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Why we won't see tropical plants in Antarctica any time soon

  • 03 Aug 2012, 16:00
  • Freya Roberts and Verity Payne

55 million years ago, East Antarctica probably looked a lot different than it does today. Warmer temperatures back then mean that a familiar icy environment may have more closely resembled a leafy forest.

These are the findings of a  new study in Nature. It's received a fair bit of media coverage - a lot of which was  relatively accurate and  creatively written, while some just got creative in a photoshop kind of way.

Penguins And Palm Trees
Fig 1. The Mail Online provides a visual aid to help readers interpret the research

Perhaps the real reason this story has captured everyone's imagination though is because it highlights what could be possible if we keep emitting greenhouse gases. As co-author Dr. James Bendle, University of Glasgow, told  the Independent:

"The samples are the first detailed evidence we have of what was happening on the Antarctic during the Eocene, this vitally important time."

"Our work carries a sobering message. Carbon dioxide levels were naturally high in the early Eocene, but today CO2 levels are rising rapidly through human combustion of fossil fuels and deforestation. Atmospherically speaking we are heading rapidly back in time towards the Eocene."


But whilst it's fun to conjure up images of a vast tropical paradise, is this actually a realistic future for Antarctica if the current warming trend continues? First let's look at the research in a bit more detail:

What was Antarctica like in the early Eocene?

The researchers drilled cores from the seabed just off the Wilkes coast to find out what past climate in East Antarctica was like and what plant life this could support.

The cores of sediment contain pollen and spores from plants growing on the ice-free ground, which were blown and washed into the sea 55 million years ago. They show that back then, the environment in East Antarctica was very different from today. 

In low-lying coastal areas, average annual temperatures reached 16 degrees Celsius (give or take 5 degrees) - warm enough for palms and fern to survive. Heading further inland, temperate forest species like beech thrived in a cooler climate, where annual temperatures averaged 9 degrees Celsius (give or take 3 degrees). 

Temperatures had to be warm all year round for these plants to grow and survive. Which means that even in winter, East Antarctica  "must have been essentially frost-free"

Is carbon dioxide to blame?

It would be easy to look to greenhouse gases to explain how lush greenery could thrive in Antarctica back then. Carbon dioxide concentrations at the time were much higher, exceeding 1000 parts per million (ppmv) - levels today are around 395 ppmv. Undoubtedly this contributed to the warmer climates, but there were probably also other factors also at play.

Lead author Professor Pross  explained:

"Another important factor was the transfer of heat via warm ocean currents that reached Antarctica."

The process is known as latent heat transfer: warm moist air is evaporated from the ocean - which uses up a lot of energy. As the air rises and cools it condenses, forming clouds, which release the energy as it rains over the land. This not only enables warmth to be transported from sea to land, but the clouds themselves have can a warming effect, trapping heat close to the earth surface.

This process may well have contributed to the more tropical climate during the early Eocene.


Is it a useful comparison for today?

One of the reasons scientists are so interested in uncovering the climate of the Eocene is that it includes a period of time thought to be the closest match in geological history to our current warming scenario - the Palaeo-Eocene Thermal Maximum (PETM). During the PETM, the average global temperature rose by between 5 and 8 °C in just a few thousand years

There are a few reasons why the current warming isn't the same as before. As we've already mentioned, carbon dioxide levels were then more than double current levels, but the rate we're releasing these gases is much faster today. 

Between 2000-2010, the concentration of carbon dioxide in the atmosphere rose by about 2 ppm extra each year - and at this speed it would take in the order of hundreds of years to reach those sorts of levels, rather than thousands. 

Another difference is that the temperature and concentration of carbon dioxide in the atmosphere were much higher before the onset of the PETM than during the pre-industrial conditions that preceded current warming.

Looking at what the climate was like during the early Eocene is a useful tool for scientists researching the implications of current warming, but while the PETM was similar, it wasn't the same - which means its not a perfect analogue for what to expect.

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