Global warming is a topic of political debate and scientific study these days. Is it happening? Scientists say the evidence is pointing in that direction.

Why Is It Happening?

Some say fluctuating temperatures may be linked to the Earth's distance from the sun which cycles every four hundred thousand years. Most scientists believe green house gasses are at least partly to blame. But how can we find out?

Researchers are taking a look at the last episode of global warming known as the Paleocene Eocene thermal maximum. It started sixty five million years ago. The Earth went through a series of warming events called hyperthermals, the most severe occurring about fifty six million years ago. Ocean temperatures rose nine to about eleven degrees Fahrenheit, ocean acidity increased, and many deep sea species went extinct.

Was The Earth's Distance From The Sun To Blame, Or Was Something Else Happening?

To discover the cause of the warming, one group of scientists pinpointed the ancient thermal maximum by using uranium and lead isotopes to date zircon minerals from volcanic ash deposits. They found that the warming did not happen when the Earth was closest to the sun.

Other scientists used argon gas trapped in volcanic minerals to date the time period. They found that volcanic activity spewed more than two thousand gigatons of carbon into the oceans and atmosphere. This included methane and carbon dioxide, two greenhouse gasses. It was the release of carbon dioxide that made the oceans acidic and caused species extinctions.

The Future...

Today, there isn't as much volcanic activity, but humans are adding about twelve gigatons of carbon into the atmosphere each year by burning fossil fuels. Is this "human volcano" pushing us toward another thermal maximum? Time will certainly tell.