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.
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.