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Published 23:06, April the 26th, 2009

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Photo: GETTY IMAGES
 

Climate change: As old as the hills

Humans cause global warming, right? Well, not always

As dire warnings attributed to man-made global warming persist that New York City risks being washed out by rising sea levels and melting glaciers at the poles will cause a worldwide shortage of freshwater, itís worth noting that events like these are nothing new in the Earthís very long history.

For millions of years, our planet has seen a continuum of one ice age thawing into a warming period, then refreezing into another ice age. And it might surprise you to know that we are living through an ice age right now, known as the Holocene period. Ice ages are made up of glacials and interglacials. Glacials reference a time when the Earth is cooler and the buildup of ice expands around the globe. Interglacials are periods when temperatures rise and the planet thaws, making it more conducive for human inhabitance. Carbon dioxide is only one explanation for the shift in cooling to warming and vice versa. There are a host of other natural explanations.
 

 

Click on chart to enlarge

click here to enlarge

 

 

WHEN THE PLANET COOLS

3 causes

 
 
4

The number of major ice ages the Earth has experienced, dating back 2.7 billion years ago, according to scientists. metro 

 

1. A reduction in carbon dioxide
When tectonic plates are positioned in a way that alter wind and oceanic currents, the natural weathering process does not scrub CO2 from land and emit it into the air, keeping temperatures cool.

2. Flow of warm water

The nearly landlocked Arctic Sea retains colder water at the North Pole while Antarctica rests directly over the South Pole, blocking out warm water. This allows ice sheets to form, which reflects the sunís radiation instead of absorbing it, keeping temperatures cool.

3. Variations in Earthís orbit
Though still under study, scientists have found a link between glacial and interglacial periods and the tilt of the Earthís axis. When the Earth is positioned at a larger distance from the sun, combined with a tilt away from the sun, the Earth experiences cooling. The reverse is true during warming. This happens every 100,000 years. metro
 

 

WHEN THE PLANET WARMS

3 causes

 
 
11,000

Number of years the current interglacial period we are living in has lasted. Most scientists predict that interglacials last an average of 12,000 years.
 

METRO
 

1. An increase in carbon dioxide 
The Earth naturally emits thousands of tons of carbon dioxide every year. Before humans inhabited the Earth, this natural process was one of the single most important factors in warming. Human activity has added to already naturally high CO2 levels through deforestation and industrial pollutants.

2. Variations in the sunís intensity
Scientists predict the sunís output increases by 10 percent every billion years. In one billion years, that extra 10 percent widely increases the amount of water vapor on Earth, which traps heat and contributes to global warming.

3. Volcanism
Scientists determined that underwater volcanoes may have produced enough methane to help heat up the ocean and melt the ice that formed atop it. Though itís not enough on its own to end glacial periods, it probably helped.