to the ocean over tens of thousands of years.

Co-author of the study Dr Tali Babila from the School of Ocean and Earth Sciences at the University of Southampton added: “We know that our current climate is warming much faster than the Miocene Climatic Optimum so we won’t be able to rely on these slow natural feedbacks to counteract global warming. But this research is still important because it helps us understand how our planet works when it is in a warm mode.”