The Snowball Earth Paradox
The main problem was explained by Joseph Kirschvink, a geologist at the California Institute of Technology, and his colleagues in a 2008 paper. When large, reflective ice sheets cover the planet, they reflect most of the sunlight back into space, cooling the surface. Without a significant greenhouse effect, this cooling could cause the ice sheets to spread even farther, eventually covering the entire planet in a thick layer of ice. This state is called a 'Snowball Earth'.
As long as the ice sheets persisted, the planet would remain frozen, and life would be impossible. But this is not what happened on Earth. Despite the Snowball Earth phases, life managed to survive. Somehow, the planet thawed out and became ice free again, allowing life to flourish once more.
The Role of Clouds
Kirschvink and his colleagues suggested that clouds held the key to understanding the Snowball Earth paradoxes. They proposed that during the snowball phases, clouds thickened worldwide and that these clouds absorbed large amounts of sunlight, causing the planet to warm up and eventually melt the ice sheets.
The team used a computer model to simulate the effects of clouds of the thickness observed in present day storms on the climate. They found that the additional clouds raised global average temperatures by about 20 degrees Celsius, enough to melt the ice and make the planet habitable again.
Implications for the Modern World
The findings of Kirschvink and his colleagues have implications for the modern world as well. They suggested that clouds could act as a natural climate regulator, preventing the planet from becoming too hot or too cold. This natural process could provide a self-correcting mechanism for the climate, stabilizing the temperature and making it possible for life to survive.
