Study shows how high latitudes may change with increased CO2 levels
By Summit Voice
SUMMIT COUNTY — If the past is any indication of the future, tropical plants could one day again thrive in Antarctica, just as they did about 52 million years ago during an intense warming phase when global atmospheric carbon dioxide levels were about twice as high as they are today.
New test drilling by German researchers shows that palms and relatives of tropical baobab trees grew along the coast of Antarctica, with the interior dominated by temperate rainforests characterized by southern beech and Araucaria trees of the type common in New Zealand today.
The research, published in the journal Nature, helps illustrate the relationship between climate change, variations in atmospheric carbon dioxide and the reaction of Earth’s biosphere. The results highlight the extreme contrast between modern and past climatic conditions on Antarctica and the extent of global warmth during periods of elevated atmospheric carbon dioxide levels.
“If the current CO2 emissions continue unabated due to the burning of fossil fuels, CO2 concentrations in the atmosphere, as they existed in the distant past, are likely to be achieved within a few hundred years”, said Jörg Pross, a paleoclimatologist at Frankfurt’s Goethe University and member of the Biodiversity and Climate Research Centre.
“By studying naturally occurring climate warming periods in the geological past, our knowledge of the mechanisms and processes in the climate system increases. This contributes enormously to improving our understanding of current human-induced global warming.”
Computer models suggest that future climate warming will be particularly pronounced in high-latitude regions. Until now, however, it has been unclear how Antarctic terrestrial ecosystems responded in the geological past to a greenhouse climate with high atmospheric CO2 concentrations.
The team led by Pross analyzed rock samples from drill cores on the seabed, which were obtained off the coast of Wilkes Land, Antarctica, as part of the Integrated Ocean Drilling Program. The rock samples are between 53 and 46 million years old and contain fossil pollen and spores that are known to originate from the Antarctic coastal region. The researchers were thus able to reconstruct the local vegetation on Antarctica and, accordingly, interpret the presence of tropical and subtropical rainforests covering the coastal region 52 million years ago.
Winter temperatures on the Wilkes Land coast of Antarctica were warmer than 10 degrees Celsius at that time, despite three months of polar night. The continental interior, however, was noticeably cooler. Additional evidence of extremely mild temperatures was provided by analysis of organic compounds that were produced by soil bacteria populating the soils along the Antarctic coast.
These new findings from Antarctica also imply that the temperature difference between the low latitudes and high southern latitudes during the greenhouse phase 52 million years ago was significantly smaller than previously thought.
“The CO2 content of the atmosphere as assumed for that time interval is not enough on its own to explain the almost tropical conditions in the Antarctic,” Pross said. “Another important factor was the transfer of heat via warm ocean currents that reached Antarctica.”
When the warm ocean current collapsed and the Antarctic coast came under the influence of cooler ocean currents, the tropical rainforests including palms and Baobab relatives also disappeared.