Picture a land of swamps and conifer trees; one where the annual mean temperature is around 53.6℉ (12℃), similar to locations in the Ohio River Valley in the United States, today. According to a new study from the Alfred Wegener Institute in Germany and Imperial College London, just such a temperate rainforest climate characterized much of the continent of Antarctica 90 million years ago.
The discovery came in the form of a core sample of sediment taken by researchers from the seabed near western Antarctica. When the core sampled was examined in a C-T scanner, it revealed a dense network of roots that had been fossilized, traces of pollen, and spores of flowering plants. By matching up what type of conditions the evolutionary descendants of these ancient plants thrive in today, along with temperature and precipitation indicators in the sample, the research team was able to reconstruct what this much milder Antarctica was like.
Although the continents have shifted positions from where they were 90 million years ago, Antarctica was not that far away from its current position, with much of the landmass within the Antarctic Circle near the South Pole. Thus, despite months of total darkness, plants still managed to thrive and there was no ice cap near the South Pole, according to the evidence from the core sample. In fact, the research team found that average summer temperatures in Antarctica back then were 66℉ (19℃) with rainfall similar to that over Wales today.
The major culprit for such a warm climate 90 million years ago, the warmest the global climate has been in the last 140 million years, was the high concentration of the greenhouse gas carbon dioxide (CO2), estimated at between 1120 to 1680 ppm, compared to today's figure of 414 ppm. One major drawback to having global temperatures as warm as they were 90 million years ago is that sea level was 558 feet (170 meters) higher than today, with large swaths of present-day North America, Europe, and North Africa under water.