BIRMINGHAM, Alabama – The atmosphere of the warming Earth passed a feared milestone this week.

Concentrations of the most important heat-trapping gas, carbon dioxide, reached levels not seen for at least three million years portending possibly catastrophic changes to the planet's climate and sea levels, according to scientists.

Today's New York Times reports that on Thursday scientific instruments in Hawaii showed that levels of carbon dioxide had reached an average daily level of 400 parts per million, a measurement that many in the scientific community fear is a harbinger of declining conditions believed necessary for at least a tolerable climate.

Scientists believe that for most of man's time on Earth, about 8,000 years, carbon dioxide levels were stable. But, scientific evidence shows that since the beginning of the Industrial Revolution and the increasing use of fossil fuels that there has been roughly a 41 percent increase in carbon dioxide in the atmosphere.

The gas acts to trap heat from escaping the Earth resulting in what climate scientists say is a gradual increase in the surface temperature of the Earth's surface and seas, conditions which if left unchecked could endanger life on Earth scientists have warned.

That the Earth is warming is a fact in most of the scientific community. But the causes of the warming are still in dispute in some quarters, especially in the United States where for years the fight to decrease greenhouse gases, like carbon dioxide, has divided politicians, businesses and environmentalists.