FROM GREENHOUSE TO ICEHOUSE
An ancient event, known as the “Palaeocene-Eocene Thermal Maximum” or PETM occurred about 55 million years ago. Global temperatures spiked, sea levels rose, the oceans became more acidic, and some species disappeared forever. It was one of the most rapid and dramatic instances of climate change in Earth’s history.
There was a subtropical climate on Earth around this time and we know that lush forest existed across Gondwanaland (a giant continent in the southern hemisphere that included Arabia, Africa, South America, Antarctica, Australia, New Zealand and the peninsula of India)
After 50 million years ago we know from deep sea records of sedimentary rock deposits off the coast of Antarctica that global temperatures were falling and that carbon dioxide was decreasing.
Because carbon dioxide traps heat in the atmosphere, a lessening of atmospheric carbon dioxide concentrations allows more heat to escape into space. The result is a decrease in the Earth’s average temperature.
Ice only began to build up in Antarctica about 34 million years ago. As Global temperatures cooled Antarctica changed from a greenhouse into a refrigerator
Why was it decreasing?
Well, the general idea is that the carbon dioxide was in a state of balance because volcanoes were emitting CO2 but vegetation and algae in the oceans was soaking it up.
But after 50 million years ago CO2 was getting soaked up faster and taking it out of the atmosphere resulted in cooling. A few things that would help decrease it are a lessening of volcanic activity and increased rainfall, dissolving CO2 into carbonic acid which reacted with calcium-containing minerals to form calcite deposits such as limestone. There are probably many reasons.
From three drilling sites in Antarctica we have a pretty much continuous record of the changes in Antarctica from 34 million years ago when the ice sheets formed up until 17 million years ago.
We know that Antarctica was a warmer place, that it had an ice sheet in the middle but along the coasts there were beech forests.
These forests came and went in a cyclical fashion as the ice expanded and retracted over thousands or millions of years and this could only be happening if the amount of CO2 in the atmosphere varied. However, the pace of the expansion or contraction was aided by cyclic variations in Earth’s rotation and its orbit, called Milankovitch cycles.
These cycles influence the amount of solar radiation at different latitudes, thereby influencing climate but they are not enough to cause major changes.
There is a lag of about 800 years before the CO2 levels rise but once they rise they speed up the process which is what we see happening now. CO2 is the major contributor to this process even if it was started by an increase in solar radiation.
The Antarctic Ice Sheet finally covered Antarctica about 14 million years ago and today Antarctica is covered almost entirely by ice that averages about 1.6 kilometres (1 mile) thick.
Climate change is extremely complex and though the climate debate is over in the minds of scientists, it is far from over amongst the general population. This is because they have been continually misinformed by powerful and wealthy vested interests.
The ice in the Arctic and the Antarctic (especially on the peninsula) is melting faster than expected and the general consensus is that things are heating up. Whether you believe it is man made or not is really a moot point now. There will be winners and losers in a warmer world and whether we combat the changes, adapt or succumb to them only time will tell.