On Thursday, May 9th, 2013, Federal scientists overseeing the oldest greenhouse gas monitoring system situated in Hawaii, reported that worldwide levels of carbon dioxide, the chief culprit behind global warming had reached 400 parts per million, a milestone never been encountered by humans before.

According to Pieter Tans, a researcher at the National Oceanic and Atmospheric Administration, the last time the earth encountered this high a level of carbon dioxide was about 2 million years ago during the Pleistocene era. During this time the earth was much warmer, Greenland was actually green - comprising of forest instead of ice and the sea levels were at least 33-66 feet higher.

So how significant is this number which happens to be a daily figure? The reality is that it is no worse or better than levels measuring 399 or ever 398 parts per million. Its significance is largely symbolic in warning us that unless something drastic is done soon to reverse this trend, things can only get worse.

While there a number of greenhouse gases, carbon dioxide is the most watched, thanks to the fact that it accounts for three-quarters of the planet's heat trapping gases. And while methane is more efficient at trapping heat, it has a shorter lifespan. Carbon dioxide on the other hand stays in the atmosphere for centuries, causing temperatures to rise over time.

The good news is that the trend can be reversed, because the increase in carbon dioxide, which is the by-product of the burning of fossil fuels like coal for electricity and oil for gasoline, is a direct result of human activity. According to experts, in 2011 we managed to add an average of 2.4 million pounds of carbon dioxide into the air every second, totaling a massive 38.2 billion tons for the year. China leads the pack with over 10 billion tons of carbon dioxide per year, with the amount increasing 10% annually. The U.S. is in second place with 5.9 billion tons, but thankfully, the number is decreasing every year.

What's concerning scientist more than this unprecedented milestone of 400 parts per million, is the rapid pace at which the greenhouse gas is increasing. They believe that plants and animals can adapt when climate changes occur slowly over thousands of years, but not if the changes come within a short period of time, which is what is happening currently. What is even more alarming is that if the oceans were not absorbing some of the gas, the levels would be even higher! Hopefully, the world will start to take heed soon and try reverse this rapidly worsening situation.

Resources: huffingtonpost.com, weather.com