Levels of carbon dioxide in the Earth's atmosphere are at near record highs, totaling the most concentration since modern humans came into existence.

According to climate scientists, the last time CO2 levels were at their current 400 parts per million (PPM) levels, world seas were up to 100 feet and the global average surface temperature was up to 11°F warmer.

With seasonal CO2 levels also set to soon spike, scientists warn ppm levels could hit 400 as early as this month in the Northern Hemisphere.

Carbon Dioxide Viewed as Most Significant Global Warming gas 

Carbon dioxide is widely considered the most important long-lived global warming gas. Upon being emitted by burning fossil fuels such as coal and oil, a single CO2 molecule can remain in the atmosphere for hundreds of years.

Globally, CO2 emissions eclipsed a record high of 35.6 billion tonnes in 2012, a nearly 3 percent increase from just five years ago. Carbon dioxide is among a number of greenhouse gases that heat the planet by absorbing the sun's energy and preventing warmth from escaping back into space.

Adapting to Changes Could be Challenging 

While there have previously been times here on earth where temperatures were actually warmer, scientists are concerned the rate of change now taking place is quicker than at any other time and will more than likely be much more difficult to adapt to.

"The increase of carbon dioxide is everywhere, even as far away as you can get from civilization," said Pieter Tans, a carbon-monitoring scientist at the Environmental Science Research Laboratory. "If you emit carbon dioxide in New York, some fraction of it will be in the South Pole next year."

It's conceivable that the South Pole Observatory could see readings fall dip 400 ppm, but new research highlights that the shows planet as a whole has likely crossed the 400 ppm threshold for the foreseeable future and beyond.