What causes an ice age and what would happen if the Earth endured another one? 072820210134

What is an ice age?

Key points:

• The last ice age was 12,000 years ago
• At that time the sea level was 120m lower than today
• The onset of an ice age is related to changes in the Earth's tilt and orbit
• The Earth is due for another ice age now but climate change makes it very unlikely

An ice age is a time where a significant amount of the Earth's water is locked up on land in continental glaciers. 

During the last ice age, which finished about 12,000 years ago, enormous ice masses covered huge swathes of land now inhabited by millions of people.

Canada and the northern USA were completely covered in ice, as was the whole of northern Europe and northern Asia.

At the moment the Earth is in an interglacial period - a short warmer period between glacial (or ice age) periods. 

The Earth has been alternating between long ice ages and shorter interglacial periods for around 2.6 million years.

For the last million years or so these have been happening roughly every 100,000 years - around 90,000 years of ice age followed by a roughly 10,000 year interglacial warm period.

The onset of an ice age is related to the Milankovitch cycles - where regular changes in the Earth's tilt and orbit combine to affect which areas on Earth get more or less solar radiation. 

When all these factors align so the northern hemisphere gets less solar radiation in summer, an ice age can be started.

 

Are we due for another ice age?

Based on previous cycles the Earth is probably due to go into an ice age about now. In fact, conditions were starting to line up for a new ice age at least 6,000 years ago.

"If you look at what was happening prior to the industrial revolution, summers were actually getting colder in the northern hemisphere. They've been getting colder for at least the last 6,000 years, so we were definitely on that trend," Dr Phipps said.

But that trend has now been comprehensively reversed because of greenhouse gas emissions, according to Dr Phipps.

https://www.abc.net.au/news/science/2016-06-15/what-is-an-ice-age-explainer/7185002